Active Summing mixer using THAT Ic's and some...

[radiance]

Ok, this should be it. One more question though. Right now I've the ground from the master fader connected to G1.
Is this correct or should it be G2?

[JR.]

Bingo...

If that opamp is driving the outside world perhaps add a 50-100 ohm resistor in series. Also good practice to use small cap in parallel with 100k feedback R with similar cap across R to G2 (for symmetry. I'd tune that RC for say 200 kHz or so (say 10pF).

JR

[radiance]

Thanks again...I'll report back sometime next week.
Have to move some more stuff to France from the Netherlands within the next few days.

I've driven about 20.000 KM the last couple of months. Feel like a trucker he he...

[radiance]

Hey John,

I tried your approach on a piece of prototype board.
There was not much difference (noise & hum wise) as compared to my previous attempt. I think this way of doing things is more for big consoles. My mixer fits into a 4 unit rack case
Thanks again...

[JR.]

If there is little difference between the two grounds you won't notice an improvement from referencing. One thing to keep in mind the output ground can change and be influenced by what external gear is connected, shield currents, and who knows what. If the internal local grounds don't track with this output ground the differential referencing may prove more useful.

In a physically small chassis if all of the grounds are brute force bonded together this might be ignored. I try to avoid brute force when dealing with factors I can't control (like external gear).

if the simpler approach works, it works...

Good luck..

JR