Anything "heavier" than a RAT?

[KORGULL]

KORGULL? Was this circuit noisy? What kind of a guitar are you using?

The noise isn't very bad as long as I keep the gain control down around 9 o'clock. Once I go past that point I start to get a lot of noise, but you don't need to turn the gain up very much at all to get loads of very good sounding distortion.
I used shielded cable for the input wire, but don't really know how much of a diffeence it made since I didn't try it without the shielding for comparison.

After I made my previous post, I realized that I didn't try the pedal with a single coil pickup yet - so I'm not sure how that will work out. I am using an EMG-81 pickup.
Gotta go to bed now or I'd give it a try and post results. Maybe tomorrow.

[RaceDriver205]

Yes, definately try Dr Boogie - an excellent (I think best DIY) high gain pedal. Its no good for low gain though, and needs good sheilding to keep hum at bay.

[brett]

Hi.
My Gibson Lucille (while I had it) used to do a good conversion from fat dual humbuckers to skinny single-coils via the "varitone" control.  Set to position "3" it sounded kinda like a strat.  The phatness was more or less gone.  I believe that the varitone was just a series of caps which cut bass, but someone should know for sure.  Once you work out what sort of filter was used in the Varitone at position 3 you could make a filter with the opposite effect and turn your strat into a fat 335/Lucille.
good luck

[WGTP]

It would be easy enough to use a dual op amp and create a Double Rat with the tone control in between the 2 or at the end and just do a single Jfet buffer stage.  You could use a dual 100K pot for the distortion.  I have more or less done that on the bread board with LED's and it cooks.  Or, you can do a TS into a Rat, or vis versa.   

[jrc4558]

thank you all for suggestions!
I will probably try Dr. Boogie, once I get a chance to etch the board for it.
WGTP, I tried a TS into a RAT, but it didn't quite produce the envelope characteristics I was hoping for. The gain factors seem to be approximately what I would want them to be, but the dynamics of the sound suffer enormously... And it is already a modded TS, with almost no bass cut in the clipping stage. 
So yeah, its breadboard time!
Thank you gentlemen for an enlightening discussion!

[WGTP]

I was looking for the Duece Tone, but found a new, non-Rat.  The Solo.  3 Asymmetrical clipping choices and a mid filter.

http://www.procosound.com/ratindex.htm

[tcobretti]

I didn't realize proco made so many distortions.  Rats sound pretty good, so I would imagine that solo is a cool pedal.

[WGTP]

It is good to see the 3 way switch on the SOLO.  They have gotten a lot of milage out of using the same basic design with only the clipping diodes being different on the Vintage, Rat II, Turbo, etc.   

Check out Tonda's mods  http://www.diystompboxes.com/pedals/ratmod.gif

[jrc4558]

Dont throw rocks at me, but I found a modification for the stock circuit that did what I wanted it to.
The bias supply resistor on the input - 100k and an input capacitor of 0.0068µF. Sounds just fine with an open back 212 speakers too! All the sloppy low end is gone. Its tight, nicely compressed and artificial harmonics are begging to be played.

Dropped D - here I come!

[WGTP]

I know that I forget about adjusting the input cap on op amp circuits, because of the caps coming off the feedback loop, but by combining them, the bottom can be taylored to taste.  With the Rat having 2 RC networks coming of the FBL, it has plenty of opportunities for tonal tinkering.  I think lowering the bias resistor to 100K reduces the highs.  This also can be accomplished in several ways.   

[Phorhas]

I think lowering the bias resistor to 100K reduces the highs

Yep. Combined with the lower bass response (100k & 6n8 -> 234 Hz) - produces a more significant mid boost (relatively to the original)... this is pretty good when it comes before a clipping stage when you are looking for a "metalish" tone. it's one step in the right direction IMHO.

[jrc4558]

It seems to me that a good way to get a tight sounding distortion is to let only the mids into the clipping stage and boost bass and treble after the clipping has occured. Like on SnasAmp.

[Mark Hammer]

Looking here ( http://www.generalguitargadgets.com/diagrams/rodentsc.gif ), the "low" ground leg resistance (R5) on the Rat provides, in conjunction with the 2.2uf cap (C6), an additional boost for upper mids and treble.  R4/C5 still provide lots of gain for the entire spectrum, just not as much as is provided for the high end.  So, the Rat sound is a combination of full-range and high-end boost in the gain/clipping stage.

To alter the relative gain and harmonic spectrum generated, consider doing the following.

1) Replace R4 with 220R.

2) Replace R5 with 22R.

3) Install a 500R pot (linear is probably optimal) such that the wiper goes to pin 2 of the op-amp (where the junction of R4/R5) used to be tied to) and the outside lugs of the pot go to the "new" R4 and R5.  If 500R pots are hard to find in the size/taper you want, a 1k with suitable parallel resistors between wiper and outside lugs should be fine.

So, what do you have now?

This pot is capable of getting very close to mimicking a stock Rat.  Rotate it in one direction (where "R4" = 220R and "R5" = 22R+500R) and the amount of extra "top boost" is reduced compared to a stock unit while the amount of full-range drive is increased beyond what the Rat normally does. "Full range boost" has a low end rolloff around 150hz and "top boost" rolloff drops to around 140hz (i.e., cancelled as a boost for all intents and purposes).  Max full-range boost is now x450, compared to x180.  That's some serious grunt.

Rotate the pot fully the other way, and now R4 = 220R+500R and R5 = 22R.  The max full-range boost changes to x140 with a low-end rolloff of 47hz, and the max top-boost changes to an insane x4546 at around 3.29khz.   Hmm.  Maybe better change that from 22R to 39R.  That will change max top-boost to x2565 starting around 1854hz.

Alternatively, consider tacking an inductor between C6 and ground.  Remember that the ground leg of the "pot" formed by R3 and R5 dictates not only how much or how little negative feedback is applied but to what portion of the spectrum.  Using only a cap to shape that means that only negative feedback above a certain frequency will be shunted to ground (enabling more gain for that part of the spectrum).  If an inductor is factored in, what gets shunted to ground isnow going to be above some frequency and below some other frequency.  Use any LCR calculation to figure out what the desired inductor might be to get the mid-boost you want.  A simple SPST toggle that bypasses the inductor changes you back to a stock Rat.

Actually, I kind of like this idea.  Strikes me as a very simple mod to do to a variety of pedals of similar architecture.  There may well be some judgment needed with respect to pot-value selection and possible parallel resistors needed, but in principle, this can spruce up a TS-9, a DOD250, and a bunch of other pedals.  Ideally, you want something that absolutely "nails" the stock setting.  That could be as simple as measuring the pot in different positions and marking the chassis.  Alternatively, use a SPDT toggle to select between the inverting pin (pin 2) going to the variable network or the fixed network.

[WGTP]

Cool idea Mark.  I had thought about using a cab blend in that location, or a 10K pot between the cap and the loop, but this is very interesting.   I guess you could put a notch filter coming off the FBL, but it might be difficult to get the resistance low enough. 

[Mark Hammer]

The problem with sticking a notch filter in the feedback loop is that it would need to go in parallel with the gain pot, which would essentially screw up the notch filter.  If the gain was set by the ground leg (i.e., resistance from '-' pin to ground) as in the case of the Distortion+, and the feedback resistor value was fixed, it would be much easier to work out what such a notch filter ought to be.

Alternatively, you adapt the circuit from the Ibanez Supertube ( http://www.diystompboxes.com/pedals/SUPTUBE.GIF ), and make it a stage BEFORE the high gain clipping stage.  Or, insert the Anderton Frequency Booster stage between the input buffer and LM308 gain stage.  I stuck one of those in a 4049-based overdrive, and it delivers the goods with minimum overhead.

What I suggested for Constantin is basically the most bang for the smallest circuit change, using cheap easy-to-get parts.  Only two resistors need changing, and one pot is added, but it should deliver a broader range of tones.

Nothing says you can't stick a larger cap in the feedback loop either, to offset the extreme treble boost.  The stock 100pf unit provides a rolloff around just under 16khz, which I suspect is directed at op-amp stability more than anything else.  Hiking that up to 220pf chops the rolloff at max gain down to 7.2khz, and 330pf drops that to 4.8khz.  In tandem with the filter control and "gain prejudice" control, that should be able o get a variety of mid-boosts when the treble boost and complementary treble cut are applied.  Note that with the 100k gain pot reduced to almost zero, such feedback cap changes start to become moot at low gain.

[Paul Marossy]

I personally like the Dr. Boogie more than the RAT clone that I built. 

[Mark Hammer]

I haven't put together a DB, but I was A/B-ing my "Rodent" against a couple of other distortions last night, and I like it a lot, actually.  If I have any complaint, I guess it would be the Gain pot taper, but that is easily adressed by means of a parallel resistor suitably chosen and placed.

Where can I find the DB schem?

[WGTP]

It seems I saw someone replace the stock tone controll with a BMP tone control.   

[Doug_H]

The Danelectro Fab Metal will do right out of the box better than anything we've got here.

YMMV

RDV

Haha! That's what I was going to say and you beat me to it.

$15 and you're there.

Doug

[WGTP]

But that is cheating...   ... Joe Davidson Obsidian.