Proco - Rat 2 (early 90s)

soulsonic · Post by **soulsonic** » 05 Nov 2007, 02:24

I traced out my Rat 2 today. I'm looking to do some mods to it and I wanted to have a "stock" schematic for reference. None of the schematics I could find on the 'net matched my unit (AG's is close and the one on TonePad is close), so I decided to trace the whole thing out and share it. It was a good exercise - probably my first full "official" trace of a stompbox... an easy one too.

http://www.aronnelson.com/gallery/d/175 ... o+Rat2.gif

It's the entire circuit, including the LED switcher that inspired R.G.'s Millennium circuit. I think it would make a handy reference for people wanting to do mods. My unit is a stock early 90's Rat 2 - the same one that I'm sure millions of folks have around the world, so I'm surprised to see that there hasn't been a 100% trace of it yet.
I'd kinda like to compare it to others from the same era to see if there's differences.

Mods to come soon....

edit: typo

bajaman · Post by **bajaman** » 05 Nov 2007, 05:13

Thanks Soulsonic

bajaman

indyguitarist · Post by **indyguitarist** » 05 Nov 2007, 07:02

soulsonic wrote:I traced out my Rat 2 today. I'm looking to do some mods to it and I wanted to have a "stock" schematic for reference. None of the schematics I could find on the 'net matched my unit (AG's is close and the one on TonePad is close), so I decided to trace the whole thing out and share it. It was a good exercise - probably my first full "official" trace of a stompbox... an easy one too.

http://www.aronnelson.com/gallery/d/175 ... o+Rat2.gif

It's the entire circuit, including the LED switcher that inspired R.G.'s Millennium circuit. I think it would make a handy reference for people wanting to do mods. My unit is a stock early 90's Rat 2 - the same one that I'm sure millions of folks have around the world, so I'm surprised to see that there hasn't been a 100% trace of it yet.
I'd kinda like to compare it to others from the same era to see if there's differences.

Mods to come soon....

edit: typo

There's a 10k across the lugs of the volume pot? odd!

BTW, one of my favorite mods, remove the stock tone pot, insert a big muff variant or a 3 band tonestack, remove the jfet buffer and install a jfet gain stage. I like 5v zener diodes in place of the 4148's too, sounds nice to me.

Also, for a more compressed and 'overdrivey' type tone, install assym. diodes across the gain pot (lugs 1 and 3). I like to put this on a switch myself.

give it a try and let me know what you think!

Brian

soulsonic · Post by **soulsonic** » 05 Nov 2007, 08:11

The "extra" 10K resistor is there to keep the output impedance low enough that the LED switcher will work correctly regardless of the volume pot setting.

Thanks for the mod suggestions! I'll take them into consideration as I begin experimenting - one thing though, I'm certainly not looking for a more compressed tone, it's too compressed sounding to my ears already. The main thing I'm wanting to go for is less compression and more sizzle - less mushiness and more attacky-ness. When I first got this thing back when I was 16 or whatever, I seriously thought it was broken! The low-end mush that it has just seemed completely inappropriate to me for a pedal that people were saying was good for a "metal" tone. My opinion about that hasn't changed, and what I want to do is get it to have more of what I'd consider a "metal" sort of tone. Best way I can describe it is that I'd like to keep about the same amount of distortion and possibly add a little more, and keep the same basic vibe, but get rid of the sloppiness at high gain settings. I've always liked how tight it sounds at low gain settings and I want to retain a similar character at high gain levels.

I hate to say it, but I might have to fool with the compensation cap.....

indyguitarist · Post by **indyguitarist** » 05 Nov 2007, 15:32

soulsonic wrote:The "extra" 10K resistor is there to keep the output impedance low enough that the LED switcher will work correctly regardless of the volume pot setting.

Thanks for the mod suggestions! I'll take them into consideration as I begin experimenting - one thing though, I'm certainly not looking for a more compressed tone, it's too compressed sounding to my ears already. The main thing I'm wanting to go for is less compression and more sizzle - less mushiness and more attacky-ness. When I first got this thing back when I was 16 or whatever, I seriously thought it was broken! The low-end mush that it has just seemed completely inappropriate to me for a pedal that people were saying was good for a "metal" tone. My opinion about that hasn't changed, and what I want to do is get it to have more of what I'd consider a "metal" sort of tone. Best way I can describe it is that I'd like to keep about the same amount of distortion and possibly add a little more, and keep the same basic vibe, but get rid of the sloppiness at high gain settings. I've always liked how tight it sounds at low gain settings and I want to retain a similar character at high gain levels.

I hate to say it, but I might have to fool with the compensation cap.....

You might change the negative feedback values - maybe 150hz or so? I would probably start there too...

bw

JHS · Post by **JHS** » 05 Nov 2007, 16:45

The schem is typical for a late '80th RAT, IMHO nothing special.

It's a RAT 2, and instead of the 10k in parallel with the Vol. pot they could have used a 10k pot. , but with the 10k they had been able to use 100k pots throughout.

The main reason for the use of the 10k was that Proco wanted to sound their RATs softer, smoother and less harsh compared to the RAT 1.

The next change in the RAT 2 was a 220k or 100k BIAS-R instead of the 1M/2,2M for an even softer sound with way more mids. It seems that they wanted to duplicate the Anthrax-style or metal-style distortion tone.

The 1M BIAS-R for the FET wired from gate to ground is a bit uncommen with a 2N5458, this wiring is often used in RATs with BF245 in the buffer circuit.

JHS

indyguitarist · Post by **indyguitarist** » 05 Nov 2007, 17:14

JHS wrote:The schem is typical for a late '80th RAT, IMHO nothing special.

It's a RAT 2, and instead of the 10k in parallel with the Vol. pot they could have used a 10k pot. , but with the 10k they had been able to use 100k pots throughout.

The main reason for the use of the 10k was that Proco wanted to sound their RATs softer, smoother and less harsh compared to the RAT 1.

The next change in the RAT 2 was a 220k or 100k BIAS-R instead of the 1M/2,2M for an even softer sound with way more mids. It seems that they wanted to duplicate the Anthrax-style or metal-style distortion tone.

The 1M BIAS-R for the FET wired from gate to ground is a bit uncommen with a 2N5458, this wiring is often used in RATs with BF245 in the buffer circuit.

JHS

That makes sense RE the 10k in parallel with the volume. I was wondering why they just didn't use a 10k pot.
bw

DougH · Post by **DougH** » 05 Nov 2007, 17:19

soulsonic wrote:The "extra" 10K resistor is there to keep the output impedance low enough that the LED switcher will work correctly regardless of the volume pot setting.

Thanks for the mod suggestions! I'll take them into consideration as I begin experimenting - one thing though, I'm certainly not looking for a more compressed tone, it's too compressed sounding to my ears already. The main thing I'm wanting to go for is less compression and more sizzle - less mushiness and more attacky-ness. When I first got this thing back when I was 16 or whatever, I seriously thought it was broken! The low-end mush that it has just seemed completely inappropriate to me for a pedal that people were saying was good for a "metal" tone. My opinion about that hasn't changed, and what I want to do is get it to have more of what I'd consider a "metal" sort of tone. Best way I can describe it is that I'd like to keep about the same amount of distortion and possibly add a little more, and keep the same basic vibe, but get rid of the sloppiness at high gain settings. I've always liked how tight it sounds at low gain settings and I want to retain a similar character at high gain levels.

I hate to say it, but I might have to fool with the compensation cap.....

I've breadboarded the Rat and ratlike circuits a few times and have observed similar things. Once the gain knob crosses a certain threshold, the lows get pretty spongy sounding, more like a "fuzz" than a "distortion". I suspect this threshold may be where the slew-limiting starts taking effect, as there is a noticeable high freq rolloff, but it's just a hunch. I've never verified that. I do like that sound of the highs when it is in high gain, and I like the way it "squeezes" the notes. But it would be nicer if there was a way of tightening the bass.

Part of the issue, I suspect, is that it has to be very high gain to push the op amp into "doing its thing". Lowering the comp cap helps clear up the mud, but I found it difficult to keep it from oscillating when I did that. Another part of the problem is that the timbre seems to change pretty dramatically, below and above the threshold. This forced me to re-tune the EQ for different gain settings.

I finally gave up and decided it is what it is. It was a happy accident that defined a genre of guitar sound back in the 80's. It's good at what it is does, but like anything else, it's imperfect and limited. And, there are other ways of squeezing notes than relying on the high gains required to force slew-limiting.

kagaxdx · Post by **kagaxdx** » 05 Nov 2007, 17:20

That makes sense RE the 10k in parallel with the volume. I was wondering why they just didn't use a 10k pot

This it only lower the impedance right? But it STILL can have almost 100Kohms in SERIES with the output when vol pot near minimun...??

snail · Post by **snail** » 05 Nov 2007, 18:55

Does the MO'D have the same "flaws" noted here about the bass???

Thanks

snail

soulsonic · Post by **soulsonic** » 06 Nov 2007, 01:10

I've updated my blog at http://www.illuminist.tk with a bunch of gigantic gutshot pics of the unit I traced.

Also, I put up a nice little build report on a cool buffered A/B box I built last week for a friend.

Check it out, yo!

Dirk_Hendrik · Post by **Dirk_Hendrik** » 07 Nov 2007, 10:06

soulsonic wrote:I traced out my Rat 2 today. I'm looking to do some mods to it and I wanted to have a "stock" schematic for reference. None of the schematics I could find on the 'net matched my unit (AG's is close and the one on TonePad is close), so I decided to trace the whole thing out and share it. It was a good exercise - probably my first full "official" trace of a stompbox... an easy one too.

http://www.aronnelson.com/gallery/d/175 ... o+Rat2.gif

I wonder,
This one has been on my site for some 2 years:
http://www.dirk-hendrik.com/proco_rat.pdf and has been posted on diystomps as well. The 3 differences I do see is the biasresistor for the opamp 2M2 vs 1Meg, as well as the gain pot. Of that one I do know that I took the measured value since it was too far off to be a convincing 100k (as seems to be the case in RG's version, see remark below).
Finally there's the LED FET bias resistor that differs.

However This makes one wonder wether there's component changes in non-critical places within one version of the RAT already..... And jus to make sure, did you record the PCB texts on your RAT as well (like" the baddest bos for the baddest axe")

Other than that,

Can this schemversion of the Rat:
https://www.diystompboxes.com/pedals/PCRAT1.GIF

become forbidden? It's wrong wrong wrong wrong. (And let's nut fuzz about that input FET but let's do fuzz about that opamp with positive feedback!!

indyguitarist · Post by **indyguitarist** » 07 Nov 2007, 13:08

Dirk_Hendrik wrote:
soulsonic wrote:I traced out my Rat 2 today. I'm looking to do some mods to it and I wanted to have a "stock" schematic for reference. None of the schematics I could find on the 'net matched my unit (AG's is close and the one on TonePad is close), so I decided to trace the whole thing out and share it. It was a good exercise - probably my first full "official" trace of a stompbox... an easy one too.

http://www.aronnelson.com/gallery/d/175 ... o+Rat2.gif

I wonder,
This one has been on my site for some 2 years:
http://www.dirk-hendrik.com/proco_rat.pdf and has been posted on diystomps as well. The 3 differences I do see is the biasresistor for the opamp 2M2 vs 1Meg, as well as the gain pot. Of that one I do know that I took the measured value since it was too far off to be a convincing 100k (as seems to be the case in RG's version, see remark below).
Finally there's the LED FET bias resistor that differs.

However This makes one wonder wether there's component changes in non-critical places within one version of the RAT already..... And jus to make sure, did you record the PCB texts on your RAT as well (like" the baddest bos for the baddest axe")

Other than that,

Can this schemversion of the Rat:
https://www.diystompboxes.com/pedals/PCRAT1.GIF

become forbidden? It's wrong wrong wrong wrong. (And let's nut fuzz about that input FET but let's do fuzz about that opamp with positive feedback!!

yikes! I never paid that close of attention to this old rat schem.
On a side note dirk, I'm sending you a pm..
bw

Dirk_Hendrik · Post by **Dirk_Hendrik** » 07 Nov 2007, 13:37

Got it!!

soulsonic · Post by **soulsonic** » 07 Nov 2007, 20:14

Sorry Dirk, I didn't see your scheme before - that is certainly the closest one to what I have. I tried searching around in the usual places, but no links to yours came up anywhere. In the future, I make sure your site is on my list of places to look for schematics!

If you check out my blog, you will find a bunch of pics of the board which includes good views of the various text found on it.

Blues Lyne · Post by **Blues Lyne** » 07 Nov 2007, 23:56

soulsonic wrote:Thanks for the mod suggestions! I'll take them into consideration as I begin experimenting - one thing though, I'm certainly not looking for a more compressed tone, it's too compressed sounding to my ears already. The main thing I'm wanting to go for is less compression and more sizzle - less mushiness and more attacky-ness.

You might want to try a switch to take the clipping diodes out of the circuit. It actually sounds pretty nice and less compressed without them.

soulsonic · Post by **soulsonic** » 09 Nov 2007, 10:01

I finished the mods this afternoon. I'm pretty happy with how it turned out. I've started a new thread in the Workbench area, and you can find all the details in my blog.

Next, I tackle the Pro Co Brat, with some more extensive mods....

soulsonic · Post by **soulsonic** » 12 Nov 2007, 21:03

All the details can be found here:
https://www.freestompboxes.org/viewtopic.php?t=937

And always be sure and check my build blog - I try to always keep it updated with my most recent projects.

ieatyouforbreakfast · Post by **ieatyouforbreakfast** » 12 Dec 2007, 03:34

JHS wrote:The next change in the RAT 2 was a 220k or 100k BIAS-R instead of the 1M/2,2M for an even softer sound with way more mids. It seems that they wanted to duplicate the Anthrax-style or metal-style distortion tone.

can someone point me out to this resistor? i hate the presense of overwhelming mids (almost haunting) in this pedal.. i have no idea where to find the "BIAS-R"...

soulsonic · Post by **soulsonic** » 12 Dec 2007, 06:10

In my schematic that would be the 2.2M resistor right before the input of the opamp that connects to the junction of the two 100K resistors.

Proco - Rat 2 (early 90s) [schematic]