Carey,

You did not say why you want to connect the mixers together so it's a bit 
of a guess what you are up to.  But nothing good will happen if you connect 
the summing nodes together.

Assuming both opamps are working linearly, then both negative inputs are 
equal to both positive inputs which are both at ground potential.  Thus, 
the capacitor you show added will have the same potential (zero volts) at 
both ends of it and no current will pass.  So there will be no signals 
coupling from Audio 1&2 to Audio 3&4.

As far as problems, the capacitor could make one or both amps 
unstable.  Much depends on the type of amp, the layout, etc.

If your goal is mixing all four input signals, you will need to do 
something different. For example, remove the bottom opamp and connect the 
two summing nodes with a piece of wire.  Then you will have four inputs 
being summed and the resulting output appearing at the top opamp's output.
MD

At 06:31 PM 11/9/2004, you wrote:
>I need to connect two mixers together in an
>existing circuit and I only have access to
>the summing junctions of each mixer.  Will
>a circuit as shown below work with the two
>mixers summing junctions connected with a
>capacitor (C)?  What problems should I expect?
>Carey Fisher
>(view with fixed font)
>                                        _R_
>                                   |---|___|---|
>                                   |           |
>                                   |           |
>                      _R_          |           |
>           Audio 1  -|___|-----.   |           |
>                      _R_      |   |   |\|     |
>           Audio 2  -|___|-----o---o---|-\     |
>                               |       |  >----o----  Mixer Out
>                               |      -|+/
>                               |     | |/|
>                            C ---   ===
>                              ---   GND _R_
>                               |   .---|___|---.
>                       _R_     |   |           |
>            Audio 3  -|___|----|   |           |
>                       _R_     |   |   |\|     |
>            Audio 4  -|___|----o---o---|-\     |
>                                       |  >----o----
>                                      -|+/
>                                     | |/|
>                                    ===
>                                    GND



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