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Graham Slee Power Amplifier

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




Edited by Graham Slee - 08 Mar 2011 at 10:44pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Analog Kid Quote  Post ReplyReply Direct Link To This Post 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?




Edited by Analog Kid - 09 Mar 2011 at 1:05pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post 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.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ServerBaboon Quote  Post ReplyReply Direct Link To This Post 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.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post 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
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post 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





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

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