Stewart Pinkerton wrote:

On Sun, 16 Jan 2005 19:36:48 +0000, Nick Gorham
wrote:

Iain M Churches wrote:
"Eiron" wrote in message
...

How strict are the negative feedback rules?

It has to be single ended with no NFB as far as I recall.

I presume a Darlington pair or triple is allowed but if I use a triplet
of NPN/PNP/NPN or even an NPN/PNP pair then someone is going to argue
that it has a load of negative feedback even though it behaves like a
high gain transistor in emitter-follower mode.

The SET uses two halves of a 6SN7 and then a 300B, so three stages
per channel.

I may join in then, my 211 only uses three stages per chan as well :-)

But doesn't that have a *lot* more power?

My paper design does indeed have three stages, a central MJL4281
voltage gain stage which dominates the 'sound', flanked by emitter
followers at input and output. Four transistors in all, very simple
design, 5-8 watts of Class A operation, no loop feedback. Frankly, I
don't care what Turner et al think, it is a KISASS design which uses
BJTs in a way suited to that technology, in the same way that the
6SN7/300B is used in a way suited to that technology.

We know you don't care, but it doesn't worry us.
Your'e using FOUR bjts, not TWO.
Initially, you said you'd achieve simplicity with no loop FB.
But I betcha you are using a lotta NFB to get a result.
I think you have to, because those naughty bjts are unlistenable without it.

Have you considered two fets?

Feel free to use a choke feed to the mosfet drain, and cap couple to the load.

Patrick Turner.






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Stewart Pinkerton | Music is Art - Audio is Engineering