Introducing the Flexidrive

[Harry Palms]

Looks a little like a cousin of an OS-2.

[Mark Hammer]

In one sense, yeah, except that the OS-2 (if the posted schematic is accurate) uses qualitatively different approaches to generating the distortion.  Well, not THAT qualitatively different.  One "side" is essentially a pumped up SD-1, give or take an inch, and the other "side" is essentially their take on a Rat (give or take an inch) with a gentle scoop added.  Neither side attempts to cover one segment of the frequency spectrum in a dedicated way.  So think of it like a "Sparkle Drive" where neither side is particularly clean.

What I tried to do with this was divide-and-conquer in a more flexible way that was not quite as complicated as the Quadrafuzz.  The TS-9 and SD-1 attempt to equate "proximity-to-clip" for the frequency spectrum by using a shallow filtering of the low end going into the clipping stage (low end usually being closer to the clipping threshold than high end, simply be virtue of the physics of strings).  This was intended to yield a "smoother" distortion tone by not clipping the low notes more than the high ones.  Treble-cut filtering at, and just after, the clipping stage restores some of the tonal balance, but not enough, to hear many TS-9 users complain about the need for more bottom (and to see the number of TS variants int he boutique market that attempt to respond to this).  What I thought I'd try was simply differential clipping of the lows and mids/highs so that you could get as much bass-drive as you wanted, while still being able to dial in how much treble/bass you wanted as well without resorting to a nasal-vs-muffled choice from the BMP tone control.  How much this reduces intermodulation distortion (one of the stated goals of the Quadrafuzz) is anybody's guess at the moment, but my own guess is "Not much".

This is a slightly different in approach than what the Rat does, which is to demand noticeably more gain from the treble content than the bass via a fixed network (the two ground legs of the gain stage), while still permitting ONLY global gain increase/decrease.  True, you can filter out harshness and still keep all the meaty bottom on a Rat, but what I wanted to do was provide a choice of where you wanted the drive to be situated most.

Hopefully I can iron out the kinks this week and go beyond the mere promise implied by a picture and this discussion.  I am convinced that, in principle, it WILL work.  It's just a question of some circuit refinements and component-value adjustments.

[Doug_H]

Looks great, Mark!

[Connoisseur of Distortion]

i look forward to building one of these. unfortunately, i'm not near a soldering iron for another ~3 weeks... hopefully some sound samples'll be squeezed from the circuit by then! 

I never got around to making soundclips of my RoseyRay... I really should figure something out for that.

[Mark Hammer]

Wait until I have one up and working flawlessly and THAN lament your lack of proximity to iron.

[WGTP]

Another interesting concept.  A cool thing about the OS-2 is that the TS/SD-1 distortion section is very midrangey and the DS-1/Rat has a midrange notch, so you are mixing some EQ by panning between the 2 different sections.  The highs and lows are DS-1 and the Mids are SD-1

Of course that is different than what is going on here, but depending on your preference, you may prefer the highs of a SD-1 vs. a DS-1 or vise versa.  Certainly appears to be an easy mod.  Or, you could make each stage switchable.  Awaiting Tone Report.   

[markm]

This circuit looks quite cool for sure, I'm going to wait for the final "tweaking" and perhaps give it a try.
Please keep us informed on your progress Mark! 

[mydementia]

How's this coming along?  I was just about to make a PCB layout for it when I read that you are still tinkering... I'll wait until you settle on component values...
Mike