Buzz/static from pots

[timsch]

I've got a Hofner import archtop that has a buzz from the pots. The tone pot is worst when turned to higher treble and almost disappears when turned to lowest, with an almost linear change in buzz volume from high to low . The volume pot has the same buzz, but not at full volume or no volume, so all through the range other than at the extremes. I've fished the pots out and sprayed them with Deoxit D5, which didn't change anything.

I've run different amps and different cables and the issue remains the same. Same amp and cables using my Telecaster all work fine.

So what would the problem be? shielding/ground issue? something else? thanks.

[timsch]

No ideas on why the pots are acting like this?

[John A.]

I've got a Hofner import archtop that has a buzz from the pots. The tone pot is worst when turned to higher treble and almost disappears when turned to lowest, with an almost linear change in buzz volume from high to low . The volume pot has the same buzz, but not at full volume or no volume, so all through the range other than at the extremes. I've fished the pots out and sprayed them with Deoxit D5, which didn't change anything.

I've run different amps and different cables and the issue remains the same. Same amp and cables using my Telecaster all work fine.

So what would the problem be? shielding/ground issue? something else? thanks.

It sounds like a wiring issue to me (i.e., the wiring isn't well shielded and is acting as an antenna, and/or there's a ground loop introducing noise) When you turn the tone control down, that attenuates the frequency range that the buzz fall into. This is normal tone control behavior, so it's probably not a bad tone pot. My guess with the volume control is that when it's turned all the way up it's essentially out of the circuit, so whichever wiring connected to it causing the buzz is also out of the circuit. When it's turned all the way down, there's no signal, and no noise, which is also normal behavior for a working pot.

I'm leaning more toward this being a ground loop rather than a shielding problem because you say that your telecaster with (I assume) single coils is not buzzing in the same environment. If the Hofner's lack of shielding were causing it to buzz, think the tele would be noisy too (as is the nature of single coils in an environment with a lot of EMI), but that's not 100% proof. Sounds to me like you have to get the wiring out of the guitar to check it.

Those are my guesses, anyway.

[rpjazzguitar]

I'd need the wiring diagram to be certain, but I wonder if a broken ground connection at one of the pots might cause this.

Reheating all the solder might be a good idea if it's not too difficult to get access to it.

Maybe attaching alligator clips from the pot shafts to the outside of the output jack (ground) would help diagnose it.

[KirkP]

I’d guess it’s most likely to be a grounding issue in the guitar. If the buzz drops in volume when you touch the metal shield on the jack but does *not* drop in volume when you palm the strings, the tailpiece is not properly grounded. I’ve had two guitars with that issue, and I fixed both by restoring that connection.

[Cunamara]

I had a similar thing happen with my archtop guitar. I fought with this for some 16 years with different pickups, different pots, adding a string ground but that helped only a little bit. Then one day I discovered that the Mogami shielded wire going from the volume pot to the jack was not properly grounded. If you look for a wiring diagram for the Fishman, tailpiece jack, you'll see that there is a place to ground the shield. Mine wasn't; I fixed that and the buzz was gone even with my favorite CC style pickup!

[timsch]

Thanks for the suggestions. I haven't been able to get to it yet, but will post back when I fix it.

[timsch]

I finally pulled this off the back-burner. I was playing the guitar tonight and when I reached in through the f-hole to touch the pot body, the buzzing quit. This was true for both pots, although it may have been more pronounced with the volume pot, IIRC. Just wiggling the wires didn't do much.

I pulled both pots out with the jack to inspect wiring. Nothing pretty, but nothing broken. I have soldering skills and can do what needs to be done, but I don't have the experience to know what would best correct this. Any pointers will be greatly appreciated.

[sgosnell]

I don't see a wire going to the tailpiece. I might be missing something. The tailpiece should be connected to the volume control, or some other ground, in order to ground the strings. The ground lug of the output jack is a convenient place to connect the tailpiece ground. The output jack is rusty and could stand to be replaced, but that probably isn't the source of the noise.

[nevershouldhavesoldit]

Compare the soldered grounds on the pots. The bottom pic shows the solder to have flowed out over the back of the pot. It’s smoothly covering the surface and the wire is in the solder. The top pic shows what appear to be two blobs of solder, one on top of the other. The edge of the solder sitting on the back of the pot is curled under, rather than smoothly flowing out. The middle pot pic also shows some blobbing.

The cause of that blobbing is inadequate heating of the metal. The metal components being soldered together all have to be hot enough to melt the solder, so it flows over them all while molten. The correct technique for soldering is to hold a well tinned tip against the components until the solder melts when touching each of them. Just melting the solder on the tip of the iron and letting it drip or run onto the metals will not produce a solid, conductive junction. This is the most common cause of “cold” solder joints, i.e. joints that have significant electrical resistance. The more metal mass you have to heat, the more powerful your iron and the hotter the tip need to be. You have to heat fast to avoid damage to connected parts and protect vulnerable items like caps and resistors. I use a small clamp (alligator clip, hemostat etc) on component leads as a heat sink.

The other common cause of cold joints is movement of any of the pieces being joined before the solder has fully solidified and cooled. The hallmark of this is a dull or hazy joint. Solder that was undisturbed during cooling will be shiny. You can see that the flat joint in the bottom pic is hazy, and the blobs are shiny. So neither was perfectly done. But the bottom one looks shiny around its edge, so the bulk of it was probably solid because heat dissipates into the metal pot body faster than it does into the air. The mild surface haze is most likely from a little shifting of some strands of the shielding before the very top solidified completely.

If I had to guess, I’d pick the blobby joint as the bad ground. The definitive way to find it is to check the resistance between the ground lug on the jack and the backs of the pots. If there’s any measurable resistance, the joint is cold. If there’s infinite resistance, it’s open. You can get a decent little multimeter today for $20 - it’s very handy if you work on guitars and amps.

Resoldering is easy, but just reheating isn’t enough. There will be oxidation and dirt in and on such a joint. You should heat it fully, disassemble the joint, clean all mating surfaces, and redo it. The only vulnerability to heat here other than the insulation on the wire is the resistive element in each pot. I don’t know of a way to protect it, and I’ve never damaged one soldering to it. But be sure to use a hot tip on an iron that has the power supply to maintain it when it touches the cold metal being soldered - and work quickly to avoid excess heating.

Every soldered joint should first be mechanically secure. Wires should be twisted, crimped or whatever works mechanically. It’s not possible to physically secure a wire to a flat metal surface, so you need to position the wire so that it’s being pressed against the pot. Secure the pieces with clamps, clips, vise grip or whatever you have to maintain stable physical contact. I also scuff the back of the pot with Scotchbrite or coarse abrasive paper (NOT sandpaper - you don’t want to leave any particles to get in the joint).

[timsch]

Thanks for the replies.

The jack has the braided wire shielding soldered to the ground lug. There's not an additional wire to go there that I can see. All grounds are this braid in this setup. Are there dual wires with shield that are used in these applications? If there's better, I can replace all wiring.

I have a 250W Weller soldering gun, but I'd imagine that'd be way too much heat input. I also have a good Weller soldering station (probably ~ 40W) that has a digital temperature selection (up to 700+ degrees, IIRC). Assuming that's what I should use, what temperature should it be set at to quickly heat the pot metal? I've soldered plenty, but typically just wires together or onto lugs, and never wires onto sheet metal.

[Jimmy Smith]

You want the braided wires. The ground wire on the outside shields the signal wire on the inside. There's no such thing as quality of wires so don't worry about that. Is the tailpiece grounded?

The variable temp iron should be good to use. If there's a big piece of metal that will require a lot of heat to bond, you should turn it up as high as you can without burning up the solder. For lugs on a pot that can get destroyed, you want the temp as low as possible but that will still only take a moment to melt the solder.

[timsch]

I didn't have to disconnect anything from the tailpiece when removing the jack and pots, so the tailpiece is most likely not grounded. Sgosnell asked that but I didn't pick up on it. I'll look into it. It is a wooden tailpiece, but probably has metal brackets. If so, I'll make sure they're grounded.

Thanks again, everyone.

[Jimmy Smith]

You want to get a ground wire to the bridge or some big piece of metal. This is a chassis ground - a secondary ground in addition to the main ground out the jack - that helps dissipate noise.