is there any improvement or change that can be made by adding a capasitor to a guitar that only has a volume control pot?if so where in the signal line do you add it? what change or improvement in sound would it make?
You can put one across the volume pot so it doesn't get so muddy when you turn it down, or you could put a cap and resistor in place of a tone pot to reduce the treble a bit.
The first thing I mentioned may or may not be useful depending on your rig, the second one is kind of silly.
With out some sort of resistor a cap would shunt all the highs to ground be like having the tone pot at 1 all the time. You could put it on a switch with a fixed resistor or a trim pot. If you dont want to drill any holes for a pot you can use the existing volume pot and put a stacked pot in there. This would give you volume and tone in one position.
it'd probably be better just to take out your tone pot(s). even with tone pot at 10 it takes your highs too. try that. its worth a try.
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I don't know if this is already linked somewhere, but it is without a doubt the most beneficial read I could ever find online about guitar wiring and electronics, and will answer your question and much, much more: