Old Rat / New Rat Differences

[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]

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?

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?

[culturejam]

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

Yeah, here's the before and after pics of the soldering:

BEFORE




AFTER

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.

Interest point. I never even thought of this.  I've always thought it would be cool to have a trimmer cap (in series with a small base value cap) between pins 1 and 8 on Rat and Rat-like circuits. Surely someone must have done this at some point.

[Jazznoise]

*ahem*

http://www.youtube.com/watch?v=bpTv2jAree8

I'd put it down to swapping the caps!

[culturejam]

*ahem*

http://www.youtube.com/watch?v=bpTv2jAree8

I'd put it down to swapping the caps!

Seen that one about a dozen times. I agree in general, but there is a quite a bit of difference in a Rat if you use a LM741 or TL071 instead of something that is externally phase compensated, like a LM301 or CA3130. Just try it. If *I* can hear, it's there. I've not got golden ears and I don't sniff corks.

The Rat is the only circuit I've been able to hear a noticeable and significant (to me) difference with an op amp swap.

[Chugs]

The Rat is the only circuit I've been able to hear a noticeable and significant (to me) difference with an op amp swap.

Agreed. Particularly when swapping between an internally and externally phase compensated opamp.

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?

You will have slightly less treble cut with the 0.0027 than with a 0.0033. I personally wouldn't notice a difference if you swapped 1N194's for 1N4148's or vice versa. Swapping for 1N4001's might give a mild difference in tone.

[soupbone]

The Rat is the only circuit I've been able to hear a noticeable and significant (to me) difference with an op amp swap.

Agreed. Particularly when swapping between an internally and externally phase compensated opamp.

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?

You will have slightly less treble cut with the 0.0027 than with a 0.0033. I personally wouldn't notice a difference if you swapped 1N194's for 1N4148's or vice versa. Swapping for 1N4001's might give a mild difference in tone.

Aren't 1N914's and 1N4148's the same thing?Just wondering.

[culturejam]

Aren't 1N914's and 1N4148's the same thing?Just wondering.

For our purposes, yes they are the same thing.

[John Lyons]

Keep in mind that the old rats used a few tantalum caps as opposed to film and electrolytic.
Not saying one sound better than the other but they should sound a bit different.

[soupbone]

Aren't 1N914's and 1N4148's the same thing?Just wondering.

For our purposes, yes they are the same thing.

Cool.Thanks!

[geezer15]

I tried a 'mightier mouse' mod on a turbo RAT. I put 1n914's on one side of the switch and put in an LM308 chip. It sounds nothing like my Rat2 or vintage Rat, yet I understand the circuit is the same except fot LED diode clipping. The tone is 'less bright' and 'thinner' So there is definately something else that makes the tone.

http://www.beavisaudio.com/Projects/FKR/images/MightierMouse.gif

[ryanuk]

I was never a fan of the Rat pedals until 2 months ago. Ive owned a prodcution model for years but have never been able to get the juicy tones from it that others rave about.

I decided to breadboard and played with the values using some internet sources.

I ended up with an incredibly fat and rish soudning pedal. Here's a list of the subs I made. (Part numbers from the schem on Analogguru's website).

C1 – 220n
C2 - 47uf
C8 – 10uf
C7 – 47pf
R10 – 22k
C11 – 10uf

I also played around with the diode clippers, adding in an LED, using 2xLEDs/Ger, but I kept coming back to 2xSil. No switches. Simple.

The substitutions that made the most sonic impact was C1 and R10. C1 to 220n made the sound a lot fuller; changing R10 to 22k gives a fatter sound and more usable filter. I tried 47K at first but that was just too dark. Not sure electronically what I doing by changing R10 – it does alter the filter range and overall bassy-ness of the circuit.

Whats interesting is that I tried the circuit with both an OP07 and LM308. I found very little between the 2 but preferred the OP07. I sounded ever so slightly more compressed.

In summary, the LM308 and OP07 both work fine, other circuit components have much more impact.

[GGBB]

Not sure electronically what I doing by changing R10 – it does alter the filter range and overall bassy-ness of the circuit.

All this would do is change the filter range as you said - our more technically it would change the range of the filter's cutoff frequencies.  The filter pot plus R10 in combination with C9 form the variable low pass RC filter circuit that is the filter control.  In your case, the increase in value would make the filter cut more high frequencies, so the filter opened right up on 10 would be less bright than before, and at zero it would be duller than before.  This would be a good mod for those who find they always leave the filter in the lower ranges.  Swapping the pot for a 50k would give you more precision when adjusting the filter, albeit with a reduced range, but you'd need to adjust R10 to suit and possibly (perhaps preferably) C9.  For example, the stock configuration gives an approximate filter range of 475Hz-32.2kHz.  A 100k pot plus a 22k resistor gives a range of 395Hz-2.2kHz - quite a bit darker.  A 50k pot plus a 22k resistor gives a range of 670Hz-2.2kHz - a lot of control over a limited range.  A 50k pot, stock 1.5k resistor, and a 4n7 cap gives a range of about 658Hz-22.6kHz - a good choice if you never use the lower settings and want more precision.  A 50k pot, stock 1.5k resistor, and a 6n8 cap gives a range of about 455Hz-15.6kHz - a good option if you like it a little darker but still want a fair bit of range as well as a little more precision.  Since the filter setting is often stated as the key to dialing in the right RAT tone, these can be great mods to experiment with and find your personal ratopia.

[mremic01]

Last I decided to mess around with a few different Rats and I grabbed the nearest pick available, which was a regular size .73mm tortex. I normally use  .73mm jazz picks. With the standard size pick, the difference between each Rat was much less pronounced. They sounded nearly identical. So I tried playing with jazz picks and there was a clear difference between pedals again. It seems like one might be more responsive to pick attack then the other, which is something I'll have to mess around with some more.

[kirs]

I have a 2005 Rat 2 modded by Keeley and always thought it sounded great.  I just built the gaussmarkov Rat and it's almost night and day.  The Keeley is very thin sounding next to the classic Rat circuit.  Just a fuller sound overall.  It's unmistakable.  The Keeley has a metal can LM308 chip.  I still like the sound of it but in an A/B test the classic circuit has much more balls.

[ode2no1]

i have a turbo rat (modded with ruetz and replaced one clipping led with a 4148) and decided to go ahead and give the old lm308 chip a go. i honestly prefer the od07....by far, in fact. true, i'm using the pedal in ruetz mode exclusively, so this may not matter to those who are using a stock rat tone, but the od07 just sounds tighter...yet in no way lacking low end. i also built up a rat about two years ago with the diodes on switches (led/4148) and somehow i couldn't get it to sound like my modded turbo rat. the closest i came on duplicating the sound of my production model was actually using it on turbo mode, with both diodes being led's, and using an lm308. weird. so i don't know if the lm308 is magic, or if it really just depends on your build, but i've found both to be great sounding...just funny that i do prefer the od07 in my production unit.

[rosscocean]

I did the ruetz mod, opamp switch to lm307 and a few cap changes on our bass players modern rat.

I bought a new vr rat cheap cos it had had a couple of dry joints on the switch. I've not been happy with my stock vr whenever I've plugged it in.

I'll try and sit down with them both soon. I remember liking the ruetz mod a lot more than the stock version. It made the sound a lot thicker, less fuzzy and reduced the gain. To my ears it sounded a bit more Marshall-like.

Don't know if that helps?!

Ross