Synthrotek ADSR - DIY Build

For our latest build, we take on the new Synthrotek ADSR. This ADSR is a small (only 4HP) and simple envelope generator that has a CV additive available in its ADR stages giving it a unique controllability that few ADSR modules have.

It is well known that as one dives deeper into the world of modular synthesis, it becomes apparent that certain types of modules are needed to compose dynamic sound. ADSRs can dynamically change the “movement” of sound due to its ability to alter parts of the sound waves. 

Before we jump into the build, we have to state one thing.An ADSR is a must for any modular artist, and the Synthrotek ADSR is an excellent choice!

What is an ADSR?

By definition, ADSR stands for Attack, Decay, Sustain, Release. It’s a must-know concept for all types of music production and sound design. Together, they make up the ADSR envelope which can alter the shape and sound of audio giving you dynamic music.

This concept of ADSR applies to all sound no matter what kind of source you’re using. ADSR controls are most commonly found on VST synths, hardware synths and samplers. Now, enough with the jargon, lets get on with the latest build… 

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Synthrotek ADSR ... The Kit...

Synthrotek does a great job of providing clear and concise documentation for their kits. The ADSR documentation is no different.

Documentation is not only included in the package, but it is available on their website. (We have placed some quick links below to speed that process up if you are in search of them). 

The kit has all of the components clearly separated, almost to perfection which makes building one of these kits a little easier. This build would be considered intermediate in nature and this goes without saying that one needs to have a clear understanding of how to interpret a BOM prior to jumping right into the build. 

Synthrotek ADSR - Time Lapse Build

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Let’s start with resistors and diodes…

Diodes are polarized, so it matters which way they are mounted. Make sure the black stripe on the diode lines up with the silk screen on the PCB. Messing this up will cause module failure.

One cool thing about resistors is that they are not polarized and they can be mounted either way you wish. When it came to soldering parts into place, a top down soldering method was used on both the diodes and the resistors.

Crystal and Voltage Regulator

The crystal is non-polarized just like the resistors. Feel free to mount this in whatever direction you choose. 

Voltage regulators on the other hand are polarized and its VERY important that you mount these according to the silk screen. Once you get these parts mounted, flip the PCB over and tack everything down.

Capacitors, IC sockets and Power Headers…

The ceramic capacitors and electrolytic capacitors are two totally different beasts. Ceramic are like resistors, you can place them in whatever direction you would choose according to the BOM.

Electrolytic capacitors are polarized like the voltage regulators we just mentioned. (Make sure that the long leg goes into the square hole). 

Power headers are the shrouded versions which are included in the Synthrotek kit. Both the header and the IC are flush mount, so it is recommended to place some solder into one of the sockets mounting holes. Once this is done, you can gently (let gravity work) push on the component while heating the solder and the part will click into place. This allows the part to be held in place as you flip the board over and finish tacking everything down.  

Note: DO NOT place the ICs yet!

The Completed ADSR Module

The Control Board…

Now that the logic board is done, let’s move on to the control board. You will start with the right angle headers that connect the two boards together. When these are inserted, align the ‘right angle’ pins with the indication on the silkscreen. Do not solder them directly to the board, or the two boards will not fit together properly.

(Trust us when we say this, it will make for some VERY difficult board mating if you mess this part up).

Just like the IC sockets and the power header, solder 1 pin of each header before soldering everything into place. Once one pin on each soldered, hold the board up, and make sure that everything is straight. If everything looks good, go ahead and solder the remaining pins. 

Completing the control board…

After completing the control board headers, clip the tips so the sliders can be mounted on the other side of the control board. We do recommend reflowing the solder after clipping the joints. (This just makes the build look better and it ensures a good solid connection). 

Populate all of the front panel components next, making sure that everything is sitting nice and flat, but DO NOT SOLDER ANYTHING YET.

Also, don’t forget to place the 10mm hex standoff onto the board. Hold a screw up through the hole from the bottom, and twist the standoff down onto it until it is fully seated on the PCB. (Got that done!)

Wrapping up the Synthrotek ADSR module..

After all of the control board components have been set, grab the panel and line everything up. Hand tighten the nuts onto the jacks to help hold the panel in place. You can also use the black hex screw and tighten down the stand-off. This will give a little more rigidity to the non-soldered parts. When everything is lined up and solid, flip that board over and tack everything down. 

Two boards become one…

Now the fun part… you get to mate the logic board to the control board. Gently align the right angle headers from the control board assembly so that they fit into the holes on the logic board.

Solder just one leg on each like you did with the power header/socket. Next, make sure that the spacing (gap) between the two boards is the same all the way down the board and ensure the logic board is as close to a 90 degree angle as possible.

Once you are sure that everything is straight and even, solder the remaining pins on the headers.

One last thing ...

Now that the boards have been mated and all of your parts have been soldered into place, take some time to double check your joints. Correct anything that needs to be reflowed and grab the x3 IC chips that came with the Synthrotek ADSR. Match the dots or indents on the IC’s with the silk screen/IC layout on the PCB. If these are turned around, you will have a broken module. 

After completing IC’s, we tested our ADSR power by plugging it into our Synthrotek TST module to ensure we had good power and no shorts. (btw.. you don’t want to see or smell smoke here!!). If everything tests out ok, mount the ADSR into your case and then you can run through the above linked calibration test. 

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Features and Specifications


Stage Lengths:

    • Attack: 4ms-2 seconds (up to ~ 4 seconds with CV)
    • Decay: 4ms-2 seconds (up to ~ 4 seconds with CV)
    • Sustain (based on gate length)
    • Release 4ms-2 seconds (up to ~ 4 seconds with CV)
  • CV over ADR and Release
  • Exponential or Linear Curves
  • Self-cycling

Current Draw:

  • 30mA @ +12v
  • n/a @ -12v
  • n/a @ +5v


  • Module Height: 3U
  • Module Width: 4HP
  • Depth: 40mm
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Synthrotek ADSR - Purchasing Options

Synthrotek has a couple different options when it comes to purchasing the ADSR module. The 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!

Assembled Module
Panel/PCB/IC Combo
White Synthrotek Logo

Synthrotek ADSR - Documentation

Our Final Thoughts . . .

As you finish up the build, testing and calibration, one has to admire the aesthetics of the Synthrotek ADSR module. The sliders are illuminated and give the looks of the module a nice ambience.

Little does this 4HP module know how much chaos it will bring. Its future is bright and its ability to manipulate sound is uncanny. By mastering what an ADSR can do, you can open up a whole new world of audio possibilities. 

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

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