Archive of the former Yahoo!Groups mailing list: MOTM

----- Original Message -----
From: Cary Roberts <cary.roberts@...>

Maybe I'm missing something here, but do you need more than one
opamp for gain make-up? I thought the goal was the less the better.
Personally I'd like to see all the inputs treated equally. If
people want AC coupling on a few of the inputs they can tack solder
a cap on the input jack. Or use TRS jacks - half-inserted would
be AC coupled, all the way in would be DC coupled.
----------

List - Sorry for the DIY content, but I know no other way to describe what I
am thinking.

Cary,
I think you are missing that NONE of the op amps that could be selected for
AC would be good for high accuracy DC (at least that is what I read - not
trying to put words in anyone's mouth). In my suggested design no signal
would go through more than 2 op amp stages (minimum if you do any summing
anyhow). Total op amps = 1-1013 and 2 1/2 OP-275s or similar. The
difference with what I am suggesting is 2 different outputs. Output 1 for
DC only where the high accuracy DC (2 or 3 inputs) hits only the 2 stages in
the 1013. The other output where each AC/DC input hits first a OP275 (or
Paul's audio choice). The final summer is a OP-275 with inputs from the
other 275s and the first 1/2 of the 1013. All the polarity ends up right
and you can have up to 7 inputs (8, if you give up the panel space needed
for master on the output stage). Remember one of the DC only inputs is
1/volt oct and no attenuation.

Larry H

P.S. All you guys wanting the dual-function, auto-retracting, super
knob/controls keep to yourself. <snicker>