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volume knob whoosh

rollyfoster

Silver Supporting Member
Messages
17,185
i'm cross-posting from the luthier section because I have no idea if this issue is with the guitar or the amp...hopefully someone will know something!

The volume knob on my Kirn tele has a lot of static and whooshing when plugged into either of my tube amps. Guitar's barely over a year old so it's not an old pot by any means. In fact, I had a suhr T with humbuckers that did the same thing so it may not even be isolated to this one guitar.

Happens with different cables and with or without pedalboard. BUT if I'm plugged into the board and have a pedal turned on then it's fine. No scratching or anything. I can roll the knob all over the place with no issues as long as a pedal is engaged. Turn it off and the whooshing is back.


However, if I plug it into my Yamaha THR10 it's completely silent. No scratching or anything.

Any ideas as to why this is happening solely with my tube amps? I figure if it's a problem with the volume pot it would happen on any amp including the THR
 

Vanyu

Member
Messages
738
Sounds like a dirty volume pot to me. Try rapidly turning the control and try to work out the dirt and see if it goes away.
 

rollyfoster

Silver Supporting Member
Messages
17,185
Sounds like a dirty volume pot to me. Try rapidly turning the control and try to work out the dirt and see if it goes away.
That's what I thought at first but it's more than one guitar making the same noise. It goes away when a pedal is turned on and it doesn't exist at all when plugged into my modeler amp...

It's more of a low whooshing swish noise than a crackle, too.

At this point I'm wondering if it could be related to the house electrical.
 

darkfenriz

Member
Messages
206
The first tube in your amp is leaking some DC current through its grid.

The DC goes up and down each time the pot's wiper loses contact or does anything else than just a smooth and steady wipe... hence the noise.
The pedals, if on,provide buffering and/or AC coupling capacitors.

Time to change the tube or go solid state.
 

pdf64

Member
Messages
8,238
So that's the input stage tube of both amps, often designated V1 or V2; provide some detail of your amp models if you would like help identifying them.
 

rollyfoster

Silver Supporting Member
Messages
17,185
The first tube in your amp is leaking some DC current through its grid.

The DC goes up and down each time the pot's wiper loses contact or does anything else than just a smooth and steady wipe... hence the noise.
The pedals, if on,provide buffering and/or AC coupling capacitors.

Time to change the tube or go solid state.
So that's the input stage tube of both amps, often designated V1 or V2; provide some detail of your amp models if you would like help identifying them.
It's the volume knob of the guitar making the noise, not the amp knob, if that makes a difference. Amps are a Swart AST and a Suhr Bella, although I don't have the Bella in hand at the moment. Seems odd that it would happen with 2 different amps and 2 different guitars....

The Swart had had the tubes changed recently. Did it with the old and the new tubes.
 

pdf64

Member
Messages
8,238
If you've got a test meter, you could verify the diagnosis by plugging a lead into the amp's input and checking for Vdc at the guitar jack plug end (turn the amp volume down!).
 

rollyfoster

Silver Supporting Member
Messages
17,185
If you've got a test meter, you could verify the diagnosis by plugging a lead into the amp's input and checking for Vdc at the guitar jack plug end (turn the amp volume down!).
Just a regular multimeter? Is this something that could be related to the wiring in the house too? I don't think this has happened in other places like gigs and practice spots.

Edit: heading to work in a few but I plugged in a cable and used a multimeter on both the tip and sleeve of it. Nothing registered. Assuming that I did it right, that is....
 
Last edited:

Rod

Tone is Paramount
Gold Supporting Member
Messages
23,642
Sounds like a dirty volume pot to me. Try rapidly turning the control and try to work out the dirt and see if it goes away.
And spray it with DeOxit
 

MKB

Silver Supporting Member
Messages
8,773
That's what I thought at first but it's more than one guitar making the same noise. It goes away when a pedal is turned on and it doesn't exist at all when plugged into my modeler amp...
IMHO this is a strong indication that there is some sort of issue with the grid of the first tube. Pedals without true bypass (most Boss and Ibanez for example) have an internal buffer that has one or more series capacitors that would isolate most grid issues such as leakage from being affected by the guitar volume control. If the guitar is connected directly to the first grid with no blocking cap (as in many tube amps), a guitar volume pot change would vary the DC resistance seen by the grid from a short to around 7k ohms or so (the DC resistance of the pickup in parallel with the volume pot).

Another thing that might be at fault is the resistor from the grid of the first tube stage to ground, usually a 1meg. If this resistor is open or not properly attached at both ends, and the grid depends on the resistance of the volume pot to complete the grid bias circuit, it could conceivably cause noise.
 

JunkGear

Silver Supporting Member
Messages
1,073
The first tube in your amp is leaking some DC current through its grid.

The DC goes up and down each time the pot's wiper loses contact or does anything else than just a smooth and steady wipe... hence the noise.
The pedals, if on,provide buffering and/or AC coupling capacitors.

Time to change the tube or go solid state.
Sounds like DC leaking back to the guitar to me too. Listen to these guys and try to isolate the problem. Like already stated, something is not sending it to the ground connection properly.
 

Jeff Gehring

Gold Supporting Member
Messages
6,831
I'd like to clarify, if indeed your issue is DC leakage from the first preamp grid circuit, it is in no way dangerous or harmful, just (as you have found) annoying.
 

rollyfoster

Silver Supporting Member
Messages
17,185
I'd like to clarify, if indeed your issue is DC leakage from the first preamp grid circuit, it is in no way dangerous or harmful, just (as you have found) annoying.
Cool thanks. What are the odds this would happen on 2 different amps simultaneously?

The other weird thing is I'm pretty sure they're ok when I'm at a gig or practice. I don't recall hearing it then.
 

Jeff Gehring

Gold Supporting Member
Messages
6,831
If you want to nail it to being the amp(s) for sure, if you've got a low value, aka junker guitar cable laying around, you could do this:

View media item 51616
If it doesn't make the noise when you use this cable, the problem is coming from the amp(s).
 

rollyfoster

Silver Supporting Member
Messages
17,185
If you want to nail it to being the amp(s) for sure, if you've got a low value, aka junker guitar cable laying around, you could do this:

View media item 51616
If it doesn't make the noise when you use this cable, the problem is coming from the amp(s).
Thanks for the tip. Don't have the equipment to do that but I just took it to a rehearsal spot and messed around with it. Was hoping the sound would disappear but it didn't (so I can rule out house wiring at least).

It turns out I think I just have TERRIBLE luck with JJ tubes. I tried 3 different NEW 12ax7s in v1 and the noise was there. Last ditch effort with an old Mesa tube and the issue was pretty much resolved. There's still a tiny amount of scratchiness but it's nowhere near what it was with the whooshing of the other tubes.

My last 3 amps have all had issues with new/factory installed JJs whether it's terrible 6l6 rattle or microphonics, rectifier rattle, or whatever the hell is going on with these preamp tubes or the ones that arrive with rattling I can hear before even opening the box.
 




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