Blue Box, E-H Frequency Multiplexer, etc.

[WeAreAs1 at aol.com]

Hello all,

I have found another sub-octave circuit that looks pretty interesting.  It is 
designed by Mathhias Grob, co-inventor of the Oberheim Digital Echoplex 
(every echo-looper's dream machine).  He calls it the "PARADIS POLYSUBBASS".  
It is intended to be used with a hexaphonic pickup, with one POLYSUBBASS 
circuit for each string.  The octave divider circuit is monophonic, but with 
one for each of the three lower strings, you still get to play chords.

His circuit has a couple of other useful functions that differentiate it from 
other octave boxes:  

1.)  A low-note priority system that senses the lowest string that is 
currently being played and mutes the octave output for the other two strings, 
allowing you to play big, full chords and still have the lowest note of the 
chord doubled with the octave bass note.  This keeps the sound from getting 
too muddy, as it would if all three of the low strings were octave-doubled.

2.)  An envelope detector on each string that drives an LM13700 VCA, so the 
octave-doubled bass notes will actually follow the dynamics of your playing.  
This is something that's sadly missing from pretty much all of the other 
commercial octave pedal circuits.  I imagine you could also use the envelope 
follower to drive a LPF for each string, which would further enhance dynamics 
and tonal possibilities

I haven't tried building it yet, but it looks pretty straightforward, and 
uses no exotic parts.  I may try building it into my Roland GR-300 one of 
these days.  I have a feeling that a GR-300 with an additional low octave on 
the three lower strings may very well provide Magnus Danielson the definition 
of "fat" that he was looking for a few days ago (in the "New Old Stuff" 
thread).

Here are the URL's for Matthias Grob's web pages:

His home page and directory to his various interesting stuff:

<A HREF="http://matthias.grob.org/">http://matthias.grob.org/</A>


The POLYSUBBASS page, including complete schematics:

<A HREF="http://matthias.grob.org/pParad/polymod.htm">http://matthias.grob.org
/pParad/ParaPoly.htm#Polysub</A>

Have fun!

Michael B.