Feedback Loop Squealing

[solarplexus]

Hi again,

built myself a Beavisaudio Loop, which is pretty simple, but the feedback is not working properly.  It squeals like hell until I turn it around 3 o'clock which then it doesn't do anything.  I plugged it on a momentary switch.  Here is the design:



Any idea what could cause this?  The loop is working fine. 

[Taylor]

What do you have in the loop?

Are you sure it's not working right? Squealing sounds about right with a feedback loop.

[solarplexus]

I tried it with a Boss PH-2 running on batteries.

I know it should have some sort of squealing, but the pot is working weird (more squealing when turned down than up) and I'm pretty sure the squealing pierced my ears and then my soul and then... lol

Is this normal?  If yes... it's certainly not as cool as I thought and I'll just remove it.

[Taylor]

I can't say for sure. Maybe you built it wrong, but it is about as simple as pedals get, so if you have a little experience it's unlikely you messed it up.

Feedback loops work differently with all different pedals. That's part of the fun, but can also be annoying when things aren't as interesting as you expected. Try it with some other pedals if you can before you write it off completely.

An oscillator can be made with an amplification stage with feedback. That's what you have whenever you hook up a pedal in a feedback loop, so getting a squealing oscillation is quite normal.

[petemoore]

  It looks like a feedback loop.
  Output goes to input, if there's any gain involved, the feed amplified becomes a larger feed signal at the input [hence called 'feedback'].
  Inverting and verting circuits will introduce negative or positive feedback.
  I had to scroll to see where the compli-switch did enough to type what I did so far, otherwise it kinda looked like the 500k is supposed to damp down the feedback [shunting it?]?
  And then whatever pedal has gain or what...and it's settings, also determining the amplification gain factor in the loop.

[solarplexus]

Ok so I've tried it with another pedal, the heartthrob trem that I'm currently trying to fix  and it works fine.  What can we learn from this experience?  Never use a Boss PH-2 in a feedback loop, unless you want to get deaf.

Thanks for everyone who helped, it's greatly appreciated!

Matt