Sidecar aux summing

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Cosmonaut

Well-known member
Joined
Aug 25, 2009
Messages
135
Location
Vigo, Spain
I'm planning my new sidecar made with trident 65 channels, the main L-R will be done with the ACA boards, but I'm trying to design a board with 8 summing mono devices with balanced outs, for using them as aux summing.
It would be done taken the signals from the aux bus, the bus R is 12k on every bus, and using a circuit similar to the one used in the original, trying to use the same voltage rails (+18/-18), the minim number of electrolytics in the signal path, a modern low noise opamp: AD8512, LME49720... and feeding the outputs from these to a That 1640 for balancing purposes.

My first will be a copy of the trident aux schematic with other opamps, measuring stability HF and offset.

Anything else to take into account?
 
Looking at the datasheets seems that AD8512 and LME49720 will not work at +/-18...I have many OPA2134, do you think is worthy to try them for summing?
 
> That 1640

Doesn't that part need a LOW source impedance for low THD? Apologies if I've mixed it with another part.

Typically you find gain after the master fader. At least equal to the amount of reserve you want "in hand". If levels are set so master sits at -12dB normally, you have many dB to "push" a weak mix passage; and this normally means 12dB gain post-master.

> not work at +/-18

It will, if it NEVER sees 18.1V. (Even then it may last years.)

But I would not be shy about putting say 330 ohms in each supply rail, 470uFd to ground. This decouples some rail-hash, sneak-back from other stages, and also drops a few volts. +/-15V ought to be enough for any modern studio output.
 

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