Radio In My Wah Pedal

[Paul Marossy]

So this morning I had a visit from the radio station again. This time I more closely looked at the cause of it and found that the problem originated at the output jack. Once again if I wiggled the cord a little bit the problem went away. I also noticed that its ground depends on its contact with the enclosure since there is no ground wire soldered to it so I added a wire from the sleeve to ground. I'm confident that was the problem, the dodgy ground in conjunction with the coil cable apparently acting like an antenna.

[stallik]

So, you could isolate the jack from the chassis then earth through a variable resistor. Make it foot-switchable and you could use it for an intro to a song ala Floyd

Glad you found the issue

[Agung Kurniawan]

This is one is happen to my BOSS MT-2, once I set the gain pot at max, the treble at max, middle were max, and mid freq about 3o'clock. Its like russian talk to each other (while I live in Indonesia)

[bool]

A wah circuit directly feeds back the output to the input node - it "injects" what the output receives back into the circuit, and since the output impedance isn't super-low the circuit does actually "receive", so what happened to you isn't surprising ...

[Paul Marossy]

A wah circuit directly feeds back the output to the input node - it "injects" what the output receives back into the circuit, and since the output impedance isn't super-low the circuit does actually "receive", so what happened to you isn't surprising ...

That's a good point. Apparently it doesn't take much of a dodgy ground to turn it into a one station radio. The weird thing is that in heel down it's loudest and at the other end it almost disappears. I guess the pot acts like a volume control too when I'm tuning into whatever talk radio station it picks up. 

[bool]

Stuff like that can mess up your Hi-Fi amps - it's not uncommon for RFI to creep back into the amp via speaker cables; find its way back to the input LTP via the NFB and mess up the workings ...

One way to make these symptoms less severe is to add a RC filtering to in/out nodes of your pedal.

In your case, I would try to solder a 220pF cap across the output jack ("hot" lug) and the shortest contact to the metal case (ie. "ground")

With a bit of trial and error, you should be able to minimize the "radio"; with adjusting the cap value and listening to changes in to the wah tone. (there will be some so it's a compromise...)

[Paul Marossy]

Stuff like that can mess up your Hi-Fi amps - it's not uncommon for RFI to creep back into the amp via speaker cables; find its way back to the input LTP via the NFB and mess up the workings ...

One way to make these symptoms less severe is to add a RC filtering to in/out nodes of your pedal.

In your case, I would try to solder a 220pF cap across the output jack ("hot" lug) and the shortest contact to the metal case (ie. "ground")

With a bit of trial and error, you should be able to minimize the "radio"; with adjusting the cap value and listening to changes in to the wah tone. (there will be some so it's a compromise...)

Thanks for the tip. If the problem should appear again, which I don't think it will but if it does, I will try that.