Erica Synths POLIVOKS-INSPIRED VCA User manual

GUIDE TO ASSEMBLY OF ERICA SYNTHS POLIVOKS-INSPIRED VCA
If you are reading this, most probably, you are about to build Erica
Synths DIY Polivoks-inspired VCA. This module is 35mm deep, skiff
friendly, has solid mechanical construction and doesn’t require
wiring. The Polivoks VCA has distinctive architecture –two
differential opamp (Russian ICs K118UD1B) based VCAs in series
each for LFO and ADSR control over signal amplitude
independently. Control voltage to attenuation behavior of this VCA
is nonlinear and not logarithmic. It is kept authentic to the
response of ПОЛИВОКС, and it uses same differential opamps, as
used in the original ПОЛИВОКС. Most parts of the VCA have been
improved to achieve compatibility with eurorack signal and CV
standards, higher dynamic range, better reliability, lower noise,
accept higher signal levels, keep consistent behaviour, self-tuning
of two internal offsets and higher linearity, though the heart of it is
kept the same. Also we redesigned audio signal path, so that you
can use it as two independent VCAs or two VCAs in series as in
original Polivoks, plus summed signal output.
The DIY Envelope kit comes in three versions:
1) 2PCBs + 2xK188UD1 ICs + connectors,
2) 2PCBs + 2xK188UD1 ICs + connectors + panel,
3) Full kit.
FEATURES:
•Single or Dual VCA mode
•CV level adjustment for each VCA
•Summed audio output (lower signal gain, though)
•Skiff-friendly design
SPECIFICATIONS:
•VCA gain 1,2
•CV level -10V…+10V
•Attenuation@0V CV 80dB
•Panel width 8HP
•Module depth 35mm
•Power consumption 24mA@+12V, 18mA@-12V
1
3
4
2
5
6
1
2
3
4
5
6
Adjust CV attenuation level for the first VCA! It
also sets VCA bias. If you use VCAs in series and
no CV is applied to CV1 IN, you must turn CV1
LEVEL knob all way CW to open the first stage.
Switch between single or dual VCA modes.
These are CV inputs.
These are audio signal inputs.
These are audio outputs. On MIX OUT you get
mixed signal from both VCAs in dual mode. It’s
bonus feature, but signal level will be than on
regular outputs.
Adjust CV attenuation level for the second
VCA! It also sets VCA bias.

Take precautions with regard to electrostatic discharge (ESD) safety. Handling components should be done
in electrostatically safe environment. Use personal and workplace grounding. Any discharge (even a minor
one) from body to a component may permanently damage it.
Our PCBs have silkscreened both component values and designators nevertheless we highly recommend
you to print out files with component placement before you start assembly of the module. And, please, at
least take a look on this manual!
Some components are marked as NU (not used) –leave those unpopulated! Some components are market
as OPTION (those are for optional modifications) –leave those unpopulated for now.
ASSEMBLY
1Solder horizontally placed resistors and diodes on both PCBs (Controls board and Main board)! Pay attention on
orientation of diodes! Use wire jumpers for 0ohm resistors on the main board.
2Solder IC sockets on the Main board, ferrite beads on the Control board and capacitors of both boards!
Controls board
Main board
GUIDE TO ASSEMBLY OF ERICA SYNTHS POLIVOKS-INSPIRED VCA

3Solder electrolytic capacitors, transistor and
trimpots on the Main board! Mind polarity of
electrolytic capacitors and orientation of transistor!
Also solder 1x8 male connectors!
5Install the front panel
4Turn the Main board around and solder resettable
fuses, 10V voltage regulator and electrolytic
capacitors! Electrolytic capacitors should be placed
horizontally! Bend resettable fuses down.
6
GUIDE TO ASSEMBLY OF ERICA SYNTHS POLIVOKS-INSPIRED VCA
Negative lug of
electrolytic
capacitor is marked
with a stripe!
Also solder 1x8
female connectors
and PSU connector!
Use M3x6 screw to
fix 11mm spacer.
Connect the PSU and
do some control
measurements!
Make sure, you have
+12V and -12V on
capacitors C3 and C4
and +10V on
capacitor C17!
Connect both boards together (white lines on
both PCBs have to match) and fix them with
M3x6 screw!
6Install potentiometers knobs and –congratulations –you have completed building Erica Synths DIY
Polivoks-inspired VCA!

CALIBRATION
Calibration is easy. The best way is to do it with oscilloscope, but you can calibrate modules on ear, as well.
1. Set MODE switch to DUAL.
2. Set CV1 LEVEL potentiometer to 3 o’clock
3. Connect 10Vptp (-5V to +5V) saw wave to IN1!
4. Connect OUT1 to oscilloscope or amplifier! Adjust trimpot R20 until you get 10Vptp signal on OUT1. If
you do not have an oscilloscope, just try to set equal volume of incoming and outgoing signal.
5. Activate and envelope generator (0 to +10V envelope) ; make sure, release is not too long, and
envelope falls back to 0V. Connect the envelope generator to CV1 IN! Adjust trimpot R18 to find a
point, where VCA closes down completely –when envelope level is 0V audio signal is not present on
the output.
6. Same goes with IN2 and OUT2. Connect 10Vptp (-5V to +5V) saw wave to IN2, set CV2 LEVEL knob to 3
o’clock and adjust trimpot R21 to have 10Vptp sawtooth wave on the OUT2.
7. Connect the envelope to CV2 IN and adjust R19 to to find the point where audio is suspended.
8. Calibration complete!
GUIDE TO ASSEMBLY OF ERICA SYNTHS POLIVOKS-INSPIRED VCA