Synthrotek RND - DIY Build

The Synthrotek RND (Random) is a 4HP random voltage generator that is part of the slider series from Synthrotek. With its ambient LED sliders and black panel, the module is a perfect fit for anyone trying to toss a little spice into their tracks. 

RND carries its own internal clock or it can be patched by an external clock, giving the user a varying degree of control with regard to tempo. Apart from this, it also has a CV (control voltage) of the clock, so that your random voltages will always be in sync with whatever you patch into it. 

Sounds cool huh? We thought so too and now let’s get on with the build. 

Let's start with the logic board...

Like the other modules in the slider series, the Synthrotek RND is a relatively quick and easy build thanks to the detailed assembly instructions that are provided via the Synthrotek website. As we jump into the build, we start with the diodes and resistors. Since there are only a few of each, we placed everything prior to tacking it down.

We did use top down soldering on all of the resistors and diodes since there was plenty of room to get your iron into the soldering points. Once this was complete, we flipped the PCB over and trimmed the leads. This is a good spot to double check the flow of solder and reflow anything that needs it. 

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Logic Board - Diodes and Capacitors

Following the resistors and caps were the IC sockets and the capacitors. The IC socket has to mount matching the silkscreen on the PCB, whereas the capacitors can go either direction. Do not place the IC’s yet, just the sockets. A trick to getting these nice and flat is to only solder one or two pins of each socket, and then reflow the solder joint while gently pushing on the top of the socket to seat it flat against the PCB. 

Lastly, the electrolytic capacitor is polarized. Ensure that the longer leg (the leg that is further from the stripe indicator on the body) goes through the solder pad with the little ‘+’ symbol next to it. Once placed, tack it down. 

Synthrotek RND - Time Lapse Build

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Logic Board - ICs and Transistors

Transistors and the regulator are all polarized, so make sure you mount them according to the PCB. It is very common to mix these components up and its very easy to do. Make sure you double check the number on the side of the part to ensure you are placing the correct part in the correct place. 

Headers… all sorts of headers...

There are multiple types of headers that came with the kit. The 10 pin power header and the ICSP header. If you are going to re-program the RND at a later date, or sourced your own parts and need to program the module after building, you will need to populate the ICSP header and solder it in place. If you purchased a pre-made kit from Synthrotek or one of their distributors, you don’t need this header.

The 10 pin power header is next up. Make sure that when you are populating this that the notch in the header is lined up with the notch designation on the silkscreen. (it’s on the side closest to the edge of the PCB). When you have it oriented correctly, carefully flip the RND over and solder it in place.

Control Board - More Headers...

The last set of headers that come with the Synthrotek RND are the right angled headers that will be used to connect the logic board to the control board. When you place these, the side of the header without the bend in it goes through the control board. The black plastic stopper should be resting against the board. Flip the control board over and tack down one of the middle pins to hold everything in place. 

Once everything is flush to the control board, solder down the rest of the pins and then flip the control board over. Now, clip the pins as flush as you can so that the slider pots will not be affected when they are mounted. 

Here come the sliders….

Next up are the slide potentiometers. These will only fit in the PCB one way, but the legs can get a little bent during shipping or general handling, so take your time and make sure they all get fitted properly into their respective solder pads.

Start by soldering just one leg on each side (top and bottom) of the slide potentiometer. Then, while gently applying pressure, reheat the solder joint to fully seat the potentiometer against the PCB. This will ensure they are all the same height after the front panel is assembled.

Once you are happy with how they are sitting, finish soldering the rest of the legs.

Completing the control board…

The jacks are next up on the list and they go relatively fast. Tack down the ground pins and don’t be afraid if they touch when tacking them down (their grounds), but do not solder the rest of the pins until we line up the panel. After placing the jacks, grab the lonesome switch and place it on the pcb. 

Pop on the panel to the Synthrotek RND and hand tighten the nuts on the jacks making sure everything lines up where it should. Once everything is lined up, flip over the control board and tack down the rest of the remaining components. (Don’t forget about the standoff as well. This needs to be installed at the top of the panel/control board PCB). We used our Synth DIY tool set to tighten down the jacks at this point in the build. 

Wrapping it all up…

The last two steps are quick and easy. When you mate the boards together, take your time. You might need to push on a pin to line things up and when doing this, use very little pressure as you don’t want to permanently bend the pins. Once everything lines up, solder the pins on the opposite side of the logic board. Then, clip the extra pin length on the back of the board so that they will not be tempted to touch anything else in your case.

It’s now time to pop in the IC’s and test the module. Make sure that you place the ICs in the correct orientation. This is crucial and it could be detrimental to your module should you mess this up and mount them the incorrect way. A quick test in our TST module (by Synthrotek) and we were good to go. We mounted up the module and began patching.

The Completed RND Module

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Features and Specifications


  • Clock Speeds With NO CV:
    • Slow Range: 0.5Hz to 2.7Hz
    • Medium Range: 1Hz to 10.8Hz
    • Fast Range: 8.3Hz to 86.7Hz
  • Clock Speed Range with CV Input (sliders all the way up):
    • Slow: 2.7Hz to 5.1Hz
    • Medium: 10.8Hz to 20.5Hz
    • Fast: 86.7Hz to 164.4Hz
  • Linear CV control over clock speed and range.
  • Over and Under voltage protection on CV inputs.
  • Keyed Power Header.
  • Reverse Polarity Protection

Current Draw:

  • 16mA @ +12v
  • 0mA @ -12v
  • 0mA @ +5v


  • Module Height: 3U
  • Module Width: 4HP
  • Depth: 40.3mm (1.58in)
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Synthrotek RND - Purchasing Options

Synthrotek has a couple different options when it comes to purchasing the RND module. We wanted to keep it simple by just placing images of the options and linking out to the direct purchase. The prices are excellent and the quality of this build is way worth it! Head on over to SR and tell them we sent ya!

Assembled Module
Panel/PCB/IC Combo
White Synthrotek Logo

Synthrotek RND - Documentation

Our Final Thoughts . . .

As we were building this module, we thought to ourselves “did we really need another clock or random module?”.  Once we build was complete and we patched the module, we thought to ourselves “we might need another one of these kick ass RND modules” and “damn, those sliders look great”.

Random modules are fun for many reasons and the Synthrotek RND not only looks great, but it has a small footprint (it only takes up only 4HP). The clear BOM and assembly instructions make this build a relatively easy one and we would recommend it to beginner or intermediate builders. Do yourself a favor, go pick up the Synthrotek RND and tell them we sent ya!

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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