SYNTHESIS TECHNOLOGY
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19
MOTM-110 ASSEMBLY
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OPERATION
In this section, we will discuss how the MOTM-110 is used in various applications. Of
course, these are only a few things to try. Experiment!
VCA
NORMAL OPERATION
The VCA section is designed for a 0 to +5V control voltage, and a +-5V audio signal. When
the GAIN pot is set to 0, a +5V control voltage sets the VCA to unity gain. This is the
setting most commonly used.
‘BURIED OPERATION’
If the GAIN pot is set in the BIAS region, then it takes more control voltage to achieve
unity gain. If the pot is set fully counter-clockwise, then it takes +10V control voltage for
unity gain. However, note that this is not a SCALED input, (the CV MOD pot is used to
interface to +10 volt envelopes, for example), but an OFFSET adjustment.
Effectively
,
the CV is ‘ignored’ until it reaches the BIAS level, then the VCA acts normally.
Let’s go through an example.
Let’s say you had a +8V envelope signal, and the BIAS was set all the way to maximum.
This corresponds to a -5V offset. So, the +8V envelope would not have any effect on the gain
UNTIL it rose over +5 (-5 bias + (+5V) = 0 volts, which is the point the VCA starts to
operate). The VCA responds to the envelope as long as it stays above +5V. You can think of
bias as ‘clipping’ the bottom off the envelope. When the envelope drops under +5V, the VCA
shuts off. You can get some interesting-sounding tremolos playing with the settings.
‘BACKWARDS OPERATION’
The GAIN pot can be set past the ‘zero volt’ point so that the VCA turns fully on. Now, if
you apply a negative CV (say 0 to -5V) the VCA acts ‘backwards’. It attenuates the signal
as the control voltage goes more negative. Normally, one thinks of a VCA ‘amplifying’ the
signal as the CV goes positive.
The ever astute reader will then realize that if you have 2 MOTM-110s, you can set #1 for a
0 gain, and #2 for a 1 gain. Applying a +-5V peak-to-peak sine wave or triangle wave to
BOTH CV inputs makes a voltage controlled panner!
RING MODULATOR
As stated previously, the main effect of a ring mod is to generate metallic/robotic sounds.
The thing that you must be aware of is something called
carrier suppression
.
Ideally, the ring mod ONLY produces the sum and difference frequencies, and NONE of
the original frequencies. However, this is never the case. Circuit design limitations are
