I built my first bass cut knob last week and used the cheapest ceramic capacitor I found.
I was wondering if this would affect the sound when the cut is on. I know that the type of capacitor has no influence on the sound of the guitar when used in a tone knob, but Franlin Pickups website states that this is because of the tone knob design:
“The type of cap is not as important as the value of the cap, for guitar. In an Amp, your cap type is much more important, as the signal is being passed through the cap all the time. In a guitar, you’re not hearing the cap itself, you’re hearing what the cap is impeding”. Lindy Fralin
So, is the cap style more important when used in a circuit were what goes through it is sent to the hot wire, as in a bass cut or (I believe) a treble bleed? My ears tell me no. I don't here anything happening to my tone when I turn the knob besindes the lowest frequencies going out. But I'd be interested to hear the opinion of people with better ears and more experience thant me.
I avoid using ceramic caps for tone controls, not because I think they will sound differently, but because they are typically contructed to poor tolerances and aren't high quality. Caps are relatively inexpensive, so it's not an area I look to save a couple of pennies. I usually use the polypropylene "greenies".
An amp is a different situation entirely. I don't think the analogy to a passive guitar circuit is a good one whether we're talking bass cut or treble cut. If you've built this and it sounds good, trust your ears. No reason to go rooting around in there just to change the type of cap.