ProCo Rat Modifications

[enigmur]

Hi I just scored a 1991 ProCo Rat re-issue for really cheap.

Now after playing with it, I'd like to tame down the distortion, and cut off some of the treble.

Now I can't read schematics, but if anyone knows which components alter what, I would be stoked if you could share any mod's you have come across.

I have successfully modified my V847 Wah, and know there are always resistors you can swap around to alter frequencies ect.

The circuitboard looks really straight forward in this pedal.

So if any of you guys have ideas, or a link to a site, thanks in advance -

Cheers, David

[ambulancevoice]

I'd like to tame down the distortion, and cut off some of the treble.

isnt that what the filter pot is for?

[slacker]

Sounds like you need the Ruetz mods or use the search, there's loads of info on RATs.

[enigmur]

Basically I want to use it as an overdrive more than a distortion pedal.

The filter does help but it is still pretty trebly with the filter on full. I'd rather not have to buy a mod kit online just because of the hassle of credit cards, shipping ect.

I have found a layout of a modified RAT, im not sure if it is the Vintage like I have.

I have searched and looked through but can't seem to find a basic layout and some simple mods like which resistors to change in order to cut some high end out ect.

There are a lot of threads on here but I couldnt find one which suits me.

Basically I would like to add a LED (I have a 3PDT switch in it). And I'd like to tame down distortion and treble, I have seen certain mods which claim to do this - I'd like to know what exactly they change to do it.

Thanks for the help,

David

[ambulancevoice]

if i were you, id remove the stock clipping diodes, install sockets, and experiment with some clipping diodes (germanium, silicon, LED), because most yield interesting results,

[brett]

Hi for heavier filtering, increase the standard cap (I think it's 2n2 or 3n3 standard).  Double it and you'll be losing a LOT of treble.

(That is, if the filter pot is working on yours.  In standard form, the filter is fairly strong, so it's a bit surprising that you've still got too much treble)
good luck

[Ed G.]

Replacing the diodes with LEDs turns it into a Turbo Rat, which is more like an overdrive. You get less distortion, more volume.

[enigmur]

Replacing the diodes with LEDs turns it into a Turbo Rat, which is more like an overdrive. You get less distortion, more volume.

Hi, yeah I did read about doing this.

What voltage LED's can I use? Just standard Red LEDS's or am I safely able to try different ones. This would be quite cool because I wanted to add an LED to it anyway. Though I dont think I'll drill any holes, because it will probably sell for more stock.

I have a couple of LED's lying around which I might try out.

Also, I havent been able to find any sockets I hear of often in modding pedals, is there anything you can use instead?

[Hanglow]

I use cut up DIP sockets like these for socketing things like transistors etc. you should be able to get them online easy from small bear or mouser etc.

[brett]

Hi
the forward voltage (Vf) of a diode indicates the tones you'll get when using it as a clipper.

Germanium = 0.3 V = low headroom, lots of distortion, soft tone when distorted (eg 1N60, 1N34)
Silicon = 0.7 V = medium headroom, medium distortion, tube-screamer style tone (eg 1N4148, 1N4004)
Red LED = 2.2 V = high headroom, little distortion, harsh tone when distorted

cheers

[enigmur]

Thanks a lot Brett, that was really helpful.

I'm not sure what the standard Diodes are?, there seems to be three, two are together and one is at the bottom left near the 3PDT switch.

Which ones do I need to change? Do I only bother with the pair together?

I think I will try with red LEDS at first, since I am not looking for distortion from this pedal - my amp does that ; ).

I guess I could try a slightly higher voltage silicon diode - but having LED's would be a bonus.

What happens if you use different rated LED's for clipping?

[tcobretti]

A very simple thing you could do is solder a very small cap from the tip to ground on the output jack.  I'd try 50pf to 220pf.  220pf would be a lot, but that may be what you want.

[enigmur]

Hi for heavier filtering, increase the standard cap (I think it's 2n2 or 3n3 standard).  Double it and you'll be losing a LOT of treble.

(That is, if the filter pot is working on yours.  In standard form, the filter is fairly strong, so it's a bit surprising that you've still got too much treble)
good luck

The filter definately does work, but it isnt as smooth sounding as i'd like it to be.

By increasing the standard cap, which cap do you mean? I thought caps were measured in pf and uf?

I heard changing the filter pot to something of higher value can help with treble? Is this true? And which value is good?

I think I will definately put LED's in it, perhaps try the cap on the output, maybe switch the pot if it does anything, and if you can help me out which which cap you meant I can change, and what value - I'll try that too.

I can take a picture of the guts of the pedal if you want, it may be easier to point me in a direction then.

Thanks for all the help guys!

[bwanasonic]

I have a 10n cap soldered across the wiper and ground lugs of the volume control of my Rat. Makes for a much smoother and useful tonal range. Give it a try. I'm sure I read about it here, but I don't remember who to credit for this simple mod.

Kerry M

[brett]

Hi
1 nF = 1000 pF = 0.001 uF
n=nano, p=pico, u=micro

the diodes of interest are the parallel ones.

If you want lots of headroom AND softish clipping, try multiple diodes (e.g. 2 pairs of 3 x 1N4148 or 2 pairs of 5 x 1N60).

The Rat is a really unusual pedal to turn into an undistorted booster.

[enigmur]

Cheers Brent, that clears things up.

Yeah it possibly is an odd pedal, but I need an overdrive/boost for driving my tube amp. If i can get this to do it, i will be happy, if not I will sell it along. I'm not going to do any un-doable modifications for that reason.

One thing I noticed was at high distortion the volume seems to fluctuate, any ideas what this could be? I'm pretty sure they put a brand new battery in when they gave it to me, so I doubt it's that.

It's not a biggie because its only when it is cranked up full.

Cheers for the help guys, I'll make a time to go into the components shop and take in your suggestions. I'll have a look for something i can use to make sockets for the board from (I'd like to get some sockets for my wah aswell)

Cheers

[enigmur]

Is there a way of finding values of diodes? I have a junk chorus pedal which is riddled with them, was wondering if I could salvage any parts if I could find out what they are.

[enigmur]

I had the 0.01uf cap I swapped out of my Vox Wah there and tried that on the output jack for the hell of it (even though the value is probably way too high...)

It was quite strange. I didnt notice much of a treble difference with the pedal on, but when it was being bypassed it was very noticible.

I would have thought there would be a resistor or capacitor I could change out which changes the levels of treble (Like in modding Wahs).

Looking at the schematics for the pedal I also noticed the distortion part of the circuit marked out. There is a resistor in line before the diodes, I thought maybe changing that would change distortion amounts, but I guess the clipping is only done in the diodes themselves?

There must be resistors which play around with tone in there somewhere? I thought that's kinda how it works. Or is that only relevant to Wah pedals?

Cheers

[tcobretti]

The cap on the output jack not working makes perfect sense.  It was my bad idea and I take responsibility for it.  The problem is that it is removing highs all the time, even when the pedal is off.  The smarter way to have done it (if I had thought things thru) is to run the cap from the output of the circuit (where the output wire connects to the PCB) to ground.  This way only the circuit has it's highs removed and it shouldn't come into play when the effect is bypassed.  You may be able to just solder the cap to the bottom of the PCB.  You might want to try a larger value since that didn't remove as many highs as you want.


Another thing you could try that I have read about but not done myself is find the 47 ohm and 560 ohm resistors that connect to the 2nd leg of the IC.  Replace them with 1k pots so you can tune the pedal's EQing.  I would pull the pedal from it's enclosure, install the pots, find a sound you like, then measure the pots' resistance when they are set to the sound you like.  Then I'd take the pots back out and put in resistors with the same value as the pot setting you liked.

My recommendation is to just build a booster.  They are very simple, and modding your Rat to point that it is a clean booster is counter productive.  You could even buy a PCB from generalguitargadgets or tonepad to simplify things even further.

[enigmur]

Thanks for the info, I'll give that a try tonight.

The Rat is so close to what I want, it does overdrive nicely and makes an awesome fuzz, but I just need that tiny bit more control over tone to get the overdrive just right.

Otherwise it is fine. It can make the most awesome Tubescreamer tone which I really like, but I just need to roll the treble off a bit more to get the smooth overdrive I would like to access aswell.

Adding that cap may actually do the trick though - it it does I will be stoked.

I'm really grateful for all the information and help I am recieving here, you guys rule.

Cheers, David.