inverting amps and impedance

[Marco Pancaldi]

If I use a simple classic scheme for a little mixer - inverting opamp with 10k input resistor for each source - what is the correct pot value to use BEFORE the input resistor? Schemes on the net have 10k pots before 10k "summing" resistors, but I think a 10K pots needs larger input Z after them, in the 100k range.
Comments?

Thanks
marco

 

[pstamler]

You're correct about needing a larger resistor after a 10k pot. The tradeoff is that a 100k resistor generates more noise. If this is an all-line-level mixer that may not be a problem.

Peace,
Paul