MOTM

My two cents:

Make it switchable.

DC (and "precision audio") path is around a low offset voltage opamp
that's fairly good for audio range as well (i.e. an LF411, but no OP-07).

Plus a discrete, no multistage feedback, "vintage" mixing amp.

You need a 2p2t switch to select between both options. One half of the
switch chooses the output, and the other half handles the virual summung
node to prevent the vintage path from compromising the precision path.

Precision path might be ordinary virtual GND summing node.

A similar thing for the vintage path might be the emitter of a transistor
with its base grounded.

From each input pot there would be two summing resistors, one to the
precision summing node, one (AC-coupled) to the almost-virtual-GND
emitter summing node. When the output is switched to select the precision
path, the emitter of the vintage path would be connected to GND to
avoid any talkback over the finite emitter impedance.

Hey, think of it: There are many compromise designs that try to cover
both worlds, and there are some dedicated designs which are good for
one but bad for the other application - so why not make the module
switchable. This would also allow the user to demonstrate the difference
in sound with the flick of one switch ...

JH.




-----Urspr\ufffdngliche Nachricht-----
Von: J. Larry Hendry <jlarryh@...>
An: <motm@egroups.com>
Gesendet: Mittwoch, 19. Juli 2000 02:23
Betreff: Re: [motm] Mixer thoughts


> Paul S wrote:
> So, I have toyed with at least 4 different ways to go, including a 100%
> discrete cascode JFET design. But what I'll have to do is just 'bite the
> bullet' and pick the best compromise part.
> ----------
> Well, since the MOTM module design already centers around AC mixers on the
> inputs, why not make the killer DC mixer for now and the killer AC mixer
> later?  Would it be such a shame to have two?
>
> Just another thought to add to the "different ways to go"  list.
>
> Larry H
>
>
>
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