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My son, Dan, got new pickups (two humbuckers) for his Epiphone SG. As I had to rewire it for him, anyway, I thought if we used stacked, concentric pots, he could have individual volume and tone controls for each pickup in place of the single volume and tone control that it started out with. The guitar appears to have been constructed in a hurry and without much care--the inside front face of the control cavity to which the hardware mounts was not consistently flat nor of a consistent thickness--so when I went to mount the new hardware (we replaced the 3-way switch and mono jack with better quality parts, as well) it was not a pretty sight. Some shafts came through crooked and in the case of others, not enough of the threaded bushing came through for the nut to grab on and hold it in place. I responded to this by putting the guitar body flat on my drill press table and using Forstner bits of a diameter slightly greater than that of the individual pieces of hardware, I drilled away a bit of wood at the site of each device to leave a quite flat circular area consistently of nearly exactly 1/8" thickness at each place. Then the hardware mounted perfectly.
I mention the following now because, as things turned out, I suspect it was part of the problem with the humming that this thread refers to. With the two humbuckers, there was no convincing need for pickup shielding, but my son had on his own taken some conductive paint I had on hand and painted the pickup routs and the control cavity. Plainly the guitar had worked "fine" when new without this shielding. Of course, when I drilled into the front face of the cavity as described above, the conductive paint was removed where I drilled. Inasmuch as I did not see need for the paint in the first place, I could not imagine that removing part of it in this fashion would have any adverse effect.
I wired the guitar up initially based on a wiring diagram I found on line that was reported to be styled after Gibson's manner of wiring an SG with 2 humbuckers and a volume and tone control for each (my schematic attached). Basically the pickups were wired directly to the volume pots, the capacitors were wired between the volume pots and the tone pots, and the pickup selector switch went between the wiper on the volume pot and the tip of the jack. We found this worked out crazy. I could not find that I had wired anything up wrong, but the volume controls worked unreliably, the sound might turn on or off without obvious cause, and one of the tone controls could influence the tone of the other pickup, even when the pickup associated with the tone control was turned off!
In response to that, I devised my own wiring, based more on typical Fender wiring practices (although I am not aware of any Strats with 2 humbuckers!; my schematic is attached) and rewired it. In this case, the selector switch was between the pickups and the volume controls, the capacitors were between the tone pot and ground, and the wiper of the volume pot went directly to the tip of the jack. We got it all wired up and, at least at first glance everything seemed to work fine. Both pickups worked reliably together and alone and the volume and tone controls influenced the sound of the pickup they were supposed to control.
Night before last, I asked Dan how the guitar was working out, and he said it was great, "except if I touch the bridge or the knobs when I'm plugged in, I get this awful hum." I asked him to bring it down so I could take a look.
Yesterday morning I took it apart and did a little head scratching. I was afraid I might have forgotten to solder the bridge to ground connection, but that was fine. Everything looked okay. Everything was soldered to ground as it should be, and I had grounded both pots to each other on the stacked pots.
The only thing that looked odd (not in an electrical sense to me, but just in the sense that it was not a typical thing to see) was to have the cavity painted with conductive paint, except where it was drilled away to fit the hardware. Again, given that the guitar did not need conductive paint in the first place, I had a hard time believing that that would be part of the problem--those pieces of hardware had been attached directly to wood when the guitar was new, so I could not understand how having the hardware attached directly to wood now would cause a hum, just because there were some adjacent areas covered with conductive paint that none of the hardware came in contact with.
Anyway, being unable to find anything else to try, in the end I covered the bare wood areas around the hardware with copper tape carefully overlapping the pieces, I soldered a bare ground wire from piece-to-piece to more definitely connect those pieces of tape together, and then I soldered the end of that wire to the back of one of the pots.
When I first put it back together I freaked out, because the guitar was dead--no sound whatsoever. After a little more head scratching, I came to recognize that with the copper tape lying right under the volume pots with their hot leads, that the terminals were bent down and contacting the copper, shorting the signal to ground. I cautiously used a pair of needle nosed pliers to bend those terminals up away from the copper, and then the guitar worked fine--good sound, all controlled as it should be, and no more hum when I contacted the bridge or the metal control knobs. I banged away on the guitar for about an hour until Dan got out of bed and I could show him the improvement.
I am sorry for the length of this. I hope it does not inhibit anybody from reading it enough to respond! It was just a complex enough unfolding that I did not know how else to put it. Does it make sense to anybody, given that the guitar as initially built did not need to have grounding where the hardware was attached to the bare wooden face of the cavity, that it should need grounding there now just because some adjacent areas are covered with conductive shielding paint?
Thanks for consideration! Rob R
I mention the following now because, as things turned out, I suspect it was part of the problem with the humming that this thread refers to. With the two humbuckers, there was no convincing need for pickup shielding, but my son had on his own taken some conductive paint I had on hand and painted the pickup routs and the control cavity. Plainly the guitar had worked "fine" when new without this shielding. Of course, when I drilled into the front face of the cavity as described above, the conductive paint was removed where I drilled. Inasmuch as I did not see need for the paint in the first place, I could not imagine that removing part of it in this fashion would have any adverse effect.
I wired the guitar up initially based on a wiring diagram I found on line that was reported to be styled after Gibson's manner of wiring an SG with 2 humbuckers and a volume and tone control for each (my schematic attached). Basically the pickups were wired directly to the volume pots, the capacitors were wired between the volume pots and the tone pots, and the pickup selector switch went between the wiper on the volume pot and the tip of the jack. We found this worked out crazy. I could not find that I had wired anything up wrong, but the volume controls worked unreliably, the sound might turn on or off without obvious cause, and one of the tone controls could influence the tone of the other pickup, even when the pickup associated with the tone control was turned off!
In response to that, I devised my own wiring, based more on typical Fender wiring practices (although I am not aware of any Strats with 2 humbuckers!; my schematic is attached) and rewired it. In this case, the selector switch was between the pickups and the volume controls, the capacitors were between the tone pot and ground, and the wiper of the volume pot went directly to the tip of the jack. We got it all wired up and, at least at first glance everything seemed to work fine. Both pickups worked reliably together and alone and the volume and tone controls influenced the sound of the pickup they were supposed to control.
Night before last, I asked Dan how the guitar was working out, and he said it was great, "except if I touch the bridge or the knobs when I'm plugged in, I get this awful hum." I asked him to bring it down so I could take a look.
Yesterday morning I took it apart and did a little head scratching. I was afraid I might have forgotten to solder the bridge to ground connection, but that was fine. Everything looked okay. Everything was soldered to ground as it should be, and I had grounded both pots to each other on the stacked pots.
The only thing that looked odd (not in an electrical sense to me, but just in the sense that it was not a typical thing to see) was to have the cavity painted with conductive paint, except where it was drilled away to fit the hardware. Again, given that the guitar did not need conductive paint in the first place, I had a hard time believing that that would be part of the problem--those pieces of hardware had been attached directly to wood when the guitar was new, so I could not understand how having the hardware attached directly to wood now would cause a hum, just because there were some adjacent areas covered with conductive paint that none of the hardware came in contact with.
Anyway, being unable to find anything else to try, in the end I covered the bare wood areas around the hardware with copper tape carefully overlapping the pieces, I soldered a bare ground wire from piece-to-piece to more definitely connect those pieces of tape together, and then I soldered the end of that wire to the back of one of the pots.
When I first put it back together I freaked out, because the guitar was dead--no sound whatsoever. After a little more head scratching, I came to recognize that with the copper tape lying right under the volume pots with their hot leads, that the terminals were bent down and contacting the copper, shorting the signal to ground. I cautiously used a pair of needle nosed pliers to bend those terminals up away from the copper, and then the guitar worked fine--good sound, all controlled as it should be, and no more hum when I contacted the bridge or the metal control knobs. I banged away on the guitar for about an hour until Dan got out of bed and I could show him the improvement.
I am sorry for the length of this. I hope it does not inhibit anybody from reading it enough to respond! It was just a complex enough unfolding that I did not know how else to put it. Does it make sense to anybody, given that the guitar as initially built did not need to have grounding where the hardware was attached to the bare wooden face of the cavity, that it should need grounding there now just because some adjacent areas are covered with conductive shielding paint?
Thanks for consideration! Rob R
Attached Files
) along the same lines. It is almost too obvious to bother asking, but if I am wrong in my presumption I'll have to unsolder and re-solder a bunch of ground connections, so I'd rather make sure before I jump in.
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