"Opening up" a RAT

[Michael Allen]

I'm not happy with the way my RAT sounds. It sounds really muddy and like my ears are being covered. Doesn't put out much but bass. I'm thinking of changing the Filter, to something like a Big Muff tone stack, and playing with the values a bit. Does anyone have any other usefull mods that they've liked?

Thanks,
Michael

[aron]

Go to the search and search for "Rat mod".

There are a number of threads on this. When I do a cursory look at the Rat schematic, I don't see a lot of caps to ground. I wonder if it's the chip itself that gives it that sound?

[amz-fx]

The Rat has a lot of high end boost in the gain stage... and then a  really heavy tone control filter.   Make the capacitor after the tone control pot smaller in value and see if that helps.

regards, Jack

[Michael Allen]

Thanks Jack!

If you don't mind my asking (just say so if you do!) what are the main changes that you made to the Fat Gnat? In general terms so i have something to play around with. I'm not asking to reveal your secrets.....

THanks!
Michael

[timrand]

I have a RAT modified by Keeley I really like it its like a marshall in a box. However most of the distortion pot is unusable it needs a different taper. When I opened it up I see he has added an LED to the circut however the mod is covered in glue I suggest getting the thing modded by him

[amz-fx]

what are the main changes that you made to the Fat Gnat?

They are detailed on this page:

http://www.muzique.com/fx/fat-rat.htm

-Jack

[bobbletrox]

Are there Big Muff mods included in that Rat/Muff ebook too?  I might have to buy that.

[amz-fx]

Are there Big Muff mods included in that Rat/Muff ebook too?

Yes, certainly!  http://www.muzique.com/ebook.htm

regards, Jack

[Mark Hammer]

Personally, I had to make a number of changes to my Rat clone to *make* it capable of sounding "muddy".  So what I'm wondering is, how did this come so easily to yours?  And here is the question I arrived at, or rather 3 questions:

1) Is this a home-brew or a purchased Rat?

2) If a DIY clone, are you sure the value of the compensating cap (30pf) is correct?  When it comes to small valuje caps, it is often easy to make mistakes because the value coding systems seem to be much more diverse than those of bigger electrolytics, and because the print is so damn small.  You didn't happen to accidentally sub a 30n[/n] for a 30p, for example?

3) Is the pedal capable of large amounts of gain and substantial output volume relative to bypass?  It ought to be.  If not then there may be something amiss with the orientation of the FET pins, or perhaps even an error in using a Millenium bypass.

Again, not to diss your building chops.  It's just that what you describe as the chief complaint seems way too radical to simply be a matter of tweaking to taste.

[Michael Allen]

Thanks for the analysis, I wasn't aware that this pedal was supposed to be so edgy, because mine isn't.

Yes this one is DIY. I made it about a year ago and it sounds killer in my little practice amp. But I just tried playing it thourgh my Sovtek Mig 50 and it sounds completely different. Big Muff and OmniDrive sound good through it, but this RAT sounds horrible.

So first, I used a TL071 with this instead of the LM, so there is not compensation cap at all because I was told this chip is internally compensated already. Second, I'm positive about the FET orientation because in my initial build I had it reversed, and after debugging I got it placed right. And third, I get a huge boost in volume when playing through my practice amp but when I plug into my Sovtek, the volume is about the same as bypassed. This is the same with my Big Muff, which has an INSANE boost of volume. When played in my Sovtek it becomes about unity as well.....So maybe this is an amp problem?

Thanks all!
Michael

[petemoore]

The Rat's sound built around the compensated chip.
 the Small cap adjustes the compensation of the highs amplified in the chip.
 Changing to a compensated chip, LM308, or the one Jack suggested should make it more Rat-like.

[Mark Hammer]

Hmm....

Okay, clearly it isn't a FET orientation or compensating cap problem (though I'm glad those could be eliminated as possible leads...always helps to narrow the range of possibilities when troubleshooting).

One possibility...sometimes...is the value of the volume pot and problems with loading.  But in this case it's the same damn output pot value, whether BMP, Rat or Omnidrive.

I'm stumped.  Just out of curiosity, what happens to the tone if you stick something else between the Rat and amp, like a chorus or phaser?  If the muddiness disappears, then clearly it is some kind of amp/pedal matching-related issue.  If not, then maybe it's a question of a tonal difference which is unapparent with other amps but apparent with the Sovtek.

Incidentally, does the tone control work properly?  If there was an issue of the wiper not making proper contact, then the tone pot could be "stuck" at max resistance, which would, in turn, provide maximum treble rolloff and a muddy tone.  Of course that would be true no matter WHAT you plugged it into.

(P.S.: Ignore the weird parenthetical things in boldface in my previous note.  I was attempting to hand-code HTML and screwed up.  It was supposed to say "30n" and "30p" in boldface.)

[Dai H.]

I'm not happy with the way my RAT sounds. It sounds really muddy and like my ears are being covered. Doesn't put out much but bass. I'm thinking of changing the Filter, to something like a Big Muff tone stack, and playing with the values a bit. Does anyone have any other usefull mods that they've liked?

Thanks,
Michael

Hard to believe that you can't move the sound away from muddy (by turning the distortion and filter knobs). Have you ever compared yours w/a real one? They seem pretty ubiquitous in music stores, so maybe you can find someone who has one to try(?).

[WGTP]

The TL070 is a direct replacement for the lm308, with external compensation.  Jack likes the NE5524 which also is externally compensated and sounds nice.  Tighter bass and sweeter highs.

When I built mine I found the tone control always maxed, so I replaced it with Jack's diode warp control.  

[Winged Eel Fingerling]

Hi Michael,
I too have a Sovtek Mig 50 an I'm 95% sure the problem is with the Sovtek. I have one of the early mark 1 models and it only has a master volume, I don't know if they were all made like this but most of my favourite effects sound god damn awful through my Mig 50. I tried my R2DU ( two rats in a rack ) and yes it sounds like poop even my DMI Fuzz Face sounds crap the best results I got was with a Big Muff ( sovtek of course ! ) and ( I was real shocked by this ) a Boss ds-1. The ds-1 sounds fantastic very dynamic and really transparent not one of my favs but through the Mig it's awsome.
I think the problem is to do with the fact the Sovtek only has a master volume so to get the valve's to distort you have to run it at near full volume !! sounds great but the rest of the street ain't to keen!
It is the same for the Fender Bassman 50 ( which the mig 50 is a copy of ) I lent a friend's an it's the same deal...god damn loud and very clean.
Just thought I'd let you know so you don't blame your Rat.
Cheers
Dave

[Michael Allen]

Thanks for the tips guys...I'll try and find another amp to plug into and see if the prob is the amp. If it is the amp, would doing some mods to Marshall values solve any of this problem?

Tone works, and the effect is the same with something else after it (SmallStone, EANTrem)

Thanks a lot....

Michael

[aaronkessman]

my DIY rat goes from muddy to ear-blasting treble. fully half of the tone range is unusable because it makes the tone too piercing.

just so's you know ;-)

Aaron