Introduction

[Mark Smart]

Hi, I'm Mark Smart from Champaign, IL, guitarist/guitar 
synthesist/engineer.

I like modifying my equipment, but haven't really built any synths from
scratch. Gear:

Roland GR-50 Guitar Synth on Ibanez Les Paul Copy Guitar
Jerry Jones Electric Sitar
Epiphone Sheraton II for jazz
Washburn Banjo
Roland GP-16 Processor for Guitar
Boss SE-50 Processor for GR-50
Roland GR-300 Analog Guitar Synth
ARP Axxe
Casio CZ-101
Fender Rhodes 73 Stage Piano
Roland MIDI Keyboard whose name I forgot 
Various guitar pedals
Homebuilt stuff including mods to GR-50 to make sustain function more
  flexible and a guitar feedback generator which creates Hendrix effects
  at any volume.

Musical Influences:

JAZZ (Wes Montgomery, John Abercrombie, Jim Hall)
70's prog-rock and fusion bands: (Genesis, Yes, Crimson, Weather Report,
   Mahavishnu Orchestra, Return to Forever)
Ravi Shankar
Earl Scruggs
Igor Stravinsky
Bela Bartok

This mailing list came into existence just in time for
me as I am planning a big project. I wrote a note about this on Analogue
Heaven a while back, but I'll reiterate. 

I've been using a Roland GR-50 guitar synth in my band for about two years,
and I am frequently frustrated by its tracking problems. Like a lot of
pitch-converter guitar synths, it sometimes misses notes (especially with
me since I play very lightly) and jumps octaves, trying to track the second
harmonic of the string rather than the fundamental. Last year I saw a much
older (1980-85) Roland GR-300 synth in a store and was amazed at the fact
that it tracks much better than the GR-50 in spite of having a much more
primitive synthesizer section. So I have become determined to modify this
old analog beast to control another, more flexible and programmable, analog
synth, probably my friend's Sequential Six-Trak. Thinking about this
problem and analyzing the workings of the GR-300, I have figured out that 
some external circuitry needs to be built to allow this:

1) Comparators to turn the GR 300's sawtooth output into square or pulse
waves. I might add octave dividers as well as I have been playing the synth
through a guitar octave divider pedal and dig the sound.

2) Comparators and one-shots to produce gate and trigger signals from the
GR-300's guitar envelope followers, allowing it to drive external envelope
generators.

3) Log conversion. The GR-300's VCO uses a control voltage proportional to
the PERIOD of the guitar signal. So a circuit must be designed which turns
the period voltage into logarithmic frequency (1 V/octave, probably). I
found a couple of circuits in Bernie Hutchins' Electronotes which will do
just this, but I'm worried about temperature stability problems. It seems
to me Rick's Moog circuit with the multiple transistor package could be
adapted for this purpose.

I plan to just run the GR-300's modified oscillators through the Six-Trak's
VCF and VCA with its envelope generators, but I'll probably try controlling
its VCO's, too, just to see how this works. I would appreciate any
suggestions you fellow wire freaks might have for this undertaking.

Thanks!

Mark Smart