Possible cause of radio interference

[alfafalfa]

I would like everybody to benefit from my experience with my pedals suddenly becoming sensitive to picking up radio stations.

First I tried to remedy it by putting a resistor in front of the first stage, has worked for me in the past.

But after picking my brain for some days it turned out to be a loose wire in the power chord to my (tube) amp !!
The wire was making intermittent contact.

It had got loose and was causing all this radio interference. So if you have trouble with radios spoiling your sound don't forget to have a look at loose wires.

I should have known because years ago I had an amp which kept on making a crackling sound which I thought had to do with some malfunction of the amp itself.   And this too turned out the be a bad connection between one of the socket pins and a wire in the powercable.
 

Has any of you had something similar happen to you ?

Alf

[petemoore]

But after picking my brain for some days it turned out to be a loose wire in the power chord to my (tube) amp !!
The wire was making intermittent contact.
 Akkk ! Good thing it called your attention to it.
 Oh yea, similar wire-wierdness-es, but never radio coming from a ''semi-connected'' power wire.
 It's getting better, I'm spending less time with thwarting problems, finding solutions..the other day a speaker wire/plug, tests perfect [continuity between +/tip and -/sleeve], plays dead...I pulled the inspected/injected/detected to pass scrutiny of all DMM applications [wouldn't click with battery on Sp Coil, figured it was the speaker coil burnt].
 Since the battery test and DMM/visual tests didn't agree, I pulled the old wire/plug connectors, the speaker coil made the '9v-click' [proving continuity]...I put a new wire/plug on the Jensen 10'' Alnico speaker, put that in the Bassman 20 amp [JJ's and Tung Sol's too], and have been recording with [my beautiful new, old] combo amp for days now !
 Plenty are the times when I was 'over there' looking at batches of wirings when the actual problem was outside the scope of my debugging efforts.

[petemoore]

  What seems to have made it 'better' [debugging method] is starting at one end of the chain and examining/inspecting/scrutinizing etc., every link, starting with an 'end link', some links are easist to test when a spare for swapping answers 'problem?' questions.
  Such as:
  The other speaker works fine.
  The other amp fixes 'it'.
  The other cable makes the hum go away.
  These types of items can sometimes be difficult to sufficiently scrutinize, otherwise.

[punkin]

in the case of rf being detected its important to understand how this can happen. rf modulated signals to be heard need to be demodulated and amplified. amplification isnt a problem with what we're doing. the demodulation typically requires a PN junction of some type. the dead ringers for this is diodes and transistor junctions. a couple ideas in preventing the PN junction rectification would be to prevent the rf signal from riding across the junction by adding an rf bypass capacitor across the suspected component. this gives the rf signal an alternate path rather than through the component(s). another idea is to get the rf out of the circuit by proving a low impedance path to ground. again a small bypass capacitor to ground may be helpful. good luck.

[alfafalfa]

Yes , Pete you're quite right, trying to solve these kind of problems it's always better to follow a "logical route".

But  I didn't include the powerchord into that route and that was my big mistake so it seems.

Punkin, would it be a good idea to use your own modded powersockets to prevent rf trouble ?

I mean with two caps ( high voltage) going from the + and - going to ground and maybe a varistor in between them ?

Or would that be unsafe ? Isn't this what certain commercial powerstrips have ?


Alf

[punkin]

I donno that I would be modding the power strip...I suppose you could but not knowing where the RF is entering the circuit, you may be simply wasting parts and time. Personally, I would simple get a small capacitor and start probing the circuit with it...jumper across the collector/base, emitter/base junctions and diodes and see if you can bypass the rectifying device. Similarly, using a small cap again as a probe decoupling RF signal to ground. An O-scope would be very helpful in finding where the RF become audio but not everyone has one handy.