You need a cap after the pot because the opamp input is DC elevated.Mark Tillotson said:The capacitors should be before the pots, not after, so they see a constant load impedance and keep fixed frequency response.
But they are not in parallel, they are in series. Assuming a low impedance source, the maximum output impedance from a 50k pot will be 12.5k. The total series resistance is thus 112.5k. With a 10k pot it will be 102.5k, so you get 0.4dB less noise - not worth worrying about.
But with 10k pots you can change the 100k's down to a much lower value, with a big effect on noise.
Shoot! This has got me thinking: I have been using Log pots in my original 10k pot mixer circuit.Use linear 10k pots, with input resistors 10k.