Unusual volume pot interaction with new pickups

[Steve A.]

Turn pickup, flip magnet, use vintage type, two pickup wiring. It doesn't seem like a complex enough set of variables to expect widely variable results. But I'm far from an expert on PAF's and don't have personal experience with this mod. Just trying to put your mind at ease.

I was thinking the same thing. Speaking of pickup wiring I have often screwed around replacing the classic Gibson single conductor shielded cable with an ugly gray 4+ conductor shielded cable. However I eventually decided to leave the single conductor cable alone but add an additional shielded cable with the needed conductors (1 conductor for a coil tap or phase switch, 2 conductors for both or 3 conductors for full switching capabilities.)

By doing it that way I can always return it to stock wiring if I want...

Steve Ahola

P.S. To avoid a ground loop the added cable shield should be grounded only on one end (like the back of the pot.) Not that I am positive that it makes a difference...

Steve Ahola

[Chuck H]

IME grounding in a guitar must be very forgiving. When I was in my early teens I replaced a couple pickups in cheap guitars with Dimarzio, Duncan, whatever, and made other modifications as well. Now, as an adult, I would punch myself in the face if I were looking over my shoulder at the horrid job I was doing. Grounds all over the place too. It never caused any problems when I would connect both ends of a shielded lead in a guitar. I don't do it now as a matter of good practice, but I don't remember any objectionable noise from those early efforts.

[pdf64]

I can't see how a ground loop could be formed in a guitar wiring arrangement?
It seems very different scenario to ground loops within / between amps.

[Steve A.]

I can't see how a ground loop could be formed in a guitar wiring arrangement?
It seems very different scenario to ground loops within / between amps.

You are absolutely correct- I used the wrong term... it's not a ground loop but a loop antenna that we are trying to avoid. Les Pauls were wired up with a ground wire going from pot to pot to pot to pot- but not back to the first pot. And I doubt if 12 inches of cable shielded on both ends would create much of an antenna. However... sometimes it is sometimes a lot easier when you skip connecting the shield on both ends when it is not required (like soldering an extra ground shield to the metal pickup plate!)

As for sloppy wiring I used to treat grounds and signal returns as being exactly the same in my custom wiring harnesses. I figured that if I kept the wires as short as possible it would make for a quieter guitar. And then I studied the original GuitarNuts site back in 1998(?) with the main premise being to incorporate a star grounding scheme in a guitar. The idea was to lump all of your signal returns together and then connect them to ground at a single point (usually the back of a pot.)

I never did any A/B tests but my custom harnesses seemed to be a lot quieter when I incorporated the GuitarNuts premise, which I still follow to this day. Why? Your shields and grounds are picking up crap and by keeping them isolated from the signal returns as long as possible could make for a quieter guitar. For one thing some of the crap on the ground bus could get cancelled out when you sum them together.

Steve Ahola

[dai h.]

there's no (or only very very tiny) currents flowing (so you can't have the problem of higher current loop returns getting into lower current return paths), so if there is any possible problem maybe it would be through induction (like a transformer, with the ground loop created susceptible to induction--sort of how a transformer works with loops next to each other)?

[Steve A.]

Your shields and grounds are picking up crap and by keeping them isolated from the signal returns as long as possible could make for a quieter guitar. For one thing some of the crap on the ground bus could get cancelled out when you sum them together.

Along these lines I think that it would have been better if guitar cables had always been wired with two center conductors, both of which were isolated from the shield.

With existing guitar amps a two conductor cable could be used if the guitar was rewired with the signal returns going to the ring of a TRS jack. The other end of the cable would have a mono plug, with the signal returns connected to the ground at that point.

However I think it would be even better to use a 2 conductor cable and rewiring your amp with a TRS input jack with the signal return going to the ground associated with the first tube stage.

Steve Ahola

[Steve A.]

there's no (or only very very tiny) currents flowing (so you can't have the problem of higher current loop returns getting into lower current return paths), so if there is any possible problem maybe it would be through induction (like a transformer, with the ground loop created susceptible to induction--sort of how a transformer works with loops next to each other)?

Does the higher current/lower current interaction explain why you can get really strange results if you connect the tail of a BF tone stack to the wrong ground point? One of those mysteries I never did understand...

Steve Ahola

[dai h.]

basically "electronic circuits" (as the "circuits part implies) are made up of loops, AC, DC, or both. Some of the return paths go through ground, so they need to be wired correctly, or the result can be noise, instability, weirdness.

(As one example) here, in R.G.'s article:

http://www.geofex.com/Article_Folder...ing%20amps.pdf

he talks a bit about the (high current) charging pulses going into the 1st filter cap after the rectifier. The ripple (which is AC which you are trying to remove with the chokes, resistors, and capacitors) is very high (since the power hasn't gone through much filtering yet). So this ripple (since it came from the power transformer (and the wall and power plant)), it has to go back (return), and the path for the residual ripple (AC pulses) returns towards the source through ground (to the B+ winding through the B+ center tap which is connected to ground). Since the ground wire has a small, finite resistance, the pulses cause a voltage drop. If you wire this return path portion together with a preamp stage ground, the ripple can get into the signal, causing that annoying buzz and hum.

re: the BF tone stack, I gather that's the typical BF/SF one with plate follower directly followed by tone stack, and the tone stack pots are sort of going from top to bottom, with mid to ground? (I think the signal loop for that would be from plate to tone stack caps, then pots to ground and back to the cathode.) That ground would be very small current signal ground, and sure I suppose if you put it somewhere inappropriate it could cause a problem.

Probably the more a person understands the circuits, all the loops and what that entails, the more efficient their layout will be, less (and better) use of wire. For example, on some Fender custom shop amps, they use a large bundle of wires for star grounding, even though a) it isn't necessary, and b) it's wasteful of resources, so costs more in materials and labor (and presumably for the end consumer), and possibly c) makes the amp harder to fix or maintain if a big bundle of wires have to be moved out of the way (note that my criticism is only on this narrow particular point--in general they seem to be well regarded).

re: the guitar cavity loop, (maybe an easier to understand example I had in mind). If you have a typical (unbalanced RCA plug) stereo out from a CD player (I know, getting dated), DVD player, or whatever going into another stereo input, you have a ground loop since both wires have a ground (as an aside, one thing this says to me is that not all ground loops are so drastically problematic when created). (Typically in reality this probably won't happen since many typical stereo RCA interconnects are "stuck together", but) if you separated the two cables and made a big physical hoop, this would make a big antennae for any signals nearby sort of like a winding on a transformer in which a current/voltage could be induced into. So I was thinking *possibly* some weirdness along those lines was going on when someone reports a problem when making ground loops inside a guitar cavity (but I'm not sure and I suppose I would have to think about it).

(Also, looong ago, I tried cutting one ground from RCA cables from cassette decks, CD players, etc, but I couldn't really tell any difference.) Anyway lots of little interesting things (one of my pet interests, noise, grounding, layout) done with grounds like separating the grounds on headphones (relatively higher currents flowing so "crosstalk"(not 100% sure if it's correct to call it such) through the shared ground for the drivers can cause reinforcement and cancellation of the signal), brute forcing, mixing signals using balanced lines (to separate/negate the effect of the common return), etc., etc.