Hum when strat volume rolled down to 8

tpk1

I have a new Mexican Fender Deluxe Strat with vintage noiseless pickups. The pickups are noiseless at volume 10 but when I roll the volume to 9 there is a hum coming through the amp. When I take the volume to 8 the hum gets louder and after that gets quieter as the volume goes to 1.

The volume of the hum doesn't change as I move the pickup selector switch. 

The volume of the hum becomes quieter when I touch the strings. 

I am usually running this through a Fender Blues Junior but I also tried:

Roland microcube (mains powered) - the hum is still there

Roland microcube (battery powered) - the hum is gone! 

Has anyone got any ideas what might be causing the hum? 

ICBM

Sounds like some sort of mains-borne interference, probably from a lighting dimmer, computer power supply, phone charger, modern TV etc.

The noise getting quieter or disappearing when you touch the strings is normal. You need to get into the habit of keeping your hand on the guitar.

545454

Might be worth checking if the volume pot is loose at all.  I had a problem once with the washer on the pot shaft not being tight enough - the whole pot was rotating inside the cavity and the solder tag was shorting on something. 

tpk1

Yes, keeping my hand on the guitar is definitely the solution!

I'm just trying to figure out if it's an issue with the guitar or the power supply.

If it's the power supply, is there anything I can do to stop the hum? 

ICBM

tpk1 said:

Yes, keeping my hand on the guitar is definitely the solution!

I'm just trying to figure out if it's an issue with the guitar or the power supply.

If it's the power supply, is there anything I can do to stop the hum? 

More shielding in the guitar could help, but otherwise this is just a normal issue with passive electric guitars.

markblack

incase its any use...

http://www.thefretboard.co.uk/discussion/36536/hum-noise-increase-turning-down-volume-on-a-strat#latest

Funkfingers

tpk1 said:

Roland microcube (mains powered) - the hum is still there

Roland microcube (battery powered) - the hum is gone! 

Has anyone got any ideas what might be causing the hum? 

1. What wall wart PSU are you using to power the Roland Microcube amplifier? 
2. Is it plugged into to the same mains adapter as any other musical equipment? e.g. Effect pedals or a recording device.

You may have a mains ground loop. 

Somebody I visited earlier today has a cheapo PSU that causes his Blackstar overdrive and Rocktron chorus pedals to hum and/or oscillate. A proper smoothed and regulated PSU may be the solution.

tpk1

I'm using the Boss PSU that came with the microcube and because the hum is also there on the blues junior I think the issue is something to do with the mains supply. 

There is no hum from either amp when the guitar is not plugged in. If there was a ground loop wouldn't they hum on their own without the guitar? 

ICBM

tpk1 said:

I'm using the Boss PSU that came with the microcube and because the hum is also there on the blues junior I think the issue is something to do with the mains supply. 

There is no hum from either amp when the guitar is not plugged in. If there was a ground loop wouldn't they hum on their own without the guitar? 

Yes. The noise is being picked up by the guitar - or probably by the cable - that's certain from the fault description. The reason it goes away when the volume control is at 10 is because the fairly low impedance of the pickups (compared to the pot at half volume) then suppresses it. How it's getting to the guitar (or cable) is the issue.

When you're not touching the strings your body acts as a sort of aerial for airborne noise. When you touch the strings you divert this to ground, add a bit of extra capacitance to the guitar's ground connection and also provide a bit of shielding behind the pickups, which all also helps suppress the noise.

tpk1

I've tried different cables and the hum is there with all of them, so I don't think the cable is to blame.

Because the hum is there on mains power amp but not on battery power amp this must mean that it's something to do with the mains power, mustn't it? 

ICBM

tpk1 said:

I've tried different cables and the hum is there with all of them, so I don't think the cable is to blame.

Because the hum is there on mains power amp but not on battery power amp this must mean that it's something to do with the mains power, mustn't it? 

Yes, the noise is getting in via the power supply and being picked up by the cable, the guitar wiring and you, which all act as aerials to some extent.