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Subject: Re: [motm] some questions

From: "Richard Brewster" <pugix@...>
Date: 2003-08-09

> 1/ multiple outputs to mults
>
> While this may not damage the modules, it is certainly not recommended.
> The outputs are low impedance stages and are not meant to be
> crosscoupled. The mults are for taking a single output to multiple
> inputs.
>

Actually if the outputs go through 1K resistors (MOTM-300, MOTM-410,
MOTM-440, etc.) there is no harm in connecting these together by a multiple.
They will mix fine. In fact this is one of the design reasons for using 1K
resistors on the outputs, as noted in Electronotes. The signals mutually
attenuate each other, so that the combined peaks will not exceed the normal
output level (usually +5 to -5 V).

But not all modules have a 1K output resistor. In particular the MOTM-820
has low impedance outputs for driving longer cables. Something similar is
true of the Oakley Multimix. So these outputs may not mix well in a
multiple.

It is hard to damage an op amp by connecting its output to another output or
a ground. You don't have to worry that shorting an output to ground when
plugging patch cords will do any damage. I once repaired a pre-built Serge
module where one of the op amp outputs was directly grounded by a short in
the circuit board etch. The symptom was that no matter where I patched into
the Serge, I always got the signal output of that module. It was driving
the ground! After I cut the offending etch, it all worked fine again.

-Richard Brewster