[Don Pearce[_3_]]

On Mon, 07 Nov 2016 13:52:57 GMT, (Don Pearce) wrote:

On Mon, 7 Nov 2016 05:36:04 -0800 (PST), wrote:



I disagree strongly about there being no problem with DC bias on modern
electrolytics, but there ought to be a couple volts across C2 and C3 if
I read this right.

C1 is the more interesting case.

m

It is. It has to be big to keep a low impedance relative to 22 ohms in
the high gain situation.

But looking at the topology it is clear that both C2 and C3 could have
been eliminated by returning the overall feedback (R12) to Q1. That
would have set the DC bias in the front end, and C1 could have been
dispensed with too. A matched pair for Q1/3 - preferably in a single
can - would make that more than feasible.

d

Should have added: Maximum gain is set by the collector current of
Q1/3, which is of the order of 1mA. That gives an intrinsic Gm-based
emitter resistance of about 26 ohm (total 52) which appears in series
with the actual 22 ohm resistor.

d

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