Rat/Turbo Rat circuits

johnnyseven · Post by **johnnyseven** » Mon Oct 07, 2013 9:37 am

Can anyone tell me the there are any differences between the Rat and Turbo Rat circuit other than that the Turbo Rat uses LED clipping and the Rat doesn't?

Also, can anyone tell me if there any differences between the Turbo Rat LM308 circuit and the IC they use now, other than the type of IC they use?

h8mtv · Post by **h8mtv** » Mon Oct 07, 2013 1:14 pm

The only diff is LEDs. As far as the IC I am sure there are some cork sniffers out there who will disagree, but I can't hear a difference when I swap them in the same circuit.

Pens · Post by **Pens** » Mon Oct 07, 2013 3:30 pm

There is indeed a difference in how the LM308 operates to the newer chip. The slew rates and frequency response are different. The LM318 is an acceptable alternative and those I cannot hear any differences between, but the opamp they put into the Turbo rat sounds different.

Concretebadger · Post by **Concretebadger** » Mon Oct 07, 2013 6:07 pm

Swapping the circuit from a OP07DP to a LM308 chip made my RAT sound better (to my ears anyway), but since Mike basically rebuilt the circuit from scratch, the difference could be the op-amp and/or upgrades to the other components. It's a noticeable difference, but not a huge night-and-day "it's a totally different pedal" difference. It sounded like a RAT before and it still sounds like one now. Just closer to my 'ideal' RAT sound I guess. It's more amp-like and less harsh. But then, the harshness might work in favour of some players and situations.

h8mtv · Post by **h8mtv** » Mon Oct 07, 2013 6:53 pm

I don't discount what Pens is saying, but I sat and jammed, and then finally ran the looper while swapping the chips and I couldn't hear any audible difference. I'm not sure what chip is in mine. I do play thru a bass head and 2x15's tho so there's that.

Pens · Post by **Pens** » Tue Oct 08, 2013 4:09 pm

Er you swapped the chips but you didn't look at the chip to see which one you put in? I'm confused by your statement.

The difference is going to be subtle, much like Concretebadger said, the LM308/318 has a higher slew rate and frequency response to the chips they started using when the 308 became scarce and expensive. Generally the difference I have heard is less harshness, but it might not be apparent dependent on what settings you use. You hear it most (to my ears) when the gain is only about halfway up, in breakup territory but not full bore, and with the filter down completely.

I don't have one without the 308/318 to A/B right now, so I can't demonstrate. There's been plenty of articles about it, I know I'm not alone in hearing it.

Brandon W · Post by **Brandon W** » Tue Oct 08, 2013 4:28 pm

i thought they sound quite different. It could be in my mind. I have an old rat..From the 80's i think..

71Smallbox · Post by **71Smallbox** » Tue Oct 08, 2013 5:51 pm

I am with Pens on this. The sound of the distortion isn't as muddy with the LM308 chip. I've done side by side comparisons with exact model Rat 2 pedals. It's very slight but audible.

h8mtv · Post by **h8mtv** » Fri Oct 11, 2013 11:15 am

Pens wrote:Er you swapped the chips but you didn't look at the chip to see which one you put in? I'm confused by your statement.

The difference is going to be subtle, much like Concretebadger said, the LM308/318 has a higher slew rate and frequency response to the chips they started using when the 308 became scarce and expensive. Generally the difference I have heard is less harshness, but it might not be apparent dependent on what settings you use. You hear it most (to my ears) when the gain is only about halfway up, in breakup territory but not full bore, and with the filter down completely.

I don't have one without the 308/318 to A/B right now, so I can't demonstrate. There's been plenty of articles about it, I know I'm not alone in hearing it.

I am not sure which chip I left in, op07 or LM308.

johnnyseven · Post by **johnnyseven** » Wed Oct 16, 2013 8:54 am

I thought it would perform my own LM308 test on my Turbo Rat and fittted an IC socket and LM308 last night. First of all, i'm not very electronically minded and my soldering skills are rudimentary at best, so I was amazed that after fitting the pedal actually worked! The sound after the mod, to my ears, is slightly different. Playing at bedroom volume, I think it sounds warmer and slightly fatter, not amazingly different though.

Bill Oakley · Post by **Bill Oakley** » Fri Oct 25, 2013 8:56 pm

The 308 tends to be a little noisier also.

johnnyseven · Post by **johnnyseven** » Thu Mar 06, 2014 2:46 pm

I emailed Proco to ask if there have been any differences in the circuit over the years from the big knob/cts pot/LM308, big knob/cts pot/OP07 and small knob/non-cts pot/OP07 versions of the Turbo Rat and this is the reply I got (I have slightly reworded so it would make sene on here):

New vs Old:

The primary change between them is in the pots- the smaller pots have the same value, but have a different taper, thus two pedals, one of each "pedigree," set to the same settings, are going to sound different. However, you should be able to get quite close setting them by ear. Another factor would be that the circuit board layout is different, which no doubt has some effect, however small, on the overall sound of the pedal.

Still, I'd say for me, the most desirable aspect of the older Rats is the smooth, even sweep of the large format CTS pots.

Neither the values of the components, nor the quality of the components used have changed over the years, however based on availability we no doubt would have switched vendors on various components from time to time. I would expect this to have a minimal effect, if any, on the sound of them. Of course in an analog pedal variations are to be expected due to component tolerances, which if anything would be tighter on the newer Rats.

As for the old LM308 turbo vs the non-LM308, I would expect that to be the only difference in the circuit to be the LM308/OP07.

I have one older TR with CTS pots and one newer model with non-cts pots and smaller knobs. The main difference I have noticed is the sweep of the distortion pot on the cts pots version has a wider range in the lower gain range, which I really like. The newer version goes for low gain to high gain very quickly, which is less appealing.

laterallateral · Post by **laterallateral** » Thu Mar 06, 2014 3:41 pm

Doog has covered the LM308 / OP07 before.
Granted, it's pretty hard to discern that level of subtlety on teh youtubes but it's there.
The newer circuit sounds a bit treblier and less compressed than the older ones, which is completely in line with my IRL impression.
The difference is too minimal for me to champion one chip over another and I use mine completely interchangeably but for naysayer, reactionary anti-corksniffer circlejerkers:

EAT IT BITCHS!

johnnyseven · Post by **johnnyseven** » Thu Mar 06, 2014 4:00 pm

I have compared the LM308 and OP07 chips in the current version of the Turbo Rat and there's definitely a small difference, but some people may not notice it or really care as both sound good. The LM308 sounds smoother to me. However the CTS pots used in the older versions make much more of a difference to the sounds available, they allow a wider range in the sweep of the distortion knob so more lower gain settings are available - people may put this down to the LM308, but the older versions with the OP07 do the same. The LM308/OP07 can be dialled to sound very similar though.

Concretebadger · Post by **Concretebadger** » Thu Mar 06, 2014 4:31 pm

Nice of them to reply and explain a few things.

johnnyseven wrote: The primary change between them is in the pots- the smaller pots have the same value, but have a different taper, thus two pedals, one of each "pedigree," set to the same settings, are going to sound different.

I have one older TR with CTS pots and one newer model with non-cts pots and smaller knobs. The main difference I have noticed is the sweep of the distortion pot on the cts pots version has a wider range in the lower gain range, which I really like. The newer version goes for low gain to high gain very quickly, which is less appealing.

This is exactly the issue I had with mine prior to the rebuild: everything happened between minimum (7 o clock) and quarter of the way around (10 o clock). It didn't affect the sound as such, but made it more awkward to use. The MBM rebuilt version is still going strong and is easier to dial in, especially with foot tweaking.