MXR 90/100 Schematics? (Was Re: LED/LDR VCF)

[Sean Costello]

Hi y'all,

Anybody out there in DIY land have schematics for either the MXR 90 or MXR
100 phase shifters?  I would love to see how these circuits work.  I have a
few schematics that I can trade, if you want them.  A few aren't currently
up at Leper's Schematics or DMZ:  a few Vox schematics, the Tychobrahe
Octavia, and some other stuff.

Thanks,

Sean Costello

P.S.  If anyone wants the Tychobrahe Octavia schematic, just send me e-mail
and I'll send it out to you (I've scanned it in already).  It's a pretty
messy schematic (I drew it by hand, as I don't have a good schematic capture
program), but it apparently works (I fixed a few errors after feedback from
R.G. Keen - thanks, R.G.).  The pedal is a rather simple full-wave rectifier
that gives you a super distorted, compressed "octave-up" sound, a la
Hendrix.  Playing a monosynth through it is weird, as the perceived volume
of the note becomes LOUDER as the synth VCA envelope decays away (at high
input volumes, the Octavia becomes very thin and trebly).  The original
Tychobrahe pedals sell for $800-$1000 nowadays; pretty high price for such a
simple circuit.  It might mess with anything placed after it, though, as it
has a lot of DC in the output (is the term for that "DC offset"?  I'm new at
this electronical stuff. :).

At 04:43 PM 7/18/96 -0700, Barry Klein wrote:
>My Electronic Music Circuits book has a circuit for a voltage controlled
>phaser using LDR's.  I used Vactec Vactrol series 5C4-2, which are dual
>photoresistors in one package (with 1 LED).  This series has the resistance
>range you need and the speed is pretty fair.  This is what MXR used in
>their Phase 100 phaser stomp box and that I used in a Music Man guitar
>amp years ago.  You can also use FET's or OTA's for VCF designs.  
>
>The Vactec stuff may be available from either Allied Electronics or Newark
>Electronics.
>
>klein_b at a1.wdc.com