Seriously simple mixer... But I need help!

[Broadwave]

After all these years of sucessfully building various modules, I've come across something that is so mind bogglingly simple... but I just can't seem to think straight.

I have two very basic 4 input mixers with individual outs, but I need to switch them at some point to create a single 8 in mixer.

Is the rough drawing below ok? If not, then I need help (possibly a Lobotomy!)... any pointers?

Thanks.

EDIT: Or could I just put in a switch to join the 2 x 4 inputs together at the inverting op-amp inputs?

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[bubzy]

you seem to have two outputs there, it might be better to switch the signal AWAY from the lower opamp instead of adding it.

just my (mostly uneducated) opinion

[Broadwave]

[Sebo]

If you want duplicated output, I think the switch have to be before the resistors between the OpAmps.

[JingleJoe]

[bubzy]

like this i meant.
please excuse the awful drawing
on reflection, the switch is SPST.....brain not work good today

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[blue hell]

I would rather not short the outputs of them two opamps, if you switch then you do it after the the resistors, but I think the original schematic will just work ... although I cant quite get ny brain around it either

[bubzy]

yeah i guess that makes more sense. just move the switch to after the resistor, that way you eliminate one of the two outputs, you could, of course as joe said, put the switch before the input of the lower (or upper) op amp after the 4 resistors and switch between 4 and 8 inputs into one op amp

[elmegil]

Looks to me like the switch needs to be spdt though, not just simply shorting them together. Closed to second output amp, or closed to first output amp.

[diablojoy]

you could of course drop the switching by adding 2 more inverting opamps
to sum both of the existing outputs and then add a third output jack which would be the sum of all 8 inputs
that way both configurations are available simultaneously.
A fourth inverted output jack could also be added tapped off the output of the first extra opamp, if you want to send to 2 destinations for say 8 VCO's to 2 VCF's which might be interesting

[richardc64]

Add another input R to the top output amp and wire the switch to connect it to the output of the bottom input amp. The top mixer is switchable 4 or all 8 inputs and the bottom mixer is always 4 inputs.
Or add Rs to both output amps' inputs and use a dp switch to select 2 separate 4-inputs or one 8 with two outputs.

I like the first way for versatility.

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[andrewF]

switches are expensive
whynot add a 5th input to one on the mixers, no need for an attenuator pot, just the socket.
when you need 8>1, just patch the output of the 4 input mixer into the 5th input of the other.
it also means you now have a 5 input mixer.

If you are using minijacks, this could be hard-wired to the switches on the sockets so no need for a patchcord.

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[Broadwave]

Thanks for the ideas guys.

Who knew that such a simple problem would elicit so many responses : )

@AndrewF - So simple, and such an obvious way to go about it!

Cheers.

[Uncle Krunkus]

Would it add too much stuff to make all 8 inputs panable to either of the two outputs?
Then you'd get the best of all 8 inputs. Send this one here, that one there, etc.

[Broadwave]

[fonik]

[vladosh]

I see you replaced the switch with a waveform ..smart O_o

[JingleJoe]

[vladosh]

No Joe .. it's waveform ..i'm sure! ))

[vladosh]

..if you turn the switch a bit and make one more connection you can get sanmple and hold too ))

[richardc64]

[JingleJoe]