noisy wah

[David B]

Hello,

I have an old Vox wah that has gotten very noisy, sounds like frying bacon . So far I check the grounds, switch & pot with no luck. Anyone know what the likely culprit might be, where I should look next?

Thanks,
David

[Mark Hammer]

The resistive strip in the pot is pressed-together particles, much like pavement on the road. The pot wiper is a bit like a shovel pressed up hard against the road to make constant contact as it moves. Over time and rotations, the friction of the wiper will scrape away little particles of the resistive strip, much the way moving a shovel back and forth over the same piece of asphalt will eventually scrape off bits of it.

What we hear as pot noise is essentially the sum total of many discontinuities in contact. Much like the pavement example, those discontinuities can be because there are parts of the pavement missing or because there is stuff sitting on top of the pavement (i.e., tiny pits in the resistive strip or residue/dirt on top of the resistive strip). Both will momentarily interfere with contact between the tire/wiper and road/strip.

In some instances, the preponderance of noise comes from residue and dirt that can be easily cleaned off with spray, or by removing the back of the pot and cleaning the resistive strip with a Q-tip or similar.

In other instances, the overall noise can be a result of residue/dirt and pits than can be cured by application of certain substances. In still other instances, there has been enough erosion of the resistive strip from cumulative use of the pot, that even after cleaning off the residue and dirt, the pits still produce much objectionable noise.

Clean the pot first, as per instructions on the spray can, and if that doesn't work, you may need to buy a new pot. It happens.

[52 Bill]

Is the "frying bacon" noise constant or as Mark suggests, when the treadle is moved?

[Mark Hammer]

Bill makes a good point. Constant sizzle would be circuit-related, while crackle when you move the treadle would be pot-related. Different problems, with different cures.

[David B]

Sorry I didn't give a more detailed account of the symptoms, the noise is constant. Checked a few things including swapping the pot, the foot switch and verifying the grounds and the problem persists.

Looks like a circuit issue, I have some caps & resistors to try but will need suitable transistors if the caps & resistors check out OK



thanks again

David

[Mark Hammer]

Okay, now we're on track.

When there is a constant crackly sound, the culprit is frequently an electrolytic cap. If it is an "old" Vox wah, there is a high likelihood one or more of them is dried out and needs replacing. Luckily, they are a damn sight cheaper and easier to find and replace than wah pots!

[David B]

Changed the 4mf cap and swapped my only only .01uf in both positions , still no dice.
Also swapped Q1 for a 5117 I had laying around but that didn't make a difference so Q2 is next and the .22uf's
Did find that the 470r that goes from Q1 emitter to ground was out of spec so changed that and some improvement, could be these old cc resistors.Also wondering if the inductor could cause this? Not much left to check...

[Mark Hammer]

While "frying bacon" IS pretty descriptive (a helluva lot more descriptive than much of the ad copy I see for pedals and pickups!), perhaps an audio clip might assist. No promises, but sometimes a verbal description doesn't pinpoint as easily as actually hearing it.

BTW, is this somethng that starts the moment you plugin and continues without change? Is it something that varies with the battery you put in? Does it happen when another pedal is in series before the wah?

[52 Bill]

Isolate the two halves of the circuit and see if you can find out where the problem is located. If you pull Q2 and it still makes noise, check all of the parts related to Q1. If the noise stops check the circuit around Q2.

Or just try swapping out Q2 with the original Q1.

[David B]

Yup starts right away & doesn't matter if its by itself or with other gadgets.Still have to try Q2.
Ah changed two more resistors,a 10K & 22K and no more noise

thanks guys

David