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Graham Slee Power Amplifier

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Analog Kid View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Analog Kid Quote  Post ReplyReply Direct Link To This Post 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.








Edited by Analog Kid - 12 Mar 2011 at 1:11pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ServerBaboon Quote  Post ReplyReply Direct Link To This Post 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.


 



Edited by ServerBaboon - 12 Mar 2011 at 8:57pm
Steve

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Various bits of GSP Kit ..well two so far, unless you count the cables that is.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post 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/

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
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post 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?

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Post Options Post Options   Thanks (0) Thanks(0)   Quote tg [RIP] Quote  Post ReplyReply Direct Link To This Post 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.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post 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). 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...




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Post Options Post Options   Thanks (0) Thanks(0)   Quote ServerBaboon Quote  Post ReplyReply Direct Link To This Post 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

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