Summing circuit idea

[chrissugar]

At the Gearslutz forum Tim Farant (BuzzAudio) posted an interesting ballanced summing circuit:
http://gearslutz.com/board/showthread.php3?t=30281

chrissugar

 

[matta]

I for one would like to see how this develops... Anyone more experienced keen on drawing a circuit and fabbing boards for something like this? I wouldn't mind a decent 8 channel summing mixer that fits into a 1U rack? Anyone keen?

Cheers

Matt

 

[Samuel Groner]

I think it was Igor who pointed out the faults with this approach, imbalances, grounding issues etc.

I don't think there are too many faults with this approach. For good CMRR, you need to match the resistors and caps around the opamps pretty well, and the transformer itself needs good CMRR. BTW, driving a transformer with 150 Ohm source impedance will not yield lowest distortion and best frequency response.

Are there ways to design a virtual earth amp (without transformer) that does not amplify common mode signals?

Samuel