I was really impressed with the dylan159 Rat, it sounded amazing, I needed to make an original Pro Co Rat. Here is the schematic I used.
I made a PCB with Eagle PCB. I forgot to put a name and version on it, and the labels are missing from the pads, not sure why Eagle was not helping me out. That said the PCB is working.
I used an OP07 for the op-amp from StompboxParts.com. These were used in some versions of the Rat.
The original used the LM308, which is hard to get, except for that bag of chips I got from Alliexpress. Can’t believe, I got DIP-8 when I could have gotten LM308 in a can! I’m sure these are totally legit.
Anyway, I don’t think I’d hear a difference.
Speaking of the sound. I think a more interesting comparison is between the dylan159 Rat and the original.
The dylan159 Rat uses a dual op-amp and replaces the JFET follower with the extra op-amp. The circuits are otherwise almost the same. The follower in the original Rat is unity gain, other circuit drops the low pass filter on the input, C2 in the schematic above, and output stage has a gain of 4 and a little bit filtering.
My first impression is that I like the dual op-amp version better. I haven’t spent much time with these yet, so a definitive answer will have to wait. They both sound like a good hard clipping distortion. The dual op-amp version is a little “smoother” to my ears, could be the extra filtering on the output?