Synthrotek MIXIV - Eurorack Modular DIY

MIXIV Completed Front

As February came around, we were pondering Eurorack mixing and how to achieve the best possible mix of either CV (control voltage) or audio. We had always used mixers outside of the racks, but we wanted something more portable.

The gang over at Synthrotek had just the released their first SMD module and it was right up our alley. The 4HP MIXIV by Synthrotek is in its simplest form is DC coupled and can mix audio and CV signals with the quick slider of a knob.

Prior to the MIXIV (pronounced Mix 4) build, we wanted to get the close up view and picked up a digital microscope in order to “see” what we were doing more precisely. This also gave us the chance to record some sweet videos to post in our time lapse build. You can check it out down below.

SMD? ... What is that?

If you recall from one of our previous builds  SMD is otherwise known as Surface Mount Devices or SMT (Surface Mount Technology). These types of builds differ from the normal “hole-through” components in that their chips, resistors, caps, etc are all very, very small and they mount to the surface of the PCB. You can use soldering irons, heat guns, solder, solder paste, etc to complete the builds. How you go about it is very much up to the preference of the builder.

It is recommended that you be a more experienced DIY’er prior to just jumping into SMD soldering, as it can make or break a module if you do it incorrectly. The small components sometimes seemingly have a mind of their own and can be easily lost if you grab them with tweezers the wrong way.

Time Lapse and Build Notes

Play Video

As you can see from the build, we used both methods of heat and solder, meaning we used a heat gun with solder paste and our trusty ol soldering iron and solder wire. Tweezers are an essential to any SMD build and we recommend that you have more than one pair to work with. A very fine point is required when working with SMD and a steady hand is crucial when mounting the components. You can see from the video, the brown rusty gel (aka FLUX) gets burned off and pre-tinning the pads on the PCB allows for one to practice the tin and tack method. This method is easily described as placing a blob of solder on one pad, then holding the component with the tweezers forcefully against the blog, heating it up and allowing it to tack into place…. ie… tin and tack. 

For the IC part of the build, we used solder past and flux. After placing the chip, we ran the soldering iron across the pads in a quick like motion. The solder paste hardens and draws the chip into the correct place with the ease of flux. You defiantly do not want any solder bridges with ICs, and in our case … we were good to go.

After completing all of the caps, resistors, diodes and IC, we moved onto the rest of the board. This was the sliders, power header and jack mounting. In the video, you can see how we cut the back of the power header solder points so that the slider can sit flush with the panel. These clipped right off and we moved onto the panel mounting. Upon completing the jacks and sliders, we double checked solder points and called it done.

We took the module over to our Synthrotek TST module to ensure that there were no shorts or anything awol about the build. It powered right on and was ready to go. What about that excess flux goop that covering the board?…  Well, it was cleaning time! This was accomplished by using isopropanol alcohol and water mixture that we keep in the shop. A quick dry with a microfiber cloth, a day sit and we were good to go.

The MIXIV by Synthrotek is the perfect addition to our case and it allows for Channels 1 & 2 can have their own output when a cable is patched in to the sub-output jack. When the left-hand OUT jack is not patched, all channels come out of the right-hand OUT jack. This is something we needed for sure. (who can’t have enough mixers?)

Features & Specifications


  • Mixes audio and CV signals (DC coupled)
  • Mixes four channels together (4:1), or mixes two sets of two channels (2x 2:1)
  • Dope faders

Specs and Power Consumption

Width: 4HP
Height: 3U
Depth: 26mm

Current Draw:
   +12V: 15mA
   -12V: 10mA

Purchasing Information

Panel and PCB Combo

  • Black Panel 
  • Green Dual Sided PCB
  • A rad sticker included!
  • List Price: $19.99 USD
  • Click on the image to be redirected to the Synthrotek Store Page


  • Includes all components, PCB and Panel for assembly
  • A rad sticker included!
  • List Price: $45.00 USD
  • Click on image to be redirected to the Synthrotek Store Page

Assembled MIXIV Module

  • Fully assembled and calibrated 
  • A rad sticker included!
  • List Price: $69.99 USD
  • Click on image to be redirected to the Synthrotek Store Page

Synthrotek MIXIV - The Final Word

The slider series from Synthrotek has recently become a heavy hitter in our racks. The MIXIV is right up there with quality and ease of use. The light up LEDs on the sliders not only gives the module its unique look, it provides ambiance to the module. Combine this with other modules in the slider series and you have a pretty badass looking rack. 

As for the build itself, if you are an intermediate or more experienced builder, this is a quick and easy build. If you are a novice builder or diving into SMD soldering for the first time, you might want to pick up a practice pad before jumping right into the build. Synthrotek provides a visual BOM with their modules and assembly instructions are easily accessible on their website. 

 Final words… pick this one up if you have a spare 4HP, this is a solid mixer for any rack. Top notch Synthrotek … top notch. 

Until the next build … 

~ f i N

MIXIV Testing