My situation is specific to op-amp based LPF, but applies equally to any kind of filter/buffer/transmitter. With today's ultra low noise opamps (AD797 at [0.9/sqrt(Hz)]) resistor noise can (usually) dominate even a simple circuit.

(even an 8nv/sqrt(Hz) opamp sees a sqrt(2) increase in noise with a 4k resistor)

I would like to keep resistor values low (~1k) but such low input impedences mean that significant current (~5mA) is flowing and as a result excess (1/f) noise tends to dominate even in metal film resistors.

My first thought is wirewound resistors, but I am unsure of the inductance of the average wirewound (e.g. Vishay-Dale 3W RS) or its effect at the input, or (worse) in the feedback loop.

Can anyone comment on using WW resistors in this kind of application? Are there other ways of achieving 20-bit S/N?

Thanks for any insights.