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 :-)

I have a 13E1 design which makes 25 watts, but has two drive stages and 15 dB
global NFB.
This design like your 211 is too complex to be considered simple.

Simple is where there is no NFB, so one gain stage can be omitted, and
sensitivity
is such that there is no preamp needed, and so just a triode driver with 300B

and a horn speaker is all one needs. Power needed is about 0.5 watts max most
days
although the ceiling is 5 watts.
THD is low because PO is so low.

Patrick Turner.



--
Nick

"Life has surface noise" - John Peel 1939-2004