Norman,
This is some really great stuff. You got me thinking WHY? And then you
answered. A very thoughtful mail no doubt.
The CV input of the 700 already feeds a comparator. The + side fed by the
switch pot is already scaled for + / - 5 volts by the resistors at the ends
of the pot. So, I cannot see any reason that you could not use a voltage
input here instead of the switch pot. My lack of expertise leaves me with
some questions though.
Standard Stooge Disclaimer - I have not tried this. Do not do this. This
is for the purpose of discussion.
1 - would you need to buffer the input - I don't see why
2 - would you need a filter on the CV input like Paul has
put on the actual CV input (R9 and C7).
But, in general, it seems like you should be able to interrupt the
connection between VR1 and the LM311 pin 2. Put your CV input jack here and
set VR1 wiper to the switch on the new jack to that when nothing is plugged
into the new CV jack, VR1 functions as normal.
If you wanted to still have the biasing ability of VR1, it would seem to me
you would need to add a summing stage to add the voltages of the pot and
this new CV input prior to going to the comparator. But, that seems
unnecessary and beyond what you were trying to accomplish.
Very interesting. I like your thoughts on this.
Larry
P.S. without modification, the 822 voltage switch will only output 3.917
volts max.
----- Original Message -----
From: norman fay <NFAY@...>
To: <motm@yahoogroups.com>
Sent: Friday, February 09, 2001 6:58 AM
Subject: [motm] suggested mod for motm700 (longish)
This is a module I haven't got yet, though I do mean to get one, as I
can imagine several uses for it. At the same time, I've been looking at
the serge "com" (dual comparator) and comparing them feature-wise.
Though both modules are based around a voltage-controlled switching
function, both modules produce different results. The MOTM switcher,
I'm sure you all know about. The serge comparator, OTOH, has two inputs
marked + and -, a threshold knob and a single output per channel. what
they do is this: one runs a different voltage/signal into each channel.
If the + signal is greater than the - signal, the output goes high (+5v)
if not, it goes low (0v) Using the threshold control, one can either
generate square waves/pulses from a single input, or raise or lower the
+ signal (I think....). I've been racking my brains trying to come up
with a way for the motm700 to do this. The voltage bit is easy - set
the mode to voltage, and feed it with +5v into one input and 0v into the
other (you could use l. hendry's octave switcher to generate the 5v)
however, the dual cv inputs are a problem....the only way to do it would
be to add another cv input to each half of the module, which would
interact with the "switch" knob. In this case then, if the
signal/voltage at "cv in" is greater than that at our new input, the
module would switch one way, if it were lower, it would switch the other
way. In this case, the "switch" knob could add or subtract from the
voltage present at the new input, thus acting as a threshold control.
Now, I'm absolutely ∗sure∗ that there are folks on this list who could
perform this mod!
Now, the question you'll be asking is this: why? Well, here's a few
possibilities:
1/ from the MOTM700 page at www.synthtech.com:
"audio demo - chopped up audio switching between 2 waveforms with the cv
as a 250 hz triangle. you can hear the timbre shift as we manually move
the SWITCH control"
with this extra cv in, you could control this timbre shift with an
envelope or an lfo.
2/ with a sequencer - clock the sequencer with a narrow pulse wave lfo
signal, also run pulse wave into MOTM lag processor (fastest attack,
slower decay) run lag proc out into CV in of MOTM700, run cv source (eg
lfo or second row of sequencer knobs) into new switch CV input. 5v into
one i/o socket, 0v into other - result = VC gate time!
3/ vco triangle wave into cv input, lfo or adsr into new input, +5v into
one i/o socket, 0v or -5v into other - result = second (or third, using
both sections of motm700) pwm wave from single VCO!
pretty cool, eh? Any thoughts? Anyone fancy getting to work on this?
please!
best wishes
--
norman fay