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lumanauw 26th April 2007 03:43 AM

Mullard SS power amplifier
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Has anybody heard this amp? From the schematic it is interesting, singleton input (BC158B), level shifted to differential (2xBC147B) where the inverting input senses the output stage (via 3R3/6W). No Vbe multiplier, all NPN output stage.

AKSA 26th April 2007 04:35 AM

Hi David,

Sliding bias Class A, neat huh?

Only even order distortion, no output device ever switches off, short protected - this is a pot of gold, and appeared in the Elektor Circuits handbook some years ago.

This circuit would sound good, but there's a fair bit of compensation, and if you increase device speed with more modern semis the compensation would need considerable revision.

Only the quasi comp and output coupling cap make it unfashionable, but it's failsafe and inexpensive to make.


lumanauw 26th April 2007 09:50 AM


You have heard this amp? How do you describe the sound?
It is very interesting design. I never saw SS amp designed like this. Maybe this is a design from tube guys? Not much stages, but clever ones.

AKSA 26th April 2007 11:26 AM

Sadly, David,

I have never heard this amp, but I would expect it to sound a lot like an Aleph 5. It is, after all, single ended push pull.



destroyer X 26th April 2007 11:41 AM

Lovely schematics.
I have never listened this one...something to construct and to listen.

Maybe in November or December...when i will have time to do it.

I am scheduled with a lot of things.

Will you construct Lumanauw...i will be happy to know your evaluation.



Upupa Epops 26th April 2007 12:50 PM

... other lost treasure from shadow of antiquity.... only seven transistors, how amazing... :D

destroyer X 26th April 2007 01:35 PM

I have made simulations Lumanauw....interesting.

Keep me informed about your progress, please, if construct this one.



ChocoHolic 26th April 2007 02:03 PM

....aloha... never tried such an amp... But it is looking like I should put it to my ToDo list.
And hey guys... with modern transistors I am sure that we could strip it down to five transitors...
May be it is even possible to settle a DC-suitable biasing of the input stage+feedback. Then I could imagine to use a +/- supply and get rid of the ugly output cap.

Quite a nice inspiration for further Rookie attempts..

sometimes you are digging out real nuggets.

destroyer X 26th April 2007 02:15 PM

I love those old things, i am also trying to make it symetrical related the supply
2 Attachment(s)

We have ancient traditions that has formed my people...we have, Brasilians have, indians in our blood.

This way, the respect to old folks, old things done and tradition has some power here, in special inside myself.

Good to perceive that you have that respect too Choco.

I was watching this indian....i can see this face, this nose, hairs and many signs in each of us in this country.

They love old things, the experience of old folks.

This is nice.



latala 26th April 2007 06:36 PM

I have come across this design on two occasions from mullard
once as a germanium design and also as a silicon unit
This is pye mode operation and the amp slides from class A mode into class B as the amplifier is driven harder!
As a remember it was a nice sounding amp
Regards Trev

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