Pro Co RAT

[pontiacpete]

I have a RAT here, the volume pot doesn't seem to be working. It sounds good as far as the effect goes but nothing from the volume pot.
I checked all the connections and components in the output section, all look good. Even tried replacing the 2N5458 and still no change.
Is this something that's I'm not understanding about the operation of this
pedal?

Thanks for any suggestions!
pete

[Leo_Gnardo]

How about the volume pot itself. In any normally operated volume control, if there's a break in the side that goes to ground, whether inside or outside of the pot, you'll get the symptom you mention.

[pontiacpete]

Thanks Leo! that was the problem. Now I just need to get the right pot, all I have the usual short shaft type.

[Mick Bailey]

Is it a Rat with CTS-type pots? The track is pretty robust but sometimes the terminal crimp can come a little loose or go high resistance. A squirt of contact cleaner and squeezing up the terminal a little can give a long-term fix.

[pontiacpete]

It is a CTS type pot.
I'm not sure about 'squeezing up the terminal'. Since I ordered some, I'll experiment with this one.
Thanks for the tip!

[TomCarlos]

Ok.. old thread but same device. I came across a non-working RAT. The clean was working fine. But the distortion volume was VERY low. I pulled the pots and checked them - all ok. Two read 85K, the other 97K. I cleaned them up with DeoxIT and reinstalled. It was the DPDT switch that was bad. One side was open, the other side was shorted from the center to outer pins, no matter the clicking.

I popped in a new Carling Switch, and had to do some repair work on the traces (oh those small and delicate traces) ..... problem solved - I think.

I take it the Volume control only adjusts the distortion level? It has no effect on the clean. Is that how it works?

Tom

[TomCarlos]

Ok... a problem remains.... drats.

With no battery applied, the clean signal feeds through fine.

With the battery installed, the LED will light up IF I insert the output lead. So the switch is working. However, I have no distortion. It was working. Maybe something happened when reinserting the PC board.

[Helmholtz]

Ok... a problem remains.... drats.

With no battery applied, the clean signal feeds through fine.

With the battery installed, the LED will light up IF I insert the output lead. So the switch is working. However, I have no distortion. It was working. Maybe something happened when reinserting the PC board.

As the battery should be switched via the INPUT jack, you might have swapped input and output?

[TomCarlos]

Thank you Helmholt. No, something else is going on. I found a generic schematic for the RAT. If it comes close, I will post it this weekend and check the Op Amp. It is the old TO5-8 can. I might remove that and put in a dip socket. I have some 741 8 pin Op Amps on hand. My guess is that it might be a bad solder joint or connection issue.

[Helmholtz]

Many Rat fans swear by the original LM308 opamp.

https://www.electrosmash.com/proco-rat

[Helmholtz]

I never really liked my Rat. I found out that the reason is the 1nF cap wired between input and ground, which kills PU resonance and treble content.
Removing that cap is no option because then the Rat turns into a low kHz oscillator at higher settings.

But some years ago I found out that a buffer before the Rat makes it sound great, as this eliminates the negative effect of the cap.

[TomCarlos]

I could not tell if this was an LM308 or a 741.

[Helmholtz]

Anyway, if the output pin of the opamp sits at roughly 4.5V (50% of supply voltage), I see no reason to suspect it.