best IC and clipping circuit for RAT distortion

[powerplayj]

I have a Vintage ProCo Rat and was wanting to use it mainly for heavy distortion (Marshall, 80's metal) but, really dig the blues sound.  However, my modded TS-9 covers a lot of ground except heavy distortion so, I was hoping my RAT could fill this void.  I have already replaced a few caps to increase the base response and re-shape the filter control.  However, I was wandering if anyone has used a certain IC / diode combination to get an even heavier distortion out of this box?  I currently have a TL071 and the original LM308.  I have also ordered a Ge diode to try in the clipping region in series with the stock diode pair and I have an LED which I may place in the clipping region via an A/B switch.  I have Jack Orman's RAT ebook so, I at least have a good start in experimenting with this pedal.

[Mark Hammer]

I haven't tried a TL071 but I *like* the 308 that's in there.  The designer swears by it too.

For the most part, all manipulations ahead of the diodes will essentially tinker with the tonal balance and signal level.  Some of the distortion may well come from the 308itself, the way it comes from the 741 in a Distortion+, but my guess is very little actually does.  The brunt of it will be the diodes and the output FET.  The pair of 1N914s in there will limit signal being fed to the FET at about 500-600mv.  If you replace them with Ge diodes, that will be chopped by half.  You'll get more sizzle from the diode clipping since the clipping threshold will be lowered too, but you probably will get less out of whatever the output FET contributes.

That's actually an interesting experiment to try.   As you switch from, say, 1N34s to 1N914s, to a pair of red diodes, you should go from more impact of the diodes (and less of the FET) to less impact of the diodes and more of the FET.

[Doug H]

Because the 308 is externally compensated, the theory is it is slew-limiting do to being overcompensated by the cap. Or something like that... I don't remember all the details. Anyway, this is supposedly part of the uniqueness of the RAT sound.

You can try a TL070, another externally compensated opamp, more "modern" (relatively speaking) than the 308. It is quieter and has a FET input stage and sounds nice. I've fooled with it before and it is like a similar-yet-upgraded version of the 308.

Doug