Pickups bleeding through when completely shut off

[alpheusiam]

I have a 1965 Custom Kraft made by Supro with individual on/off rocker switches and 2 vol. 2 tone wired exactly like a 2 pup P90 L.P. except as I say with 2 on/off switches instead of 3 way toggle. With either or both switches in the off position I can still hear either or both pups (although well muted) bleeding through and vol and tone pots still affect them. Vol. pots will end bleeding when shut down. I have checked every possible thing for cross contact or a ground fault or loop. There is no short in any component or wire. I have removed harness completely from guitar and pick guard. Then by using a metal screw driver to tap test the pups the bleeding remains. I have checked all pots and switches and caps and all work exactly within specs. There is not even the slightest resistance bleed between earth and hot anywhere. I am a pretty savvy guy, and have seen this before but it is always a ground or short problem, like when the guitar's body or pick guard shielding make contact somewhere with a hot point, or when a metal pup cover needs it's ground wire pulled for series/parallel switching like on Tele 4 way switching, but since neither is a possibility, this has me completely stumped. Any ideas? By the way the guitar sounds great through either or both pups, but since pups read: bridge 8.8 neck 9.2 (this matching is not uncommon with Supro pups) but they do not come off as that hot through my 72 twin like I think they should, I have to use more volume compared to say hot Strat single coil such as Van Zandt's (the rwrp set should be tried by all on your next custom Strat, you will not be disappointed, they sound like real 62 Fenders on steroids) or even reissue Fender Strat 62's which all read under 6. I believe this bleeding is why the pups seem to lack volume compared to less hot pups and is what made me look for problems when I discovered the bleed through. How can pups send signal to the jack when the jack hot lead is killed by a switch that is definitely off and tests off with a meter ? I own more then 40 guitars and have built, reworked, custom wired and repaired too many to remember and this is making me crazy! It's like ground is acting like hot and hot is acting like ground when the switch is killed. And when pups are switched on it makes me wonder if it's doing both normal and reverse polarity and therefore killing output, does that make sense? Here's a P90 wiring diagram that is exactly as I'm talking about, my guitar is only different as to 2 rocker switches instead of 3 way, in pot values: all 250k and cap values: original .050 pio bridge and .020 pio early 60's Sprague black beauty neck. http://www.seymourduncan.com/support...?schematic=p90

[Rick Turner]

Sounds like a bad connection between volume pot lug #1 (or whichever way you choose to number the grounded lug) and ground.

[alpheusiam]

Thanks, I checked this originally, but just went back and checked while hooked to ground lug #1 on both volume pots and have perfect continuity to every earth point possible and 0 continuity to every hot point. Lugs are firmly soldered to pots and test so. Thanks

[the great waldo]

I would try wiring the pickups to another set of pots and see what happens, I have had this before and it turned out to be either bad pots or or the case of the pickup making a connection with the live pickup wire inside. I do not know why straight forward guitar circuits are always such a pain to trouble shoot. Good luck.

Cheers

ANDREW

[David King]

I agree with Andrew, I'd swap out the pot/s first. Bad pots abound.

[52 Bill]

My guess would be that the switches are constructed in such a way that they have enough capacitance between the contacts that the signal is leaking across the open switch contacts.

Try substituting a different switch and see if it stops. It could be that there is enough gunk in the switches to create the leakage.

[alpheusiam]

Switched out all pots to top quality brass shaft CTS 250k audio taper for vol. and linear taper for tone and problem still is same. Going to pull wire from lug 2 vol. pot from one of the pups (now that's a kill switch lol) which runs to one of the switches and see if that pup still bleeds. How it can I'll never know. But that will test that switch any way. Meter says both switches are perfect at all continuity levels and I did use a good cleaner that has always been miraculously dependable for pots and switches and it also made no difference. I also cut back the pup wires which are braided copper shield/ground wire single center conductor covered in cloth like old 2 wire hums or P90's and started with guaranteed perfect leads, no difference. Switches and original pots are Stackpole and all read perfect. This is almost unbelievable. Actually got out my 2 vintage Mustangs which also use switches as we know, however they are on/off/on not just on/off but none the less they have an off position and there is no bleeding what so ever. Tried all 4 of my amps, same bleed! Tried multiple 'as if' new chords same bleed! Will update results after I pull the pot wire. Thanks for the ideas!

[EtLa]

Can you illustrate your wiring with the 2 switches. Did you hook up the pickups using the center lugs of the pots or the external log?

[alpheusiam]

The 2 switches receive a live wire from the center or #2 lug from the volume pots respectively just as shown in the wiring diagram link I have included in the original thread. The only difference in my wiring harness is that each volume pot sends this center lug or hot lead to individual on/off rocker switches which each having a hot in and a 'when on' hot out. When switched off they test with zero continuity. These two switches A being neck (white lead) B being bridge (red lead) sit side by side and a bare wire jumps from B ('when on' out lead)to the A ('when on' out lead) which has a black lead that runs to the output jack. These three leads (A) white from lug #2 or center volume pot neck and (B) red from lug #2 or center volume pot bridge and black which runs from switch (A) neck remember it's jumpered from switch (B) provides for the option of neck only, bridge only or both pups and they are all (the leads) inside a braided shield cover which is grounded to earth at the pots and everything is on an EMI shielded pick guard, so ground is also connected to the switches and I have tested for this and ground is perfect everywhere. I have included some close up pictures on my profile page under my albums, they are uploading now and should be available soon but my connection is a bit slow. The guitar shown in the album is not the guitar I am discussing but just the first of my personal guitar collection pictures I will add later. I removed the hot out wire from lug #2 volume pot (A) neck and this completely eliminates the bleeding so this tells that the bleeding is not coming from a short or ground loop and I am tending to believe that it is leaking through the switches, but 2 bad switches that both test positively perfect? Seems most unlikely. I just tested them both with live 9 vdc today to see if voltage leaks when they are turned off and they both show just under 1/10th of a volt leakage. Could this be enough?

[52 Bill]

A few millivolts of leakage will become audible.

It is possible that at one time or another someone used an oil based spray to try and clean the switches. If the switch is phenolic or press board based, the oil could have penetrated the insulator and is causing the bleed through. Complete dis-assembly and a thorough cleaning of the internal elements may help.

[EtLa]

Regarding on-off switch I prefer using it to un-ground the ground lead of the pickup to shut it off.

Or right after the pickups

[jrfrond]

In my mind, there are two things that will cause this: poor grounding, or bad pots. Pots can be BAD even though they are supposedly GOOD. I don't care who makes the pot. You might have a few ohms of resistance remaining at the ends of the travel, instead of a complete short. The problem here is that most digital meters won't read that low with accuracy, unless you have a low-ohms range (one of my meters has a 20 ohm range that works for this). So, what to do? Turn the pots down, and SOLDER a piece of wire across those two terminals that need to be shorted (no clip leads!). If you STILL have bleed, you are probably looking at grounding. However, it MIGHT be switches, especially old ones with phenolic wafers that have become moisture-contaminated over the years. Take the reverse approach to check these. Cut one of the leads to the switch to REALLY open up the connection.

There's a reason why you have bleed. You wouldn't be the first, and there is no mystery, just thorough troubleshooting.

[alpheusiam]

After cleaning the switches with alcohol, lacquer thinner, naptha, and again alcohol then blow drying with a compressor and heat drying with a hair dryer, I have reduced the amount of voltage that bleeds through to 4 milivolts and they still pass sound from the pups. These are stackpole 125vdc on/off rocker switches with fiber bottoms like gray bottom pups use. I believe that the problem is definitely in the switches as I have already replaced all pots with top of the line CTS and after removing a wire from a volume pot center lug to the switch kills bleed from that pup, so it isn't a ground loop or ground problem, removing the wire kills the feed which is exactly what the switch should do. Anybody have any vintage stackpole on/off rockers laying around?

[jrfrond]

That's similar vulcanized fiberboard used for Fender tag boards, and has known hygroscopic/contamination issues under the right circumstances. Unintentional current paths are always an issue with contamination and/or carbonizing.

My guess is that you chased out most of the moisture contamination and reduced the ESR of the material, but rogue contaminants still remain, probably as a result of permanent chemical change over the years. One of the reasons Fender amps still work after all this time is the heat from the tubes that kept the boards dry. Most vintage amps don't experience tag board failure until they've been stored for extended periods in a humid environment. Your guitar never had the benefit of the heat-drying cycle over the years.

What makes you think that you'll have better luck with NOS or used switches of the same vintage? How can you be sure they aren't contaminated? Have you checked around THOROUGHLY to see if an equivalent current replacement is available? They would likely be made with a fiberglass wafer, or phenolic at the very least.

[alpheusiam]

Thanks and I anticipate that nos may be suffering from same condition. This guitar did sit unused for years and maybe one of the former owners left it sit because of this issue. I got it from an antique dealer so it's history is unknown. My only concern for new parts is obviously fitting properly in the pick guard and appearing as original. I have been looking for both new and nos anyway, so your suggestion has also been one of my considerations all along. I really believed this had to come down to the switches, it was just hard for me to think that both were bad, but they're side by side and anything from age to sweat to beer to smoke to humidity etc. etc. etc. would be very likely to end up easily contaminating them both. They are mounted in the upper left horn portion not unlike Mustang switches. Thanks and I'll be sure to get good working switches and will follow up after successful fix!