Erica Synths SUPER-SYNCABLE VCO, Manual On Assembly

Page: 1 / 9

GUIDE ON ASSEMBLY OF THE ERICA SYNTHS SUPER-SYNCABLE VCO
If you are reading this, most probably, you are about to build Erica
mechanical construction and doesn’t require wiring. The core of the
VCO is borrowed from Polivoks VCO and in exponential converter we
use the original matched transistor IC that was used in Polivoks synth.
1) we intr-10V regulators for greater stability of operation
and eliminated need for voltage references on opamps,
2) we adjusted signal amplitudes to match requirements of
contemporary modular synths
3) we introduced PWM circuit for greater variety of sound
4) we introduced 7 octave range switch, and the VCO tracks well
over 7 octaves
5) we optimized Pulse width schematics
6) but most importantly – we implemented unique Sync option that
allows to sync the VCO on Rising or Falling edge of Sync in signal.
Sync edge switch allows VCO to be locked to either rising or falling
edge of the input wave. This feature has many uses:
As the input sync wave can be of any character and from any source,
on arbitrary waves one edge may work better then the other.
Even when wave outputs of master and slave oscillator are simply
mixed together, sync lock edge will determine the resulting shape due
synced wave is square or saw, and the master is triangle or sine, edge
cancellation or boosting of the fundamental tone. When oscillators are
multiplied (ring modulated) together, especially with complex waves,
(shifted) parts of waves will get multiplied together.
Furthermore, if sync source wave is a PWM, sync edge setting
determines if synchronized slave VCO will lock to the static or moving
part of the wave. With dynamic pulse width modulation (especially -
the moving part of input PWM.
Same as in Polivoks VCO case, you can build two VCOs – VCO2 with
Detune (+-2 semitones) option and VCO1 with X-Mod (FM on audio
rate) option. In Polivoks synth VCO1 was frequency modulated by VCO2.
A Syncable VCO kit comes in two versions:
1) Set of 2 PCBs + matched transistor IC + mechanical parts
(PCB connectors, spacers and screws) + 2 rotary switches
2) Set of 2 PCBs + matched transistor IC + mechanical parts
(PCB connectors, spacers and screws) + 2 rotary sw panel