Buzzing When Volume Pot Between 3 And 8

[fguihen]

I have my tokai les paul copy (LS160) wired up with CTS pots.

on both volume pots, when i have a really high gain tone set up at high volume, there is a constant deep hum from my speakers.

Its only noticable on very high gain set up's, but it totally dissappears if volume is below 3 or above 8.

It happens for both pots. Ive checked earthing and from a wiring perspective, everything is fine.

is there a know issue with some pots where they are simply noisier in the middle of their range?

[fguihen]

I have my tokai les paul copy (LS160) wired up with CTS pots.

on both volume pots, when i have a really high gain tone set up at high volume, there is a constant deep hum from my speakers.

Its only noticable on very high gain set up's, but it totally dissappears if volume is below 3 or above 8.

It happens for both pots. Ive checked earthing and from a wiring perspective, everything is fine.

is there a know issue with some pots where they are simply noisier in the middle of their range?

In case it helps anyone, Ive discovered something interesting. The buzzing is not present when i plug into the same setup outside my house.

In my house the buzzing is worse when my laptop is turned on, so im guessing its something to do with electrical interference.

Il have to get something to even out the current used by my line 6 and speaker.

[dpm99]

The only reason I can think of as to why a volume pot would do that is that it has a messed up resistor. But you wouldn't have that on both of them. I think you're right that it has to do with electrical interference. Does it use shielded wiring on the hot leads? And if so, is the wire shielding properly grounded?

David

[fguihen]

The only reason I can think of as to why a volume pot would do that is that it has a messed up resistor. But you wouldn't have that on both of them. I think you're right that it has to do with electrical interference. Does it use shielded wiring on the hot leads? And if so, is the wire shielding properly grounded?

David

not sure what you mean by "hot leads", but the guitar was recently re-wired by a pro, and he added the same wiring as in a gibson LP.

The cable from the guitar to Line 6 X3 Live is a standard 10 euro guitar cable.

Cable between the X3 live and the neutral amplified speaker is an XLR cable ( similar to microphone cable i believe).

Both speaker and pod are plugged into a 4 plug extension cord.

My laptop is on a different extension lead, plugged into a different wall socket. when i turn on the laptop, the buzzing from my rig gets much louder. its very strange.

I tried my guitar under a very similar setup but in a rehersal studio and got zero buzz, so im thinking it has to be a problem with interference somewhere

[KeithHowell]

My laptop is on a different extension lead, plugged into a different wall socket. when i turn on the laptop, the buzzing from my rig gets much louder. its very strange.

Your wall sockets will all be wired up to a common point though: Your main distribution board.

You should get the earth on your house checked. You probably have a high resistance between your earth wiring and actual ground.

Digital things, like laptops, are notorious for injecting all sorts of noise problems into power reticulation and when the earthing is not correct the noise doesn't get shunted to ground and causes all manner of noise issues.

Keith

[dpm99]

By hot leads, I meant the ones that carry the tone directly to the output jack, as opposed to the ground leads. Think of it like a battery, or a light bulb. There has to be a complete circuit made in order for the pickups to work. I've gotten so frustrated with my current, exceedingly complicated project, I've repeatedly thought about how nice it would be to have a guitar with a P90 in the bridge position, and no controls whatsoever. This would be the wiring diagram:

In the picture, the fat gray wire represents the hot lead, or what you might think of as the output. The smaller black one is the ground. You have some fat gray wire in your guitar too, or you should, if it's wired like a Gibson. That metal braided stuff around the wire is shielding, and it's supposed to keep electrical interference from getting into the signal. However, if the shielding is not at some point grounded, it doesn't do any good. That's why, in the picture, you see the gray part connected to the ground. In real life, it looks something like this:

Except, of course, that's a very sloppy job. You get the idea though. If you can trace a line of shielded wire from your pickups to your jack, and if all those shielded wires have the shields grounded, you shouldn't be getting electrical interference in your guitar (as far as I know, and my knowledge is limited).

Anyway, that's what I meant by hot leads, but that may or not be your problem. Buzz is a hard thing to nail down.

David

[Paul Marossy]

My laptop is on a different extension lead, plugged into a different wall socket. when i turn on the laptop, the buzzing from my rig gets much louder. its very strange.

Your wall sockets will all be wired up to a common point though: Your main distribution board.

You should get the earth on your house checked. You probably have a high resistance between your earth wiring and actual ground.

Digital things, like laptops, are notorious for injecting all sorts of noise problems into power reticulation and when the earthing is not correct the noise doesn't get shunted to ground and causes all manner of noise issues.

Keith

+1

[lvs]

Plug a guitar cable into an amp with the other side unconnected and it will be very eager to pick up interference. Short the naked plug's tip and sleeve together and the interference is gone. First, the cable was "terminated" with an infinite resistance, and then with zero resistance.

A passive guitar terminates the guitar cable with a resistance that varies as follows :

With the volume pot at maximum this resistance approximately equals the resistance value of the pickup. Which is small enough to make interference unhearable.

With the volume pot at minimum this resistance equals zero.

With the volume pot between minimum and maximum, this resistance can become high enough to make the interference picked up by the guitar cable, hearable. Especially with a cable of less quality, and in a "hostile" environment, and with high gain settings. The maximum resistance, which equals the pot's own resistance divided by 4, happens approximately at the volume pot's resistive midpoint, somewhere between the minimum and maximum setting of the volume knob. For example, that would be 125K for a 500K pot, which is significantly larger than a pickup's resistance, around 10K.

I think there lies a possible explanation for your problem, or at least an important part of it. The beginning of a cure consists in using cables of unsuspected quality, and keeping them away from interference sources.

Edited May 20, 2011 by lvs