I have used the innards of a Korg Mini-KAOSS Pad to add some amusing effects to one of my electric guitars, but in order to do this I had to remove the original input connectors and wire my pickups directly to the input circuitry.
The input voltage is fine, however I do now have a problem with a high pitched digital sounding whine when using effects. My assumption is that the input connectors probably had some type of rolloff circuitry (almost certainly passive) and in removing these I am getting interference from the high frequency oscillators in the DSP circuitry.
As part of my remediation I am increasing shielding, but realise I probably need to add a filter to remove higher frequencies.
tl;dr - is there a simple circuit (ie probably just an R/C) that I can pop in to roll-off rapidly above the usual frequencies I would get from my guitar strings?