Radio Frequency Interference

[vanhansen]

I've done some searching on this and found a couple of useful topics but they pertained to FF circuits.  Mine is with the Discrete IC Buffer from GGG.

Here's the scenario.  The buffer is housed in a Hammond 1590A box, powered by a regulated supply (BOSS PSA-120T).  It sits at the end of the effect chain in the effects loop.  Here's what happens.  If I unplug the cable from the last pedal's output before the buffer, and touch the tip, I get really good reception of a local AM station, 820 WBAP to be exact.  If I touch the box, the reception fades, but not totally.  When the cable is plugged back in, the reception goes away totally.  

I'm thinking that it could be one of the 3 pins on the 741 IC I'm using, 1, 8 and 5 are not connected to anything.  Could they be connected to ground?  Would a cap from the tip to ground of the input jack work?  The layout is very compact so I'm limited on space.

On this same subject, has anyone who has a store bought or has built the ZW-44 Wylde Overdrive run in to any radio reception issues?  Mine has it, and it's store bought (traded for).  Before confirming this, I made sure the above buffer was completely removed from the signal path (not plugged in anywhere).  Same scenario, touch the tip with it on and WBAP comes in clear as day.  Plug the cable in the guitar and it goes away.  I know it's the pedal because my Marsha Valve circuit doesn't have this problem when put in its place (same guitar, same amp, same everything).  Both battery powered.

I like the station to be totally honest, but on the radio, not in my effects.  

[bioroids]

You should use a resistor/cap combo at the input of the effect. Use 1K/100pf and it should get rid of most radio frequencies. Using only the cap without the resistor can make things worse by better tuning of the radio frequeny.

On the other hand, if its silent when is correctly plugged, why would you care?  

Luck

Miguel

[vanhansen]

On the other hand, if its silent when is correctly plugged, why would you care?  

Luck

Miguel

In a way it doesn't really bother me with the buffer since all is quiet when plugged in but it would be nice to eliminate the potential for any other unwanted frequencies to creep in.  On the other hand, if I needed to check the weather or the score of the ballgame while jamming I could always make it happen.  

What is bothering me is how my MXR Wylde OD has the same problem.

[Paul Perry (Frostwave)]

I'd like to know whether this happens at other venues. It sometimes happens that the electrical wiring & architecture of a house result in a kind of tuned circuit, leading to remarkably high signal levels at a particular frequency.
A ferrite bead at the input might help.
If you are obsessive (or desperate!) it might even be possible to make a wave trap by putting a bead on & then experimentally finding a cap (soldered to the wire going thru the bead on each side) that resonates at the radio frequency.

[keysfx]

I've had this problem before, I've got an amp that works as a good radio without an effects pedal,

Two things work for me,

     1.   Run a 1M or similar resistor to ground after the first decoupling   cap, (only in unbiased circuits)

    2.    Run a reasonably large cap (2-22uF) to ground instead of the resistor if there is biasing.

Unfortunately these both kill off signal strength, so you will lose some gain.

Best idea is to try everything and see what works.

[vanhansen]

Paul, I think you're on to something.  I plugged in the Wylde Overdrive last night at home in to my practice amp, touched the tip of the cord, no radio interference, just the typical loud buzz you'd expect to hear.  Same with the buffer.  It very well could be my brother-in-law's house that's causing it.  Since it appears to be only happening there, I'm not going to worry too much about it right now.  When I get around to it I'll try some of the methods.  It will require me being dragging all my parts and iron over there to test each method out.

[dpresley58]

Excuse my ignorance, but is there a way to do this as a separate outboard box that could be put in-line or left out as required? I play a festival every year, and several of the stages on one side of the area pull in a strong but ill-defined interference. (in other words, like a radio that's not quite tuned...)

Would be nice to have a "black-box" in the gigbag to use when I run into the problem. Just wondering if it could be eliminated without modifying the various affected pedals.

[vanhansen]

Excuse my ignorance, but is there a way to do this as a separate outboard box that could be put in-line or left out as required? I play a festival every year, and several of the stages on one side of the area pull in a strong but ill-defined interference. (in other words, like a radio that's not quite tuned...)

Would be nice to have a "black-box" in the gigbag to use when I run into the problem. Just wondering if it could be eliminated without modifying the various affected pedals.

I can't see why not.  Hmm, that would be a neat little perf project.  The Anti-RF Box, or Radio Smasher.  :lol:

[NaBo]

humm.... i dont know myself, but if its just a matter of ferrite beads and an rf blocking rap...  you might want to entertatain the thought of using this circuit http://diystompboxes.com/sboxforum/viewtopic.php?t=25504&highlight=varicap

capacitance range is a little high for rf filtering but add some series capacitance and you should find a pretty useful range!  maybe, eh?

[Harry]

you should add a switch for radio on/off. that'd be great for lofi pedals.