MXR distortion pedal predating the plus?

[JCM1959]

Was wondering if any of you guys know if MXR had a distortion pedal that predated the Distortion +.  The only ones that I have ever seen are the Distortion + using script lettering(early) through the block lettering.

[Processaurus]

Don't know if its earlier, but you don't hear about this one too much

[Mark Hammer]

Nope, it came after.  In terms of floor boxes, there seem to be roughly 4-5 generations from MXR.  First, the 1590B-sized script issues, followed by the block issues, followed by the 1590BB-size units (flanger, limiter, stereo chorus, distortion II, analog delay), followed by the Commande series (plastic boxes) and the 2000 series (I think that's what they were called).

[WGTP]

http://www.lethargytartare.com/schem/

Interesting RESONANCE control.  It appears to be a parallel set of op amp feedback loop clippers with a blend control.   

[Rodgre]

Nope, it came after.  In terms of floor boxes, there seem to be roughly 4-5 generations from MXR.  First, the 1590B-sized script issues, followed by the block issues, followed by the 1590BB-size units (flanger, limiter, stereo chorus, distortion II, analog delay), followed by the Commande series (plastic boxes) and the 2000 series (I think that's what they were called).

...and the earliest boxes were made by BUD (not Hammond, but a similar size).

Roger

[Mark Hammer]

Yeah.  That's why I said 1590B-sized.  I wasn't sure if it was Eddystone or Bud or some other company.

Hey, maybe somebody oughta put together Trivial Pursuit: Gearhead Edition.    I'd buy it, but I'd probably only get to play my wife and family members once, if at all.

[B Tremblay]

What size box was the MXR Hot Tubes in, Mark? 

[Mark Hammer]

Heh, heh, heh.

Oh, THAT one.  That one is a lesson about the internet of rather biblical (or maybe apocryphal) proportions.

It resulted from a series of exchanges between myself and RG in the very early 1990's.  I forget exactly how, but I had a Hot Tubes clone that I had built in 1979 or so, based on a board a guy in the medical school tech shop had given me (I think he simply photocopied his friend's pedal and drew the PCB from that).  Somehow, our exchange of notes, and perhaps some drawings of parts layouts or something, resulted in RG drawing up a schem, which found its way to Jamie Heilman's "Leper's Archive".  It was mislabelled at the time, and while Commander Keen soon learned of the error and eventually corrected it, eventually jamie Heilman went on to other things and the Leper's archive turned into a mirror in several places, posted by folks who were not going to update or manage it, and were certainly not going to correct it.

And that's where it sits today.  A schem which was erroneously labelled and has been posted in erroneous form, never to be corrected by anyone....and available for one and all to keep downloading with erroneous information, in perpetuity.

Like I say, of biblical proportions.

[scaesic]

i have a cleaned up schematic for the dist 2, and also a pcb plan for the original (i got a seller of the board on ebay to send me a high rez picture of the track side, resized, and turned it into black and white = no sale for the seller on ebay, hehehe), if anyone wants it.

i started making a veroboard layout but its halted due to exams.

[WGTP]

Bump

What effect does the RESONANCE control have?

[Mark Hammer]

First, do not be deceived by the inclusion of "Filter" and "Resonance" controls on this box.  They may both be terms connected to filtering, but in this instance they are completely isolated functions.  The FILTER control is pretty much the same thing as the filter control on a Rat: a simple-but-effective variable 1-pole lowpass filter.

The RESONANCE control is kind of interesting  (http://www.lethargytartare.com/schem/dist2.gif).  Note that the two sections of U1 are a pair of parallel diode-clipper circuits which both feed a mixing stage (can't tell if it says U3 or U5).  The upper clipping section has a bit of upper mid / low treble pre-emphasis above 3.6khz, provided by that little 2k/.022uf network. 

The lower clipping section is fed from the same prior opamp (U2) as the upper clipping section, but has no particular tone-shaping in its path.  I would like to draw the reader's attention, however to some interesting resemblances  to the Nurse Quacky and Dr. Q ( http://home-wrecker.com/nurse-quacky.png ).  Note that in both the "Resonance" circuit, and the Nurse Quacky filter section we have: a) a high value feedback resistor, b) a cap from the output and c) a cap from one of the input pins meeting.  This forms the input to a bandpass filter.  In the case of the Dist II this is also a bandpass filter section with enough gain to clip with those two diodes (maybe even more than what happens in the primary clipping section).

You will note as well that in the Nurse Quacky and Dr. Q, as the effective resistance to ground of that transistor changes, so does the centre frequency of the filter.  In the case of the Dist II, that variable resistance is provided not by a transistor to ground, but by the Resonance pot.  So, the Resonance control moves a separate passband around to achieve selective clipping in a part of the guitar's range of the user's choosing.  Not *quite* the same as sticking a wah in front of a fuzz, but somewhere in the same family of effects.

[WGTP]

Thanks for explaining that Mark.  So we are looking at a variable mid-range boost.   

[Mark Hammer]

That's my sense of it, yes.  Of course, what is "mid" to one person may be "treble" to another or "upper bass" to someone else.  I don't know enough about the math of this filter topography to be able to tell you what the sweep range of that pot is likely to be.  It may well be much wider or or narower than either of us imagine.  We'l see once more finely-honed minds jump in.