Audio mixer for bench diy

[diy didi]

Hi all
I want to build a 4 channel audio mixer for my work bench.
I have drawn up a circuit. Just a basic virtual earth configuration with an inverting opamp.
My question is, do I have to ensure that all input signsl leave the mixer output socket, in phase? That will mean I need to use a second opamp to invert the signal again.

 

[jazbo8]

Only if you think absolute phase is important, since it’s just for your work bench, I doubt it would matter much.

 

[nigelwright7557]

Hi all
I want to build a 4 channel audio mixer for my work bench.
I have drawn up a circuit. Just a basic virtual earth configuration with an inverting opamp.
My question is, do I have to ensure that all input signsl leave the mixer output socket, in phase? That will mean I need to use a second opamp to invert the signal again.

It doesn't matter about phase.

 

[MAAC0]

If it is for Your bench and You plan to measure / compare signals on a scope, it is easier if the signals are in Phase. If it has balanced outs, just invert the pin 2 & 3 wires.

 

[rmaudio]

Similarly if using a differential input circuit then you can swap there. If you're going to be taking measurements from the mixer output and elsewhere then easier to have everything in phase. Will work either way but less possibility for confusion and one less thing to think about.

 

[jfetter]

If using to measure ie TIM,fft, phase etc , then I would use a totally passive circuit. No pots but rather multiple fixed 0,-6,-12db input jacks for each channel. Also thin film resistors. Possibly simply a single -6 on all.