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This
module is a dual utility LFO offering manually variable
wave shapes. Standard waveshapes are falling ramp
variable through triangle to rising ramp, and variable
pulse width. A fixed square wave is also available,
as is a combination waveshape that is variable between
the TRI/SAW output and the SQUARE. This is a MIX not
a morph. Two switches allow the variable outputs of
the two LFOs to be intermixed.
The
Utility LFO is based on the standard integrator/schmitt
trigger oscillator core. Two pots in the integrator
charge path allow for the adjustment of speed, and
along with two diodes, for the adjustment of
charge versus discharge time. Changing this ratio
will allow the TRI/SAW output to be adjusted from
a falling ramp through triangle to a rising ramp.
At the same time, the output of the schmitt trigger
will reflect this in the length of its output pulse.
A
0-volt referenced comparator connected to the output
of the integrator generates a square wave as there
is always an equal portion the ramp/triangle wave
above the 0-volt reference, though adjustment of the
shape of the ramp/triangle wave does change the phase
of this square wave.
Following the comparator is a buffered voltage divider
to bring the square wave down to a more suitable level
and also to drive one side of the variable output
mixer pot. The other side of the variable output mixer
pot is connected directly to the integrator output.
The variable output is buffered and used post mixer
by another op-amp.
The
JOIN switch interconnects the two VARI outputs by
swapping their ramp outputs with each other, so that
each output is a combination of that LFO's square
wave with the other's ramp.
The
SWAP switch reverses the outputs of the second LFO
so that (when JOIN is on) one VARI output
is a combination for both square waves while the other
is a combination of both ramps. When JOIN is off,
SWAP merely reverses the direction in which the second
LFO's VARI knob works.
The
Utility LFO has a top frequency of around 29Hz while
at the low end the outputs go through 1 cycle approximately
every 57 seconds (around 0.017Hz)
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