Custom guitar with a buzz

Gear
#1

Hey guys,

I made an electric guitar body in high school (bought the neck from Carvin). I’ve been mostly happy with it (been almost 15 years) but it’s always had a buzz that I could never make sense of. It’s like there’s a loose ground or something but everything seems solid and as far as I can tell, I have it all wired correctly (but obviously something is wrong). The buzz isn’t super obvious when playing but does make everything sound less clean than it actually is. The only clue I have is that the buzz goes away when I touch the volume or tone knobs. I’m hoping someone out there with a bit more experience with wiring can help me identify the problem.

I’ve included a picture of the wiring cavity below as well as a description since the cavity is a bit of a mess and the guitar only has one pickup with no toggle switch.

  • The pot on the top is for volume and of course the one on bottom is for tone.
  • The bottom left corner is the jack
  • The yellow wire is connected to the bridge and soldered to the copper tape (when I made it, I was told that this wire and the copper tape would help prevent feedback but maybe it’s the problem?)
  • The black wire coming from the top is the bundle coming from the pickup (Screamin Demon from Seymour Duncan)
  • The white and red wires coming from the pickup are soldered together and taped off with electrical tape.
  • The green and bare wires coming from the pickup are both soldered to the copper tape lining the cavity.
  • The small black wire coming from the pickup is wired to the outer prong (left side of the picture) of the volume pot. That same prong has another wire (black) going to the outer prong (right side of the picture) of the tone pot.
  • The middle prong of the volume pot is going to the jack and the outer prong (on the right side) is soldered to the copper tape.
  • The volume pot is also connected to the tone pot via a single wire soldered to the top of each (thinking about when the buzz goes away, this seems like it could be the problem)
  • The middle prong of the tone pot is soldered to a capacitor which is soldered to the copper tape.

I think that’s everything.

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#2

I’m guessing there’s another wire connecting the copper tape and the sleeve lug of the output jack. Probably that thicker green wire in the photo. Is that correct?

If the hum goes away when you touch the pots, but not when you touch the strings, then most likely your strings are not properly grounded. My guess is that the yellow wire is not creating continuity between the bridge and the copper tape, but we won’t know for certain without some additional information. So here’s a couple of questions to aid diagnosis:

  1. Are the knobs metal?
  2. Are the bridge saddles metal?
  3. Do you have access to a multimeter?
  4. Could you post a photo of the front of the guitar?

By the way, the purpose of the yellow wire is not to prevent feedback, but to ground the strings. The purpose of the copper tape is to provide a ground plane and some shielding for the control cavity. (The shielding will work better if the back of the access plate is also covered in copper tape, and if the tape on the cover touches the tape that’s lining the cavity.)

Also, if both pot bodies are touching the metal tape, then the wire connecting them is extraneous, and has the possibility of forming a ground loop. This could add hum, but that hum probably won’t go away when you touch the pots. This probably not your main problem, but I’d consider removing that wire anyway.

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#3

Thank you very much for the help.

That is correct.

Yes
Yes
Yes
Yes

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It sounds like I’ll probably want to rework the entire cavity to clean it up and improve it which isn’t so bad but I’m hoping the problem isn’t the grounding of the strings since that would require popping the bridge out.

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#4

Nice guitar!

I notice that the yellow wire is thicker than the rest, meaning that it would require more heat to properly wet to the solder and get continuity to the tape. With any luck, all you need to do is remelt that solder joint. But first, let’s test the hypothesis.

With your multimeter, check continuity between the following points and post what you find. Let if you need help figuring out how to check continuity.

  1. The strings and the copper tape
  2. The strings and the output jack ground
  3. The strings and the exposed end of the yellow wire
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#5

Thanks :slight_smile:

So I have to look up how to use a multi-meter every time I go to use one but I think I got it right for this scenario. I set it up how it looks in the picture below and when touching two random pieces of metal that I know have zero connection, there is no beep. There was a beep for the strings to the tape, the strings to the jack ground, and the string to the exposed yellow wire.

Edit: I don’t remember exactly what the capacitor does (I think it’s what actually allow for the tone to be modified?) but I noticed that the middle prong on the tone pot and the other end of the capacitor and/or copper tape, doesn’t beep when touched. I’m not sure if that’s normal because of how a capacitor works (reduces/stores the energy?) but I thought I’d mention it just in case.

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#6

This year finished my own guitar. It can be frustrating sometimes )

So, does noise disappear when you touch your strings? Is wiring standard? (sorry it’s hard to see from the photo).
I might suggest to use shielded wires for signal path with shields grounded at one point (volume pot would fit). In my case it worked well even with cheap korean pickups.

#7

You appear to be using the multimeter correctly. The beeps indicate that the strings are grounded correctly, so my hunch has not been confirmed.

The capacitor is how the tone control works. Capacitors are continuous for AC signals but discontinuous for DC. So the lack of continuity makes sense here.

Let’s try another measurement. Rotate the multimeter dial one click clockwise (200 ohms) and post the meter readings for each of these combinations:

  1. strings to tape
  2. strings to jack ground
  3. volume pot body to jack ground

If you have a soldering iron available, try removing the wire that connects the volume pot body to the tone pot body, tells us what happens to the buzz, and get a new reading for #3. (Without a soldering iron you can just clip that wire, but you won’t be able to reconnect it if necessary.) Also check the reading for volume pot body to tone pot body.

Can you post a short video that demonstrates the hum? Show what happens when you touch the strings and the knobs both separately and together. Make sure the volume is loud enough that we can hear the hum in the video.

#8

Something like this (sorry for my mad Paint skills)
1

#9

Pre pot-to pot connection removal
Strings to tape was 2.6-3.0
Strings to jack ground was all over the place at first but once I got a consistent read it was also around 2.6-3.0
Volume pot body to jack ground was only about .3 (wire too small or poor connection maybe?)

Unfortunately, removing the pot to pot connection didn’t seem to have any effect on the buzz. I haven’t got a clue why but it did seem to increase the readings for each test.
Strings to tape was around 5
Strings to jack ground was up around 50 but that could just be the way I was touching the jack ground the first time?
Pot to Jack ground varies from around .3 to about 2 depending on how I touch each with the probes

Video is below… didn’t realize until making the video that touching the bridge and tailpiece get rid of the buzz too. Touching the strings does appear to help with the buzz, just not a lot.

#10

Wiring is probably not super standard and the picture being messy is why I described the connections in the beginning. With the exception of some of the connections being to the copper tape lining the cavity instead of the pot bodies, I think that’s how I’ve got it set up.

#11

Wow, this is super-confusing.

The readings are for resistance. You want the number to be as small as possible. You are getting better connectivity for the pot bodies than the strings or bridge, but 2-5 ohms is no big deal at all.

50 is pretty high for our purposes. Your video indicates that you are getting good continuity between the bridge and ground, but not between the strings and ground, which is very confusing since the strings and bridge are metal, so they should transmit continuity. Also the bridge and tailpiece are connected only by the strings (right?), and both of them have a good ground connection. Something strange is going on.

Do you remember how the yellow wire is attached to the bridge? Is it soldered or connected to a washer or something?

Do you have a wire available that’s long enough to touch one end to the strings and the other end to the output jack ground lug? Any difference buzz-wise compared to touching the wire from bridge to ground or knobs to ground?

#12

That’s what I thought. Strange thing. And the fact that touching thinner strings reduces the noice while with thick ones nothing happens.
And at first I thought that it might be just super high-gain but in that case we would definitely hear string noise after touching.

One thing I would check also is pot to tape resistance. May be there’s a bad contact between signal ground and tape…

#13

The more I think about it, the more I think it’s only connected to the tailpiece and I think that the wire is just exposed at the bottom of the hole and tailpiece mounts are pressed down on top. However the resistance between the tailpiece, bridge, and yellow wire are all below 5.

resistance from pot to tape is tiny (0.3)

I thin that’s just because the EAD are coiled. If I tightly squeeze them, it has a similar effect as touching the GBE strings.

#14

Are you using coated strings? Elixers, etc.

#15

Yeah, I just put on some new elixirs a few days ago.

#16

Ah. That explains quite a bit. The coating on Elixers is non-conductive. This does not appear to be a problem with your guitar as much as a by-product of non-conductive strings.

The coating is generally only on the wound strings, so if you are touching any of the unwound strings, the buzz should be reduced, which explains why that happens in the video.

Have you tried non-coated strings? That may solve or at least reduce your problem.

But I would expect that you would generally be touching one of the unwound strings most of the time while you’re playing. So maybe the problem is just excessive buzz, whether you’re touching the knobs or not? Maybe you could post a short video where you’re actually playing so we can hear the problem in a musical context?

#17

I can’t remember the last time I had non-coated strings but I want to say the problem has always existed with or without. I think what I’ll do is get my hands on some more copper tape and redo the entire cavity using your advice as well as just being more organized and using some better wire. Once I do all that, if the problem persists I’ll return with a fresh video.

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