lemmee tell ya a little story 'bout a man named Chip!
people talk a lot of op-amp smack (because they don't understand what these circuits are ACTUALLY doing), but the fact of the matter is that the difference is subtle... the main thing with the 308 is that its a really shitty old device from teh birth of integrated circuits that has AWFUL audio performance, so the rat is really taking advantage of its poor bandwidth and piss poor slew rate. A rat with a better chip will sound a skidge different at lower gain settings, but still good. I beleive the turbo rat uses a more modern chip that's actually designed for audio but the turbo rat and dirty rat clip a lot more and way earlier so you aren't 'hearing' the chip... it just doesn't matter in these revised circuits. Personally what I lvoe about the rat is that it makes a surprisingly nice OD or dirty boost with gain turned down and in that situation you're not eharing the diodes, just the chip, unelss you dig in real hard. I would say that the original rat is the only IC-opamp based pedal where the choice of chip impacts the tone. People talk a lot but this is the one.... thing is, you ay not like the chip's tone, its a sound, but a more modern, hifi opamp is also a good sound in this circuit, tis just a less less 'ratty' at low gain. FOr abss I would venture that the LM308 is probably not a great choice, its going to smear your low end. Inf act, if Iw ere doing a bass rat I would use a very hifi burr brown opamp and I would take out a good deal of the high apss filtering and maybe add a midrange notch into the circuit with a 2 pole RC filter.
Anyway, what you're hearing at any gain level above like 2 ona rat is the diodes and those are the same in all the rats as far as I know. In fact, even if they're not? one silicon diode is just like another, man. THey clip the same way at the same forward voltage. CHange materials to germanium or to LEDs? that's another story... but any back to abck pair of solicon diodes tog round will do rpetty much the sameshit, man. In my opinion you are eharing what people are telling you to hear... its a rgeat way to sell a rat with a 308, onne of the cheapest chips out there, for inflated prices. Based on parts cost an LM308 rat should cost LESS than one with a more modern opamp designed purely for audio use.
that's my .02... that said, my actual rat is a late 80s or early 90s one with a 308.... but that's only because I think I bought it in the 90s and that's what was available used for cheap when I wanted one. I have never once worried about what opamp was in there or in my tubescreamer. If Iw ere designing a mic pre I would care, for a pedal that's lopping off the signal with diodes? Mountains.... molehills...
