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Old 28th July 2009, 08:15 PM   #1
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Default Class A power follower

Just wanted to share an excellent sounding little power follower that I have been working on. It uses the Aleph ccs concept to control bias. Sorry I dont have time to give more info atm, more later tonight.
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Old 28th July 2009, 08:39 PM   #2
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Triple emitter follower and servo with a positive feedback?

Looks interesting.
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Old 5th August 2009, 12:58 AM   #3
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Oops, positive feedback in the dc servo was a mistake on my part. I guess thats what I get for doing things in a big hurry. Heres a revised schematic including the power supply regulators. Will give a parts list etc.. later. Have to go back to work.
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Old 5th August 2009, 01:07 AM   #4
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Why did you decide to use a symmetrical topology, if anyway it is a class A amp? Symmetry is nice when you want to save an energy, but for class A it is suboptimal.

Here is the concept that I've found still the best for class A amp:

A counter-modulated current source on bottom minimizes current variations through an output source follower, while an additional source follower on top minimizes voltage variations between it's drain and source. As the result, distortions caused by capacitive load of the previous (tube) stage, of variations of capacitances and transconductance with voltage, current, power (hence temperature) are minimized without any additional feedback, hence without additional high order distortions.


Click the image to open in full size.

I am currently working on a new prototype that uses this concept:

http://www.diyaudio.com/forums/showt...39#post1889739
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Old 5th August 2009, 07:52 AM   #5
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Here is the power supply with Radio Shack part numbers.
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Old 5th August 2009, 07:55 AM   #6
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The regulators with part numbers. The 2sc5200/sa1943 I got from here http://cgi.ebay.com/2SC5200-2SA1943-...d=p3286.c0.m14
The bd139/140's I salvaged from a couple broken Nikko RC cars.
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Old 5th August 2009, 09:58 AM   #7
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3 lowpass filters in a high gain loop?
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Old 5th August 2009, 05:48 PM   #8
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Yours more stable and higher impedance than trying to drive two
complimentary Alephs directly into the emitters. And the single
emitter drop across the split sense resistor(s) makes for less
resistance seen in series with the load. I've got two emitters
drop, and usually throw schottkys in there to take up some of
voltage gap. But, I am also biased for AB....

I'm still not sure which emitter, or the center, is the best place
to hitch the bootstrap. It definitely affects stability.

Was my intent to copy a triode's plate voltage swing and both
share the load, such that it appeared a much bigger triode.
Needs just such a follower to make that happen the right way.
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