Tone Capacitor Help

[Peter Maxwell]

Hi Everyone,

First of all, I'm new here and am building my first guitar, so apologies if I write anything that doesn't make a ton of sense. Second, I did my best to make sure this topic hasn't been discussed elsewhere on the forum, but if it has, my apologies, and I'd appreciate a link to the thread.

I'm building an electric semi-hollow, and I'm having an issue with the tone control, and specifically the tone caps (I believe), that I can't figure out. I finished wiring the prototype last night, and after some troubleshooting (bad volume pot, had a treble bleed resistor/cap acting as a ground loop) everything's in working order except that I get no audible response from the tone control - you turn the pot, and nothing happens. My guesses were either (a) I screwed up the wiring, (b) the pot is bad, or (c) the cap is bad. I'm using a 500k pot and a .047uF capacitor. However, I don't believe the wiring is screwed up or that the pot is bad, because when I wired a 100uF cap in parallel to the .047uF, I get a tone response as I'd hope for. However, I also believe the cap is sound, because I appear to be able to both charge it and track a discharge using a multimeter (I'm charging it with the ohm/resistance setting, and then testing the voltage as it drains). Also, the fact the the 100uF cap seemed to work really threw me, as from what I understand that rating is way higher than you would typically use for a tone cap. Any thoughts?

I've attached the wiring diagram below, and my apologies if it's hard to follow - while it works for me, I'm also guessing it isn't typical. It includes a Ghost piezo system (the terminals on the left, battery, need for ganged pots, etc.), and, ugh, a lot of switches. Two notes:
1. The two horizontal blue lines connecting the two volume pots and two tone pots are just to show that the pots are ganged and do not represent a wired connection
2. The light blue lines that connect the left terminals on the volume pots to the middle terminals on the tone pots DO NOT connect to the left terminals on the tone pots (just a consequence of the program i used to draw the diagram)

Let me know if there's any additional information I can provide to help clarify things. Also, thanks a ton in advance for the help - I feel like a lost half the hair on my head last night...

Peter

[David King]

That looks right to me. You just need a variable resistance in series with a cap going from hot to ground and that's what your diagram is showing. My best guess is that it is working but it's too subtle to hear the difference because your cap is a bit too small. You might try a .1µF and see if that helps.
Could it be that you're using a very long and low quality cable into a not very stellar amp? High cable capacitance into a low input impedance can overwhelm passive circuit but if your Ghost system is buffering the mag pickups, there's no excuse.

[Peter Maxwell]

David, thanks - I hadn't thought about the cable/amp possibility. I'll try that out when I get home today. I was using an 8' cable, but i'll just use my pedal patches and see if that helps at all. And I'll also try to get a hold of a capacitor tester to try out a few ratings. Thanks again for the thoughts - Peter

[Donl Mathis]

I'm confused about the PWR connection. From a Ghost document I found somewhere, it looks like it's supposed to provide power to (truly) active mag pickups, i.e., the ones that have circuitry built into the pickup itself. In your diagram, it's connected through a big capacitor to the summing point for the magnetic pickups. Since a big capacitor blocks DC voltage, it can't be providing voltage to active pickups (if they are).

Did you find that connection on some other document somewhere? What were your thought processes with that bit? I'm just wondering if (1) it's not necessary, and (2) could be placing an undue burden on your main signal path.