Print Page | Close Window

Graham Slee Power Amplifier

Printed From: Graham Slee at Hifi System Components
Category: And the rest
Forum Name: Amplification
Forum Description: Share your interests or views on amplifiers, preamps, etc
URL: https://www.hifisystemcomponents.com/forum/forum_posts.asp?TID=1052
Printed Date: 29 May 2020 at 8:26pm
Software Version: Web Wiz Forums 12.01 - http://www.webwizforums.com


Topic: Graham Slee Power Amplifier
Posted By: Graham Slee
Subject: Graham Slee Power Amplifier
Date Posted: 21 Feb 2011 at 11:55am
A Graham Slee Power Amplifier?

Most people know me for Phono Preamps and Headphone Amps and maybe a few Interconnects, but as for the rest of the kit: Power Amps, Line Preamps etc, most people could think its not my area...

However, many years ago, power amps and line amps were just about all I did professionally.

The phono stages were just something I did for myself!

In fact, headphone amps were the first thing I started selling that I'd previously done professionally. I took a look at my old professional designs and figured out how to make them suitable for home use, and then I took a look at an old portable amp I'd designed for studio racks room engineers and turned the idea into the Voyager!

For a long while now I've been trying to launch a little preamp - you may remember a thread discussing it on here some looong time ago. The problem has been being able to audition my design work on that. What I really needed was a good power amp and speakers to make it the best.

Well, I reckon after making some modifications to some little Usher's (I can't get floor standers in here and many of you have the same problem too) I have some great speakers to audition with.

But as for the power amp, the absolute best sounding one to date is a PA amp! Believe it or not, the 500 Watt Citronic pro500 that's curving the bottom shelf of my rack because of the sheer weight of its transformer iron, is the best I've ever heard, but it just lacks that extra spatial info I know exists.

So I just thought I'd let you know I'm working on a power amp design - not a high powered one, but something around 30-35 watts - but it will sound big!

And no, it's not a gain clone - this will be an all-discrete neat little design and it won't get productionized until it sound-stages like the phono stages do in the best systems.

Keep following this thread and watch me develop it...

Graham


-------------
Not simple enough for Google-Bot to understand...



Replies:
Posted By: Fattybatty
Date Posted: 21 Feb 2011 at 3:57pm
Very interesting Mr Slee.............................

-------------


Fattybatty


Posted By: less
Date Posted: 22 Feb 2011 at 11:41am
Very interesting Graham, looking forward to this!

Can you tell us which Ushers and what modifications you made to them? I ask because I am using a pair of stand mounted Ushers, which actually sound very good. Just wondered what changes you felt were necessary for the ones you are using.

Still waiting for your invoice by the way

Regards

Les


-------------
I don't do mediocrity!

Les Sutherland


Posted By: mrarroyo
Date Posted: 24 Feb 2011 at 11:26am
This would be very cool! Look forward to the outcome.

-------------
Miguel


Posted By: iamalexis
Date Posted: 27 Feb 2011 at 1:01pm
looking forward to hearing more on this


Posted By: Analog Kid
Date Posted: 27 Feb 2011 at 1:05pm
Will it be Class A?  Tongue


Posted By: Graham Slee
Date Posted: 27 Feb 2011 at 1:27pm
Originally posted by Analog Kid Analog Kid wrote:

Will it be Class A?  Tongue


Partly Wink


-------------
Not simple enough for Google-Bot to understand...


Posted By: BAK
Date Posted: 28 Feb 2011 at 8:19pm
Graham, Have you seen the Dynaco ST-120A power amplifier? I has a linear 72 volt regulated supply with built in over-current shut down and each channel has short-circuit and over-current shut down. Mine is now 38 years old (rebuilt in 1996 with 1% resistors and 105 temp caps and all new semiconductors). It recently took a direct short (my fault testing new speakersDead) on the right channel and only the zener in the amp protection circuit shorted! The other channel still worked fine and the regulator was still at 70 volts with one channel shut down! I replaced the zener, scrutinized all other semiconductors in the right channel and repaired a burned PCB land on R17, then compared all voltages with my "as-built" measurements from 1996; ALL WORKED FINE. The design description is very accurate in stating this amplifier can handle shorts, I know it would have been better if that weak solder joint on R17(right) did not open up.
If you like I can send you any info needed on this unit, including specs, updated schematic, my personal upgrades.Wink
 
There is a website for this model: http://home.indy.net/~gregdunn/dynaco/components/ST120/index.html - http://home.indy.net/~gregdunn/dynaco/components/ST120/index.html
Notice the feedback circuit...Smile
I think you would like this design. It is very simple and yet has specs like the highest top end units.


Posted By: Graham Slee
Date Posted: 01 Mar 2011 at 8:01am
Yes, it is to a degree intriguing. The multiple negative feedback to the DC coupled pair input stage configuration was much loved for its quite complex but educational baptism into transistor biasing techniques. With so much gain however, there is a considerable "Miller" capacitance on Q2 which sets its HF limit - this is compensated by C13 to hopefully assure stability. Short circuit protection looks as if it all depends on the zener diode, but I still have to get my head round that - I've only studied it a few minutes (just waking up). The output stage bias is really clever - D2 and 3 pulling Q4 emitter into conduction - however, C6 that shunts D2 and 3 can upset the HF or should I say VHF? R28 offers additional local negative feedback to the phase splitter (Q4 again) but whether it was thought as that or became essential for stability is not known - PNP transistors back then were not known for their good HF performance. Q1 offers the qualities of an inverting input in a non-inverting design (clever) and provides excellent input linearity (it is essentially a summing node or virtual earth). Much as I hate plagiarism, this is very tempting indeed.


-------------
Not simple enough for Google-Bot to understand...


Posted By: Graham Slee
Date Posted: 01 Mar 2011 at 6:49pm
Originally posted by Graham Slee Graham Slee wrote:

Q1 offers the qualities of an inverting input in a non-inverting design (clever) and provides excellent input linearity (it is essentially a summing node or virtual earth).


I must be going blind! Didn't see C5. Without C5 it becomes a summing node or virtual earth input, but with C5 there is no local negative feedback and the open-loop input linearity of the entire amp is down to the transistor base and its emitter resistance. As the junction between R4 and Q1 is a summing node due to the negative feedback paths from R9 R10 and C15, then it's the transistor base and its intrinsic (unseen) emitter resistance (25/Ic) which determine open-loop input linearity. R1 and R2 help in a small way but linearity is only assured closed-loop by the negative feedback via R9 and R10.

So what's the problem? With a sine wave it's not a problem, but with a complex signal the speaker load and component imperfections can cause phase shifts or delays and therefore the portion of the signal fed back can be at odds with the input signal, and when it's at odds the input linearity is screwed-up.

The answer is to add emitter resistance between Q1 and the junction of R4, R9, R10 and C15. However, that reduces Q1's gain which may not be a good thing for the overall amplifier stability.

It is exactly the same with the JLH 10 watt class A amp as can be seen by examining TR4 emitter. Great idea compromised by open-loop input linearity - 60mV p-p for inputs that are much more than 60mV!








-------------
Not simple enough for Google-Bot to understand...


Posted By: Graham Slee
Date Posted: 03 Mar 2011 at 2:34am
I think I ought to move or continue this post in the Amplification section, and will do so shortly.


-------------
Not simple enough for Google-Bot to understand...


Posted By: BAK
Date Posted: 03 Mar 2011 at 9:58am
Topic: Graham Slee Power Amplifier
Posted: Yesterday at 9:34pm By Graham Slee
I think I ought to move or continue this post in the Amplification section, and will do so shortly.
Graham, I would like to follow your thoughts on this. Wink I will look next on the Amplification section.
Please note my comments on piezo tweeters. In that thread I mentioned my test results for the Dynaco ST-120.
Distortion is rated at "less than 0.5% ae full output power and much less at lower power".
 Also, the driver transistors were upgraded to TIP-31C and TIP-32C.
 
I only thought you could gain some ideas from this design.Big%20smile
I don't think anyone is using this design any more unless they have a Dynaco ST-120.
What makes this amp unique is the output transistors don't draw the idle (quiescent) current, R16 and R17 do. This reduces heat building up in the output and thus stabilizes the amplifiers' heat dissipation and transfer curves.
All is described in the "Servixe Notes 1" and "TIP mod info" in the website mentioned earlier.
 
At full power the outputs only get warm, not hot to the touch at all. The power supply regulator does get warm idling, and hot at full power , but still not over 135 f. Of course, I have beefed up the heatsinks.
 
Bruce


Posted By: Graham Slee
Date Posted: 03 Mar 2011 at 6:30pm
Bruce, I've just been simulating the Dynaco ST-120 in Easy-PC in an attempt to learn about its amplifier circuit. Some of the features are indeed unique and provide uncomplicated (to some...) and novel output protection. The resulting plots show that it's quite wide-band - considerably so, without the input filter. Not having the exact transistor models I substituted Q2, 5 and 6 for something closely similar. The phase margin is a bit slim and the gain margin could be better, but here I must add that this amp was designed in 1966, 45 years ago, long before the advent of simulation, so Ed Laurent (amp designer) puts me to shame Cry

I will have a play with the design if only to completely understand it. My immediate thought is that the secondary negative feedback which includes the output cap doesn't do the bottom end frequency response (and phase) any favour (puts a slight hump at 2Hz), but then again is probably needed during output stage protection.

It is stated that the output is class B but I would not want anyone to believe it has true class B crossover distortion, it cannot as the output transistors have some forward bias demonstrated by a quiescent voltage drop across R27.

I will write some more on the subject in a while.


-------------
Not simple enough for Google-Bot to understand...


Posted By: mrarroyo
Date Posted: 03 Mar 2011 at 11:39pm
This is very exciting!

-------------
Miguel


Posted By: Graham Slee
Date Posted: 08 Mar 2011 at 10:42pm
Prototype Mini Power Amp

Starting prototyping...

This is the 25 watt monoblock - I may be able to squeeze a bit more power out of it, but it'll be quite ample for most average sensitivity speakers, taking them near to 100dB.



Front view of amp is side of case (looking along line of fins).

2.5 DC socket to be replaced by 4 pin mini-din power connector (external PSU shown to left of amp).

Phono socket to be replaced by an XLR.

Still working on the circuit development.

PS. It's that size to screw to the back of speakers but it can be used sat on the rack too.




-------------
Not simple enough for Google-Bot to understand...


Posted By: Analog Kid
Date Posted: 09 Mar 2011 at 1:03pm
Originally posted by Graham Slee Graham Slee wrote:

Originally posted by Analog Kid Analog Kid wrote:

Will it be Class A?  Tongue


Partly Wink


So not pure class A and not pure Class B, but class AB you mean?
I was hoping for 100 watts of pure class A power.Big%20smile


But maybe if your design is ultra-linear it does not need to be class A?
You once mentioned that forcing solid-state HiFi amps to get hot by
pushing the bias into class A quarters, could help get rid of
the transistor sound but then you mentioned a disadvantage,
which I don't remember anymore. Could you explain it again perhaps?




Posted By: Graham Slee
Date Posted: 09 Mar 2011 at 1:47pm
Yes AK...

My answers are based on data sheets and are based in the real world of Physics (the name we give to observations of what holds the entire universe together - although there are plenty around who would have it otherwise... God help us!)

1] Power output falls or the device blows (whichever happens first - see power de-rating curves on data sheets - oh! I see manufacturers have stopped including that - they must be desperate... )

2] Current gain increases, which at first sight is a good thing, but often results in instability - it makes the input of the device much less linear versus frequency, resulting in a sharper high frequency roll-off, turning it into a radio frequency oscillator... and the device blows.

3] Base - emitter voltage falls so the device conducts harder leading to thermal runaway... and the device blows.

4] 100 Watts of real class A requires a heatsink to dissipate around 1,000 Watts. If the heatsink was rated 1 degree per watt the resulting fire.... (but the device would have blown first)

.... therefore, the heatsink would need to be 0.01 degree per Watt to operate safely for the device (and within several laws), and good luck in finding such a heatsink.

Forced fan cooling would be an option but think of the noise?

And those manufacturers who claim pure class A have an odd command of the language because they all secretly bias these amps into class AB to stop all the above happening, and what's pure about that?

The best real class A amp I've come across that doesn't "lie" is the JLH from 1969 and the best it could do reliably was 10 Watts (TEN) and it gets too hot to let children or animals near, and therefore breaks at least one European law.

One hi-fi press pioneer discovered what really caused the transistor sound back in the very early 80's but had no clue on the solution. I've been working on that ever since and found out how recently - and I call it "Ultra-Linear".

Therefore I will not be doing anything "pure" class A unless it's a preamp.


-------------
Not simple enough for Google-Bot to understand...


Posted By: ServerBaboon
Date Posted: 10 Mar 2011 at 7:51am
Is that your power supply and if not will you be designing your own?


Speaking as a layman I understand (I think) that an amplifer is dependant on the ability of the power supply to cope with the dynamic swings in music and that is why some mains filters/surge suppressors can kill music as it interferes with the ability of the power supply to react to sudden power demands.  

I know you use external power supplies in your products  but I assuming in simplistic terms that the bigger power output of the power amp = bigger power swings = bigger dynamic load and current demands from from it.

I suppose its a question of is the brick man enough Smile






-------------
Steve

-------------

Various bits of GSP Kit ..well two so far, unless you count the cables that is.


Posted By: Graham Slee
Date Posted: 10 Mar 2011 at 9:52am
Originally posted by ServerBaboon ServerBaboon wrote:

is the brick man enough Smile


It should be - listening tests should reveal all.

And no, it isn't mine, it's one of those far-east switched-mode things we're forced to use because of Man's interference in our pleasures (single voltage linear's were banned here on 20/04/2010* although very few British manufacturers seem to realise it).

-----------------------

* this means any linear single voltage external PSU that wasn't already placed on the market before 20/04/2010 - and you have to have proof of that


-------------
Not simple enough for Google-Bot to understand...


Posted By: Graham Slee
Date Posted: 11 Mar 2011 at 1:55pm
Some pictures of the prototype in progress...






I'm not a fan of "Veroboard" (stripboard) and I know it can be troublesome but if it works well on this it should work a lot better on a proper PCB. And if this idea doesn't pan out, then I didn't waste money on a prototype PCB.

Next is the double/triple check on connectivity and the wire-up, and hopefully it won't go bang! Nuke







-------------
Not simple enough for Google-Bot to understand...


Posted By: tg
Date Posted: 12 Mar 2011 at 4:51am

Looks very neat ATM, nice layout, must have taken a deal of thought to arrange like that.

Interesting that the camera has made the top appear longer than the bottom.

Note the little loop thingies, assume these are your wiring takeoffs, never seen anything like those - are they GS "specials" made in house ?

Be interesting to see how you connect 20 wires from top to bottom and get it together and keep it as neat.  Not that I don't think you can do it, but I would bet "London to a brick" that if I did it it would look like the pup's brekkie.

They are supposed to go bang when you play the Telarc 1812 Wink



Posted By: Analog Kid
Date Posted: 12 Mar 2011 at 1:05pm
Originally posted by Graham Slee Graham Slee wrote:

And those manufacturers who claim pure class A have an odd command of the language because they all secretly bias these amps into class AB to stop all the above happening, and what's pure about that?


All of them?
Pure class A must be an illusion then. Cry

There is one Japanese HiFi company that manufacturers a 2 x 60 watts (@ 8 ohm) "pure" class A
stereo poweramplifier. It has the capability of operating in bridged mode, where one
stereo poweramplifier becomes a 240 watt mono block. I would have assumed in bridged
mode the power would double up to 120 watts at the very most,
when each side is combined.
I find it hard to believe the amp can pump out 240 watts of real class A power.
Sounds like it secretly switches to class AB operation when used in bridged mode.
What you think?


I can send you a link to the PDF brochure in a private
message, if you want a closer look.








Posted By: ServerBaboon
Date Posted: 12 Mar 2011 at 8:55pm

 

Originally posted by Analog Kid Analog Kid wrote:

 

All of them? 

Pure class A must be an illusion then. Cry

There is one Japanese HiFi company that manufacturers a 2 x 60 watts (@ 8 ohm) "pure" class A
stereo poweramplifier. It has the capability of operating in bridged mode, where one
stereo poweramplifier becomes a 240 watt mono block. I would have assumed in bridged
mode the power would double up to 120 watts at the very most,
when each side is combined.
I find it hard to believe the amp can pump out 240 watts of real class A power.
Sounds like it secretly switches to class AB operation when used in bridged mode.
What you think?


I can send you a link to the PDF brochure in a private
message, if you want a closer look.




I think I may know what you are talking about and I don't think you have to be too circumspect, HiFi News reviewed the Luxman 600 series amplifiers where the reviewer commented on on how much more powerful sounding the power amplifier sounded than its 30w (8ohm) Class A spec suggested. The technical review (by Paul Miller) pointed out that the only the first 30 watts was Class A where upon it switched to class AB to reach a maximum of 115 watts (8ohm)

Interestingly he also mentioned that the power consumption also went down by 100+ watts after an hour of use.


 



-------------
Steve

-------------

Various bits of GSP Kit ..well two so far, unless you count the cables that is.


Posted By: Graham Slee
Date Posted: 13 Mar 2011 at 9:11am
Originally posted by tg tg wrote:

Looks very neat ATM, nice layout, must have taken a deal of thought to arrange like that.


It's a pain in the you know what...

Originally posted by tg tg wrote:

Note the little loop thingies, assume these are your wiring takeoffs, never seen anything like those - are they GS "specials" made in house ?


I bought them from the Vero online shop http://www.verodirect.com/ - http://www.verodirect.com/

Originally posted by tg tg wrote:

Be interesting to see how you connect 20 wires from top to bottom and get it together and keep it as neat.  Not that I don't think you can do it, but I would bet "London to a brick" that if I did it it would look like the pup's brekkie.


It probably will for me too Wink

Originally posted by tg tg wrote:

They are supposed to go bang when you play the Telarc 1812 Wink


Sh*t! Cry


-------------
Not simple enough for Google-Bot to understand...


Posted By: Graham Slee
Date Posted: 13 Mar 2011 at 9:19am
Originally posted by ServerBaboon ServerBaboon wrote:

I think I may know what you are talking about and I don't think you have to be too circumspect, HiFi News reviewed the Luxman 600 series amplifiers where the reviewer commented on on how much more powerful sounding the power amplifier sounded than its 30w (8ohm) Class A spec suggested. The technical review (by Paul Miller) pointed out that the only the first 30 watts was Class A where upon it switched to class AB to reach a maximum of 115 watts (8ohm)


They're all sliding bias ("ana-slog" amps that is) - they all operate class A to a greater or lesser degree Wink

Originally posted by ServerBaboon ServerBaboon wrote:

Interestingly he also mentioned that the power consumption also went down by 100+ watts after an hour of use.

Probably sounded all over the place in the first hour too?



-------------
Not simple enough for Google-Bot to understand...


Posted By: tg
Date Posted: 13 Mar 2011 at 10:36am

Having a think about the connections (here he goes again trying to teach nan to suck eggsDisapprove)

I might think of running the lower connections below the PCB to a 20 pin IDC type socket at one end of the board and then wire the upper section using 20 wire ribbon (floppy drive) cable with a crimp plug on the end for the socket.  Could be a neat arrangement.



Posted By: Graham Slee
Date Posted: 13 Mar 2011 at 5:06pm
I make it 15 but I could be wrong - we'll soon find out though.

One piece of test gear required to test a power amp is the "dummy load". Obviously a signal generator and analyser is also required but we have these. But as the last power amp I tested was some 13 years ago in somebody else's factory, I don't have a dummy load, until today that is...







So here we have it!

I have no idea what the heatsink is rated at but would guess less than 1 degree K/watt. The best match to 8 Ohms has to be made up from available values, and here I've used 3R3 and 4R7 in series. The resistors are rated 50W but in use will probably derate to 25W each due to temperature rise. They are advertised as non-inductive (see http://docs-europe.electrocomponents.com/webdocs/0aad/0900766b80aad9a6.pdf - http://docs-europe.electrocomponents.com/webdocs/0aad/0900766b80aad9a6.pdf ). Although they have 5% tolerance, after measuring a short to subtract meter inaccuracy, you can see they're bang-on 8 Ohms per channel. As I'm working on a monobloc I can "piggy-back" the channels together and get a 4 Ohms load.

By choosing non-inductive resistors I can measure what the amp does into a purely resistive load. Then I can introduce some capacitance to mimic real cables. However, some "real" cables are very capacitive - the "snake-oil" types I mean. These can exhibit 2,000 - 3,000 pf and can do real damage to power amps. I'll test the monobloc to 2,000 pf which I tried on the simulator. After that who knows what will happen? I could put extra inductance in the output but that usually causes instability with good speaker cables... You can't win with "snake-oil"!

OK, here are the photos of the board after checking. I found one or two mistakes and the "eagle-eyed" may spot one after refering to earlier pictures...






-------------
Not simple enough for Google-Bot to understand...


Posted By: ServerBaboon
Date Posted: 13 Mar 2011 at 5:20pm
Originally posted by Graham Slee Graham Slee wrote:

I make it 15 but I could be wrong - we'll soon find out though.

    However, some "real" cables are very capacitive - the "snake-oil" types I mean. These can exhibit 2,000 - 3,000 pf and can do real damage to power amps. I'll test the monobloc to 2,000 pf which I tried on the simulator. After that who knows what will happen? I could put extra inductance in the output but that usually causes instability with good speaker cables... You can't win with "snake-oil"!


My amplifiers require low capacitance speaker cables, trouble is though no one tells you what is low enough, I'm currently using some some ofc solid core cables which may not be the best match ( The manufacturer was punting Nordost ) but they are only three metres and help to control the bass a little.



-------------
Steve

-------------

Various bits of GSP Kit ..well two so far, unless you count the cables that is.


Posted By: mrarroyo
Date Posted: 13 Mar 2011 at 5:48pm
Blue Jean Cable ( http://www.bluejeanscable.com/store/speaker/index.htm ) uses the Belden 5000, you can find the specs at: http://www.belden.com/techdatas/english/5000FE.pdf

-------------
Miguel


Posted By: ServerBaboon
Date Posted: 13 Mar 2011 at 6:54pm

Thanks, but I am bi amping so I need 4 conductors, the Canare cable could be worth a play with sometime though.





-------------
Steve

-------------

Various bits of GSP Kit ..well two so far, unless you count the cables that is.


Posted By: Graham Slee
Date Posted: 13 Mar 2011 at 7:06pm
Originally posted by mrarroyo mrarroyo wrote:

Blue Jean Cable ( http://www.bluejeanscable.com/store/speaker/index.htm ) uses the Belden 5000, you can find the specs at: http://www.belden.com/techdatas/english/5000FE.pdf


Although a shielded cable it could be used for speaker wiring. However, if one conductor was connected to the shield (the ground side makes sense), then adding the capacitances: conductor to conductor and conductor to shield, 10 ft (3.3 metres) is around 1.8 nF (1800pf), and reduces phase and gain margin considerably.

Ignoring the shield should improve matters by reducing the shield capacitance 50% but that's still going to be more capacitive than a similar length of side by side speaker cable. The one I'm using at present is something like 79 strand. It measured 160pf for something in the order of 10 feet (I wasn't measuring the length at the time - just cutting it to fit).

The CAT5, almost "knitted", cables I've heard about on the 'net measure incredibly high capacitance. These and similar proprietary speaker cables do change the sound! If you take an amp close to instability you get "ringing" ("hanging onto the note"), which does emphasize spatial content, giving the feel of super hi-fi/enhanced "holography" - but it's simply not real, and if it's not real it cannot be high fidelity. At the same time people are risking their amps, but then again, I guess they can play dumb and let the dealer/distributor/manufacturer pick up the tab... Wacko


-------------
Not simple enough for Google-Bot to understand...


Posted By: Graham Slee
Date Posted: 13 Mar 2011 at 11:17pm
So how did it go?

Well, attempt number one isn't going to make it into production. Based on JLH's class A amp of 1969 (circuit diagram below), it simply doesn't perform, period!



It probably would perform as shown but then again I believe the design to be flawed as when modeled it has little phase or gain margin, and as JLH mentioned in his article, it readily oscillates with a small capacitance across R3, the NFB resistor. Other designers may think that obvious, but with sufficient margin it should not - although the capacitance does reduce the margin, and therefore the original circuit had little leeway in this respect.

My simulation model based on this circuit was absolutely stable, and it was in practice too. However, what I was trying to do is back bias it so it wouldn't run so darn hot. The result being that it added crossover distortion which in my opinion was beyond the acceptable. I could have increased bias to the point this distortion became within acceptable limits, but the temperature rise would necessitate a much larger heatsink, and hence larger case leading to a much more costly product - and would it be salable?

What I do like about this configuration is its sound. Camouflaged extremely well, it appears in a number of great sounding op-amp output stages. Indeed it also features in the much revered "gain-clone" amplifier, but as yet I have to obtain a simulation that I feel has the right stability margins: the LM3875 data sheet tends to labour the point regarding additional stability components, suggesting it doesn't have much margin which is borne out by the open-loop frequency response plot (see data sheet here: http://www.national.com/ds/LM/LM3875.pdf).

Another point about the LM3875 is its non-existent flat portion of its open loop response - it falls all the way from a few hertz at 20dB/decade and all the good points about the output stage will be negatively dominated by this - it is not "ultra-linear".

For now it's back to the drawing board. I am determined to find a way of biasing this superb sounding output stage into class AB and the LM3875 proves that can be done.


-------------
Not simple enough for Google-Bot to understand...


Posted By: Fatmangolf
Date Posted: 14 Mar 2011 at 7:42pm
Originally posted by Graham Slee Graham Slee wrote:

The CAT5, almost "knitted", cables I've heard about on the 'net measure incredibly high capacitance. These and similar proprietary speaker cables do change the sound! If you take an amp close to instability you get "ringing" ("hanging onto the note"), which does emphasize spatial content, giving the feel of super hi-fi/enhanced "holography" - but it's simply not real, and if it's not real it cannot be high fidelity. At the same time people are risking their amps, but then again, I guess they can play dumb and let the dealer/distributor/manufacturer pick up the tab... Wacko
 
Graham, I was considering braiding an old cat 5 cable into short speaker cables to see what the fuss was about. Now I won't bother because you have explained the effect involved. Smile I shall stick to my figure 8 cables!
 
Even if it's just me that found your post very useful, thank you Graham.
 


-------------
Jon

Open mind and ears, whilst owning GSP Genera, Accession, Elevator EXP, Solo ULDE, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links, and a Majestic DAC.


Posted By: tg
Date Posted: 15 Mar 2011 at 11:35am

There are often little nuggets of such information in these discussions.

A good reason to follow along even when sometimes half of it is over my head.

Pity it would not play as hoped for.




Posted By: Graham Slee
Date Posted: 16 Mar 2011 at 2:23am
"Plan B" is playing Big%20smile

In fact it's in mono because I only built the one channel, and although some amps sound "flat" only doing one speaker, this is far from "flat" sounding.

There are a few warts to sort out but I think they're only minor, but it returned 0.04% THD at almost full power into 8 Ohms and -76dB noise. OK, not fantastic measurement figures but I never intended it to be a specification star. I intended it to sound great and it's showing tendencies in that direction.

The simulated transient response showed rise and fall rates close to 28V/uS. 80-plus degrees phase margin and near on 30dB gain margin. This is what makes music.

So what is it? Well, I'm not giving away the circuit but the VAS (voltage amp stage) is the good old direct coupled NPN transistor pair (not the usual "long tailed pair") directly driving a Darlington coupled pair in the upper half and a complementary Darlington pair in the bottom half - I'm sure the technical amongst us can imagine what that looks like (it bears some similarity to the Dynaco ST-120 but it's not a Dynaco ST-120 by a long-long chalk).

It won't make it to stereo until the breadboarded unit has had chance to settle in and I get some proper PCB's made up. For the time being I'm enjoying mono Cool



-------------
Not simple enough for Google-Bot to understand...


Posted By: tg
Date Posted: 16 Mar 2011 at 10:52am

Time to break out the early Beatles records then Wink

Sakuma San would approve Evil%20Smile



Posted By: Graham Slee
Date Posted: 18 Mar 2011 at 12:59am
The trouble with mono and a directional stereo speaker is it doesn't quite sound full... Solution, connect both speakers in parallel and then you don't suffer the omni-directionality. It also shows that the power amp drives 4 Ohms (as I knew it could).

Now enjoying this prototype amp just as much as my very first power amp design playing many of the same records - Trevor Horn's "Yes" album "Drama" hasn't changed one bit. The main difference so far is this amp isn't broadcasting it on AM radio like my first one I built while living back at Mum's place (it's been a long time - somewhere in the region of 30 years). I had to add an output inductor on that one, but this one hasn't got an output inductor and I've trawled long, medium, short and FM bands and haven't picked anything up... thank God for design simulators!

But it's no good getting down to the PCB design yet because one important ingredient is missing - the balanced input stage - or to term it correctly: the unbalancing input stage, because it takes a balanced input and makes it into a "single ended" unbalanced signal for feeding the level control and then the power amp itself.

Now, this can be done with an op-amp, but seeing the power amp is all discrete transistor I thought I'd give a discrete unbalancing (or differencing) stage a try. And here's a photo of the just built but untested breadboard.



Whilst building it I had a bit of "fun" with our new Antex temperature controlled iron...



As you can see, it wasn't controlling the temperature all that accurately...

Solution found however: the replacement tips (unleaded solder burnt the first one out Angry) have a foil insert, and when replacing the tip it stopped me from being able to push it fully home. Thus the temp sensor was misreading. Now rectified. Oh the joys of R&D Wink


-------------
Not simple enough for Google-Bot to understand...


Posted By: Graham Slee
Date Posted: 18 Mar 2011 at 3:23pm
Balanced input stage now tested and tagged onto the now very overcrowded case - will it ever fit? Don't worry - I tell myself - I've had worse than this to make into a neat PCB Cry



I keep forgetting to measure the frequency response but the simulator tells me it's considerably more than the power amp and my ears are telling me it's OK too. The rest of the actual real life measurements of the balanced input stage came out like this: THD+N (distortion) 0.0096% at 10 Hz, 100 Hz, 1kHz, 10kHz and 20kHz; Gain +3dB (don't need much here); Noise -86dB with no shielding; Balance (between phases) 0.32dB.

Tagged onto the power amp (stuck out to the right) I'm only using it one sided using the "hot" (non-inverting phase) input, as I don't have a balanced output to drive it yet. The other ("cold") input is taken to ground otherwise you lose its 3dB gain (you'd wire an XLR "shield" pin 1 and 3, "hot" pin 2, to utilise a single ended output into a balanced input in just the same way).

Listening begins all over again with this input stage added. Right now, with only 30 minutes on it, the sound is slightly "over enthusiastic" as you'd expect with new gear, but the power stage was like that after first switch on just 3 days ago and improved considerably in such a short time.

I had been toying with the idea of an output relay to ensure clicks and pops of the big caps charging and discharging doesn't reach the speakers, but I switched the mains power off and waited - and waited - and there was no off "thump". Likewise there was no on "thump". I shall have to try just unplugging the DC between PSU and amp. The only use for an output relay would seem to be the avoidance of decaying distorted sound if the source was left playing when the amp is switched off. I have to ask is it really necessary?

The next thing I have to consider is output short circuit protection. The output devices can do 7.5 times what's required (15 Amps to be precise) and I reckon the power supply would be pulled down first, and as such a simple fuse could be all that's needed - we shall see when a "sacrificial" unit gets the dead-short treatment. If the fuse goes every time and the amp still measures perfect, then short circuit protection seems to be a tad redundant.

The story continues...





-------------
Not simple enough for Google-Bot to understand...


Posted By: tg
Date Posted: 19 Mar 2011 at 1:06am

Development proceeds apace - how excitement Thumbs%20Up

(that is the hottest 75C I can recall seeing - must be OK quality if the handle didn't suffer from that)



Posted By: Graham Slee
Date Posted: 20 Mar 2011 at 4:25am
Originally posted by tg tg wrote:

(that is the hottest 75C I can recall seeing - must be OK quality if the handle didn't suffer from that)


Well, it's doing it again so I'll be phoning RS Monday morning.


-------------
Not simple enough for Google-Bot to understand...


Posted By: Graham Slee
Date Posted: 21 Mar 2011 at 9:17pm
Measured specification time!

For those following this topic thus far who have seen the pictures of the veroboard lash-up which I hope to turn into a production monobloc power amplifier may be surprised that the said lash-up could return the measured results below - but it did.

Prototype Mini Monobloc Power Amplifier Specification

(Including balanced input stage and input filtering)

Maximum output: 26 Watts (measured rms) into 8 Ohms, 47 Watts (measured rms) into 4 Ohms; ref 1% THD+N at 1kHz

Power bandwidth into 8 Ohms: 5Hz - 50kHz (half power points = -3dB), 10Hz - 27.6kHz (-1dB)

Power bandwidth into 4 Ohms: 9.5Hz - 47.8kHz (half power points = -3dB)

Following measured at worst case 1/4 power (-6dB on level control) where output devices are under maximum power dissipation -

Frequency response (-1dB and 8 Ohms load): 10Hz - 27.6kHz

Frequency response (-1dB and 4 Ohms load): 19Hz - 31.4kHz

Distortion (THD+N, 8 Ohms load): 100Hz 0.0381%, 1kHz 0.0325%, 5kHz 0.0589%, 10kHz 0.0949%, 20kHz 0.141%

Distortion (THD+N, 4 Ohms load): 100Hz 0.0702%, 1kHz 0.0559%, 5kHz 0.0858%, 10kHz 0.123%, 20kHz 0.164%

Signal to Noise ratio: 93dB "A" weighted, 86dB 22Hz - 22kHz quasi-peak

Class Ab bias (quiescent) current (at temp: 25 degrees C): 62mA (approx. 3 watts total output stage dissipation)

Sensitivity for full power (approx.): 450mV rms



-------------
Not simple enough for Google-Bot to understand...


Posted By: Fatmangolf
Date Posted: 21 Mar 2011 at 10:25pm
Not surprised but definitely impressed Thumbs%20Up, Graham.

-------------
Jon

Open mind and ears, whilst owning GSP Genera, Accession, Elevator EXP, Solo ULDE, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links, and a Majestic DAC.


Posted By: iamalexis
Date Posted: 28 Mar 2011 at 11:27pm
enjoying following the development of this. what's next...


Posted By: Graham Slee
Date Posted: 04 Apr 2011 at 11:29pm
Originally posted by iamalexis iamalexis wrote:

enjoying following the development of this. what's next...


The PCB.

I'm now at the checking/optimising stage of the PCB design. For my personal ease it's laid out on old DOS CAD software I've used for 20 years on an equally old 386 with a new 22 inch flat screen monitor which helps my eyes. It's then laboriously moved over to the Windows version on a modern PC on 3.5 inch floppy for printing so I can check. I'm a bit of a "stick in the mud" I guess.




-------------
Not simple enough for Google-Bot to understand...


Posted By: Graham Slee
Date Posted: 10 Apr 2011 at 7:26pm
Got the PCBs back from the manufacturer and now I'm working on the case. I had always wanted to make an amp small and compact enough to fit on the back of a small monitor loudspeaker, and saw it as a challenge to use the same extrusion we have made here in England for many other items in our range (you are allowed to use it on the hi-fi rack/shelf as well! Wink).

The heatsink for the time-being is a "donor" item bought off the shelf. I hope to be obtaining "cast" lengths of a similar extrusion having slightly lower profile, and that runs full length of the case, and have it machined so that no fixings are seen. Colour will match the case (natural/silver anodise - don't worry, it will dissipate the heat).

The PCB is inverted (in the top of the case) with components under-slung apart from the power transistors. I guess some could see it a drawback in that the connectors are mounted upside down but I'm not going to let that put me off.

With professional connectors and balanced input (which can be wired unbalanced) it could be attractive to the professional market too.





-------------
Not simple enough for Google-Bot to understand...


Posted By: Graham Slee
Date Posted: 29 Apr 2011 at 2:15am
Now at the "ugly duckling" stage of turning some great electronics into a "beautiful swan"...

Don't let your eyes deceive you - a pair of these midget 26 watt (rms into 8 Ohms) amps can deliver serious amounts of very controlled musical power. Remember, the main reason for making these small is so the user is able to bolt them to the back of a loudspeaker to make it into a powered monitor and get a much more punchy sound which is what you normally get by avoiding long speaker cable runs.

Tested by myself and staff using a variety of sources as well as movies via a DAC they sound really promising - movie sound tracks really coming alive with plenty of tight bass weight, but subtlety where needed - everything you'd want from a power amp.



We may have to break with convention here and make these in black because - although the heatsinks will work perfectly adequately in silver anodize there are a few issues in the "invisible fastenings" being visible in silver. As I may have mentioned, the production heatsinks are to be lower profile and full case length so as not to look silly. The level/volume control knob will be something more fitting for a high class product.



The circuit board shown is the prototype issue and there are one or two slight mods meaning the final board will look slightly different. Much final tweaking going on right now to get the sound to what we want... "it'll do" will not do.

And the name? "Proprius"


-------------
Not simple enough for Google-Bot to understand...


Posted By: mrarroyo
Date Posted: 29 Apr 2011 at 11:20am
Graham should you offer a version w/o volume pots? I mean some may want to use these as power amp letting their current pre-amp take over the volume selection function.

-------------
Miguel


Posted By: Graham Slee
Date Posted: 29 Apr 2011 at 1:41pm
Originally posted by mrarroyo mrarroyo wrote:

Graham should you offer a version w/o volume pots? I mean some may want to use these as power amp letting their current pre-amp take over the volume selection function.


I'd thought of that too. However, setting the pots up full effectively puts them out of circuit handing full control to the preamp of the users choice.


-------------
Not simple enough for Google-Bot to understand...


Posted By: Graham Slee
Date Posted: 04 May 2011 at 11:11pm
More news on the Proprius mono block power amplifier...

Like I said in my last post, "it'll do will not do!"

I believe for an amp to sell it's got to make the speakers "disappear" and that means a rock solid sound stage. You hear a lot of talk about slew rate but maybe some are confused by it?

Slew rate put simply is how fast the amplifier will react to a step change in output. To be honest, a nice sound is obtained from amps in the 50 watt region for only around 2 Volts step change in a micro-second. The problem is that amp will be struggling to do a believable sound stage.

It's the fast changes the amp needs to do and with less than adequate slew rate those fast changes are going to be out of phase with the rest of the music - it's not about us being able to hear the high frequencies that make the start of a note fast and snappy - it's the stability it's done with.

Phase differences introduced by a slow amp trying to react to a fast step change cloud or veil the image - sometimes it's heard as distortion or if there's sounds like the tide breaking on the shore or rain drops (often found in popular genres) it sounds more like frying fish.

However, too high a slew rate puts the amp on the very edge of stability and there's insufficient phase and gain margin, which, guess what? Yes, it's going to lead right back to the fish fryer!

Somewhere in-between there's a happy medium. With the Proprius mono blocks the original prototype sounded really nice but remember it was a single channel and I was listening in mono - no sound stage! In stereo it was a different story. OK there was a sound stage but not the jaw dropping sensation that there was no discernible output from the speakers but sound from everywhere else, so further investigation was needed. As a result I found I could double the current required to drive the "miller" stability capacitor of the voltage amplifier stage (VAS) and not run into stability problems - that's a property of the unconventional type of voltage amp stage I'm using.

In fact, with a conventional VAS the amp often only has 60 degrees phase margin in its quest for maximum slew rate - a far better sound is obtained nearer to 90 degrees, but if you read up on amplifiers they'll always tell you 90 degrees sounds slow and sluggish. What they're really saying is at 90 degrees they have to compensate so much that there's insufficient bandwidth to have a good slew rate. It's all down to developing enough current to drive the "miller" stability capacitor.

What's also good about the Proprius mono blocks is the giant ultra fast output transistors that have a transition frequency (where they run out of gain [when they reach a current gain of 1]) of a staggering 30MHz!

This means we can achieve something in the order of 4MHz where the entire amp's output falls to a gain of 1 and the fall-off is a nice stable and gradual 90 something degrees. Even so the educated amongst us will be able to work out a slew rate of only 1.2V/uS. But here the VAS which is emitter degenerated (in other words a good thing) brings that up 15 times higher - in the region of 18V/uS.

Now that's only OK if the input doesn't try to "hunt" (or overtake) the output and that means an input filter (which the educated reader will have heard of) to slow down the input slew rate to below that of the output. In the case of the Proprius mono blocks the result is an input slew rate of 8V/uS measured on the scope - that's 4 times faster than the minimum required - and the output is faster still. And that's why after only a few days burn-in the prototypes are starting to make the speakers "disappear".




-------------
Not simple enough for Google-Bot to understand...


Posted By: tg
Date Posted: 05 May 2011 at 3:56am

I think you are saying that you might have made something a bit special here then.

Thumbs%20Up



Posted By: Graham Slee
Date Posted: 23 May 2011 at 3:42pm
Originally posted by tg tg wrote:

I think you are saying that you might have made something a bit special here then.

Thumbs%20Up



Trying to!

What I'm working on now is the open-loop gain - the gain the amp has before application of negative feedback.

Most amps would have incredible low frequency gain, rolling off from a few tens or a couple of hundred hertz. All that achieves is phase modulation - a form of distortion sometimes measured as intermodulation distortion but that doesn't tell the full story.

I think it better to make the amp have the widest open-loop bandwidth as possible and then apply just sufficient negative feedback to reduce distortion and noise to acceptable levels, and it also widens out the bandwidth.

Because most of the audio bandwidth is flat, then after applying negative feedback the amounts of phase modulation will be substantially lower.

Too little negative feedback and the bass becomes too sloppy (like valves), but we don't want that much negative feedback that it sounds solid-state - I want it to sound like all the good points of a valve amp.

So far the esses on Peter Gabriel's vocals off the So album (vinyl via Music Maker III, modded Rega/Tabriz, Reflex M) are perfect and totally devoid of sibilance.




-------------
Not simple enough for Google-Bot to understand...


Posted By: Graham Slee
Date Posted: 01 Jun 2011 at 12:49am
Further progress on the Proprius monoblock power amps...

Now running with just 20dB NFB - only twice as much as the Williamson but that was a valve amp - obviously distortion is higher than a high open-loop design, but still only in the region of 0.033% at half power (3 o'clock on the volume dial). Not bad for solid state Wink

I tried the class A route, but when all's said and done it really isn't truthfull class A. As mentioned in another topic 200-250mA quiescent current only does 1/3rd to 1/2 a watt, but so many commercial designs claim "pure class A" for that Shocked

Although it's got absolutely no short circuit protection there is a supply fuse, and it would be rather remiss of me not to test what would happen with output shorted. Well, the amp on test didn't die! In fact I tested it at varying output levels and at frequencies up to 10kHz where there's very little time for any protection to work let alone a fuse. Using a 1A fast blow supply fuse, the fuse always opened. Using a 2A fast blow supply fuse, it didn't open, but the 120W switched-mode power supply went into shutdown instead. In both cases the amp survived and the short circuit was applied for around 3 seconds each time. The amp then went on to test to specification as if nothing had happened. I will not however claim it's short circuit proof and will warn the user to avoid short circuiting the output.

I guess now it's time to get the power supplies ordered, set about fine adjustments to the PCB and get the casework sorted out.

As always, I will update regarding further progress.


-------------
Not simple enough for Google-Bot to understand...


Posted By: BAK
Date Posted: 01 Jun 2011 at 5:41am
Graham, this is truely a superb design. I am anxiously anticipating your refined product being available for purchase.Smile
 I am interested to see and hear your final specifications.
To all members following this project;
Graham is using a design method most commercial designers do not: that is designing in reliability by chosing parts that can handle much more current than actually being used.
I like the fact that the output transistors can handle 15 amps. I can imagine this fact (among others) is what gives the higher gain margine, but it does increase the amps' overload capability.Thumbs%20Up
 Graham, I imagine you are getting close to a finished product.
Please add me to your list of enthusiastic buyers. Yes I want 2 each to start, maybe more.Wink


Posted By: Fatmangolf
Date Posted: 01 Jun 2011 at 6:54pm
Also awaiting roll-out with interest! Big%20smile And now I've eaten my tea, I am going to add my respect to BAK's words...
 
An overspec'ed (almost indestructible) amplifier with the transparency of the other GSP units is well worth the wait.


-------------
Jon

Open mind and ears, whilst owning GSP Genera, Accession, Elevator EXP, Solo ULDE, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links, and a Majestic DAC.


Posted By: Graham Slee
Date Posted: 01 Jun 2011 at 10:22pm
And I haven't even mentioned the price yet Cool

If this was the seventies a decent amp cost in the region of £50 - £100.

What's been the inflation over the last 40 years?

Well, petrol's gone up 22:1. £6.50 a gallon today; 30p a gallon back then.

Beer's gone up 25:1 in pubs. A pint in the early/mid seventies was 12p.

Prices used to double every ten years, so that's 16:1.

So let's take the last example and a decent £50 - £100 amp in the seventies would be £800 - £1,600 today.

So if I said £541.67 plus VAT each - that's £1,083.34 plus VAT a pair (£1,300.00 including VAT) would anybody be offended?





-------------
Not simple enough for Google-Bot to understand...


Posted By: BAK
Date Posted: 02 Jun 2011 at 3:04am
What if I am stuck in the 70's?Clown
I am stuck for the music of the 70's and the 80's.


Posted By: Graham Slee
Date Posted: 02 Jun 2011 at 3:24pm
Originally posted by BAK BAK wrote:

What if I am stuck in the 70's?Clown
I am stuck for the music of the 70's and the 80's.


I know the feeling Wink


-------------
Not simple enough for Google-Bot to understand...


Posted By: Fattybatty
Date Posted: 02 Jun 2011 at 8:50pm
Certainly interesting Wink

-------------


Fattybatty


Posted By: BAK
Date Posted: 03 Jun 2011 at 5:44am
Will this be available as a kit?
I love building circuits for my own use.
I also look for a lower price in kit form; I know the transistors and caps require hand selection for matching. That would increase the price above standard parts.
I have an extensive parts inventory that covers most projects I am planning to build and then some.
 
Bruce


Posted By: Graham Slee
Date Posted: 03 Jun 2011 at 10:11am
Hello Bruce,

You would probably be able to make it but I doubt that all constructors would be all that successful. Great if you get it right first time but I doubt many will have the patience or skills to be able to take it apart and troubleshoot it after making a fatal mistake.

I forgot to solder just one pin and although it took out just one driver transistor, which I found by the usual resistance range test after de-soldering all the transistors, it also damaged one or more of the passives as suggested by the spec test (and you'd have to have a £7,000 Audio Precision or similar for that), and that amp is still waiting to be fully fixed - even I don't have the time for that right now.

We could possibly save £150 for you in kit form, but then we'd have to think about the costs involved in after-sales/warranty. The real cost of shipping a small item overseas is around £70 (sometimes as much as £90 [UPS prices]) - we subsidise that down to £39.37 out of our profit on a new sale, but we'd soon be out of pocket on after-sales fixing kits that go wrong. OK, I have seen power amp kits that look really easy - and I've also noticed other things about them (copies of copies of copies that I probably built myself 30 years ago).

My old Amstrad IC2000 Mk4 from '72 (before I had a brain) cost in the region of £40. Going on UK inflation it should be at least £640 today, but I doubt anybody would part with that much for such an item today (sorry Lord Sugar...)

That sort of thing would now be shoved out to a Chinese firm and probably still cost £40! Curry's will sell you a home cinema audio system for £99!

And this is how time stood still!

But in the real world it's hard to get your bathroom fully refitted, tiled and floored for £200 (1970's prices) - more like £3,000 on a tight budget.

Take a look at this: http://www.canford.co.uk/Products/22440/20-302_CANFORD-UTILITY-POWER-AMPLIFIER-Mk2-2x-45W8-balanced-inputs-rackmount-1U - http://www.canford.co.uk/Products/22440/20-302_CANFORD-UTILITY-POWER-AMPLIFIER-Mk2-2x-45W8-balanced-inputs-rackmount-1U

Just £353.40 including VAT! However, that's to the studio trade and if it were sold via a dealer as our products usually are, it would be nearer £589. Even at that I don't know how they do it - I designed the discrete 35 watt MKI version - it must be chip-amps now to get that price.

I'm not asking Ongaku prices - it's not £29,000.

(click here to see where 40% of your money goes http://www.high-endaudio.com/reviewers.html#Disc - http://www.high-endaudio.com/reviewers.html#Disc - Arthur Salvatore used to disclose distributor margin also, but I cannot find that on his site anymore. Therefore I have to be some sort of miracle worker to make something out-of-this-world and that also retails at an affordable price. I hope you are not too shocked by this as the £50-£100 amp in the 70's had very similar margins. Finally regarding this comment of mine: with a total of (inc. me) three workers with their families to support, which is the same with all good businesses who value their staff (they get paid a salary in other words lest we forget), then if we do sell something direct (we sell 14% of what we make direct due to poor dealer coverage) we obviously get the dealer margin as well, and that goes straight into the R&D budget - and it also paid for the FREE Genera phono preamp design. I hope you all think this fair especially in the light of there being something in the region of 70% margin for designed over here - made over there goods, which we don't do...Wink)


-------------
Not simple enough for Google-Bot to understand...


Posted By: iamalexis
Date Posted: 05 Jun 2011 at 10:56am
graham, with the spec for the mono blocks up to "watt" size speakers are they best suited? also will you being offering any beta testing?


Posted By: Graham Slee
Date Posted: 05 Jun 2011 at 11:37am
80dB SPL for 1 watt or higher should suffice. However, for those with large (well sound insulated...) rooms wanting rock or orchestral concert sound levels, 90dB SPL for 1 watt or higher would be required. The amp is being designed to do 20Hz to 20kHz to a tolerance of -1dB (10Hz - 40kHz -3dB) and will deliver 25 or 26 watts into 8 Ohms and 45 watts rms into 4 Ohms which should adequately deal with the impedance dips of most nominally 8 Ohm speakers. Unusually for a class AB design - one that I might add runs with more bias than the norm for class AB - the Proprius has a regulated power supply. It is actually a switched mode power supply. I can find no downside with switch mode in this application, the upside being its ability to shut down under short circuit conditions which enables me to dispense with the usual output fuse, which would otherwise result in considerable distortion, and included in the NFB loop would require lots of NFB. As such I can get away with only 20dB NFB. However, even after testing short circuit behaviour I am not guaranteeing it short circuit proof.

I will be releasing a pair for beta "auditioning".


-------------
Not simple enough for Google-Bot to understand...


Posted By: Fatmangolf
Date Posted: 26 Jun 2011 at 8:02pm

Moved by Jon to http://www.gspaudio-community.activeboards.net/forum_posts.asp?TID=1129&PID=8519#8519 - http://www.gspaudio-community.activeboards.net/forum_posts.asp?TID=1129&PID=8519#8519

Back to topic, the Proprius is sounding very good indeed. How long is the list of Beta Testers at the moment, please?

-------------
Jon

Open mind and ears, whilst owning GSP Genera, Accession, Elevator EXP, Solo ULDE, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links, and a Majestic DAC.


Posted By: BAK
Date Posted: 28 Jun 2011 at 3:39pm
Graham wrote"
"I hope you are not too shocked by this as the £50-£100 amp in the 70's had very similar margins. Finally regarding this comment of mine: with a total of (inc. me) three workers with their families to support, which is the same with all good businesses who value their staff (they get paid a salary in other words lest we forget), then if we do sell something direct (we sell 14% of what we make direct due to poor dealer coverage) we obviously get the dealer margin as well, and that goes straight into the R&D budget - and it also paid for the FREE Genera phono preamp design. I hope you all think this fair especially in the light of there being something in the region of 70% margin for designed over here - made over there goods, which we don't do...Wink)"
 
Graham, I for one do think this fair. I was just asking. I have a motto of "It never hurts to ask".
I have done many R&D projects and I know it can be very ugly sometimes.
When I completely rebuilt my DYNACO ST-120A, I blew out 2 sets of output transistors before discovering an ultrasonic oscillation!Ouch I then had to redesign the feedback takeoff point at the output capacitor with added inductance and an extra .056uF to ground for output stabilization. I had a design goal of making a good design last longer, I have reached that goal as this amp has lasted over 15 years and the voltages measured at rebuild have not changed more than 0.1% maximum and it sounds great.
 I learned about long-life designing in my military and biomedical electronics experience and in my engineering college courses. Very careful selection of all parts (working in concert) used in a design will produce a longer life expectancy for the design. I have noticed Graham, you use much of the same knowledge. Wink
 R&D can be very frustrating and take weeks even months to work out all the bugs and reach the intended design goals.
 
All, in appreciating Graham's diligent persistence to produce his excellent product designs, I applaud his dedication to reaching for design goals greater than the rest of the audio manufacturers do and then reaching even higher.Clap


Posted By: Fatmangolf
Date Posted: 01 Jul 2011 at 8:56pm
Well written BAK. On top of the investment in product innovation, the "dealer margin" on direct sales funds this forum and some of it gives us as members up to 10% discount.


-------------
Jon

Open mind and ears, whilst owning GSP Genera, Accession, Elevator EXP, Solo ULDE, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links, and a Majestic DAC.


Posted By: BAK
Date Posted: 03 Jul 2011 at 4:56am
I wanted to give an example of a design that I consider "long-life" (below).
Graham has previously explained how this amp design is lacking in it's audio qualities.
I do believe he is on to something with the Proprius design.
 
I may have forgotten mention that I bought this amp in 1973 as a kit for $150.00. It worked good for over 20 years but the regulator was  not regulating very tight. The regulator transistor had a voltage gain of less than 10 (beta hfe). I rebuilt the amp in 1996. It is now 28 years old total, and 15 years since rebuild with longer life parts. I have kept the spares from that rebuild hoping to keep it going should repairs be necessary.
 After recent voltage and gain checks, I have seen less than 0.1% maximum variance, I am expecting another 5 to 10 years before next repair.
 


Posted By: BAK
Date Posted: 06 Jul 2011 at 3:11am
My last post was referencing a DYNACO ST-120A:
"I wanted to give an example of a design that I consider "long-life".
Graham has previously explained how this amp design is lacking in it's audio qualities."
 
 
I do believe Graham is on to something with the Proprius design. It may well be a long-life design. The way things are assembled with care and the way parts are selected are some of the production requirements for long-life expectency.
 


Posted By: Graham Slee
Date Posted: 07 Jul 2011 at 1:03am
BAK, it's probably not that bad, in fact most amps made back then probably had the same stability issues. SPICE modeling was around in a few universities and large corporations running giant "James Bond" style mainframe computers, but PCs like we have today were just a dream. Any Amp manufacturer worth their salt would have a proper audio analyzer, but these didn't (and still don't) have the frequency response to analyze amps for high frequency stability/instability, and neither the low frequency response to see the kicks in really low bass (the only stimulus being artifacts like record warps). Back then I didn't even have that equipment - just a scope and signal generator - and I was blissfully unaware, until I picked up a taxi radio transmission or found a transistor radio in another room playing the self same music, that what I'd made was unstable.

One or two amp manufacturers would be lucky to take on an engineer or post graduate who'd had experience of SPICE and they became the leaders of the pack. I remember Audiolab moved in radio frequency analyzers for the same purpose. It was around this time we heard all the talk about power being wasted on unnecessary frequencies which was the marketing man's way of saying "we've cured the instability of previous models" without admitting they were unstable.

Even though today a SPICE program of sorts can be downloaded for free, few really understand the parasitic behaviour in circuits and take it as being read that their circuits are stable, but on-screen SPICE components are "perfect" whereas real components are not. SPICE is just one tool, albeit a good one in the right hands, in a "toolbox" that has to also include the audio analyzer and a good set of ears.

Whilst on the subject of audio analysis, the advent of the sound-card has made it possible for near on anybody to analyze audio gear - just buy the probe and software - so is this going to make it so all and sundry can produce leading audio gear? My answer to that is, if it were the case, then Audio Precision, Neutrik (NTi) and the likes would not be around today. The fact they are tells us that the probe and sound-card brigade are either just stingy with their loot, or don't sell much for obvious reasons.

To make the best audio gear requires an extraordinary effort, tonnes of R&D, many double ended "burning candles" and sometimes "burned bridges" and personal sacrifice by investing the profits into the best test and simulation products rather than taking the big dividend and becoming a socialite.

No, these old amps may have some shortcomings of the age they were made, but I'd rather own one of them than the garbage turned out by the socialites with their merry following of vociferous ignoramuses. Wink




-------------
Not simple enough for Google-Bot to understand...


Posted By: BAK
Date Posted: 07 Jul 2011 at 8:03pm
Thank you, Graham for your perceptive and reassuring comments.
I just saw a mistake I made calculating the age,
"It is now 28 years old total" should read 38 years old total.
At any age over 10 to 15 years, capacitors dry out and resistors' values drift.
I have found that high temp electrolytic caps (with low ESR) and 1% metal film resistors do last longer. And so do well-made, hand-selected semiconductors.
 
One experience I had with a 20+ year old AM tube radio was it worked OK but the audio and the reception were week (customer's complaint: It would sometimes quit playing). I checked the whole power supply and found a power resistor that looked burned. It was in series with the filaments and the DC voltage B+. When I tried to turn it over to see a value, it when poof! and turned into dust leaving 2 leads hanging in air.
Well, then I had to R&D the value (35 ohms, 10 watts) and I replaced the filter cap.
It then played like new.
 
Point is parts can look like they are working and are in fact way out of tolerance or even ready to go POOF!
And, even 1% metal film resistors and good capacitors do have hidden inductance that can cause instability. So hand selecting parts is a very important step in production.
 
Graham, again, thank you for your attention to detail.
 
Bruce
PS: I used one of those giant "James Bond" style mainframe computers in 1973 in college.
It filled a whole 10 x 12 foot room, air conditioned to 65 degrees F, made of tubes.
All we were allowed to do was complex calculations for harmonics study, Fourier transforms. All other calculations were done with a slide-rule.
 


Posted By: mal4mac
Date Posted: 25 Aug 2011 at 2:20pm
Originally posted by Graham Slee Graham Slee wrote:

A decent £50 - £100 amp in the seventies would be £800 - £1,600 today.


Maybe from inflation figures on some products, but electronics just haven't gone up in the same way.

I bought a NAD 3020 in the early eighties. It cost £129 in 1985, according to an article in Gramaphone archive - I think that's about what I paid for it! It's generally considered a "decent amp", and I certainly think it is, for that price range. The nearest equivalent today, that I can see, is:

NAD C 326BEE Stereo Integrated Amplifier

BEE stands for Bjørn Erik Edvardsen, the designer of this amp and the original 3020.

NAD leaves the selling to third-parties. "The oldest HiFi store in the country" sells it for £330.



Posted By: Graham Slee
Date Posted: 25 Aug 2011 at 8:37pm
Yes, but where is the NAD made?

Just to remind our readers, we make the entire thing (apart from some of the plug-top power supplies) here in the UK.

http://www.gspaudio.co.uk/news/presszone.htm - About Us / Factory Tour

We don't import the finished product from the the far-east, nor do we do the final build on major assemblies made in the far-east, or even developing countries. The printed circuit boards are also made in the UK, and so are the cases (except for the Voyager case which is moulded in Canada but engineered in the UK) whether injection moulded, extruded or sheet metal. The PSU1 and our rare A170 power supply transformers are also made over here. Somebody has to support this country or it would be completely third-world!!!

It may have escaped mal4mac that to keep up the mortgage payments, gas and electric bill etc, and feed a family, which each of us 3 engineers here have, costs a decent whack here in the UK.

I therefore have to find the salaries for 2 qualified and highly talented engineers (who hand build and individually test each and every product), and unfortunately for the spendthrifts, I cannot get away with the minimum wage and would not want to either: they are the salt of the earth as far as I'm concerned, and as far as the vast majority of our customers are concerned too!

As for myself, I take a dividend, and if people buy in sufficient quantities I can earn a few percent more than my engineers. However, they don't mind because they know I thrash my brains to develop some of the best audio products on the planet, and that keeps them in a job.

I think some in the UK need to wake up and realise the cheap spending spree they've gotten used to is unsustainable. They'd need a strong financial sector to keep it going and the UK lost that for good in 2009. The money required to sustain a countries infrastructure has to come from somewhere, but here in the UK the majority of the population are living on the chucky time bomb. We have an aging baby-boomer population who believe things will continue nice and hunky dory. What they don't realise is you need a fully employed younger generation of equal numbers for that. Instead we have fewer youngsters than oldies and near on 1/5th of those youngsters are unemployed.

This sort of talk must be symbolic of their struggle against reality!


-------------
Not simple enough for Google-Bot to understand...


Posted By: discrete badger
Date Posted: 30 Sep 2011 at 1:30pm
I'm looking for a better power amp at the moment, and the Proprius looks very interesting.

But I have electrostatic speakers, which seem to be generally regarded as something of a "challenge" to drive.

Is the Proprius likely to work well with them?



Posted By: Graham Slee
Date Posted: 30 Sep 2011 at 4:22pm
I'd say 84dB sensitivity, which I think the Quad ESL is, would be the lowest I'd go.

If it's a big room, you may need more than the little 25 watt Proprius pair can deliver. However, with a bigger amp you risk arcing, so the self control of not over-driving the Proprius (into clipping) may be a good thing.

The falling impedance with rising high frequency of a Quad ESL will be easily handled with the Proprius.


-------------
Not simple enough for Google-Bot to understand...


Posted By: Analog Kid
Date Posted: 05 Dec 2011 at 10:00pm
Any plans for a high-powered design in the future (50 to 100 watts)?
Or do you prefer sticking to power amplifiers in the 20 to 25 watt range?



Posted By: Graham Slee
Date Posted: 06 Dec 2011 at 8:35am
Thanks AK, the problem in this fine world we have today (full of petty squabbling...) is that - unless you're a household name - there are only 63 customers in any particular country for any particular product in any year (except for China which is a mega country). I've researched that figure over many years and just like the Answer to the Ultimate Question of Life, the Universe, and Everything is 42, 63 is the limit!

Now, in the UK (and Europe until old Neville Camoron finds we've been kicked out of the EU by next March) I can get away with sticking a big transformer in a box also containing transistors, pcb etc, and call it a power amplifier. All I need to do is provide a paper trail and declare it meets CE.

Now, that's a lot of effort for only 63 sales.

To sell around the rest of the planet to eke out a living for the 3 poor souls who work here, I being an obedient sort of chap, have to comply with all these different countries rules regarding what and what not I can export to them.

Their governments don't allow a mains transformer in any box unless the whole thing is approved, and it would seem that all my distributors and dealers are just as obedient as I am, and won't or dare not break their countries rules, like some companies distributors do.

I can take the mains transformer outside the box and put it in another box, making the power amp remote powered, but then I'm up against two stumbling blocks. I still have to comply with the first one which is safety and please consider that the PSU1 cost £10,000 to have safety approved - a power amp would need a completely new remote power supply and the cost of getting that safety approved could be £15,000 if it went through first time (if you get it wrong then you pay £15,000 for a fail mark and pay another £15,000 and so on until you get it right to the test house satisfaction). The second stumbling block is called Eco-design where all the previously mentioned £15,000's pale into insignificance when you learn that through legislation your remote power supply is illegal! See: http://ec.europa.eu/energy/efficiency/ecodesign/eco_design_en.htm" rel="nofollow - http://ec.europa.eu/energy/efficiency/ecodesign/eco_design_en.htm

Therefore little me has to comply and in doing so I have to buy a power supply from a chap who's good at jumping through hoops, and that chap is a China man.

He makes standard things because to sell in batches of 1,000 pieces to make his operation viable non-standard items don't fit.

So I'm stuck with 48 volts.

So the maximum output I can do is - here comes the math....

The maximum r.m.s. voltage swing from a 48 volt power supply is (48/2) x (1/root2) or 16.97 volts.

And to convert that into power into 8 Ohms we square the voltage and divide it by 8, which gives 36 watts!

The problem is that the very amplification devices get in the way by consuming volts, such as saturation voltages and base-emitter voltages, so the maximum r.m.s. voltage in reality will be around 14 to 14.5 volts and a maximum power of 26 watts.

It's not that I don't want to make a higher powered amp, or that I can't. I have proven to sufficient people over the years that I can make amps up to 100 watts (into 8 Ohms). It's just that to make sufficient items to make it viable this beautiful world of ours puts its glass ceiling on you. I can see that glass ceiling but you and others don't even know it exists. You would do if you were to one day believe me.

There are ways to increase power output on 48 volts but then the power supply has to be around twice the output current. And all the Chinese power supply producers I have come across don't yet realise that the output cable needs to be seriously beefy, or you'd laugh at me.

I can do anything (within reason) but the world stops me.


-------------
Not simple enough for Google-Bot to understand...


Posted By: Graham Slee
Date Posted: 06 Dec 2011 at 9:46am
Just a quick aside...

For many years the BBC had numerous 50 volt glass batteries in the basement at Bush House.

BBC monitor speakers are generally 6 Ohms.

From 50V you can obtain 37.5 watts into 6 Ohms.

Could that be why most UK radio station studio utility amplifiers were 35 - 40 Watts?

Last century many European loudspeakers were 6 Ohms.

So, if 35 watts is sufficient for a broadcast studio, then it should be sufficient for the average guys listening room. And if the standard for speakers were 6 Ohms, then all you need is a Proprius... 34 watts into 6 Ohms Wink


-------------
Not simple enough for Google-Bot to understand...


Posted By: Fatmangolf
Date Posted: 06 Dec 2011 at 9:16pm
Thanks Graham, that clarifies a lot of stuff. IMO this would be plenty of power in reserve for listening to a reasonably efficient loudspeaker of 86dB/1W or better.

-------------
Jon

Open mind and ears, whilst owning GSP Genera, Accession, Elevator EXP, Solo ULDE, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links, and a Majestic DAC.


Posted By: tg
Date Posted: 07 Dec 2011 at 1:06am

Since this topic has re-surfaced, it might be time to enquire as to the current state of development of this project.

IIRC the last mention was that the naughty Harbeth monitors had indicated that some further work on the circuit might be necessary to achieve the level of performance expected.




Posted By: Graham Slee
Date Posted: 07 Dec 2011 at 8:25am
I wish I was able to create the perfect machine. Unfortunately you need a machine to help you create a machine. Take the humble refrigerator for example - it needed several machines to be able to create it. The cabinet required a number of metalworking machines, the liner required a vacuum forming machine etc. No wonder it took so long to invent the wheel!

In the case of a power amp it needs a preamp - not any old preamp but a reference preamp or you could be tuning to no avail.

Also you need reference speakers and a reference "auditorium". These need to be similar to what the typical user has, to be able to feel comfortable that he/she receives the desired result.

Small manufacturers, or should it be "micro" manufacturers are stuffed when it comes to a budget for things like loudspeakers. I've managed to put together an "array" of much modified Leak Sandwiches, the "naughty" Harbeth M20's and Castle Acoustics Trent's. I also had Usher 520's and JPW Sonata's at one point.

The "naughty" Harbeths weren't being naughty at all really, although they've been laughing their little cotton socks off at me when I've got something wrong, and I don't mean something as major as a faux-pas here. They didn't like my output inductor at all: "not my cup of tea old chap" they were uttering. That particular episode taught me the wisdom of bypassing the output inductor with a 10 Ohm resistor, although my reasoning, the XSPICE, the other speakers and the test gear all disagreed. On the other hand they were not nonplussed with the amendment!

As for the reference preamp, I do have my worries. I doubt if there is another preamp like it that is so well behaved. I'm not being conceited when I say this, just that I have to ask myself if I've had to make a preamp to fit the power amp's behavior? And if that is the case, should I be designing an integrated instead?

The Harbeth's also spelled out the difference between wire-wound and metal film output stage emitter resistors, and when the wire-wound resistor inductance was measured and modeled in simulation it told me why. The simulation showed a quite different phase and gain margin indeed! OK, I should have known better.

There are one or two things about the Proprius design I'm still not 100% happy about, and so it's proving to be a bit of a long drawn out birth.


-------------
Not simple enough for Google-Bot to understand...


Posted By: tg
Date Posted: 07 Dec 2011 at 9:06am

Thank you for taking the time for that update.

It sounds like the Harbeths are proving a valuable tool in the development work.

To me, it gives a greater insight into the many (to most of us) unknowns, that can affect the interaction of components when assembling a system and lead to less than satisfactory outcomes when putting together a system of components from different manufacturers.

It helps to explain the "synergy" for which we strive, where the components play nicely together and the whole is greater than the sum of the parts.



Posted By: Cyreg
Date Posted: 07 Dec 2011 at 1:33pm
Right Graham, thanks for the update on the power amp(and pre).
I already had been wondering for some time about its status Wink


-------------
TecnoDec/RB250/MP110>GramAmp2C/PSU1; Cyrus CD8SE; Cyrus FM7 > Exposure XXXV > Harbeth C7ES-3 '35th Anniversary'
cables: DNM V3 Ic's; Exposure DMF-two LScable;    
   


Posted By: Graham Slee
Date Posted: 07 Dec 2011 at 5:03pm
Another update: here's an example of some of the complexities involved...

Earlier today I'd mentioned that by shunting the output inductor with a resistor the results through the Harbeths were much improved. Having swapped to the Castles it was immediately apparent that the hunt was not over. What I was hearing was a loose upper bass and some exaggeration in the mids plus a degree of "digitalis" (digital unease).

The search was therefore on because there was no way I was going to even contemplate finalizing this little amp for production until it gave me the satisfaction I know is possible. I suppose I could have tried things Willy-nilly but that could have taken an age, and an age I don't have. This is where the XSPICE simulator comes in - it cannot answer every question but can give a good clue to most.

By my reckoning the power supply input was chief suspect, simply because IMO I've tried everything else for this particular design. Whether the simulation results and their real life remedy prove to be a success I will not know for some time because the new components need... you guessed it - some burn-in.

The following screen photos show roughly what was going on...



Initially I'd done the typical "card input filter" comprising L3, C1 and C2 with their respective inductances (L1 and L2) and series resistances (R3 and R4) modeled in. The 100 Ohm (R7) load representing the power amp operating at lowish volume. Changing R7 to 8 Ohms to represent a full volume power supply load made very little difference to the results.

The first result is the red curve which is hidden behind the green curve for most of its excursion. The exposed part shows a peak at around 500Hz. This translates to the power rail being less than taught and that could have explained the loose upper bass. A 0.3 Ohm 3 Watt wire-wound resistor modeled here as R6 and L4 in series shows a reduction in impedance from around 50Hz (green curve). As it's in series with the card input inductor the small series inductance, L4, of R6 has no real significance. The switch mode power supply is quite capable of delivering clean power at low frequencies but they're pretty crap to abominable the higher up in frequency you go, so tuning the power rail and getting it right is of ultimate importance.



The second plot shows the much nicer green curve as far as low to mid frequencies are concerned, but then it goes off at a tangent at around 80kHz - in fact, it starts "losing the plot" around 20kHz so any high frequency stimulus could very well mix with the rising impedance and any switch mode nasties that allows through, to produce signal modulation throughout the audio spectrum.

The problem in bypassing a great big electrolytic, C1 (actually 2 x 2,200uF in parallel), with a smaller film cap (C2) is that because of C1's relatively large inductance, you have a tank or tuned circuit just like that of a radio tuner, but at sub-r.f. frequencies. Here the tank circuit resonates at 80kHz. It then dives to a really low impedance a decade higher at 800kHz (now in r.f.) - all within the gain bandwidth of the amplifier.

The solution turns out to be some small series resistance, this being 1 Ohm, modeled in place of C2's series resistance (which it swamps). The resulting "card input filter" impedance plot is then depicted by the red curve (of the second picture) nicely falling away with a couple of shelves but no glitches.

Finally, the capacitor series inductances shown may depart slightly from reality, however they're a long way from make-believe. I have tested a 200u 63V electrolytic at 0.5uH so the 1uH for the two 2,220uF caps in parallel may actually be on the conservative side. Much depends on the particular electrolytic technology employed by the capacitor manufacturer, and they like to keep that information secret.



-------------
Not simple enough for Google-Bot to understand...


Posted By: Fatmangolf
Date Posted: 07 Dec 2011 at 8:50pm
Two Three thoughts come to mind:
1) you are tantalising us! Wink
2) this attention to detail is why GSP Audio equipment is great Big smile
 
3) This is the first time I have read a technical and musical explanation of one of these filters that made sense, thank you.


-------------
Jon

Open mind and ears, whilst owning GSP Genera, Accession, Elevator EXP, Solo ULDE, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links, and a Majestic DAC.


Posted By: Graham Slee
Date Posted: 08 Dec 2011 at 8:33am
Originally posted by Fatmangolf Fatmangolf wrote:

Two Three thoughts come to mind:
1) you are tantalising us! Wink
2) this attention to detail is why GSP Audio equipment is great Big smile
 
3) This is the first time I have read a technical and musical explanation of one of these filters, thank you.


1) I'm actually playing for time... Wink

2) I don't get the lucky breaks other designers get Ouch

3) It helps me absorb what I'm doing


-------------
Not simple enough for Google-Bot to understand...


Posted By: Fatmangolf
Date Posted: 08 Dec 2011 at 8:42pm
I belatedly realised that I left some key words out in my first post! Sadly the orginal text has been quoted.

-------------
Jon

Open mind and ears, whilst owning GSP Genera, Accession, Elevator EXP, Solo ULDE, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links, and a Majestic DAC.


Posted By: Graham Slee
Date Posted: 09 Dec 2011 at 3:52am
Originally posted by Fatmangolf Fatmangolf wrote:

I belatedly realised that I left some key words out in my first post! Sadly the orginal text has been quoted.


We can always do take-2 and I will delete take-1 ? Smile


-------------
Not simple enough for Google-Bot to understand...


Posted By: Fatmangolf
Date Posted: 09 Dec 2011 at 7:58am
No problem, it's fine! Thanks though.

-------------
Jon

Open mind and ears, whilst owning GSP Genera, Accession, Elevator EXP, Solo ULDE, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links, and a Majestic DAC.


Posted By: suede
Date Posted: 11 Jan 2012 at 5:23pm
This may certainly be way too late to make it onboard the Aria, but have you ever thought about implementing an absolute phase switch on any of your amps Graham? Could this even be done simply and without compromising the quality of the rest of the amp?
I don't know, but it bugs me that a lot of my music is in reverse phase polarity and will never sound as good as its full potential since it's 180 degrees out of phase with my system.

Johan


Posted By: Graham Slee
Date Posted: 12 Jan 2012 at 9:05am
Johan, I will have a try at incorporating it. The PCB is not yet finalised. So far, in all the 12 years this business has been established only you and previously Scott Faller (TNT and Enjoythemusic.com reviewer) have asked for such a thing. Therefore in strict business sense I should ignore your request but for one thing -- what it says here: Matthew 25:45


-------------
Not simple enough for Google-Bot to understand...


Posted By: suede
Date Posted: 12 Jan 2012 at 7:38pm
Graham, I hope you don't feel obliged to implement something on my account alone, but only if there are more people than just myself who covets such an addition. Myself, I might even have to wait a while before getting the Aria/Proprius since I should really get a phono preamp first as my next upgrade. (I'm thinking the Era V or the Reflex M maybe Big smile. Not sure if my current Debut III Esprit TT is good enough to justify getting the Reflex M directly though.) I just thought such a phase switch would make a swell addition and something I've only ever seen on some vintage high end Grado headphones before (depicted, not seen them in person).

Most people I've read posts by on online forums seem to deride the absolute phase issue claiming that perceiving these differences is more or less equivalent of hearing the grass grow. But as I posted in a thread a while back, to me at least these differences are not only perceivable but can make the difference between slightly dull and glorious. And since a lot of recorded music sadly is 180 degrees off phase I find it puzzling that this kind of addition is not implemented more frequently on high end gear. But maybe I'm just overly fussy? Confused
Here's a blind test anyone with a good computer DAC connected to their stereo can take, but bear in mind that if you haven't adressed the absolute phase issue before it might be reversed and you could end up hearing the inverted file as more correct than the original:

http://www.audiocheck.net/blindtests_abspolarity.php

I got 8 out of 10 on my try but to be fair the sample is not great and it's much more evident with high resolution well recorded music.


Posted By: BAK
Date Posted: 13 Jan 2012 at 2:12am
Graham earlier stated; "So if I said £541.67 plus VAT each - that's £1,083.34 plus VAT a pair (£1,300.00 including VAT) would anybody be offended?"
Is this price still posible?Smile
What would that be converted to US $?
Please explain what "VAT" stands for.Confused This forum is the first place I have heard it mentioned.
I can imagine it has to do with taxes and/or export duties.
 
Would each Proprius mono block amplifier require it's own 48volt power supply?
(That would make sense to have the PS close to the mono amp when located at the speaker.)




Posted By: BAK
Date Posted: 13 Jan 2012 at 2:33am
Graham, could I use a 48volt power supply of my own for the Propius?

-------------
Bruce
AT-14SA, Pickering XV-15/625, Technics SL-1600MK2, Reflex M, Lautus, Technics SH-8066, Dynaco ST120a, Eminence Beta 8A in custom cabs;; Using Majestic DAC
Enjoy Life Your Way!


Posted By: Graham Slee
Date Posted: 13 Jan 2012 at 2:56am
I'm trying to make it possible.

£541.67 is currently $834.17 (exchange rate $1.54 to £1)

VAT stands for Value Added Tax - a tax that doesn't add any value unless you're her majesties government. It used to be called purchase tax but they changed its name to levy a higher level of tax -- nowadays they just increase it in broad daylight.

VAT here is 20%. In the USA import duty should be 5% and unless in a tax-free state, purchase tax was 10% -- which may have changed -- making it 15.5%.

Yes, they require and are supplied with their own individual 48 volt 120 watt power supply.

Listening earlier to Emerson Lake and Palmer: "Emerson Lake and Palmer", 1970 (vinyl), The Three Fates, especially the Clotho movement played on the Royal Festival Hall Organ, the power, bass depth and stereo field these little mono blocks deliver has to be heard to be appreciated. The breadboarded Aria preamp did for most of the time, but we ran them straight from one of the balanced output Reflex phono stages -- the mono blocks having their own volume control -- which we'd been making yesterday which just blew the breadboard Aria away. Obviously when the Aria gets built on its own PCB we expect the same breathtaking performance.

I think these little mono blocks will be bargain of the century at twice the price -- but don't worry, we'll keep the price within reason. I only get enthusiastic like this when we break down the perceived barriers.


-------------
Not simple enough for Google-Bot to understand...


Posted By: Graham Slee
Date Posted: 13 Jan 2012 at 3:04am
Originally posted by BAK BAK wrote:

Graham, could I use a 48volt power supply of my own for the Propius?


Without warranty.

The issued power supplies share the protection job because they have an over current shut down. Any other power supply wouldn't have the exact same characteristics and would risk blowing the gutsy 15 Amp output transistors should the speaker leads be shorted.

The power supply over current shut down operates much higher than their rated 2.5 Amps as proven by driving 4 Ohms at 45 watts continuous r.m.s.


-------------
Not simple enough for Google-Bot to understand...


Posted By: BAK
Date Posted: 14 Jan 2012 at 3:31pm
Thank you for your excellent description of VAT.
Just to clarify, VAT is an export tax?
I would think buying direct would save me the US dealer's markup,
so export and import duties are expected.
 
ELP is one of my favorites to test sound quality. I have 2 copies in vinyl.
 
I understand the power supply is maximum current matched, a good over current shut down protection method.
 
I may have to start saving my $!


-------------
Bruce
AT-14SA, Pickering XV-15/625, Technics SL-1600MK2, Reflex M, Lautus, Technics SH-8066, Dynaco ST120a, Eminence Beta 8A in custom cabs;; Using Majestic DAC
Enjoy Life Your Way!


Posted By: Graham Slee
Date Posted: 15 Jan 2012 at 9:56am
No.

VAT is a European tax which operates within EU member states (including the UK Thumbs Down)

We have a duty to charge VAT on every sale and every 3 months to pay it over to Her Majesty's Revenue and Customs (the UK treasury).

If we export (sell to you in the USA), Her Majesty does not expect any VAT (she wants us to do well and bring in lots of foreign cash which helps sort out the trade-balance and she knows she'll get corporation tax on that cash out of our profit), so we sell without it.

But Uncle Sam says everything that enters the US has a value and therefore expects to charge import duty on it (it goes to the US treasury). He expects us to be honest and declare the correct value on the commercial invoice we send with it. If we are dishonest he will do nasty things to us, so we behave.

If all the world were a level playing field and there were no sanctions or trade blockades, very similar rates of duty would apply everywhere, and then we'd charge you the same VAT inclusive price that we charge here, but use that extra money to pre-pay the import duty so you didn't have to.

However, utopia has yet to arrive. So it remains really complicated for you.... and for me.


-------------
Not simple enough for Google-Bot to understand...


Posted By: Analog Kid
Date Posted: 22 Jan 2012 at 11:07pm
Can someone please explain to me the whole principle
behind 'Value' Added Tax (aka Sales Tax)?
Anyone who has an income is already paying income tax where
a percentage of our income is cut off and given to the state.
But then whenever we purchase commodities
or services, we are paying tax again to the state from the money
we have left after we paid income tax. Why are we being double-taxed?




Posted By: tg
Date Posted: 22 Jan 2012 at 11:38pm

AK,

after our Federal Government in the preliminaries to the introduction of our very own copycat VAT, known here as GST, promised that no further taxes would be levied on prices including GST.

Our State Government nonetheless levies Stamp Duty on the full price (including GST) and so reaped an immediate 10% increase in Stamp Duties.

The short answer to your question seems to be that they make the rules.



Posted By: Fatmangolf
Date Posted: 24 Jan 2012 at 10:06pm
Hobbes wrote about the social contract. Tolstoy wrote of the two certainties of death and taxes. However Phil Silver's sharing technique in "it's a mad mad mad world" may offer genuine insight.


-------------
Jon

Open mind and ears, whilst owning GSP Genera, Accession, Elevator EXP, Solo ULDE, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links, and a Majestic DAC.


Posted By: suede
Date Posted: 25 Jan 2012 at 8:48pm
"Don't ask me what I want it for
If you don't want to pay some more
'Cause I'm the taxman, yeah, I'm the taxman" Wink



Print Page | Close Window

Forum Software by Web Wiz Forums® version 12.01 - http://www.webwizforums.com
Copyright ©2001-2018 Web Wiz Ltd. - https://www.webwiz.net