Radio In My Wah Pedal

[Paul Marossy]

I was using my Fasel equipped Italian Vox wah pedal this morning and it was picking up only one radio station all of the sudden.  It would get stronger and more distorted when in heel down position and would almost go away when in toe down position. I guess somehow it was acting like a tuner? When I adjusted the coiled cables in the jacks it went away. So I'm guessing that the cable(s) were acting like antennas?

Anyone ever had this experience and/or can explain why the heck that happened? Pretty weird...

[roseblood11]

Maybe a bad solder joint or a cable is half-broken internally?

[GibsonGM]

Yeah, the cables do some capacitive whammy-jammy and can become resonant with other components...some cables have a higher C than others, so it won't do it with all of them.   Also could be damaged, as roseblood just said.     

I'd only pursue it if it became a regular radio show

[Paul Marossy]

I'd only pursue it if it became a regular radio show

It's only been a one time thing so far

[stallik]

2 things I've noted when I've experienced radio interference, an issue with earth (somewhere) and the fact that the radio station is always Russian!

[Paul Marossy]

2 things I've noted when I've experienced radio interference, an issue with earth (somewhere) and the fact that the radio station is always Russian!

Yeah... I think one cable wasn't grounding properly in one of the jacks for some reason. What doesn't make sense to me is that the circuit is in a Faraday cage (enclosure and bottom plate) and the cables are shielded too, so how could it happen?

[stallik]

Well beyond my paygrade I'm afraid. I once tried hard to build a radio and failed. Several times I've tried not to and succeeded

[Paul Marossy]

Well beyond my paygrade I'm afraid. I once tried hard to build a radio and failed. Several times I've tried not to and succeeded

Ha ha, I had one this morning and wasn't even trying to make one! But it could only get one station. 

[GibsonGM]

The signal's coming in thru your cable.  They have lots of capacitance, PLUS resistance (impedance)...if you accidentally have a situation where they are resonant at a freq. occupied by a station whose signal happens to be in your house, off you go! 

This is why some people put a small value cap from input to gnd on amps, or high gain builds...shunt those freqs. right off the bat....Can you reproduce the effect with your cable? 

Does it change if you stretch is out?  ("phone cord" type coiled cable, right?  Hendrix liked them, I hear - the high capacitance mellowed out his signal, he claimed!  Something about that capacitance working with his wah input...)

[Paul Marossy]

This is why some people put a small value cap from input to gnd on amps, or high gain builds...shunt those freqs. right off the bat....Can you reproduce the effect with your cable? 

It's only happened this morning, it's not a regular thing. I'll see if I can re-create it again.

Does it change if you stretch is out?  ("phone cord" type coiled cable, right?  Hendrix liked them, I hear - the high capacitance mellowed out his signal, he claimed!  Something about that capacitance working with his wah input...)

If I can get it to happen again I'll see if stretching the cable has any effect.

[GibsonGM]

It's great if it doesn't happen again    Hey - just thought of this, too - something has to be rectifying the RF to be audible...so, it's passing thru something non-linear, too...maybe a gain stage inside.
So has more than just the 'coupling in' going on.  Nothing I'd worry about, and if it were a problem I'd look at grounding, lead dress, input small cap to gnd...

[PRR]

> one cable wasn't grounding properly in one of the jacks

I once/twice had to run very long mike wires a mile from an AM transmitter. I had to jiggle all the plugs multiple times until I was not getting polka-hour on top of holiday concert.

> the circuit is in a Faraday cage (enclosure and bottom plate) and the cables are shielded too, so how could it happen?

Each is in its own cage, but the two cages are not firmly connected to each other. The difference (voltage caught from the air) appears across the jack, so effectively across the input. While you can't hear 880KHz directly, many guitar-level BJT inputs will rectify RF as small as 20mV.

The take-away is to get good grounds. The 1/4" jack is fairly good but not perfect. The different kinds of platings get different kinds of micro-tarnish. Vigorous abrasion is sometimes the only/best way to break the tarnish. Which is why I was jacking-off all the jacks in my mike cables.

[Paul Marossy]

> the circuit is in a Faraday cage (enclosure and bottom plate) and the cables are shielded too, so how could it happen?

Each is in its own cage, but the two cages are not firmly connected to each other. The difference (voltage caught from the air) appears across the jack, so effectively across the input. While you can't hear 880KHz directly, many guitar-level BJT inputs will rectify RF as small as 20mV.

The take-away is to get good grounds. The 1/4" jack is fairly good but not perfect. The different kinds of platings get different kinds of micro-tarnish. Vigorous abrasion is sometimes the only/best way to break the tarnish. Which is why I was jacking-off all the jacks in my mike cables.

Funny... yesterday before I saw your response I thought that maybe the bottom plate wasn't getting a good contact with ground since it has that white rubbery edge on it, so I devised a way to make sure that the bottom plate made good contact with ground utilizing a small coil spring in one of the holes which I filed a little bit to make sure bare metal was there. I also cleaned the jacks with a little acetone to make sure they were all as clean as possible. We'll see if the problem happens again. I kinda think this will be a one time freak event but time will tell...

[bool]

I "diagnose" what happened to you as a bad jack-to-socket ground connection somewhere in the signal path. This happens ... it's nothing unusual.

You can try to "sure-proof" your gear with soldering small ceramics caps around the wah transistor electrodes; e-b, b-c, c-e ... but this can alter the effect sound.

[GibsonGM]

I "diagnose" what happened to you as a bad jack-to-socket ground connection somewhere in the signal path. This happens ... it's nothing unusual.

You can try to "sure-proof" your gear with soldering small ceramics caps around the wah transistor electrodes; e-b, b-c, c-e ... but this can alter the effect sound.

Sure.  The right amount of inductance, capacitance, and resistance combined with something that can rectify a radio signal (poorly joined parts like jacks, corrosion, and so on) can at times cause this.  You inadvertently have a radio receiver system that you don't want.

Ham radio ppl complain about this stuff sometimes...there are a lot of folk tales of signals being rectified by metal gutters, etc!

[rutabaga bob]

My old man was a ham radio guy, and also fixed electronics on the side.  Every now and then a neighbor would call to complain that his signal was bleeding into their TV, so off he'd go to add some filtering.

[banjerpickin]

I once tried hard to build a radio and failed. Several times I've tried not to and succeeded

The plight of the scientist. 

[amptramp]

Well beyond my paygrade I'm afraid. I once tried hard to build a radio and failed. Several times I've tried not to and succeeded

Murphy's Law isn't the only source of frustration.  You are the victim of Gumperson's Law:


GUMPERSON'S LAW

Gumperson's Law, as explained below, accounts for the fact that you can throw a burned match out the window of your car and start a forest fire, while you can use two boxes of matches and a whole edition of the Sunday paper without being able to start a fire under the dry logs in your fireplace.

The law, stated simply, is "THE CONTRADICTORY OF A WELCOME PROBABILITY WILL ASSERT ITSELF WHENEVER SUCH AN EVENT IS LIKELY TO BE MOST FRUSTRATING."

Readers familiar with these matters will perhaps recognize another version of the Law: The Outcome of a Given Desired Probability will be Inverse to the Degree of Desirability.

Dr. R.F. Gumperson, internationally famous physicist, began serious work in 1938 on a phenomenon long known to scientists, but up until then considered as a mere curiosity. This was the fact that the forecasting record of the Weather Bureau, despite its use of the most advanced equipment and highly trained personnel, was not as good as that of the Farmers' Almanac. After four years of research, Dr. Gumperson enunciated his now famous law and was able to make a series of predictions later confirmed by other workers in the field. Some of the better known of these include the following:

(1) That after a raise in pay you will have less money at the end of the month than you had before.

(2) That the girl at the race track who bets according to the color of the jockey's shirt will pick more winners than the man who studied the past performance of every horse on the program.

(3) That children have more energy after a hard day of play than they do after a good night's sleep.

(4) That the person who buys the most raffle tickets has the least chance of winning the raffle.

(5) That a child can be exposed to mumps for weeks without catching them, but can catch them without exposure the day before the family vacation.

(6) That the dishwasher will break down the evening you give dinner for ten.

(7) That the parking spaces are always on the other side of the street.

Dr. Gumperson served as a consultant to the armed services during World War II and evolved the procedure whereby the more a recruit knew about a given subject, the better chance he had of receiving an assignment elsewhere.

There is no knowing to what further glittering heights Dr. Gumperson's genius could have led him had it not been for his untimely death in 1947. Strolling along the highway one evening, he was obeying the pedestrian rules of walking to the left, wearing light clothing, and facing traffic. He was struck down from behind by a Hillman-Minx, driven by an English visitor hugging the left side of the road.

[Plexi]

ugh... what annoying problem.. 

My 90s GCB95 is best than my old Sony radio for catching signals.
My new's V847 doesnt.

I guess the evangelic "pirate" radios (where I live, theres thousand of them), the bad house connection to ground, and live in 5th floor maybe help.

[Paul Marossy]

ugh... what annoying problem.. 

My 90s GCB95 is best than my old Sony radio for catching signals.
My new's V847 doesnt.

I guess the evangelic "pirate" radios (where I live, theres thousand of them), the bad house connection to ground, and live in 5th floor maybe help.

So far I haven't been able to recreate it, so I think it was a one time freak incident. Not so fun for you though...