SC-1 Pickup Hum?

Not trying to cross post, I started a thread w/ a TON of pix of my new SC-1 over in the "porn" section, but thought my tech question might get more views here, if that assumption is incorrect, a mod can kill or move this as needed. . .

Just acquired an SC-1 that I'm quite smitten with, but I have to admit, its a bit noisy! I've checked the ground points, all solder joints visually look good including at the copper shielding plate in the back of the elec. cavity. Cleaned the output jack with some DeOxit red, then gold. The noise seems to be RF interference, and while mildly annoying in my guitar room (which has an isolated circuit/ground just for my amps) it was pretty bad at the bar my band played Friday night. I use a lot of gain, and almost exclusively vintage Fender style single coil pups, so I'm accustomed to a "noise floor", but this seems like something more. Any ideas?

Not trying to cross post, I started a thread w/ a TON of pix of my new SC-1 over in the "porn" section, but thought my tech question might get more views here, if that assumption is incorrect, a mod can kill or move this as needed. . .

Just acquired an SC-1 that I'm quite smitten with, but I have to admit, its a bit noisy! I've checked the ground points, all solder joints visually look good including at the copper shielding plate in the back of the elec. cavity. Cleaned the output jack with some DeOxit red, then gold. The noise seems to be RF interference, and while mildly annoying in my guitar room (which has an isolated circuit/ground just for my amps) it was pretty bad at the bar my band played Friday night. I use a lot of gain, and almost exclusively vintage Fender style single coil pups, so I'm accustomed to a "noise floor", but this seems like something more. Any ideas?

You might check out (in case you have not yet) the G&L Knowledgebase. There are some posts addressing hum issues.

If you are able to resolve this, please do post a followup with your solution.

Hope this helps.

Still no luck on this.

I've traced through the whole guitar with my Fluke & everything SEEMS great. The ground lead is secure @ the spring claw, both sides of the pickup have continuity w/ the 1/4" plug at the end of a 10' cable, very low resistance. I tried heating solder joints up (not happy to spoil a guitar full of original solder joints, but I'm also not happy with the noise!!!) No change there. SO - what else can I try? The pickup is wax potted to the cover I'm not too keen on trying to open it up.

Driving me nuts though as i can A/B guitar -> cable -> amp w/ my 1960 Duo-Sonic and its MUCH quieter than the SC-1 with very similar pickup output and a good 20 more years of age. . .

SO when you checked continuity with your Fluke multi-meter do you mean you
read zero ohms along all the wiring?

What about the jack from tip to ring - in other works from the jack back
through the pickup. You would read perhaps 9k ohms (i.e. the pickup winding).

When you must around with the guitar is the hum a 60 cycle hum that changes
depending on where the guitar is and it's orientation? Or is the hum a constant
volume /tone regardless of where the guitar is and how it is oriented?

When you unplug the guitar and put your finger on the end of the plug going
to the amp is the hum the same? When you take your finger off the tip of the plug
does the hum stop?

Correct, nearly 0 ohms resistance from the very first solder joint on the negative side of the pickup coil to the ring on a 10' cable plugged into the guitar's jack. Then ~5k (correct for the early MFDs) from tip to ring on the plug end of the cable. Then the same resistance across the winds of the pickup.

The hum I'm getting DOES change when I vary my position relative to the amp & other interference sources in the room but has zero change depending on my interaction w/ the guitar (touching strings, bridge, metal bits, etc.)

When I unplug the cable from the guitar OR plug in any other guitar I own, they are all nearly silent. If I short the tip to ground w/ my thumb, I get the normal "buzz" you'd expect (the tone is in my fingers, LOL). I built the room the guitars/amp are in & ran a dedicated circuit + dedicated earth ground JUST for my MI outlet. I'm using mostly 30-50yr old gear (1964 Bassman) but the rig is very quiet. I spent several years building, modifying & repairing pedals & other MI gear for a living, so w/o tooting my own horn, I'm fairly sharp with this stuff. That said, I'm obviously missing SOMETHING as I've owned dozens of guitars & used them with this same amp, board, cabling, etc. w/o issue. Hoping the SOMETHING in question is something very simple - a "duh" if you will, and not an internal fault in the winds of the pup, or something yucky!

SO when you checked continuity with your Fluke multi-meter do you mean you
read zero ohms along all the wiring?

What about the jack from tip to ring - in other works from the jack back
through the pickup. You would read perhaps 9k ohms (i.e. the pickup winding).

When you must around with the guitar is the hum a 60 cycle hum that changes
depending on where the guitar is and it's orientation? Or is the hum a constant
volume /tone regardless of where the guitar is and how it is oriented?

When you unplug the guitar and put your finger on the end of the plug going
to the amp is the hum the same? When you take your finger off the tip of the plug
does the hum stop?

From memory the Duo Sonics have a metal pickguard which effectively shields the pickups from RF interference. I played one of the new Squier models and was absolutely bowled over by how quiet it was. So you're making a comparison with a very quiet guitar to begin with.

My G&L guitars are ALL noisier than my other single coil guitars. I would say the pickup and wiring cavities need shielding, but whether you want to line such an original instrument with Al foil or similar is another question altogether. I've shielded my S-500 and it is almost hum free now. Certainly much better than it was and on a par with my other guitars.

IIRC, Gabe from the G&L factory said in a recent post that most of the factory guys shield and star-ground their own personal G&L's.

Perhaps the Duo was a poor example. It does have a shielding plate, but it is the ONLY guitar I'm comparing that does. In my experience, its not more quiet than my Teles, Strats, Jags, Casinos, or any of the other dozens of guitars, including an ASAT special which much higher output versions of these same MFD pickups. Granted, I don't have the ASAT anymore to A/B with, but I assure you, it would've bothered me if it had been as sensitive as this guitar. And in theory, it should've hummed MORE with a hotter wind. . .

From memory the Duo Sonics have a metal pickguard which effectively shields the pickups from RF interference. I played one of the new Squier models and was absolutely bowled over by how quiet it was. So you're making a comparison with a very quiet guitar to begin with.

My G&L guitars are ALL noisier than my other single coil guitars. I would say the pickup and wiring cavities need shielding, but whether you want to line such an original instrument with Al foil or similar is another question altogether. I've shielded my S-500 and it is almost hum free now. Certainly much better than it was and on a par with my other guitars.

IIRC, Gabe from the G&L factory said in a recent post that most of the factory guys shield and star-ground their own personal G&L's.

IIRC, Gabe from the G&L factory said in a recent post that most of the factory guys shield and star-ground their own personal G&L's.

Gabe is not from the G&L factory. He was a long time poster on the original G&LDP and is a G&L historian and friend of
Dale Hyatt and Greg Gagliano. He has never posted here on the current G&L Forum nor is he even registered on the G&L Forum.
I guess he had gotten so busy with all of his projects and family that he has no time left for posting on the G&LDP
anymore.

I have resurrected a number of his posts from the past and put them in the G&L Knowledgebase, so perhaps you've mistaken
them for recent posts by him. He does use star-grounding and it is evident in a recent post of his custom built "Legsat" which
I also resurrected from the old Gallery. I did a search and that is the only post I could find with
reference to "star" and "Gabe". I don't know anything about your reference to the "most of the factory guys shield and
star-ground their own personal G&L's." quote from Gabe. I have not hear that from anyone at the factory.

Is there any grounding wire from case of the pots or pickup to the bridge?
Do you have continuity from the case of the pots or ring of the jack to
the bridge?

What happens to the hum volume if you touch the shaft of a screw
driver to one of the pole pieces (without touching the strings).

Something else might be happening that makes this problem so strange.
Can you observe the jack when you plug in the plug. In other words
something may be physically moved by plugging in the plug inducing
the problem only when there is a plug in the jack and otherwise okay
for your tests when the plug is removed. Another way to test this is
to leave the cord known to be good plugged into the guitar but unplug
it from the amp. Then you test the resistance from the far end of the
cord and it should read ~5k ohms. I may be open if the act of plugging
in the plug into the jack is moving something physically pushing on it
perhaps touch bare wires.

Another thing you can try is with the control cavity exposed using
a pencil or other probe to push on wires and controls to see if there
is any momentary connection or disconnection where the hum disappears
for a split second. IF this happen you would quickly from the problem.

I forget what you said earlier. Was the hum always a problem since
you got the guitar?

Last edited by jwebsmall on Tue Oct 25, 2011 7:57 pm, edited 1 time in total.

Is there any grounding wire from case of the pots or pickup to the bridge?
Do you have continuity from the case of the pots or ring of the jack to
the bridge?

What happens to the hum volume if you touch the shaft of a screw
driver to one of the pole pieces (without touching the strings).

I have continuity between the ground side of the pickup, the base plate of the pickup, the spring claw/springs/bridge/strings, the cans of the pots, the grounding plate in the control cavity & the ring of the output jack.

Will try touching a screwdriver to the pole pieces, but I've already tried using an alligator clamp test lead attached to ground to "probe" the guitar with it plugged in - looking to see if anything metallic might not have a good connection to ground, . . .zero change (unless, of course, I ground the pos side of the pickup coil!)

I was editing my post so you might have missed this:

Something else might be happening that makes this problem so strange.
Can you observe the jack when you plug in the plug. In other words
something may be physically moved by plugging in the plug inducing
the problem only when there is a plug in the jack and otherwise okay
for your tests when the plug is removed. Another way to test this is
to leave the cord known to be good plugged into the guitar but unplug
it from the amp. Then you test the resistance from the far end of the
cord and it should read ~5k ohms. I may be open if the act of plugging
in the plug into the jack is moving something physically pushing on it
perhaps touch bare wires.

Another thing you can try is with the control cavity exposed using
a pencil or other probe to push on wires and controls to see if there
is any momentary connection or disconnection where the hum disappears
for a split second. IF this happen you would quickly from the problem.

I forget what you said earlier. Was the hum always a problem since
you got the guitar?

I'm signing off for the night and will check this thread in the morning.

Latest round of Qs is actually answered above - I've tested at the end of a 10' cable plugged into the guitar's output jack. Have also tested with the control plate off & moved/poked/prodded/jiggled/etc.

Have only had the guitar a few days, previous owner told me it was noisy, but had thought that was normal for MFD pups. As "noise" sensitivity is highly personal, this didn't concern me. I'm also accustomed to fixing/repairing guitars & have never before had trouble like this isolating & sorting out the cause. Funny thing is, I don't consider myself sensitive to normal single coil noise at all. I play in a noisy punk/garage band, always have at least a Rat on running into a cranked Bassman, sometimes running two even three dirt pedals/fuzzes stacked into each other. Noise is my thing! But this, this is different, and it seems like something is up - and that, not being able to put my finger on it, bugs me. LOL!

I sure appreciate all the time/energy you've put into helping me shake this down!

edit: Just so its handy in this thread, thought I'd re-post this image:



^ the output jack is spaced far from the pots & has no mechanical interference with anything else in the control cavity. It has great tension against the plug & no amount of manipulating the jack/plug interface has any affect on the noise.

With the control cavity open when you plug in the guitar is it equally noisy.

With the cavity still open can you jiggle around the components to see if
the him will stop.

My rationale for doing this is the tests you are making with continuity
and resistance readings are normal. And the problem defies the logic
of the assumed circuit. But things could change when the cover is screwed
back on, etc. In other words the circuit you are testing and the circuit
that is making it hum are not one in the same, the difference being
either it closed up (cover screwed down) or plug inserted. Visual
inspection is not enough to make this determination. Inserting the
plug in the jack made be moving something you can't see visually.

If none for above changes anything then it is time to
resort to isolation testing.

For example unsolder the pickup from the circuit.
Does the hum go away with the just the cord plugged
in to the controls?

With the pickup unsoldered rig up a direct connection
of the pickup to the cord so only the pickup is in the
circuit. Does it hum now?

In other words you are isolating your testing to the
controls first and the pickups second to determine
if the hum is originating in one or the other.

(Before you go unsoldering things it would be easier
to try the shorting out of portions of the circuit
as described below.)

When you find the problem it's going to become
immediately apparent why it was so logic defying.

I had almost 10 years experience in electronic repair
and I've seen these logic defying bugs before - they
are rare and it usually comes down to one or two reasons.
The circuit you are testing (or think you are testing in
your logical schematic model and the real one in front of you
are not one in the same because something is changing
by the way you are testing it such as the cavity open verses
the cavity closed or the plug inserted or not when you are
making your continuity tests - although we have now ruled
that out) or secondly something outside the circuit is unduly
influencing it and again this not factored into your logical
schematic model that you are doing your deductive reasoning
from. Bugs like these are extremely rare perhaps the
reason the former owner lived with the problem because
nobody could fix it with deductive logic and a static schematic
model. The assumption of what's in the guitar and what we're
testing is the schematic model we are reasoning from. Hence
the logic defying phenomena.

You will find the problem provided you are willing to think
outside the box and try things that don't make logical sense
why you are bothering to try it. Change the circuit (e.g. isolation) and see if what
you observe from the change is what you would expect
from the changed circuit. When you are getting close
to the culprit suddenly you'll get something you didn't
expect and eureka you will find where the real circuit
deviates from the schematic model. it will usually be
so simple it will make you laugh.

How can you change the circuit even more than the isolation
testing mentioned above. Well one way is to start shorting
out portions of the circuit. With the hum signal shorted to ground
the hum should vanish. It will no dobut as you short out
portions of the circuit picking up the hum. If you short out on
the "otherside" of the problem the hum may not go away.

My wild guess now is that the problem is the pickup or
one of the controls itself. Short out the pickup coil (from
one wire of the pu to the other. The hum is originating
in the pu it will be shorted out and the hum will go away.)
Only by shorting (shunting it out of the circuit or isolating
it will you make this determination.) It may be you identify
the problem component but never know the reason why it
is causing the hum (assuming it is inside the pickup or
control). But any way you should be able to isolate the
problem if you are will do go through the exercise.

Just make sure you have the circuit diagrammed so you
can wire it back when you are finished.

I'm really curious what the problem is so please don't
give up before you find the bug.

Hilarious coincidence - it had not occurred to me to isolate the pickup from the vol/tone circuit, but you AND a friend on another board BOTH recommended it within 30min of each other!

Of course I had to run home on my lunch break & try it. De-soldered the leads from the pickup & used alligator clamps to connect it directly to a known good cable.

Bah, same noise level as w/ the vol/tone circuit in place.

Of course, shorting the two sides of the coil = no output, dead silent.

Hmm,. . .will keep thinking on this. I have e-mails in to a couple folks who are well known pickup builders/winders & have MAJOR experience rebuilding/winding & repairing old pickups. Perhaps one of them can shed some light on what looks, increasingly, to be a slightly noisy pickup.

On the positive side, I buttoned it up & ran SC-1 -> '77 Opamp Muff -> Delay w/ modulation -> cranked Bassman & had my way with her for a few minutes. Now running late going back to lunch, but I feel better.



OH - and I'll be CERTAIN to keep updating this thread. I've been helped over the years by the experiences of others more times than I can count - nothing more frustrating than finding an old thread w/ the same exact problem you're trying to solve, reading down through the meat of it only to find that the OP never came back to document the solution!!!

p.s. - I had an e-mail in to R. Poss asking if his SC-1s were noisy (compared to other "standard" Fender single coil equipped guitars) & he answered that they were not.

Okay - you nailed it. It's in the pickup. Like I said you could isolate
it but maybe never know exactly what is wrong in the component
causing the problem.

Are you going to have the pickup rewound or replace it with
a new one from the G&L online store (perhaps while you are
waiting to have the vintage rewound)?

My favorite job of all time was the 3 years I spent as an electronic
technician for Heathkit where I learned the art of diagnostics.
We had to earn 170% of our salary in service fees which were
fixed by the company for the particular kit we were repairing
at our 6 month review or we were put on probation and let
go if we didn't make our quota by the next 6th month review.
We had to earn 200% of our salary or we weren't eligible for
a promotion. Some kits were a disaster in how they were initially
wired. Others had extremely difficult bugs to fix. Once we
fixed a color TV that had a Moiré pattern on screen. We were
trying to fix the convergence circuit which in itself defies understanding
the effects of the filtering circuits (and next to impossible
to measure or test). It was driving us nuts. The problem?
The chassis. We replaced the picture tube even thinking that it was
somehow defective when everything else proved to okay. The chassis
was magnetized and we could not degauss it. When we remounted
all the circuit boards on a new chassis the problem
vanished. We figured the chassis metal was in a magnetic field at the forge when it cooled.
That was one of the harder bugs (trouble shooting high power RF
amplifiers is even harder because impedance coupling will forward propagate
a bug down an amplifier chain manifesting itself as a symptom after where
the bug actually is in the signal path. It's like a dog chasing a rabbit down
a hole). But there were others that were almost as infuriating. That is where
I really learned to think outside the box on that job and keep going even
when logic failed. I even had PhD electronics engineers from the Navy bringing
me gear to fix they couldn't figure out what was wrong (because they never had the baptism
of fire and learned to think meta logically - i.e. when logic fails what do you
do next to rerail your logic model.) It really rubbed them the wrong way
that this high school graduate was fixing gear they couldn't.

It wouldn't hurt to discuss rewinding with Curtis Novak: http://curtisnovak.com/

Granted, I have entirely selfish reasons for mentioning him. I've been wondering if he would ever be interested in building the vintage MFD in different form factors (like for Jazzmaster). The large-format MFD is probably my pickup style ever created.

It wouldn't hurt to discuss rewinding with Curtis Novak: http://curtisnovak.com/

Granted, I have entirely selfish reasons for mentioning him. I've been wondering if he would ever be interested in building the vintage MFD in different form factors (like for Jazzmaster). The large-format MFD is probably my pickup style ever created.

Hah! I'm actually already in touch with Curtis. He is one of my favorite builders/winders. I sent him an e-mail as soon as I wasn't able to nail down a solution myself. I have an offer to send it in for him to take a look, will most likely go that direction, just thinking hard on what my plan should be in the meantime. Bummer to have a new guitar out of commission like that & I'm NOT tickled about the idea of having to rewind a "special" pickup like this. Of course, its the right thing to do - nothing "special" about gear that doesn't work right. I'd just expected an instrument I could enjoy as "all original". Ah well.

jwebsmall - I know where you're coming from. My day job is working as a BMW factory technician. Before going to BMW, I worked at a few really great independent shops & worked on pretty much everything German + a couple years doing exclusively rotary powered Mazda tuning. I love diagnosis whether its the modern computer-aided type, or old school. Its almost an art, I think, to let your brain get flexible & see past your expectations. . .and when you DO find the solution, the feeling is tough to beat!

Yes I apply my diagnostics to software all the time. I would love working on cars especially BMW's with all their computers and such. When I was at Heathkit I kept notes on everything I fixed, what the problems were, how
I might have been fooled at first trying to trouble shoot the dogs. After the first year I had assembled a notebook and a trouble shooting strategy for each type of gear I worked on. I was running service revenues 500 to 1000% of my salary and our revenue from the service department was giving the sales department a run for their money. Within the next year we were the top service department in the country (50 stores) and top store in the country.