Screamer diodes question

[jophus]

Hi All,

Still trying to problem solve the tubescreamer I've put together, which squeals like a kettle....

I've put sockets in where the three diodes go, for a range of options. If I put 3 jupmers across those plugs, the problem noise goes away completely! But it doesn't matter what kind of diode I put in the sockets, the screech still returns...

I find this baffling! Any thoughts?


Here is a pic of my problem solving schematic- tick = clear signal, cross = screachin!
http://picasaweb.google.com/JDA.Han%^&*/UntitledAlbum/photo#5162807816670625714

[culturejam]

I built a screamer that squealed as well. I was testing it with a short cable (about 3'). When I switched to a long cable (20'), the squeal went away. I have no idea why, but that seemed to solve the problem.

I tried switching diodes and opamps, but the squeal persisted until I used a longer cable. To this day, if I plug the guitar into this pedal with a short cable, it squeals. 

[miqbal]

Hi All,

Still trying to problem solve the tubescreamer I've put together, which squeals like a kettle....

I've put sockets in where the three diodes go, for a range of options. If I put 3 jupmers across those plugs, the problem noise goes away completely! But it doesn't matter what kind of diode I put in the sockets, the screech still returns...

I find this baffling! Any thoughts?

Here is a pic of my problem solving schematic- tick = clear signal, cross = screachin!

Maybe your problem is layout related. What layout do you use? I've tried GGG with nice results. Any pic: PCB top/bottom side?

[JDoyle]

You don't have a check mark by Ca, the comp cap on the tone stage. Put that in there and see if that helps, try 100 pF, or the 51 pF of the first stage...

This could also be the reason the other poster's squeal went away with a longer cord: more parasitic capacitance cutting the highs that end up squealing...

Let us know...

Jay Doyle