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#1
07-02-2017, 02:21 PM
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UPDATED: Electric Guitar Troubleshoot
Problem - FIXED ORIGINAL PROBLEM AND BOTH PICKUPS WORKING WELL, BUT . . . HUMBUCKER GUITAR HAS AUDIBLE HUM AFTER PARTS CHANGE
'93 Gibson Studio - original pickups and electronics - worked fine before below events. I removed mount plate and original caps/pots, installed aftermarket upgraded cap/pot assembly hooked up same as original (just connected pickups and switch same as original setup aka "modern"). Both pickups - I changed the covers, soldered them as before, grounds show continuity. Pickups are grounded to the tops of the volume pots (redone twice), as before. Both pickups have OK impedance around 7.75k. Bridge pickup - I changed the magnet (alnico 5 to a 2, polarity observed). Bridge pickup is grounded to the top of the neck volume pot, as original. New CTS Pots - I checked their values before I installed them and they were all around 500k. Status - Has significant hum through amp that it didn't have before the changes, and which another humbucker guitar using same cord, etc., doesn't produce. When the amp is on and the 4-lead bundle from the switch is wiggled, it's crackly/noisy. There's apparently an uninsulated/bare wire in the 4-wire bundle from the switch (so, 5 wires total, only 4 insulated and hooked up). It was cut flush with the bundle's cover, with a few strand ends protruding - it wasn't hooked up to anything when I removed the pots/caps (there was nothing to remove, as it's cut back to the sheathing). The switch's black wire (ground) goes to a plate that also takes the switch's combined output before heading to the output jack. Does the unshielded wire serve a function in this application? If so, what? I don't see the other end attached to the switch in any way. Touching that bare wire while the amp is confirms the bare wire is able to transmit sounds of my fingers touching it - it's like it's a microphone. That doesn't seem right, so where would you look to start? Any ideas of what/where to check, values, etc., to get rid of this hum that apparently has to do with the switch-to-caps, etc. wire bundle much appreciated. Oh, and what was my stupid mistake that resulted in a too-quiet "neck" pickup? I had wired the pickups in backwards, so what I thought was the neck was really the bridge pickup, and it was flush with the body (too far from strings). And yes, I marked them so I wouldn't do that, and no, I don't know how I marked them opposite reality. When in doubt, check your paradigm. Last edited by ChrisN; 07-04-2017 at 09:31 AM. 
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#2
07-02-2017, 04:54 PM
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First things first: The 3-way is a leaf switch. It is a regular thing for building debris to catch between the leaves. Both my son and I had this problem and it turned out to be a little poop between the leaves. We blew it out and were back in commission. That's your first suspect.
Bob
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"It is said, 'Go not to the elves for counsel for they will say both no and yes.' " Frodo Baggins to Gildor Inglorion, The Fellowship of the Ring THE MUSICIAN'S ROOM (my website)
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#4
07-03-2017, 09:09 PM
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Re: Remaining hum - everything checked out fine except the metal braided sheathing covering the group of wires from the switch - it acted like a microphone when I touched it. No idea of how it might be connected to the circuit because the sheathing ends well before the switch. I suspect one of the wires, probably the output wire, was penetrated by the metal sheathing, energizing the sheathing, but that's just a guess.
I watched some vids and saw lots of grounding going on, so I peeled back that sheath to expose more of the metal braid, spun the strands together and soldered to a pot, and 95% of the hum disappeared. No idea why there wasn't a (noticeable) problem before I disassembled to install the new electronics. I'll re-wire the switch with Real Guitar Wire, put some sheathing coating inside the compartment and on the inside of the cover, and call it good. Interesting learning experience.
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#5
07-04-2017, 05:52 AM
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After reading through your revised post the two suggestions I had were to tracing the grounding or, because of the crackling when you switched, suspect voltage on the amplifier input. Congrats on tracking it down!
Bob
__________________
"It is said, 'Go not to the elves for counsel for they will say both no and yes.' " Frodo Baggins to Gildor Inglorion, The Fellowship of the Ring THE MUSICIAN'S ROOM (my website)
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#6
07-04-2017, 09:31 AM
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Quote:
Last edited by ChrisN; 07-04-2017 at 02:28 PM.
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#7
07-04-2017, 08:36 PM
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You grounded the sheath which should have been done in the first place, that excludes stray interference. Double check all soldered joints, that they are properly made. A dry joint can cause all sorts of trouble down the road. Remember too much solder is just as bad as not enough. Double check your caps, if they are electrolytic they must be installed in the right polarity or they'll not work. Apart from that, I can offer no more suggestions.
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Maton CE60D Ibanez Blazer Washburn Taurus T25NMK
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#8
07-05-2017, 09:31 AM
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Quote:
Re: Caps - Fortunately for the guitar, I left component assembly to RS Guitars. The pieces came as an assembled/soldered group I simply dropped in and hooked up. I've not heard of polarity or "electrolytic" with respect to caps, so I'll look that up. So far as I understand, the caps are CTS 500k matched and assembled using RS's proprietary audio taper. I appreciate your taking your time to share your thoughts.
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