Erica Synths Dual VCA II - DIY Build
On with the build....
Fresh off the build table comes Erica Synths Dual VCA II. The module itself is apart of the open source DIY kits that are available via the Erica Synths Github.
Our friends over at Synthrotek have painstakingly taken it upon themselves to part out these kits and package them up to make them accessible by all DIY enthusiasts. VCA’s or voltage controlled amplifiers are modules that every rack contains.
This module is a Polivoks-inspired VCA that is 35mm deep, skiff friendly, has solid mechanical construction and doesn’t require wiring. Who could pass this one up? We couldn’t!
In the end, the Erica Synths Dual VCA II is like all other kits in that the BOM is comprised of the basics … resistors, diodes, capacitors, pots and jacks. There might be a few other surprise components in there, but all in all, these are what make up the kit.
Start by laying out all of the components and the x3 boards. This kit contains a control board and a logic board so you will be going back and forth between the two boards when placing components. Resistors, diodes and ferrite beads are first up.
Diodes have polarity so prior to tacking these down, you have to make sure they are placed in the correct orientation. We used top down soldering to make quick work of these.
Note: There are a couple of resistor spots that are not used, as well as two that use a resistor leg to connect the two solder holes. (R22 and R23). You might see a couple of spaces marked “NU” as well. Leave these unpopulated as they are not needed for the build.
IC Sockets, Caps and more…
Next up are the capacitors and the IC sockets. The IC sockets can be set by placing a dab of solder on one of the mounting holes. Line up the socket and heat up the underside of the solder while gently pushing the socket down. If done correctly, you will hear a click and it will be set into its final resting spot. Flip the board over and tack everything else down making sure that the orientation of the socket matches the silk screen on the PCB.
Erica Synths Output - Time Lapse Build
As for caps, the small yellow ceramic ones do not have a polarity; you can place them in any orientation you would like. Careful not to push them down too far as the coating on the part can hinder the connection of solder to pad.
When you get to the resettable fuse, it will be placed on the backside of the logic board. You will also install a few electrolytic caps on the back of this board as well. They (electro caps) have to be bent so that the two PCBs can sit on top of each other without interfering.
Be careful placing these as their orientation does matter. There are few on the front side of the logic board as well so don’t forget these.
Transistors and trimpots…
The top of the control board houses 4 trimpots for tuning the VCA. Place these parts in their appropriate location, flip the board over and tack everything down. Next, solder the 1×8 headers (there are both male and female are in this kit).
Make sure that you place the female headers on the rear of the logic board and upon soldering the male headers, use the female ones to line them up. It is now okay to Install the standoff screw and the ICs at this point in the build.
Erica Synths Dual VCA II - Completed Module
Pots, Jacks and a single switch...
Finally, grab the control board and install the pots, switch and jacks. Do not solder anything until you have mounted the panel and made sure that everything lines up. If it does, install the set screw and complete the soldering of the knob, switch and jacks. Set the single black knob on the pot and it’s time to test that module. (We recommend testing the module’s power by plugging it into a Synthrotek TST module).
If everything has been tacked down and you have 0 shorts, pat yourself on the back because you have just completed the build of the Erica Synths Dual VCA II DIY kit. its time to place the knob and calibrate the module, which is pretty easy.
Calibration...
1. Switch MODE to DUAL.
2. Turn the CV1 LEVEL potentiometer to 3 o’clock
3. Connect 10Vptp (-5V to +5V) saw wave to IN1!
4. Patch 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. Attach a patch cable from 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. Input a 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. Patch the envelope to CV2 IN and adjust R19 to to find the point where audio is suspended.
8. Calibration complete!
Features and Specifications
Features:
- Single or Dual VCA mode
- CV level adjustment for each VCA
- Summed audio output (lower signal gain, though)
Skiff-friendly design
Documentation:
- Visual BOM – Click Here
- Assembly documentation – Click Here
- Schematics – Click Here
- Component Placement – Click Here
Specifications:
- VCA Gain – 1, 2
- CV Level: -10V…+10V
- Attenuation @0V CV: 80dB
- Width: 8HP
- Depth: 35mm
- Current draw:
- +12V: 24mA
- -12V: 18mA
Erica Synths Dual VCA II- Purchasing Options
Synthrotek offers a several options when it comes to purchasing the Erica Synths Dual VCA II. Their prices are excellent and the quality of this build is way worth it! If you are interested in buying the kit, the assembled module or just the PCB/Panel/IC, click on the images below and you will be redirected to their site to purchase! Make sure and tell the gang at SR that we sent you!
Our Final Thoughts . . .
As we completed this build, we were reminded that one can never have enough VCAs in ones rack. The Erica Synths Dual VCA II is a solid contender in the world of VCAs due to its relation to the original Polivoks VCA.
The modules esthetics are on point with the full line of DIY kits by Erica Synths as it sports a matte black panel and a singular knob. It is complex in its simplicity to say the least and is an amazing Polivoks-esque reissue VCA. Can we get another please?
Comments or Suggestions?
If you have questions about the build process or suggestions/feedback about this article, feel free to let us know by contacting us We look forward to hearing from you!
Until the next build …
