Synthrotek Quadrangle - DIY Build

The Synthrotek Quadrangle is a quad cascading triggered envelope generator with bipolar output attenuversion and is 20HP module with a lot of versatility. With 4 cascading envelope generators and user voltage control over attacks and decay/release, this module is in a class all to itself. 

As the fall season slowly began creeping in, we decided to go back and see what kits we had left to build for the year. To our surprise, we totally forgot that we had the mysterious Quadrangle from Synthrotek up on our build wall. This was partially due to the studio remodel and the continuous go go go of daily life. 

The Kit...

When we opened up the kit, the first thing we noticed was the size of the boards. This was a BIG module. 20HP to be exact. It consisted of 2 PCBs and one panel. We ordered the kit with the black panel but Synthrotek also offers a silver panel. As this kit was a big one, we knew we where in good hands with the amount of build data there would be available.

Included in the kit was a printed BOM as well as all the components you need to complete the kit.

Intermediate to advanced builders will not have an issue with this build, whereas novice builders could struggle due to tight soldering pads. 

fin Divider

Resistors and Diodes

Jumping into the build, the first thing we started with were the BAT85 diodes on the logic board. There are a lot of these and the main thing to remember is that their orientation matters.Make sure to line them up with the silk screen and that the black stripe goes where it needs to.

Moving onto resistors, we had our hands full. Take your time here and if you have to test the value of the resistors, do so. We used our component tester many times with this build and we can tell you that we did not regret it. 

Synthrotek did a great job separating everything out in their kit, but since there are so many resistors, things can easily get mixed up. Refer to the BOM and the schematic if you really need assistance. We fortunately didn’t need to and we were able to just match everything up with the visual BOM provided with the kit. 

IMPORTANT: R13 and R14 on the control board are both 100k. 

Synthrotek Quadrangle - Time Lapse Build

Play Video

The IC Sockets (a lot of them)

Next up are the IC sockets. Take care when populating these to not bend any of the legs, and to line up the notch in the end with the same notch that is displayed on the silkscreen. This notch indicates where pin 1 of the IC is. When you have them populated, carefully flip your project over and solder everything in place.

A trick to getting these nice and flat is to solder pins on opposite corners of the socket, and then reflow the solder joints while gently pushing on the top of the socket to seat it flat against the PCB. Then continue to solder the rest of the pins, periodically checking for flatness.

Capacitors and Headers

Now we can populate the ceramic capacitors. These are non polarized, and can be inserted either direction. Once they are in, carefully flip over your project and solder them in place, clipping the excess leads. Electrolytic caps are next and you need to be careful that you match the polarity of the silk when mounting these. There is a small ‘+’ on the PCB that indicates where the longer of the two leads needs to go. Once they are mounted and ready for soldering, the white stripe on the capacitor should be facing away from the ‘+’ on the PCB. Tack everything down when you are 100% positive you have mounted everything correctly. 

The power header and the ISP headers are next. They are quick and easy and its important that you make sure these are mounted flat and not at an angle. The power header has to match the silkscreen or you will fry your module upon powering it up. While you are here, go ahead and tack down the voltage regulator too. Lastly, you will take all of the board to board headers and connect them together (male/female). Flip the main board over and tack the headers down ensuring they are flat. Attach the stand-off screw while you are here as well, making sure that the screw is on top side of the PCB. 

The Quadrangle - Build Gallery

Jacks and LEDs (control board)

The only thing on your control board at this point is the board to board connectors and the 2x resistors that we mentioned earlier (R13 and R14). Start by placing all of the jacks on the control board. We like to tack down the ground pin on the jack so that we can still maneuver the jacks around but we can still flip the board if we need to. After the jacks were mounted, we placed the 4x LEDs. You can decide your color layout however you wish. Just make sure you place the LEDs in the correct orientation as they are polarized.

Pots and switches (control board)

Next up are the switches and the pots. There are 12 pots and 4 switches total. Once they are placed, pop on the front panel and use a couple nuts to hold the panel in place. Flip the module over and tack everything down but the LEDs.

If you want them flush mounted, use a piece of tape and place it over each. We just pushed them all the way through and make sure they were lined up correctly. Solder everything in place when you have the panel on and everything is sitting as it should. Then remove the panel and set it aside.

Features and Specifications


  • 4 Cascading envelope generators
  • Attenuverter’s for each envelope output (dial in that secret sauce!)
  • Attack, Decay/Release and Loop modes per channel
  • Super fast ~2 mS (Audio Rate) envelopes
  • CV over Attack and Decay/Release per channel
  • CV over ALL Attack and ALL Decay/Release
  • Bipolar Voltage SUM output of all envelopes
  • End of Attack & End of Cycle trigger outputs per channel
  • Normalized EOC to next channel Gate input (broken when jack is patched)
  • One Shot or Continuous Looping of all channels


  • Module width: 20HP
  • Module depth: 15mm
  • Current draw:
  • +12V: 64mA
  • -12V: 44mA
  • Comes with power cable, 2.5mm and 3.5mm screws
fin Divider

Synthrotek Quadrangle - Purchasing Options

Synthrotek has a couple different options when it comes to purchasing the Quadrangle module. The prices are excellent and the quality of this build is way worth it! If you are interested in buying the kit or the assembled module, 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!

Quadrangle Assembled
Quadrangle DIY Kit

Wrapping Up The Build

To close out the build, carefully line up the control board and the logic board and screw the standoff screws together to hold the boards in their final place. Insert the IC’s, making sure to line up the notches where they need to be. Refer to the BOM or the silkscreen so that you don’t put the wrong chip in the wrong spot. Pop your panel back on and step back and appreciate your build.

Prior to patching, we always test our builds with our Synthrotek TST module and go through the calibration process ensuring the module is configured the way it should be. Refer to the testing procedures to check each channel, the global stop/loop and the summed outputs. Once this has been completed, you are good to go.

Our Final Thoughts . . .

The Synthrotek Quadrangle is a beast of a module coming in at 20HP. The build is an intermediate build and novice builders should take their time. With its black panel and four colored LEDs, the Quadrangle looks sharp in the rack. Released only a few years ago, we were really glad we found the kit and dove right into the build.

While we haven’t had a lot of time to spend with the module, we know that its a beast thanks to a few other videos out there floating around on the web. In the end, Synthrotek did a hell of a job with this one and we look forward to patching the hell out of this thing. 

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 … 

~ f i N

fin Divider