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drdagor 17th July 2008 03:46 AM

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:

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

Re: Super Simple Class A MOSFET Redux
2 Attachment(s)

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:

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

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.:smash:

drdagor 18th July 2008 09:28 PM

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

drdagor 23rd July 2008 10:06 PM

Here's another worthy super simple MOSFET

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.

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