Strat buzzes when I turn volume down

mellowsun

Here's a weird one: the pickups are very quiet on my Strat when the volume is at 10 on the guitar, but as soon as I back off the volume  pot I get a noticeable hum/buzz. Worst around 9 then gets quieter as I reduce the volume further.

Any ideas?

Cabicular

Electrical interference
Happens when I'm near Lights with Dimmers (even on humbuckered guitars)

mellowsun

Cabicular said:

Electrical interference
Happens when I'm near Lights with Dimmers (even on humbuckered guitars)

I wondered that but I don't get the problem with my other guitars.

richardhomer

They all do to a greater of lesser degree.

@ICBM explained why once - I'm not sure I could articulate it properly, so best wait for him to do it!

sev112

But why higher at 9 than. 10?

richardhomer

sev112 said:

But why higher at 9 than. 10?

IIRC (I'm trying to remember how @ICBM explained it) the 'hot' and 'ground' in a guitar lead both pick up noise - but with the volume turned up, they cancel each other out. When you turn the volume down, some of the 'hot' side is grounded, which means the noise induced into the cable becomes noticeable.

On mine, around 8 seems to be the worst.

Sassafras

Only happens if I let go of the strings.

olafgarten

richardhomer said:

sev112 said:

But why higher at 9 than. 10?

IIRC (I'm trying to remember how @ICBM explained it) the 'hot' and 'ground' in a guitar lead both pick up noise - but with the volume turned up, they cancel each other out. When you turn the volume down, some of the 'hot' side is grounded, which means the noise induced into the cable becomes noticeable.

On mine, around 8 seems to be the worst.

I think it's something to do with Phasing of the noise, when you have volume up to 10, the amount of noise on the hot and ground is the same, and out of phase which then causes some noise to cancel out. When you turn the volume down, some noise from the hot is going to the ground, stopping the cancellation as the levels aren't balanced anymore. 

I've probably got something wrong, but I don't think I'm that far off. 

ICBM

It's because the impedance to ground is highest when the pot is at about 8 to 9, with a Log pot. When it's at 10 the comparatively lower impedance of the pickup(s) is in parallel, and when it's below about 8 the resistance of the pot to ground is lower.

The actual cause of the noise is poor shielding - usually because the wiring from the jack to the pot is plain unshielded wires. Try replacing this with shielded cable. Shielding the control and jack cavities will also help, if it's not done already.

mellowsun

@ICBM thanks, what's surprising is that it is a CS Strat, the cables are cloth wound and there is shielding on the back of the scratchplate.

usedtobe

Guitars, eh..?! Pfff...

ICBM

mellowsun said:

@ICBM thanks, what's surprising is that it is a CS Strat, the cables are cloth wound and there is shielding on the back of the scratchplate.

Yes, but if it's a vintage-style one I bet the cable between the volume pot and the jack is also two separate cloth wires, and there's no shielding in the cavity floors/sides. This was always a big issue with original Fenders until the Jazzmaster.

You'll need to shield the cavities with conductive paint or copper tape (I find tape more effective, you can more easily solder a good ground contact to it and solder across all the joins to make a really good shield) and replace the cable to the jack for the best effect. I don't replace the rest of the wiring to the pickups, I find that changes the tone in a not-good way (controversial ).

mellowsun

Ah great, excellent advice there, thanks ICBM, I'll get onto this.