MOTM

From: thomas white <djthomaswhite@...>
I haven't got any MOTM list messages for some time now.
Is the list OK or did I get dropped or something?

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Yes, Thomas, the list appears to be OK.  It is suffering from a case of
"everybody doing something else" I guess.  Since the list is quiet and I
cannot be therefore accused of hogging the bandwidth (something I am very
good at), I will share my latest DIY addition to my MOTM system.  This is my
second project to be completely finished into a final assembly on MOTM
proto-board.  I am having so much fun doing this, I just ordered a
"pile-o-proto boards" from Paul so I can do some more (utility type stuff).

This module is a manually controlled pitch shifter.  I started to make this
just an octave switch, as I wanted a way to shift octaves and maybe 5ths
between my MOTM oscillators without having to retune them.  I just like
having octave switches on an oscillator.  BUT, the MOTM-300's pot control
offers more range and I did not want to even THINK about modifying the
greatest oscillator module on the planet.  So, my original plan was to make
a module that put out a selection of fixed voltages that could be connected
to one of the FM inputs of the MOTM-300 to provide this feature (real simple
stuff).  There was some discussion on the list.  However, Ken Tkacs twisted
my arm around my back (a neat trick via e-mail) and told me my plan should
be modified so that the 1 volt/oct voltage keyboard CV connects to my
module, and then my module connects to the MOTM-300 or any 1 volt-oct VCO.
After first dismissing this as too difficult for a guy with a business
degree, I finally admitted Ken was right (like he almost always is BTW), and
adopted his concept for my project.

The result is a 1U utility module with three rotary switches for interval
selection and six 1/4 jacks (3 CV IN, 3 CV OUT).  Each interval switch can
be used separately, or all outputs controlled by the same keyboard CV
(normalled a to b, b, to c).  This simple circuit adds the selected voltage
interval to the incoming keyboard CV and that is the output.  This first
version has 5 interval shifts up and 5 down.  There are three channels of
shift.  The interval shift amount is completely "user selectable" by the
fixed resistor selection in a corner or the circuit board (when building).
I was going to use only octaves and 5ths.  But along the way with my
experimenting, I found many other useful and interesting harmonics (Thanks
Ken)

So, you hook your keyboard CV to the input of the module.  You hook this
module's CV outputs (3) to the 1-volt-oct inputs of your oscillators and
tune all the oscillators in unison (at the high end of the CV range BTW).
Then you can use the rotary switches to shift the intervals between
oscillators.  Of course, one oscillator (your fundamental frequency) does
not need to pass through this module.  I have the module constructed and
tuned and it works quite well.

Version # 2 of this module, will feature only 2 channels of shifting (yes,
we can get by with 3 oscillators per voice).  However, it will have MUCH
more shifting capability.  It will have 4 rotary switches and 4 jacks (2 CV
IN and 2 CV OUT).  The difference is that ANY semitone interval is
selectable.  Since each shift channel has 2 switches, one will select
octaves up and one octaves down.  The other will select intervals in
semitones +1 through +11.  So, no user interval choice will be required when
building.  Version # 2 is layed out on paper proto board but will not be
tested and functional for about a month.  I am taking a 2 week vacation to
the Washington, Idaho, Montana and Calgary, Canada.  So, I will start
constructing it when I get back.

Obviously, these are simple circuits consisting of resistor voltage dividers
for interval voltages and op amps for DC adding.  The trick has been getting
the accuracy in the 1 volt/oct CV.  If anyone has any additional interest in
either of these two utility modules, please e-mail me off list.  I don't
want to turn the MOTM list into DIY discussion for the many that don't
build.  However, since this is created in the MOTM format for use with MOTM,
I wanted to share it with the list.

Thanks to Ken Tkacs for his inspiration and to Paul for answering the one
hundered stupid Stooge-like questions.

Larry Hendry

Disclaimer:  I am not a BS/MSEE.  I am not a design engineer.  This is DIY
learning stuff.  My only claims are that:
1 - I am having fun
2 - My circuit works very well
3 - I am buying more MOTM proto boards than anyone else.