The Mutable Instruments Module Tester is a highly recommended tool for anyone doing more than occasional testing or troubleshooting of synth modules. It provides test signals including clocks, gates, CVs, and audio tones, and diagnostics such as frequency measurement. The combination of CVs alternating between two octaves and frequency ratio measured in cents makes calibrating VCOs easy; it’s almost worthwhile just for that.

There are two versions of the PCB, v0.1 and v0.2. The main differences are the former uses a 12 VAC wall wart while the latter uses an easier to obtain 15 VDC wall wart, and the former uses Earthenvar jacks while the latter uses Thonkiconns, which again are easier to get.

MI is out of business and in fact I’m not sure the Module Tester was ever a product, but it is available as an open source design.

Here’s some information on sourcing the parts to build one. Pricing and availability as of July 2023.

Quick and easy and not cheap

AmazingSynth (UK) charges £25 for the v0.2 PCB and pre-flashed AVR, and £30 for the case. The Mouser cart they link adds up to $78 at this writing. (That’s with the Mean Well power converter mentioned on the AmazingSynth page; the Traco specified by MI costs $12 more. Note this cart should not be bought blindly — there are some duplications.) Jacks from Thonk (UK) or SynthCube (US) are about £2. A 15 V power adapter (wall wart) from Jameco goes for about $10.

Total comes to about $160. Shipping would be additional.

SynthCube sells a PCB/AVR for $49, case for $49, or full kit including PCB, case, and all parts for $239. That does not include the wall wart.

Slower and harder and cheaper

These prices can be lowered considerably:


The v0.2 PCB from Pusherman (UK) is £10. Or you can get the board fabbed yourself at low cost. Gerbers do not seem to be available online, but the Eagle design files are in the MI GitHub repo and I have a fork that includes KiCad format versions; you then can use Eagle or KiCad to generate Gerbers.

(AmazingSynth says “beautiful quality gold plated board made in England at our local high end PCB plant…, These PCB’s are produced in accordance with the highest environmental protection standards, our manufacturer goes above and beyond whats required by law to minimise pollution and maximise sustainability, a real pleasure to solder, these are the best synth DIY PCB’s available!” Your money, your choice.)

If you already have an AVR you can get the PCB only from AmazingSynth for £18, but it’s not really much cheaper if you need to buy an AVR.

Modular Addict (US) sells a PCB for $14 but the image is the v0.1 board and the description does not say otherwise.


The AVR is $7.50 from Mouser. You would need a programmer or an Arduino to flash the firmware. Modular Addict lists a flashed AVR for $15 but these are out of stock at this writing.


You can make a case yourself at a lower cost. I used a cigar box.

Components (except AVR)

  • The following parts are not sold by Tayda and might best be bought from Mouser:

    • Mean Well power converter is about $11.
    • MCP4822 DAC is about $4.50.
    • Specified push buttons are about $3 plus about $3.50 for switch caps.
    • 5k trimmer, about $1.50.
    • Resistor network, about $0.40.
    • LM4040, about $1.20.
    • Neutrik phone jack, about $1.00. (Similar jacks are available from Tayda but may not have compatible footprint.)
    • Rotary encoder, about $1.65.

    Above parts may be available cheaper elsewhere, but shipping from multiple sources might eat that up. Total for these is about $28.

  • Jacks are about $2.50 from Thonk or SynthCube.

  • Most of the other parts are available at prices lower than Mouser’s, e.g. from Tayda. For instance the LCD is about $12 at Mouser but about $2.50 at Tayda. Total for these parts from Tayda is about $10. Quality may be lower in some cases. Again, your money, your choice.

Rough minimum price estimate

Item Source Price
PCB Pusherman $13
AVR Mouser $7.50
Case ? $5 depending
Various, see above Mouser $28
Jacks SynthCube $2.50
Other parts Tayda $10
Components (except AVR) total $40.50*
AC adapter Jameco $10
Grand total $76.00

* To be compared with:

  • $78 for the Mouser cart plus $2.50 for jacks.
  • SynthCube charges $141 more for the full kit than for the PCB, AVR, and case, which IMHO is highway robbery.

Shipping additional, again.