Traced My Rat 2 Today.....

[soulsonic]

I'm planning on messing around with doing some mods to my old early 90's Rat 2, so I decided to give it a look over and see if it matched up with the schematics I've found here on the 'net.....

It doesn't.

None of the schematics I've found are the same as my stock Rat 2. The closest ones I could find were the one on Analogguru's page and the TonePad one.
It seems strange to me that there isn't any schematics that match my unit. It's basically the normal generic Rat that pretty much everyone has.
So anyway, I've traced the entire thing out and drew it up to share with everyone. It's the exact circuit, including the LED switcher which inspired R.G.'s Millenium circuit.

Enjoy,
http://www.aronnelson.com/gallery/d/17576-1/ProCo+Rat2.gif

Mods to come soon......

[96ecss]

Great work. Thanks Martin.

Dave

[Processaurus]

The 10K resistor after the output cap seems weird, as the volume pot acts as a pulldown resistor.

[soulsonic]

The extra 10K resistor keeps the output impedance low enough that there will never be problems with the LED switcher not working correctly regardless of how the Volume control is set.

[bent]

soulsonic....i think i,m falling in love with you 

i just build a proco rat and tested yesterday, i didn't really like the sound of it, and when i compared with some clip sound on the net, didn't really match the sound... i was wondering if someone i know was having a proco rat to compared the parts inside, but then you come up with this schematic ... now i will modified it to be has this schematic, ...

Big thank you for this schematic....

Bent

[Auke Haarsma]

Thanks for sharing the schematic!

I'm just wondering, you say on the board is says Rev L 12/86. Wouldn't that indicate this is a mid eighties board instead of an early nineties one?

[bent]

soulsonic...i have a question....

on the lm308... does the pin 1 - 6 - and the 33pf cap are all connected together

or

33pf goes from pin 8 to pin 1 without connecting to pin 6...

thank's

bent

[Mark Hammer]

Pin 6 is the output.  Pins 1 and 8 provide the "compensation loop", whereby the response of the chip is set with a capacitor.  You hardly ever want either pin 1 or 8 to come into contact with pin 6.  The cap straddles 1 and 8.

[soulsonic]

Thanks for sharing the schematic!

I'm just wondering, you say on the board is says Rev L 12/86. Wouldn't that indicate this is a mid eighties board instead of an early nineties one?

I purchased it new in the 90's. I believe it's just that they were still using the same board that they designed in '86. I think newer boards may be different.
The board also says, "Brought To You By The Captain Of  The Universe - The Rat". And also, "The Baddest Box For The Baddest Axe".
I've noticed that ProCo puts slogans such as this on several of their boards.

I'll be posting a bunch of detailed pics in my blog later today.

[John G]

Hi,
I have a Rat 3 on the repair bench at the moment, it has been modified by Keeley and has a three way switch added.
I don't know if the thing has been extensively modded by Keeley or if Proco has made quite a few changes since the Rat 2 version.
It now has a 3 pole f/switch to accommodate true bypass.
The million dollar question is does a schematic exist on the net for the Rat 3 ver B ?? or can anyone give me the Keeley alternative parts changes.
Thanks
PS the soldering on the PCB is appalling and I have been over every joint, is it made in China ? are they using the leadless solder or is this just shoddy quality control ?
John G

[R.G.]

About lead free solder.

It's pure distilled essence of junk. There are two varieties of lead free in common use, tin-silver and tin-silver-copper. The second is much preferable, and slightly more expensive, requires lower temps and slightly different flow process. The low cost manufacturers use the two part stuff except for some times.

The best SnAg solder joints look cold compared to SnPb. They just don't get mirror smooth. Makes it kinda hard to determine when there is a good versus a bad joint, right?

'S'OK though. I feel much safer knowing that no one can use SnPb anymore.

[soulsonic]

I believe that the latest Rat is being made overseas because of the large quantities they sell. I can say for a fact that the majority of Pro Co's electronics are hand assembled in the U.S., but I think the Rat may be an exception.... I can't say about the other pedals yet, I'll ask and find out. I can also say for a fact that Pro Co has indeed switched to lead-free solder - they had to so that they could be ROHS compliant and also so they can be sold legally in California. It's unfortunate that the one you're working on has bad soldering - with mine, the only possible complaint is the flux mess on the board which probably should have been cleaned after assembly..... at least you can tell it's hand-soldered I guess.

Anyway, I have made a big update to my build blog at http://www.illuminist.tk
I have put up a bunch of huge pics of the Rat which I traced for anyone interested in seeing the unit in full detail. The circuit differences in the schematic are clearly visible in the pics.
I also have build report up for a cool little buffered A/B box I built. Check it out!

[Rob Strand]

Good on you dude!  About time someone did another one of those - if only to confirm existing schematics.

[soulsonic]

Thanks! 
Next on the chopping block is the Pro Co Brat/Roadkill. It looks like it's a slightly modified Rat with FET switching and extra cheap parts. I got mine years ago at Guitar Center for something like $20 and I was surprised at how completely different it sounds from my Rat - unfortunately, it's not different in a good way, so it's going to get crazy modded.
The plan is to do some simple, minimally intrusive mods to the Rat, and then do all the extreme crazy mods to the Roadkill.

[John G]

Hi,
Now that someone mentioned solider flux, I must admit that there was no flux evidence anywhere, maybe that was the problem. When the hot iron was placed on the joint the solder rolled in to a ball and fell off !! there appeared to be very little adhesion of the solder.
The job is now back with  the customer so only time will tell as to its long term reliability.
One bizare thing I did notice was an inclusion of an input pull down resistor of...............47 K ohm it had been added as an after thought, can someone tell me it this is standard ?(I would of thought 1-2 Megs would have been in order ) or may be this is part of the Keeley mod ?
Cheers
John G

[MetalGod]

I've got a fairly recent RAT2 with the blue 3PDT footswitch and can confirm the soldering and part placement is a bit shoddy.

[soulsonic]

A little update; it turns out that I wasn't the first one to post up a trace of this era Rat circuit. Dirk Hendrik beat me to it and you can find it here:
http://www.dirk-hendrik.com/proco_rat.pdf
This is the closest one to mine with only a couple small value differences, and it includes the "extra" 10K resistor and the LED switcher as well.