The Soundtronics MIDI Ultimate Synth

Soundtronics Midi Ultimate
(Last Updated On: 07/12/2020)

The MIDI Ultimate project is a fully-featured analogue synth with a performance comparable to many commercially available instruments. The Kit is available on The MIDI Ultimate is an evolution of the (MFOS) Sound Lab Ultimate design by the late Ray Wilson who is credited for much of the design which has been reproduced with kind permission of in the US.

Synth Features

  • Three Musically Accurate Voltage Controller Oscillators (VCOs) with sawtooth and variable width pulse wave forms, pulse width modulation, hard-sync, log CV inputs.
  • Voltage Controlled Low Pass Filter (VCF) 12db/Oct doubles as a sine wave oscillator
  • Voltage Controlled Amplifier (VCA)with log response
  • White Noise Generator
  • Active 8 Channel Mixer for all VCO waveforms, noise and external input
  • Two Attack, Decay, Sustain & Release Envelope Generators (ADSR)
  • Two Low Frequency Oscillators (LFO) with square, ramp, triangle and sawtooth waveforms
  • Repeat Gate Generator that can also double as another square wave LFO)
  • Sample & Hold (S&H) with variable sample rate and glide
  • Toggle Switch Patching with potentiometer mixing
  • Echo Effect Sound Processor
  • MIDI to CV Interface with 1-16 channel selector switch, responds to all 128 MIDI note keys
  • Headphones and Line output
  • Integral +/- 12Vdc Power supply Regulator (needs external 12Vac 500mA plug top adaptor)
  • DIY Construction with through hole components
  • Single board design with PCB mounted pots and switches eliminates panel wiring

Let’s get started with the Soundtronics Midi Ultimate

When I received the Midi Ultimate kit, all “modules” of the synth have been packed in separate plastic bags. You can solder the parts either over the whole PCB, starting with the resistors or you can proceed by “module” for “module”.

How to start

Start with the PSU, VCOs, VCF and Mixer.

There are six issues of the EPE – Everyday Practical Electronics which can be ordered as PDF for download. I highly recommend to invest this money and order the issues from Feb 2019 until Jul 2019, each for 2.00 GBP.

Start by soldering the resistors for the VCO sections (R1xx, R2xx, R3xx), in batches of the same value, noting that each VCO section is laid out very similar to each other. For example, once you have found the location for R108 in VCO1, you will find R208 and R308 in a similar position in the VCO2 and VCO3 sections. Do not solder in R103, R203 and R303 at this time! Fort the pots and switches, your require the front panel to ensure that they are all aligned before soldering them on the PCV. I’m skipping this step for now, since I’m waiting for the front panel to arrive.


Don’t make the same mistake I did. Be aware that there are two different voltage regulators. The L7812CV +12V and the LT7912CV – 12V. I soldered them in the wrong order and it got messed up when I tried to de-solder them.

VCF and Mixer

Continue with the resistors for the VCF and the mixer, followed by the remaining components as described in the general tips section above. The matched transistor pairs Q101/Q102, Q201/Q202 and Q301/Q302 each require tempco resistors R103, R203 and R303 sandwiched in-between them.Applying some heatsink compound between the transistors. For the MIDI Ultimate, form the transistor leads so each transistor is in contact with the tempco resistor and a little heatsink compound will not do any harm. The polystyrene capacitors (C105/C205/C305) can be laid over. After finishing above including the pots and switches, the article in the EPE magazine describes how to test the current build.

VCA, Echo, Noise and headphone amplifier

Continue with the VCA, Echo, noise and headphone amplifier sections. There are relatively few components for the white noise generator, but ensure to cut off the collector lead from transistor Q1 

Midi Ultimate Synth
Cut off the collector lead from transistor Q1

After the soldering of all components on the PCB and connecting all cables, I made a special version of the DCASE for the Soundtronics Midi Ultimate incl. a case for the power supply which is now located on the back of the synth.

The raw DCASE for the MIDI Ultimate
The tilt mechanism for the MIDI ultimate in action

The Midi Ultimate in a special version of the DCASE

The Midi Ultimate “Modules”

All in all it was neither an easy kit nor a super difficult one. If you want to build this synth, take your time with the soldering and check everything at least two times. The support from Soundtronics was very helpful and responded fast. If you are also crazy for analogue synthesiser and know how to solder, get a kit and build it. I think it’s much better than the original MFOS Ultimate with all the required wiring for the pots. The build-in effect processor and the MIDI functionality are a great addition to the package.

Sound Demo

5 Replies on

The Soundtronics MIDI Ultimate Synth

  • Hi. Great review and demo. Just finished my build and was wondering if your oscillators were a bit “wandery”? Mine stray randomly around 1%. Also, how does this compare to the TTSH? Thanks for any reply.

    1. Hi Stephen. I remember that I had some issues when I finished my build. Check all soldering points. I had a cold joint which caused the issue. Hmm – compared to the TTSH? Difficult to give an objective opinion. I just finished my TTSH Setup with 1601 clone and a DIY Keyboard with a small Eurorack section. This is now the center of my playground. It sounds, looks and feels fantastic and is extreme flexible. However, the midi ultimate has two fully free assignable ADSR envelops and two LFOs plus the delay effect section. Both synths sound really good. Really hard to judge

      1. Thank you Torsten. I watched your TTSH demo and was very taken with the sounds. Very spacey but organic at the same time. Both synths seem not too different, so what, if anything would you say gives the TTSH that special quality? Filter? Reverb?

      2. The filter and reverb are indeed very nice. But I love the user interface with the faders and the flexibility of the instrument. In combination with the 1601 and my DIY Keyboard it’s an extremly powerful tool which I just started to discover. I’m just recording a first video what I will most likely post later today together with a short story of my DIY Keyboard. …more videos to come 🙂 …

  • Hi Torsten, still debugging my build. The wandering VCOs have been improved, with help from the guys at MW. Let me know if you want details. Another issue has come to my notice, and I was wondering if you have a similar issue. When I tune one osc close to the same frequency as another, the frequency of one will snap to the same as the other, so I can’t get a nice detuned effect. Did you notice this, or could you try and replicate it on your machine and let me know what happens? Thanks and a very happy new year. Stephen

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