RAT mod with MOSFETs, LEDs, etc.

[wampcat1]

Alot of times I'll then add a pair of LED's across the feedback loop while keeping the diodes to ground.  This  adds alot of crunch to the sound while taking out some of the fuzzy mush. 

Later, PaulC

Good idea! I'll have to try the LED's in the feedback loop -- I like the sound of 1n34a- 1n4148 in series (x2) as well inthe fb loop.

bw

[PaulC]

Good idea! I'll have to try the LED's in the feedback loop -- I like the sound of 1n34a- 1n4148 in series (x2) as well inthe fb loop.

I liked the LED's because of the higher threshold here.  If you go to low with the diodes they'll clamp down the output of the opamp to much not letting you drive the diodes to ground as hard.  To me the trick is "timing" the two clipping sections with each other.   Push the diodes to ground up to the point where you'd almost not like them anymore, and then have the diodes in the feedback loop take over.  to me that was the problem with the rat circuit.  It takes to long for the opamp to hit the rails after the diodes clamped.

Later, PaulC

[Skreddy]

- I tried lots of options with MOSFET clipping but could not get it to work. All I had were BS170s so that may have been the problem.

Try 2N7000 mosfets.  I like 'em for clipping.  I currently use the internal diode for clipping in one of my pedals (can you guess which one?), as it renders a loud, trebly tone, and I'm still working on a reverse setup using the mosfet itself for that softer, tube-like tone.  But using it that way is a lot quieter and darker, so I'll need to change the type of diode I use inline with it as well as change the other filtering in my circuit to cut out less high end (as the mosfet cuts quite a bit all by itself in that configuration).

And a belated "thank you" to Aron and to Alfonso Hermida and to Jack Orman, et al, for posting so much cool info about mosfets.

[WGTP]

http://www.diystompboxes.com/smfforum/index.php?PHPSESSID=0d951114445dd656d8aae8ccb1307893&topic=45122.0

Check the last post out.  By adding a 2K pot to the 4.7uf leg, you can go from reduced bass (reference the stock values) to way over-the-top gain with bass boost inbetween. 

Also, don't forget you can reduce the input cap, if you have too much bass for your taste. 

When using Mosfets as clippers to ground, you will get the soft clipping until the op amp starts clipping and then get a combination of both.  For primarily Mosfet clipping, you need to use them in the feedback loop like a TS or Muff Fuzz, or one into the other, like on my breadboard.   

[dano12]

Hi Jarrick, did you get your parts yet? Be interested to hear what you find...

I updated my schematic last night to incorporate the latest things I'm thinking of:

[WGTP]

COOL   

[dano12]

COOL   

Thanks. I'm going to try and work in Jack Orman's brilliant tone-clipping concept into the hard clipping section at the end.

Imagine a full Fender tone stack, with each band driving its own clip chain.

[Seljer]

Maybe something to remove the clipping diodes going to ground? just the opamp on its own has a noticeable amount of distortion (though then again, selecting all of the diodes of tha section at once might work)

and maybe the ability to choose between opamps as well? the LM308 gives you that typical Rat sound and using something else gives a rather noticeable difference (and since you've allready got all those other controls on there you're bound to find some sort of settings that works decetnly with other opamps)

[Torchy]

Switches 12 to 19 will ground the opamp output when all switched off. I would leave off the shorting loops from 15 & 19 so you can select the different clippers or none at all.

[jarick]

Alright, just got my pedal last night.  It's interesting in stock form, but too chunky and saturated in stock form.

For now, I'm going to swap a couple of key parts due to lack of funds...probably just start off with LED/4001 clipping, then try LED/LED, then order up some MOSFET's.  Also going to do the trimpot on the bias resistor.

It's a shame that you can't find 3PDT toggle switches for cheap.  I'd like to do LED/MOSFET+germanium/4001 on each side and have a pair of switches so you could toggle between each half of the clipping.  Lots of fun to be had there...

[WGTP]

Warning:  You can make yourself mad with this diode switching stuff.  Sounds like it may already be too late for you.   

[jarick]

Haha...yeah, I was even thinking about getting a pair of those 16-pin DIP switches and having two rows of diodes all selectable by switch


Trouble

You know, that'd be a really great way for a pedal designer to zone in on the optimum diode circuit.

What's that line about a fine line between genius and insanity?

[WGTP]

If you have too much bass much, you can also try using a .002uf, .001uf or even 470pf input cap to roll off the extreme lows.  Then you can fatten it up with some of the other mods listed.   

[Sindran]

By just changing the type of caps you more than likely won't get any flatter eq response. You need to either run a low or high pass filter (or both) or gyrator (see rg keen's geofex page) to get rid of that exact frequency. You may need to boost the signal again after the filters. Here's a soundclip of my Rat with these type of mods:

http://www.indyguitarist.com/soundclips2/ratmod-706.mp3

I was searching threads about RAT mods, anf found this oldish (but good) thread... and:

That wampcats clip sounds really good!
Any chance you could share what you've done with it???
Sound reminds me of OCD with higain (drive 3 o'clock) settings and boosted with LPB1...
I'd like to get something to replace OCD in my pedal board, and I'm hoping I could mod RAT2 to do that...

[WGTP]

http://www.muzique.com/lab/zenmos.htm

Check out the second one.  It uses the diode in the Mosfet of one, to force the signal thru the Mosfet of the other.  Clipping threshold is around 2.5v with 2N7000.  Slightly higher with the BS170's I have.  You can use this in the feedback loop as well.   

http://aronnelson.com/gallery/WGTP/Moster?full=1

[Sindran]

http://www.muzique.com/lab/zenmos.htm

Check out the second one.  It uses the diode in the Mosfet of one, to force the signal thru the Mosfet of the other.  Clipping threshold is around 2.5v with 2N7000.  Slightly higher with the BS170's I have.  You can use this in the feedback loop as well.   

http://aronnelson.com/gallery/WGTP/Moster?full=1

I'm gonna try those.
Is this the way mosfets sound best as clipping diodes? Would IRC520 mosfet be good choise?
I was thinking tryign also LEDs for clipping. What guys think, is it enough if I put mosfets to the "ground"-clipping, and use LEDs in feedback loop ? Or will some magic happen if I put mosfets to feedback loop also???

I'm full of questions, again...

EDIT: 
PS: It says in Wiki that RAT and Boss DS-1 is same schematic, is this true?

[WGTP]

The problem with using the IRC520 is that the mosfet clipping is up around 3v. so it is hard to incorporate that into a clipping design, but give it a try.

There are many different possible combinations.  Try it with the LED's in both places.

The DS-1 is similiar, but not the same IIRC.   

[Steben]

There are always Zener diodes too. They act a bit the same. In one direction they have a normal 0.65V diode treshold, in the other one they have the zener voltage. 2.7V is a nice treshold one for clipping. They seem rather smoother too than LEDs.

[Sindran]

I got yesterday my Rat II pedal. (last time I posted it was in the mail)
I've been playing with it few hours and I'm surpised about the smoothness of sound and overal quality of pedal. The box is HEAVY-duty, it has 3dpdt swithch and it looks like the PCB has ready holes for modding! Maybe it's the same PCB as in ProCo Solo-pedal?

I was just wondering is it normal that the potentiometers work only at  the first quarter, between 7-10 o'clock. After that the sound is pretty much the same.
It's just like it had linear pots when it should have logs.

Oh, and I did the Ruetz-trimmer mod allready. It has more subtle effect than I expected. But is Ok i quess.
I have to see if it has more effect after I put diodes and/or mosfets to clipping and feedback loop.
(have to wait for the parts)

I was thinking that I put 3 switches in it:
1. - On/off for diodes in feedback loop.
2. - Stock clipping/alternative clipping
3. - Diodes/MosFets for alternative clipping

I'm not sure how necessary any of these mods are.
...Well, at least I know after I make them what you guys are talking about! 

PS. Rat already kicked OCD out from my pedalboard! 

[WGTP]

Yeah that box is built for some serious R&R.  Have you seen Tonda's mod's in the schematics section? 

If this is a new one, can you tell what the op amp # is?