Summing and mix buss.. question on topology and design.

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Yes Brian, that's a good move.
Back in the 70s we built the first console for the show 'Jesus Christ - Superstar' when it opened in London. It had 106 mic channels and was arranged as 6 stereo mixing buses. To keep the mix-amp noise down, I split the buses into 4 sections each with their own mix amp, then combined them in a master section.

Nowadays, I would do it balanced; there's a 3dB (or is it 6?) noise advantage in the balanced mixing, plus 6dB in overload advantage; and you can say goodbye to ground path problems.

Analag's tube mixing schematic is interesting, but I don't see much advantage in using the transformer impedance converter and tube amplifier, when you still only have an unbalanced mixing system. Would it not be more sensible to use a good low noise solid state virtual-earth type mix amp operating at low gain, then use a simple tube amplifier as gain makeup? :wink:
Ted Fletcher
 
I have implemented the pre summers per Brian's suggestion in SPICE and the results are much better. Going fully balanced would be cost prohibitive for me at this point so the virtual earth scheme is where I'll go next with this design.

Analag
 

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