More Phase Locked Loop Fun
Scott Gravenhorst, Synthaholic
chordman at ix.netcom.com
Thu Mar 14 01:54:12 CET 1996
Several months ago, I posted a schematic for my Phase Locked Loop
Harmonic Generator. It uses a 4046 type PLL and generates 7 signals on
perfect 5ths and octaves of the input signal. It has some pretty cool
sound capabilities by itself, but it occured to me about 30 minutes ago
to try something. I injected an LFO signal into the loop's VCO input
and lo and behold, I got a wonderful phasing effect from it! My
reasoning was that the PLL VCO input is normally driven by the phase
comparator output thru a lowpass filter. This filter limits the slew
rate as well as delays the phase comparator output. By injecting an
LFO signal directly into the VCO input (mixing with the filter output),
the VCO output is pushed off frequency, plus and minus, in time with
the LFO, but the center frequency still tracks the main input
frequency. When the VCO output (or one of the divider taps) is mixed
with the original input signal, there is an ever changing phase
displacement that has the characteristic phasing sound.
Due to the bandwidth I might waste, I will not repost the schematic,
but it is available on request to any interested person.
-- Scott G., Synthaholic
There is no 12 step program for synthaholics. Thank your Superior Being.
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