What can cause uncontrollable whistling feedback?

[Dr. Lo]

I have a Fender Pro Junior. When I have the amp's volume more than 2/3 of the way up, I get uncntrollable whistling feedback, especially when my OD pedal is engaged. This happens irrespective of the OD pedal (I have two) and irrespective of the guitar (Les Paul or Tele). I've tried changing the preamp and power tubes. This made no difference. This problem didn't exist a couple of months ago.

What can be causing this terrible feedback?

 

[bungalowbill]

Re: What can cause uncontrollable whistling feedback?

A microphonic pre amp tube would be my guess....or maybe try a 12 AT7 in V1.

 

[Dr. Lo]

Re: What can cause uncontrollable whistling feedback?

Already tried that, thanks. Didn't work.

 

[bungalowbill]

Re: What can cause uncontrollable whistling feedback?

Already tried that, thanks. Didn't work.

Did you test the preamp tubes or just change them? I've bought brand new 12AX7's that were microphonic.

 

[Bezmotivnik]

Re: What can cause uncontrollable whistling feedback?

Absolutely nothing else has been changed?

This is interesting. All of the several things that come immediately to mind don't apply here -- reverb pan feedback, microphonic tube, etc. :scratchch

 

[WhoFan]

Re: What can cause uncontrollable whistling feedback?

hmmm.... strange... i have no idea why really..... i'll be curious to hear the cure...

and it's not microphonic tubes or pickups i have no idea where it would come from

 

[fingerace]

Re: What can cause uncontrollable whistling feedback?

http://www.guitarnuts.com/technical/index.php

check this out it might be helpfull...

Is this with all of your guitars?

 

[kmcguitars]

Re: What can cause uncontrollable whistling feedback?

The sound your describing sounds like oscillation. In a PCB amp such as yours,I would guess it's a bad solder joint. If it's less than 5 years old It's still covered by fender. Bring it to a Fender authorized tech.

 

[ES350]

Re: What can cause uncontrollable whistling feedback?

Beside microphonic tubes, there are some lead dress issues in these amps, esp. with the ribbon cable, that can lead to oscillation and excess noise.

 

[brit84]

Re: What can cause uncontrollable whistling feedback?

try a noise suppressor, worked on my amps. However if the noise continues then it is something else.

 

[Bludave]

Re: What can cause uncontrollable whistling feedback?

Try the obvious first. Change cables. It could be a bad cable It Try a different guitar. If the problem seens to go away after switching guitars it could be a microphonic pickup. The pickup will need to be wax potted. Try the cables, guitar and amp Tech first. If the pickups need to be potted you will need to bring the guitar to a tech.

 

[MattPete]

Re: What can cause uncontrollable whistling feedback?

ultrasonic oscilations?

 

[butnut]

Re: What can cause uncontrollable whistling feedback?

Try the obvious first. Change cables. It could be a bad cable It Try a different guitar. If the problem seens to go away after switching guitars it could be a microphonic pickup. The pickup will need to be wax potted. Try the cables, guitar and amp Tech first. If the pickups need to be potted you will need to bring the guitar to a tech.

BINGO!!! I'll bet it's the cables too....same thing happened to me. One of my George L jumpers from one of the pedals went bad, fixed it easily, and the shrieking stopped...never thought a cable would cause that, but it did.