hum when rolling down volume pot

[stumble]

Hi folks,
new here (officially now), though of course I've found good info before in this fine forum.
A friendly hello to everybody !
Allow me a tough question, please, I'm in need of expert help.
On some of my guitars, mainly Gibson styles with 500k volume pots, regardless of amps or PUs, I notice an annoying behaviour :
When rolling down the volume hum is slowly increasing, between 2 and 0 it goes away again.
Obviouslly it's more noticeable with overdriven classic rock sounds or compressed cleans.
Kinman describes this exact phenomenon in the FAQ and blames the 500k pots.
Since I dearly love my Alnico 2 PUs (2x Pearly Gates, 1x Classic 57, 1x Barfuss P90, among others) I fear 250k pots might make those guitars too dull ...
Here's what I tried already :
- modern and 50s wiring
- different amps
- a good boost pedal (Xotic) immediately after the guitar hoping for an impedance buffering effect
- ground lift switch on the amps
- triple ckecked wirings, guitar cables and so on
-- none of that helps, unfortunately.
- I'm NOT talking about the classic hum when you're too close to the amp or when you have bad shielding / grounding
- I'm NOT talking about old / dirty pots

After many F-Style years I've discovered G-styles again, and a big part of the fun here is working with the volumes ...

Any help / ideas much appreciated !
Tia,
stumble

 

[Spudman]

Re: hum when rolling down volume pot

I'd like to know this too. I have a Strat that does this. Wide open with the volume knob it's just fine. Roll it back a little and it starts humming until the off position. What's up wid dat?

 

[ehdwuld]

Re: hum when rolling down volume pot

soinds like something is shorted between the jack and the volume pot

or maybe a bad pot

 

[stumble]

Re: hum when rolling down volume pot

This is what Kinman writes :

when you turn the volume control down a lot of hum/noise is introduced. This is because the amplifier input is becoming progressively unloaded and is effectively floating (like when the cable is not connected to your guitar) which results in hum/noise. 250K pots also exhibit this characteristic but not nearly to the same extent as 500K or 1Meg pots do. The higher the value the worse the problem becomes, it's part and parcel of high impedance circuitry.

The way I read this (now I'm looking at this again) it might be possible to put something between guitar and amp to work around - but what ?
Clueless,
stumble

 

[stumble]

Re: hum when rolling down volume pot

I'd like to know this too. I have a Strat that does this. Wide open with the volume knob it's just fine. Roll it back a little and it starts humming until the off position. What's up wid dat?

If you can live with slightly darker tone try a 250k volume.
Unfortunately that won't work too well for my mellow A2 PUs ...
Cheers,
stumble

 

[rts99]

Re: hum when rolling down volume pot

I've never experienced this but the point about the input to the amp "floating" is a potential problem I'd never thought of. This is a real problem in electronic circuits & there are usually bias circuits at the inputs of amplifier stages specifically to adress this probelm. If the amp is powered & undriven it can "run away" eventually destroying itself. The bias circuits are intended to prevent this condition.

My 1st thought is to try a different amplifier (different manufacturer altogether) and see if the problem persists. If this is due to a floating amplifier input as a result of the amp design you won't be able to resolve it with your current amp (at least I don't think you will).

My 2nd thought is to add an active circuit between the guitar and the amp. An amplified pedal comes to mind. This should drive the input stage of the amp preventing it from floating. Keep in mind that this may just move the problem from the input stage of the amp to the input stage of the pedal, depending on the input stage of the pedal amp. Not being a pedal fan I would prefer something that has a "clean" output but NOT a true bypass output. The true bypass output won't change the circuit & the problem will persist.

Good Luck

 

[Vincent Vespa]

Re: hum when rolling down volume pot

This is what Kinman writes :

The way I read this (now I'm looking at this again) it might be possible to put something between guitar and amp to work around - but what ?
Clueless,
stumble

Noise Gate?

 

[stumble]

Re: hum when rolling down volume pot

Thanks for all yout input !
I'll be back with more detailed info re the behaviour of different amps and FX.
Obviously a noise gate might work, but I'd rather live with the noise then, especially as the very purpose of playing with the volumes is sending different levels to the amp, so setting up the threshold would be very finicky.
Cheers,
stumble

 

[audiocheck]

Re: hum when rolling down volume pot

Hi folks,
new here (officially now), though of course I've found good info before in this fine forum.
A friendly hello to everybody !
Allow me a tough question, please, I'm in need of expert help.
On some of my guitars, mainly Gibson styles with 500k volume pots, regardless of amps or PUs, I notice an annoying behaviour :
When rolling down the volume hum is slowly increasing, between 2 and 0 it goes away again.
Obviouslly it's more noticeable with overdriven classic rock sounds or compressed cleans.
Kinman describes this exact phenomenon in the FAQ and blames the 500k pots.
Since I dearly love my Alnico 2 PUs (2x Pearly Gates, 1x Classic 57, 1x Barfuss P90, among others) I fear 250k pots might make those guitars too dull ...
Here's what I tried already :
- modern and 50s wiring
- different amps
- a good boost pedal (Xotic) immediately after the guitar hoping for an impedance buffering effect
- ground lift switch on the amps
- triple ckecked wirings, guitar cables and so on
-- none of that helps, unfortunately.
- I'm NOT talking about the classic hum when you're too close to the amp or when you have bad shielding / grounding
- I'm NOT talking about old / dirty pots

After many F-Style years I've discovered G-styles again, and a big part of the fun here is working with the volumes ...

Any help / ideas much appreciated !
Tia,
stumble

I know this is an old post, but I am experiencing the same issue. I just rewired an Gibson L pJ and am experiencing the same volume knob hum. Fine on 10 and fine on 0, but in the middle of the knobs travel the hum is loudest (max resistance). Was this resolved for the OP and how?

 

[stumble]

Re: hum when rolling down volume pot

Nope, not really.
Having some kind of buffering in line helps.
Interestingly enough, none of my PRS shows this issue, neither with PRS PUs nor with Duncans, Häussel, Barfuss.
cheers,
stumble

 

[audiocheck]

Re: hum when rolling down volume pot

Stumble
I read somewhere that it could have to do with amps input impedance tot being high enough for higher resistance guitar volume pots. Did you investigate that route? I have 2 amps at home and will see if one is a bigger offender than the other. One amp is from 1984 and the other is brand new, so good chance that the input impedances will be different from each other.

 

[stumble]

Re: hum when rolling down volume pot

audiocheck,
this definitely is part of the issue, see my buffer workaround.
I noticed that input stages vaguely inspired by 7ender circuits (Mesa Heartbreaker, Ceriatone OTS) are most sensitive to the phenomenon.
Why PRS is not plagued however is beyond me.
Can't possibly be the 25" scale ? :9:
I still would like to have a clear explanation ...
cheers,
stumble

 

[audiocheck]

Re: hum when rolling down volume pot

audiocheck,
this definitely is part of the issue, see my buffer workaround.
I noticed that input stages vaguely inspired by 7ender circuits (Mesa Heartbreaker, Ceriatone OTS) are most sensitive to the phenomenon.
Why PRS is not plagued however is beyond me.
Can't possibly be the 25" scale ? :9:
I still would like to have a clear explanation ...
cheers,
stumble

do you know the resistance of the PRS pots? just curious if they are 300K or 500K?
When I get home on wednesday, I will meter the output of my LPJ then and see if one pot (in the circuit)or two are worse offenders.

 

[stumble]

Re: hum when rolling down volume pot

500k nominal

 

[audiocheck]

Re: hum when rolling down volume pot

500k nominal

ok, so here is what I am gonna try. If I experience the same hum on both amps, I will relocate all my grounds to a single point (Star Grounding). Since I have done some complicated wiring with push/pulls, I think I may possibly have introduced a ground loop.

 

[jonljacobi]

Re: hum when rolling down volume pot

This is almost certainly a ground issue with the pot in question. Make sure that the ground are securely soldered to the pot. I've had this twice, both times it was from a solder joint that had separated from the pot during long road trips due to vibration (and crappy soldering and/or cleaning the area to be soldered on the pot)

 

[rubenuytt]

Re: hum when rolling down volume pot

EDIT: This only worked on a tiny headphone amp, but not on a real amplifier... Would it be of any use to use bigger resistors like 10M?

This is what Kinman writes :

The way I read this (now I'm looking at this again) it might be possible to put something between guitar and amp to work around - but what ?
Clueless,
stumble

Hi all you nice forum-diggers, this is the first time I actually post in a forum, because for the first time I think I can come up with a solution
And it's not that hard at all!

I ended up here because I had the same problem: I made myself a little opamp top/bass booster, sounded OK, but when I turned the volume down, an anoying hum occured... So I started digging and read this post.

The thing about unloading the amp and have the input floating, like when no cable is connected, made perfect sense to me. Since I recently put humbuckers and 500k pots in my strat, I had to check out if this had to do with the problem, so I headed into the cave and started tinkering...

What I did basically, was make a little buffer, with a single opamp in unity gain and a high input impedance using 1M bias resistors, like below:


This solved the problem for me, ofcourse I could also use the 1M bias resistors in the humming booster itself, which I made using only 470k bias resitors, but that is just my situation. Anyway, the schematic above should work, mess around with the input and output capacitor values, because I literally grabbed the first ones I could reach. Don't pick too small a value or you get a high-pass filter... I think anything around a 100nF will work, the 22uF is too big, but it works...

Good luck, hope this helps out some people around!
Cheersios

 

[rubenuytt]

Re: hum when rolling down volume pot

audiocheck,
this definitely is part of the issue, see my buffer workaround.
I noticed that input stages vaguely inspired by 7ender circuits (Mesa Heartbreaker, Ceriatone OTS) are most sensitive to the phenomenon.
Why PRS is not plagued however is beyond me.
Can't possibly be the 25" scale ? :9:
I still would like to have a clear explanation ...
cheers,
stumble

Doesn't PRS mainly use active pickups? That would explain why you don't have the problem on those guitars?

 

[Edgecrusher]

Re: hum when rolling down volume pot

Doesn't PRS mainly use active pickups? That would explain why you don't have the problem on those guitars?

I dont think I have ever seen a PRS with actives from the factory...


But be that as it may... this thread is 5 years old and there is a decent chance the guy you are replying to is around anymore to answer.

 

[Johann Cat]

Re: hum when rolling down volume pot

An old thread, but likely an enduring question. I have a Telecaster with Filtertrons and 500k pots; I also got no ground hum when the volume was full (call it 10)
but when at 8 etc.: lots of un-grounded type noise. In my case, I had a weak ground connection between the volume pot and the input jack. Resoldering was the answer.
(Jacobi above was correct in my case.)