[[email protected]]

On Monday, November 7, 2016 at 9:06:17 AM UTC-5, Scott Dorsey wrote:
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.

The bad news is that a matched pair like the THAT array dramatically
increases the parts cost but then again you're saving the cost of some caps
too.
--scott



without C1 (with C1 shorted) there is a high DC gain and any offset voltage will be amplified. Matched parts will reduce that offset but that is still a lot of DC gain.

m