DIY Stompboxes > Building your own stompbox

Old Rat / New Rat Differences

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mremic01:
I've been messing around with ProCo Rats in the last few months, and I've definitely noticed that the newer Rats sound thin while the older ones have a little bit more balls to them. I kind of like the new Rat sound though. It's tighter. If I can figure out what it is about them that makes them sound different, I'd like to make a Rat switchable between modern Rat and old Rat specs.

I just got my hands on a current production Rat that I could open up and get a look at the PCB. It's almost exactly the same as this schematic (http://www.happybob.com/rstrand/rat/pcratrev.gif). I've built that one on perf and it sounded like one of the older ones. The Rat that I just opened up is a Rat 3A Rev B. It's got an OP07CP and 1N4148s for clipping diodes. I swapped the OP07 that came with the GGG Rodent kit with an LM308 and I didn't notice a difference, but my other Rat builds have 1N914s. This Rat also has a 1N4007 protection diode and a .0027uf cap where the schematic calls for .0033uf. I'd imagine that if it were just cheaper construction and greater tolerances, there would just be less consistency in the sound of the newer ones, but even from reading other people's experiences, it seems like they're consistently thinner. Does anyone have any insight onto why they sound different from the old ones?

zombiwoof:
Everything I've heard says that swapping an LM308 into the newer production RAT's makes them sound like the old ones.   I don't know about specific component value differences in the new ones, I have assumed they are the same values but I could be wrong, possibly they changed some values in an attempt to make up for the difference in the sound of the OP07 in the circuit.  I'm surprised you didn't hear any difference between the LM308 and the OP07, most people hear a definite difference.  Of course in a DIY build who knows what the effect will be in changing opamps, it's always possible that different values were used than what are used in the production pedals, or as you said differences in tolerances of the components.  I'm no expert about RAT's, I have an old RATII that is my go-to dirt pedal, and I have no intention on modding it in any way.   I'm sure this is not much help to you, though, sorry for that!.

Al

culturejam:

--- Quote from: mremic01 on April 16, 2011, 12:46:47 AM ---The Rat that I just opened up is a Rat 3A Rev B. It's got an OP07CP and 1N4148s for clipping diodes. I swapped the OP07 that came with the GGG Rodent kit with an LM308 and I didn't notice a difference, but my other Rat builds have 1N914s. This Rat also has a 1N4007 protection diode and a .0027uf cap where the schematic calls for .0033uf. I'd imagine that if it were just cheaper construction and greater tolerances, there would just be less consistency in the sound of the newer ones, but even from reading other people's experiences, it seems like they're consistently thinner. Does anyone have any insight onto why they sound different from the old ones?

--- End quote ---

I just rebuilt the exact same version Rat as you (which is the newer, Chinese-made Rat2), and I also noticed the .0027u cap. I thought it sounded pretty thin and a little fizzy than a classic Rat. I replaced all of the resistors with much nicer metal film (mostly Vishay) and I replaced all the film caps (and went with 3n3 instead of 2n7) and the ceramics. I put a LM301 in mine (with a socket). I left the electros in. Sounds much better now, and I'm thinking it's got to be the op amp that is the biggest share of the tone difference. Oh, and I also replaced all the pots because I pulled the shafts out trying to get the damn knobs off.

I think the OP07 is just a crappy-sounding op amp in the Rat circuit. Everything I replaced was the same value (except one minor cap value difference), except for the op amp. So I'm forced to conclude that is the issue.

Chugs:
My Chinese Rat had the 2n7 cap on the filter too. Some of the resistors and caps were soldered in at pretty jaunty angles...

You can get the OP07CP to sound similar to the LM308 by increasing the size of the compensation cap across pin 1 and 8. The OP07CP has a faster slew rate than the LM308, increasing the size of the compensation cap can help emulate the slew rate of the LM308.

mremic01:
Hmm, I just swapped the LM308N back and forth a few times with OP07DP a few times in my GGG Rat and it still sounded ballsier than the current production Rat. I think there was a difference between the opamps, but it was subtle, and not the same as what seems to be making the two pedals sound different. Even when both had OP07s, the GGG still had the old Rat sound.

Is there enough difference between a .0027 uf and .0033uf to account for that? I also understand that the 1n914s and 1n4148s are supposed to sound identical, or would it be worth it to get some 1n4148s to see if that does it?

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