Best assimetrical clipping solution for a rat clone

[spatescroll]

I'm building a clone with various clipping options, my bigger doubts are about the asymmetrical clipping. Which should be the best configuration for D1/D2?

[petemoore]

Which should be the best configuration for D1/D2?
  The ones that sound good.
  For assymetric that'd be a total foreward threshold of different amounts for D1 / D2.
  Try two Si's in one direction and one in the other ..assymetric
  Or an Si and a Ge..assymetric [lower threshold = more grit, less output].
  Si with Ge one way, Si the other is less assymetric than two Si's and a Ge the other way, pretty good output.
  And all this depends on what it depends on, 'best' in this case is subjective opinions that if taken as etched in stone is misnomer...best is what sounds gooder.
  How much input signal, how symmetric is the input signal..what's happening to the 'left' of the output..is there a clean amplification system or something which augments the distortion of the Rat ?
  Starting with a high threshold, then clip on [or solder on, watch not to overheat the diodes] lower threshold diodes...use a switch or socket diodes.

[Mark Hammer]

I'm not even sure there IS such a thing as asymmetrical clipping for the Rat.  Understand that when one talks about asymmetrical clipping, you're talking about the differential likelihood that one half-cycle of the signal will clip, compared to the other half-cycle.  In the case of the Rat, when you apply gains of >1000 (which the Rat does), BOTH half cycles will clip big time and contribute lots of harmonic content in the process.  The only difference between the negative and positive half-cycles will be that their final amplitude will be different - a square wave that is tall above the waist and short below, or vice versa.   The net impact will be that you'll have more overall output level from the pedal.  As for the quality of that harmonic content, it will be something, but it is anybody's guess, and sure as shooting won't be asymmetrical with respect to whether you get harmonic content for the positive peaks but not for the negative ones, because with that amount of gain you will.

Think of it this way.  Mini-Me, a guy who is 5'7" and Yao Ming walk into a dark room.  Inside the room is a VERY tall guy with infra-red "night-vision" goggles, good aim, and a sharp sword, and very strong arms.  Is Mini-me the only guy who emerges headless, or will they all emerge headless?  True, Yao Ming's corpse WILL be longer than Mini-Me's, but it will still be equally headless.  Absolutely no "asymmetry" there.  If the guy with the sword was 5ft tall and had no night-vision goggles, there is a good chance that he'd be swinging blindly, and that Mini-Me (Vern Troyer) would come out head intact, Yao Ming would be severed at the rib cage, and the 5'7" guy would be missing a head.  Now THAT is asymmetrical.

When the gain applied and subsequent clipping is modest (which, in fairness, it IS for a small portion of the Rat's gain control), then the idea of asymmetrical clipping is plausible because one half of the wave form may well fall short of the clipping threshold while the other half exceeds such a threshold.  In the case of the Rat, unless you're using a 24v supply and a 4+2 LED arrangement for clipping, that threshold gets reached and exceeded PDQ.

I don't wish to be harsh-sounding, but it is best to stop misunderstandings dead in their tracks before they become too firmly entrenched.  I can vouch for the interesting consequences of attempts to introduce asymmetrical clipping in other circuits with more modest gain, but the Rat just isn't one of them.  Great pedal, and I like the two I made, but definitely not the raw material for examining differential clipping of half-cycles unless you turn it into something that isn't a Rat.

[MikeH]

Great pedal, and I like the two I made, but definitely not the raw material for examining differential clipping of half-cycles unless you turn it into something that isn't a Rat.

Like... a Turbo Rat?

[Mark Hammer]

Nah, I meant , you know, those guitars that are, like...double guitars?

[oldrocker]

My favorite Rat modification.

[Mark Hammer]

That one would get my vote too.  It hikes up the clipping threshold by roughly a factor of 3, allowing the user to churn out fairly high volumes (for amp distortion) without producing significant amounts of distortion in the pedal.

[nooneknows]

That one would get my vote too.  It hikes up the clipping threshold by roughly a factor of 3, allowing the user to churn out fairly high volumes (for amp distortion) without producing significant amounts of distortion in the pedal.

Well, to my ears they sounds a bit different anyhow, it's not only a matter of volume. It seems the Leds has a 'grrrowwwl' more pronounced than the silicon, which are more defined.
However I prefer Led (the Turbo Rat config) 

[WGTP]

1 LED 1 GE   

[spatescroll]

1 led 1 ge sound interesting, should be a red led and 1n34a ge? I know I should try every option, but I'd prefer not buying 1000 pieces, and an opinion from expert builders is very usefull.

[Mark Hammer]

Short answer is YES.  Red LEDs have a clipping threshold of around 1.5v, and Ge diodes, whether 1N34A, 1N270, 1N60, etc., have a threshold in the vicinity of 220-250mv.

With that sort of "stagger" there WILL be a certain portion of the gain range where one side of the waveform is clipping and the other isn't, in addition to a range where they are both clipping equally, but one half is simply louder than the other.

If you had a toggle to switch between a pair of back-to-back Si diodes, like 1N914, and an LED/Ge pair as described, that would give you plenty of tonal palette to mess with.