RAT Oscillation

[north99]

I had built 2 pcb's for the rat distortion from tonepad. Both of them, with filter and gain turned up (not at max) are sounding bad. Does anybody can give me an advice? Im tempted to use the tl071 chip. I also want to do the rodent version from ggg. I had noticed that the ggg version has different power supply stage.

Thanks in advice!

Ștefan Friptu

[Kipper4]

Doesn't the rat use an lm308 chip?
I don't think that the tl071 would be a drop in replacement.
Can you post some voltages?
Atm I'm thinking a build error or solder bridge.
I've built several and once had an issue because I put a cap in the wrong place

[GGBB]

RATs are very high gain. With any high gain circuit you need to watch your wiring, shielding etc. or oscillation can occur. Keep input and output wiring away from each other and from PS, and ideally use shielded wire.

EDIT: As Rich alluded, sloppy soldering can also cause oscillations.

[north99]

Thanks for advices. Another thing: It is normal that when you touch potentiometers, they create some buzz?(or hiss, whatever). But how about the difference in Power supply stage in tonepad vs ggg
Right now i can't post any voltages or pics, but assuming that i have distortion, i think they are good.

@Kipper4: did you used tonepad pcb layout?

[Kipper4]

Yes sir I did use tone pad layout iirc the cap was in one corner of pcb

[Fp-www.Tonepad.com]

Make sure the wires going to the pots and jacks are short.

[GGBB]

Tonepad PS section is faithful to the original RAT. GGG is arguably technically a little better, but there isn't a huge difference. Run your pedal from a 9V battery - if you still have the same issues, the PS isn't the problem.

What part of the potentiometers are you touching? Generally, yes that can create hum.

[dschwartz]

How far is the input jack from the pots?

[north99]

Not too far. I Forgot to mention that i have a 8.33 V battery. I also have one that has 8.75v but i put it tightly in a ts 808 ). Tomorrow Ill do some fixes i think, maybe remake the pcb, i Dont know. Thanks very much

Oh, i Forgot to mention that i have problems with the low strings, not with the high ones. I changed some caps in the circuit, maybe it's about tolerance the problem? Im going to tell you Tomorrow the modifications.

[ashcat_lt]

Doesn't the rat use an lm308 chip?
I don't think that the tl071 would be a drop in replacement.

The pins are all the same, except the compensation pins are unnecessary.  I don't think the external cap will hurt anything.  The opamps have somewhat different characteristics, so it might sound subtly different but it will definitely work.

[bool]

I'm not sure I understand what exactly is your question, but I have some TL071's from ST Micro that are prone to self-oscillation.

In fact, they tend to self-oscillate (at human-audible frequencies) when powered by low voltage, f.e. when a circuit on power-off goes trough capacitance-discharge sequence. (It manifests itself as an annoying "chirp"). As soon as I put a different vendors' chip in - the "chirp" goes away.

So if you have a "chirpy" chip, and you power it with a lower than normal voltage, there might be a chance for some oscillation.

ymmv

[north99]

This may be a cause @bool. I'm currently re-etching a pcb for the rat, im doing it again. The oscillation appears at the low strings when i turn the guin up.

[north99]

I had redone it, but i see that i have a problem with the third pin of the IC. I have 2,36V on it and i know that it should be around 4.1. Rolling the drive pot doesnt makes any difference. Some help please?

Forgot to mention that Vb (biasing voltage) its good, but after touching the 102 cap and the 1k res, it turns to 2,3-2,4

[karbomusic]

I had redone it, but i see that i have a problem with the third pin of the IC. I have 2,36V on it and i know that it should be around 4.1.

I'd measure output pin 6 since pin 3 may not play accurately with your meter. If the output pin shows good, then pin 3 should be good.