Volume Pot Placement

[AndrewCE]

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I want each channel of this mixer to have its own volume control, and i'm wondering what is the best place for it. Putting it before the input buffers would alter the loading characteristics, and I don't want that. Putting them after the buffers (before the 10K resistors), changing the volume would alter the mix of the channels, which arguably is what I'm trying to do, but I can see that getting complicated. Opamp-gain-altering pots might work, any opinions? What is the best way to have a volume control on these channels?