sum 4 signals without "mixing" them?

[alex1982]

Hello,

First post here, sorry for the really noob question:

I have 4 signals that output to separate plugs. I wish to add a 5th master mix output, ideally summed passively.

How do I sum the 4 signals without them getting mixed on each output?

Thanks in advance
Alex

 

[KatieandDad]

Feed each signal through a buffer before summing them.

 

[alex1982]

Thanks, KatieandDad !

I'm looking at this circuit:

Would this be suitable, repeated for each signal with outputs summed?

Thanks for your time
Alex

 

[KatieandDad]

I'd just use a quad op-amp.

 

[FoMoCo]

If each of your outputs have a low enough impedance, and the input you're driving has a high enough impedance, you can get by with 4 10K resistors, at least to try and see.

 

[richie00boy]

Look up summing op-amp circuit. It's an inverting amplifier, and by the nature of how it works all inputs are isolated from each other. This is how mixing consoles are made.

 

[alex1982]

Thanks everyone for your input!

I found this 2ch summing circuit using a 741.
Would you recommend increasing the resistor values if I was to add 2 more channels?

Thanks again
Alex

An externally hosted image should be here but it was not working when we last tested it.

 

[Mooly]

Each 10k on the input defines the input impedance and the gain for that channel. 10k is fine. The 1k isn't really needed, you can short it out. A better opamp could be worthwhile, even something like a TL071.