Class A power follower

jerluwoo · 28th July 2009, 08:15 PM

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.

Wavebourn · 28th July 2009, 08:39 PM

Triple emitter follower and servo with a positive feedback?

Looks interesting.

jerluwoo · 5th August 2009, 12:58 AM

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.

Wavebourn · 5th August 2009, 01:07 AM

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.

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

http://www.diyaudio.com/forums/showt...39#post1889739

jerluwoo · 5th August 2009, 07:52 AM

Here is the power supply with Radio Shack part numbers.

jerluwoo · 5th August 2009, 07:55 AM

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.

darkfenriz · 5th August 2009, 09:58 AM

3 lowpass filters in a high gain loop?

kenpeter · 5th August 2009, 05:48 PM

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.

28th July 2009, 08:39 PM	#2
Wavebourn diyAudio Member Join Date: Sep 2006 Location: Pleasant Hill, CA	Triple emitter follower and servo with a positive feedback? Looks interesting. __________________ The devil is not so terrible as his mathematical model! Wavebourn: We Create Creativity!

5th August 2009, 01:07 AM	#4
Wavebourn diyAudio Member Join Date: Sep 2006 Location: Pleasant Hill, CA	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. I am currently working on a new prototype that uses this concept: http://www.diyaudio.com/forums/showt...39#post1889739 __________________ The devil is not so terrible as his mathematical model! Wavebourn: We Create Creativity!

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5th August 2009, 09:58 AM	#7
darkfenriz diyAudio Member Join Date: Jun 2004 Location: Warsaw	3 lowpass filters in a high gain loop?

5th August 2009, 05:48 PM	#8
kenpeter diyAudio Member Join Date: Nov 2007 Location: Dallas	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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