Aux send/return and mix

[ricothetroll]

Hi,
I drew that circuit for using Ableton Live as a multitrack looper. As it is quite complicated to synchronize everybody's loopers (Boss RC-20), each instrument would be routed in Live in a different input, and then sent back to everybody's amp. We could also then send a metronom to the drummer (that's me ). The principle is the following (for one musician) :
http://www.wuala.com/ricothetroll/public/DI+aux.png

The audio interface is a Motu 828 mk1, using balanced line in/out.

After a first test with my guitar (single coil pickups), I noticed that I already had enough level with the line in pot at the minumum. As I want to be sure not to saturate the audio interface's input (with an active bass or a loud distortion for example), I put a pot to set the gain of the aux send.

Here is the whole circuit :
http://www.wuala.com/ricothetroll/public/Circuit.png

IC1A : buffer for the "direct" signal
IC1B : non inverting summing amplifier
IC2A : aux send buffer
IC2B : phase inverter (for balanced operation)
IC3A&B : balanced -> unbalanced

I tried to keep low value series resistors, to minimize the electronic noise. R4 and R20 may not be necessary as there is no switch.

I have two questions about that circuit :
- is the way I wired the aux gain pot ok ? I could have made IC2A an inverting amplifier and put a pot as feedback, but to keep a Hi-Z input R11 might have been big enough to cause noise issues. The pot biases both IC1A and IC2A.
- can I get rid of the coupling caps (C1-2-8-9) in order not to have those unwanted low cuts ? I calculated the values for 600 Ohms input/output.
- Should I increase R10 and R13, in case of unbalanced operation ? (SEND1(-) wound be shorted)

Best regards.

Eric

[ricothetroll]

No one ?