Rat build woes

[Widows]

Hi again everyone.

I built a Rat on verboard today as per the layout on Tagboard Effects: http://tagboardeffects.blogspot.co.uk/2012/01/proco-rat.html

It seems to be squealing a lot, and the tone of the squeal changes with the position of the distortion knob. The squeal only seems to come through when the guitar signal drops below a certain level too.

I made the following component substitutions:
Caps: 3n3 to 47n
IC: LM308 to TL071CN
Q1: 2N5458 to 2n5457

Socketed the connections for...
- pots
- 560R and 47R resistors connected to 4u7 and 2u2 caps respectively - to dick around with Ruetz mods
- 30pf cap
- diodes
- transistor - so i could recycle it easily
- offboard wires (input, gnd, +9V)
- 1K5 resistor after the Tone pot
- IC

...so I could experiment with different pot/resistor values, diode combinations, and to see what difference that 30pF cap made.
The board was connected to my breakout box, wired as per the instructions on the Beavis Board page. The power supply is a Voodoo Labs Pedal Power 2+ so I know the supply is solid.

I've built this circuit a number of times both as stock and with the subs listed above n this has never happened to me before, however I've known it happen to others; sadly the solutions they found haven't helped me. In the past I have used OP07, TL071/2 and some their various versions with different letter suffixes n not had this problem so I'm not sure what I'm missing.

I tried:
- with and without the 30pf cap between legs 1+8 of the IC - seemed to changed the tone of the squeal a little but not the volume
- Initially used a TL072CP and switched to a TL071CN (which have both been fine before), but still the same. Currently have the TL071CN in the socket

I have a voltage sag control on my breakout box, and when I turn it up n starve the circuit of some of the voltage the squealing goes away.

Could the thing be receiving too high a voltage n causing this squeal?

Could it be that I need to get myself an OP07?

Cheers in advance

[Widows]

I went n got an OP07 and all is fine now.

[rankot]

I know this is an old one thread, but however I encountered the same with my ProCo Rat build. I tried different IC's - LM308, UA741, UA776 but all of them squeeled when guitar tone is low and with gain/tone pots on pedal maxed. Rotating volume on Rat for more than noon produced squealing. I also tried to replace JFET, tried 2N5457, 2N5459 and J201 and all worked the same.

So I found a simple solution - I added 82k resistor at volume pot leg 3 and replaced volume pot with A20k. That simple voltage divider made squealing gone, although I have less volume output, it is still quite enough. Tone is not affected and everything else is quite well.