Puzzling Pot Pedal issue - can you help me troubleshoot?

[Brian Spratt]

I'm having trouble diagnosing what could be going on here. My L-120 Goodrich pot pedal makes a slight but noticeable scratchy or static-y noise (I know, I know... please keep reading) that happens only under specific conditions. This does not fit the normal worn/scratchy pot problem description as far as I can tell. Here are the pertinent troubleshooting facts:

1) When I run direct from guitar to volume pedal, there are not any noise problems. The pedal sounds great no matter what devices come after it.

2) If I put ANY kind of active circuit between the guitar and the volume pedal the scratch/static noise returns. I've swapped numerous devices to eliminate any particular active circuit/device as being the culprit.

3) I swapped in my old Ernie Ball VP Jr. pot pedal just to see if it does the same thing, and it does not. This should rule out a power supply or grounding kind of issue with my setup.

4) And this is what puzzles me most... the scratch/static noise occurs ONLY when notes or sound are going through the volume pedal. I can mute the strings and rock the volume pedal back and forth without any static noise at all. But as soon as I play anything AND rock the pedal, the noise is audible. This seems to be what rules out the typical worn pot scenario.

5) I bought this Goodrich pedal brand new less than 2 years ago and it did this even when it was brand new. At that time, I moved my tuner after the volume pedal and "solved" the problem. But now I'm wanting to experiment with some FX routing and I'm facing this problem again.

The only ideas I have are: 1) Call Goodrich and just see what they say. I actually did call when this happened when the pedal was new and they said to send it in to them so they could check it out. I didn't want to go without my volume pedal at the time so I didn't. Also, if they just hooked it up directly to a guitar, they'd probably just tell me that nothing was wrong. Or 2) Just buy a pot and swap it out and see what happens. But I'd hate to go to that expense and trouble just to be back in the same boat.

Any suggestions? Thanks!

[Bill Ferguson]

First, check your cable (s) to be sure they are of high quality and no issues. Especially the cable you use between your "devices" and the volume pedal.

After that, you really should have taken Goodrich up on their offer to take care of the problem.
I would call Goodrich and see if the offer still stands and send it to them.

There is NOTHING in a Goodrich L120 that will cause static other than the volume pot or a loose wire.
There are no active electronics in an L120.

Looking inside the volume pedal, what brand is the volume pot. Goodrich encountered many problems with the Honeywell and Clarostat pots. Have that info ready when you call Goodrich

[Dave Grafe]

I had seen this happen a time or two, and it is NOT the pot but the way some active devices respond to the shifting loads as the pot moves through it's cycle.
The pedal presents a 500kohm load in parallel with a moving tap essentially sweeping from a dead short to ground when "off" to a complex high impedance coupled with 500kohms to ground when full on. High quality buffers can be designed to do this but not all pedal makers bother with the added expense and just stick a cheap Op-amp, with its own compensation and negative feedback needs, on the output side of the circuit. Such complex and changing impedance loads can and will generate the kind of noises you are experiencing. The fact that the Ernie Ball pedal did not produce this phenomenon is likely due to the 250k pots commonly found in these pedals not reaching the critical balance found with the Goodrich 500k units at audible levels.

Try to buffer your effects outputs into the VP with a Steel Guitar Black Box or other device specifically designed for driving a passive pot VP. Another fix would be to go to a Hilton or other such active pedal which presents a uniform input impedance regardless of volume setting.

[Brian Spratt]

Thanks Bill and Dave. The pot is a Dunlop 93303024497. Bill, I think I've pretty well ruled out bad cabling, and I agree there's nothing in the pedal that should make noise aside from just the pot if it was bad or worn.

Bill, I don't have a black box or any steel-specific buffered pedal. I'm currently running the pedal into a Strobostomp HD, which I would expect to have a high quality buffer. I have a Boss DD-7 and RV-6. I'll swap those in and just see if it makes a difference. I might be able to borrow a friend's Matchbox too... I was curious what that might do.

[Dave Grafe]

Just understand that the 500k VP pot is intended to match directly with a pickup, i.e. output impedance of 15 kohms to 30 kohms, while many stomp boxes, including all those from Rolad/BOSS, have much lower output impedances of around 1 kohm in order to operate well with fixed active circuit loads as low as 600 ohms. They simply are not designed for the changing, loads presented by the configuration you are attempting, nor the input levels generated by a wide open, pre-VP PSG pickup, so some instability is inevitable.

Why you want your delay and reverb outputs to follow the VP in the first place is another question, as in the real world their INPUTS would follow the VP and their decay artifacts would thus remain unattenuated and natural, replicating natural reflection behavior.

[Brian Spratt]

...Why you want your delay and reverb outputs to follow the VP in the first place is another question, as in the real world their INPUTS would follow the VP and their decay artifacts would thus remain unattenuated and natural, replicating natural reflection behavior.

Dave, completely understood and in agreement. Moving the Boss pedals in front of the volume pedal is simply a troubleshooting step, not intended to be particularly musical. It tests the hypothesis that the issue is with the design of the buffer that comes before the volume pedal. If I try a different buffer/pedal and the issue goes away, then that's a strong indicator that my issue is indeed with the design of the buffer that comes before the volume pedal. If the issue persists, well... I keep working at it.

I've tried a few different pedals before the volume pedal, but I don't think I tried the Boss ones. I think they are supposed to have high quality buffers, so that's why I thought to try them.

[Brian Spratt]

The Boss pedals didn't seem to make a difference, but I tried putting my TONEX first in the chain and it did make a difference. It still made the noise, but it didn't seem as audible and had a different "sound" to it. I can't find published specs on the I/O impedance on the TONEX which would be enlightening. Assuming the crackle culprit is the buffer I/O preceding the pedal, I'm still stuck wondering why this wouldn't be a more common issue. I think there are a lot of guys running tuners or overdrives between the guitar and a pot pedal.

Assuming this is the root issue, what would be a good remedy? Get an active volume pedal... get a freeloader... matchbox?? Would that presumably do the trick?

[Jack Stoner]

I've been playing pedal steel for 50+ years. My effects have always been between the volume pedal and amp, NOT between guitar and volume pedal like 6 string guitar.

[Brian Spratt]

Jack, I know that many players do the same as I've done myself until recently. I think guys that use overdrive tend to favor placing the drive between guitar and volume pedal to keep the response of the overdrive smooth and consistent.

[Donny Hinson]

Have you tried another amp?

[Jerry Overstreet]

I commonly plug an analog delay pedal right into the guitar jack or a Boss Tone at different times, ocassionally a BoBro pedal and I've never experienced the phenomenon you describe. All straight out of the guitar and in front of the input into Goodrich volume pedals.

I don't know enough to offer any help but I suspect something in your v.p. electronics is causing those artifacts.

[Brian Spratt]

I've tried all sorts of routings and output options. I have a Matchbox on the way to me now... I'm going to put that first in my signal chain and see if that doesn't help.

[Scott Swartz]

I have had knee levers that I had to add a ground wire to prevent static electricity buildup and noise through the pickup.

Seems like a long shot to me but you could have a variation of this going on.

When you are hooked right to the pickup you have a low resistance path for DC through the pickup.

With a buffer in the chain the DC resistance path is the pot value.

You could eliminate this as a possibility by checking using clip leads to ground the different metal parts of the VP and see if it goes away.

[Georg Sørtun]

When I put active units/stomp-boxes before the VP - which is "the norm" for me - I always use a VP of 22K to 50Kohm. Reason is that most stomp-boxes use single 9Volt supply/battery, and an output capacitor, and work best with a load of about 10 to 25 times their output impedance (wich is about, or lower than, 1Kohm).
A 500Kohm pot will not clamp down and keep the stomp-box' output capacitor's DC charge at the output terminal permanently at GND level, and will tend to discharge over the VP-pot ... creating static noise and slowly but steadily wear out that VP pot.

A 22K to 50Kohm VP pot OTOH, will drain that DC charge quickly, and keep it down, without any static noise or pot wear. And just about any and all stomp-boxes will act as a "MatchBox"

[Brian Spratt]

Georg, sounds like you may be on to something there but it’s beyond my expertise. Goodrich support offered to swap my L120 for an Omni pedal for a modest fee. Am I hearing you say I should do it?

[Georg Sørtun]

The Omni is 500Kohm in any setting AFAIK, but as "active/buffered" it may work as you want … I simply don't know since I haven't tested it.

Here's what I use…
https://www.gunlaug.com/contents/music/ ... r.html#p23

Another solution: if you have access to a 50Kohm resistor (1/4 Watt) that can be soldered between "signal" and GND inside the Jack in either end of a short cable - to be inserted between the stomp-box "out" and VP "in", such a cable can be used to pull down and "tame" the DC charge on the output capacitor in any stomp-box.

[Brian Spratt]

Just to follow-up here on a solution that worked. After trying many things including swapping my L-120 for an Omni (thanks Goodrich support for helping me there), the only thing that actually worked was placing a Goodrich Matchbox immediately after the guitar output.

My conclusion is that the interaction between the output of my pickup and the numerous pedals I tried immediately following the pickup resulted in unwanted noise when that signal went through the pot in my volume pedal (both the L-120 and the Omni, just the same). Feeding the pickup's signal directly to the Matchbox first resolved whatever electrical issue was going on there completely.

[Georg Sørtun]

Great!
Glad you found a working solution for that particular, seriously strange, case of yours. Pity I could not have listened to, and diagnosed it, in person.

FWIW: I ended up removing the Matchbox, and other active buffers I have tested, from my setups, as they added noise rather than reduce or eliminate it when I had active units – stomp-boxes and such – in the sound-chains.
But, trying to diagnose electronic audio-setups without hearing them, is not an "exact science"…

[Kyle Van Koevering]

Apologies for resurrecting an old thread, but I've run into the same issue and this thread helped me solve it. I was running my guitar into a Goodrich L120 and then into a mixer for silent practice, and the intermittent static was unbearable. The problem seemed to go away after placing a Boss pedal between the L120 and the mixer.