Grainger - thanks for the reply. I have a PEC 1Meg linear pot (from a previous project), and will try that first with a 110k law-faking resistor, but will probably move to a stepped attenuator. I live in Hong Kong, and so I can pick up different caps, etc. fairly easily (although they aren't always particularly cheap). I think I'm going to have a go at re-working the top plate too (to move the inputs/outputs to the back).