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PostPosted: Tue May 22, 2018 12:57 pm 
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Koa
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My guitar buzzes/hisses/hums. A tele I made with a CC style pickup at the neck. When I touch the control knobs (brass) the humming goes away. I assumed some grounding issue. However I took the control panel off the back and touched the pot's housing. The humming did not go away.

Not having much experience with this stuff, I'm stumped. Touch the pot's shaft and the humming goes away. Touch the casing or ground wires, no effect. What would be the cure, doctors?


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PostPosted: Tue May 22, 2018 3:21 pm 
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Koa
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Something doesn't make sense. A metal knob has a setscrew that fastens it tightly to the shaft of the pot. The shaft is grounded to the case of the pot which is your ground common point. The case of the pot is also grounded to the metal cavity cover. I guess it is possible that the shaft is floating but I've never seen that.

Common causes of buzzing include

- cold solder joints, particularly any ground wire and certainly the common ground point (usually the back of one of the pots)

- reversing the hot and ground on the jack (its easy to do). Will still work but usually hums badly

- lack of a string ground. Run a ground wire from your central ground point to the bridge, that will put your strings at ground potential.

- Cavities should be shielded and the shields connected to your common point.

- On some neck pickups there are three wires - hot, coil ground (which goes to the switch) and pickup case ground (which goes to the common point). I had a boutique pickup that had the wire colors reversed - it would hum like crazy when I grounded the case. Reversing the hot and coil ground fixed it.


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PostPosted: Tue May 22, 2018 4:05 pm 
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Koa
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That is exactly my confusion. Touching the pot body with my finger didn’t seem to change anything, but touching the post quieted the hum. Isn’t the post and body connected?

Bad pot, possibly? Weird, weird, weird.


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PostPosted: Tue May 22, 2018 4:14 pm 
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Volume or tone knob? I am wondering if there is a cold solder on one of the capacitors.

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PostPosted: Tue May 22, 2018 6:59 pm 
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I don’t know really what a cold solder is, and I can’t find imagine what the capacitor has to do with it, but....

I think you hit it on the head!!!

I was checking the wiring for the millionth time and I bent the capacitor out of the way. Ta da! Buzzing stopped. I figured it was coincidental, but I gather somehow a bad connection with the capacitor can induce a buzz. Because... Er.... What? And that connects to the post by...

Awe heck! I admit my king fu isn’t strong. I’m going to re-solder that capacitor and hope the problem is gone for good.

Thanks!


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PostPosted: Tue May 22, 2018 9:08 pm 
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Koa
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A cold solder joint is one where the pieces being soldered (wire and pot case) weren't hot enough to get the solder to flow and evenly coat the surfaces. A good solder joint is shiny and bright, a cold joint is usually dull. Reheat it and flow a little more solder into the joint.


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PostPosted: Wed May 23, 2018 12:03 pm 
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I know very little about electric guitars but 35 years as an electrical engineer was good for something. The body is a better capacitor than it is a ground strap.

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PostPosted: Wed May 23, 2018 8:11 pm 
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The buzzing might have stopped because now the cap is shorting the high frequencies away

Do the pots have ground wires connecting them together, and to ground? Don’t rely on the control plate to make the connection.

I had this issue on one of my basses. Even though it was properly wired. I ran a second ground wire from the pots to the jack and that fixed it. Not sure why.

Also, this might be an issue with the grounds in your house where you have the amp plugged into. Are your strings grounded?


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PostPosted: Fri Aug 10, 2018 6:29 pm 
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Look up star grounding for electric guitars, and ignore any suggestion it has to do with ground loops. By using a central ground point to which all components ground directly (and never via another component) you ensure the shortest path to ground which will prevent buzzes. If you also use shielding throughout the cavity and also ground this you should be buzz free, 60 cycle hum aside (this is magnetic rather than electrical interference). You’ll know you’ve done it right when touching the strings or controls doesn’t make an improvement on how much buzz you are getting.

Final note: it’s dreadful industry-wide practice to use the back of a pot as a central ground point, and also to solder the caps directly to a pot! This makes the casing part of the circuit which is asking for trouble. Use a washer a your central ground point and run a ground strap from each pot to this. The cap should also terminate here rather than on the back of a pot.


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