Jim Thompson wrote:

Is S.E.D actually sci.electronics.DUMMIES ??

When I saw this original post....

From: "powerampfreak"
Newsgroups: sci.electronics.design
Subject: Somebody explaining this design?
Date: 9 Mar 2007 12:08:35 -0800
Organization: http://groups.google.com
Lines: 11
Message-ID: .com

I commented, "Looks like crap to me ;-)"

The response from the hot air crowd, you know, the ones posing as
guru's, was an implication that I was incorrect.

So I posed a simple question... do a hand analysis of the gain of the
circuit.

It's a simple analysis (if you're not a faker :-)

It's been about 40 hours since I posted that request/taunt.

Nary a peep.

Phil Allison answered your question.

" ** The overall gain is: 6.82 times 4000 / Rg

Where Rg is the total resistance between the two emitters.

6.82 is the fixed gain of the op-amp stage = 150 / 22.

4000 is the effective differential collector load - ie 4.4k with 44k in
parallel.

At low gain settings, the max Rg value is limited by the two 4.7k ohms.

At circa 1000 times gain, Rg is affected slightly by the effective emitter
resistance of the two 4403 compounds - about 4 ohms in total.

So, at max control setting the gain is:

27,280 / 26 = 1049

For 100 times gain, Rg = 272 ohms "


Apparently the decline in your mental faculties means you can't work it out for
yourself. It's not exactly difficult.

Graham