Super Simple Class A MOSFET Redux

drdagor · 17th July 2008, 03:46 AM

I'd like to get the discussion of super simple class A MOSFET designs going again. Up through about three years ago there were some wonderful design ideas for single FET or other simple MOSFET designs. Mads' SEWA got over 100000 look-sees. Before that the Macura/Bunta design (overall similar to Sewa but with active current sources) looked very interesting. These were built on the venerable IRFP250 and 350 respectively. And of course these owed a debt to "First Amp" and to some Elliot projects.

So what's the thinking today? Are these two designs as good as it gets for simple, follower style class A amps? Has anyone gone further with either of these two circuits? Please take a look at simple followers again and see what next steps there might be for us to try.

Schematics for
SEWA Rev A. are hiding at: http://www.diyaudio.com/forums/attac...amp=1130445540

Sadly the old imageshack shot of the Macura/Bunta MOSFET power follower is gone. Anyone got a link for this treasure?

kvant · 17th July 2008, 05:36 AM

Quote:

Originally posted by drdagor

Sadly the old imageshack shot of the Macura/Bunta MOSFET power follower is gone. Anyone got a link for this treasure?

Do you mean this one?

KSTR · 17th July 2008, 03:23 PM

... and not to forget the 99c:
http://www.audiodesignguide.com/PowerFollower/

The Macura/Bunta (and the SEWA probably, too) might also benefit from the idea behind Mr.Ciuffoli's design -- seperating the current loops. One simple but very clever idea, indeed.

- Klaus

drdagor · 18th July 2008, 09:26 PM

Very cool (for a hot amp). Ciuffoli has hit on solutions to a couple of intriguing problems. Add a common mode choke to his power supply design and this thing should have next to no hum and should be very stable to boot.

Thanks for putting me on to it.

drdagor · 18th July 2008, 09:28 PM

...for posting the Macura/Bunta circuit. That's the one I had lost track of.

drdagor · 23rd July 2008, 10:06 PM

http://www.elecfree.com/circuit/ampl...er-by-2sk1058/

This is a single MOSFET source follower running class-a.
From Mark Houston -- another Aussie amp specialist.

I wish he published his circuit for his 12AU7 tube preamp.

jacco vermeulen · 23rd July 2008, 10:17 PM

Could be a typo and he's still using the Sil. Chip 12AX7 design he assembled.

17th July 2008, 03:46 AM	#1
drdagor diyAudio Member Join Date: Mar 2004 Location: Seattle	Super Simple Class A MOSFET Redux I'd like to get the discussion of super simple class A MOSFET designs going again. Up through about three years ago there were some wonderful design ideas for single FET or other simple MOSFET designs. Mads' SEWA got over 100000 look-sees. Before that the Macura/Bunta design (overall similar to Sewa but with active current sources) looked very interesting. These were built on the venerable IRFP250 and 350 respectively. And of course these owed a debt to "First Amp" and to some Elliot projects. So what's the thinking today? Are these two designs as good as it gets for simple, follower style class A amps? Has anyone gone further with either of these two circuits? Please take a look at simple followers again and see what next steps there might be for us to try. Schematics for SEWA Rev A. are hiding at: http://www.diyaudio.com/forums/attac...amp=1130445540 Sadly the old imageshack shot of the Macura/Bunta MOSFET power follower is gone. Anyone got a link for this treasure? __________________ Dr. Dagor

18th July 2008, 09:26 PM	#4
drdagor diyAudio Member Join Date: Mar 2004 Location: Seattle	Ciuffoli -- Very cool in any language Very cool (for a hot amp). Ciuffoli has hit on solutions to a couple of intriguing problems. Add a common mode choke to his power supply design and this thing should have next to no hum and should be very stable to boot. Thanks for putting me on to it. __________________ Dr. Dagor

18th July 2008, 09:28 PM	#5
drdagor diyAudio Member Join Date: Mar 2004 Location: Seattle	Thanks Kavant... ...for posting the Macura/Bunta circuit. That's the one I had lost track of. __________________ Dr. Dagor

23rd July 2008, 10:06 PM	#6
drdagor diyAudio Member Join Date: Mar 2004 Location: Seattle	Here's another worthy super simple MOSFET http://www.elecfree.com/circuit/ampl...er-by-2sk1058/ This is a single MOSFET source follower running class-a. From Mark Houston -- another Aussie amp specialist. I wish he published his circuit for his 12AU7 tube preamp. __________________ Dr. Dagor

23rd July 2008, 10:17 PM	#7
jacco vermeulen diyAudio Member Join Date: Oct 2004 Location: At the sea front, Rotterdam or Curaçao	Could be a typo and he's still using the Sil. Chip 12AX7 design he assembled. __________________ Not so much,.......if it says "ZM" in the corner.


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17th July 2008, 03:23 PM	#3
KSTR diyAudio Member Join Date: Jul 2007 Location: Central Berlin, Germany	... and not to forget the 99c: http://www.audiodesignguide.com/PowerFollower/ The Macura/Bunta (and the SEWA probably, too) might also benefit from the idea behind Mr.Ciuffoli's design -- seperating the current loops. One simple but very clever idea, indeed. - Klaus

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