Erica Synths Polivoks VCO - DIY Build
Erica Synths have been around for awhile and while most of their previous offerings in the modular world were fully built modules, they do have some DIY kits. The Erica Synths Polivoks VCO or Voltage Controlled Oscillator is one of those modules.
The core of this VCO is borrowed from the famous Russian synth Polivoks VCO, and original matched transistor IC is the same of that was used in Polivoks. These two things give this VCO a very well rounded and beefy sound. (We liked it so much we have 2 of these).
The gang over at Synthrotek have made these kits available in all their entirety. They have several options available to purchase (links below), including a fully assembled module if you do not feel like building anything. We opted for the full DIY Kit as usual and began warming up or irons!
The Build
The kit is comprised of 2 PCBS, 1 panel and all the other parts that are required to build the VCO. Erica Synths have stayed with their matte black panel and black PCBs with their DIY line of modules so this one will fit right in with any other module you might own from them. Upon opening up the kit, we suggest separating things out and taking on one “section” or part at a time since there are multiple PCBs. We started with the resistors and diodes first as the resistors generally take up the most time placing.
The kit is comprised of 2 PCBS, 1 panel and all the other parts that are required to build the VCO. Erica Synths have stayed with their matte black panel and black PCBs with their DIY line of modules so this one will fit right in with any other module you might own from them. Upon opening up the kit, we suggest separating things out and taking on one “section” or part at a time since there are multiple PCBs. We started with the resistors and diodes first as the resistors generally take up the most time placing.
Diodes
The diodes are polarized, meaning you do have to mount them a certain way. The stripe on the part has to match the stripe on the PCB. If you are working on both boards at once, simply take your time and pay attention to what goes where. We recommend one board at a time if you are new to building modules.
After placing the diodes in their appropriate place, tack them down either with top down soldering or flip the board to complete the job. Top down soldering is our preferred method until the board becomes overly populated.
Resistors
Next up are the resistors. On the main board, the resistors will mount standing up whereas on the control board, they will mount flush with the PCB. You can place the resistors with any orientation you choose since polarity doesn’t matter with them.
When you complete this step, flip the board over and solder everything into place. The resistors on the logic board can be held in place by using top down soldering on the naked leg of the resistor.
Capacitors
There are a lot of caps in this build and you can rest easy knowing that the ceramic ones can be mounted any way you choose. They do not have polarity like their electrolytic counterparts do. With the electro caps, you will need to match the white line (negative – short leg) with the appropriate place on the PCB. The long leg of the electro cap needs to go through the PCB hole marked with a “+”. Once this is done, flip the board over and tack everything down.
Erica Synths VCO - Time Lapse Build
IC Sockets and Headers
Next up are the capacitors and the IC sockets and headers. 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. The standoff headers are the same. Simply tack one pin down and then heat it up to position. After the part has been set, go ahead and finish the rest of the pins.
Note: Do not place the ICs just yet. These will be mounted at the very last step prior to powering on the module.
Transistors
These parts have very specific mounting orientation. You will notice a flat side and a flat side on the silkscreen on the PCB. When placing these components, you will want to watch for close proximity of their solder pads. Take your time and do not keep the iron on the pad for very long. Transistors are notorious for popping under extreme and continuous heat. Once these are done, it is time to move onto the controls.
Trimmers and Variable Resistors
The trimmers are next up and they are a quick tack down. Make sure you align the screws on top of the part with the silkscreen on the PCB. There will be a couple Bourn type trimmers for fine tuning and several variable trimmer pots to mount as well. After these have been completed, it is time to move onto the control board.
Erica Synths Polivoks VCO - Buiid Gallery
Jacks, Pots and the Large Tuner Pot
There are several pots and jacks to mount on the control board. When you place the jacks, tack the ground pin down prior to moving onto the next. This will allow you to move the jack around when you mount the panel, but it also keeps the part in place as you move onto the other components.
With only a few pots, make sure you place the 10k where they go and the 100k where it goes according to the PCB. After this is done, you will turn your focus to the large tuner pot. This will be mounted to the lower PCB and it will pass through the control board and panel. Make sure you pay attention to the mounting orientation as it is critical to this pot.
Wrapping it all up…
At this point, you are pretty much done building the module. You will want to mount the stand offs prior to placing the panel and tacking down the pots and jacks. Just hand tighten the nuts on the jacks and pots to hold the panel in place when you flip the module over.
Lastly, remove the panel and place the ICs. Make sure to take special care of the KR198NT1A and the other ICs. Any static discharge can fry the IC’s and you will be left with a dead module until you get the replacement chip.
Features and Specifications
Features:
- Triangle, saw and pulse wave outputs
- Manually adjustable and CV controlled pulse width
- Great tracking across 8 octaves
- Exponential FM input with attenuator
- Synchronization input
- Octave switch – 5 octaves
- Skiff-friendly design
Documentation:
- Visual BOM – Click Here
- Assembly documentation – Click Here
- Schematics – Click Here
- Component Placement – Click Here
Specifications:
| Audio output amplitude | 10Vptp |
| Octave range | C0 – C8 |
| Panel width | 12HP |
| Module depth | 35mm |
| Power consumption | 34mA@+12V, 36mA@-12V |
Erica Synths Polivoks VCO - Purchasing Options
Synthrotek offers a several options when it comes to purchasing the Erica Synths Polivoks VCO. 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!
Knobs and Panel Placement
Connect the two PCBs at this point if you haven’t already. Use the 3mm standoff screw and tighten the boards together, making sure their header pins line up. Next, place the panel back onto the module and tighten the nuts to keep everything in place. You can choose to adjust the trimmers according to the BOM if you choose to do so prior to mounting the module in your rack.
We always test our handy work by hooking newly built modules up to our Synthrotek TST module prior to mounting in one of our racks. This just protects our other modules and power system in case we accidentally missed anything while building the module. After this is complete, rack up the module and fire it up. It is time to make some music!
Our Final Thoughts . . .
We thoroughly enjoy building the Erica Synths DIY line of modules, and this one is no different. These modules are challenging for hole-though builds due to their close proximity of components and dense layout. The Polivoks VCO is a beefy oscillator and we like it so much that we have 2 of them in one of our racks. It has the ability to manually adjust PWM and the fact that the module can be tuned across 8 octaves gives it a niche above the rest.
While we get to know this module more and more everyday, we can’t help but thinking that you can never have too many VCOs in your system and the Erica Synths Polivoks VCO is a must have.
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 …
