02.05.2019

A fully-featured analogue synth based on the MFOS Sound Lab Ultimate Design

The MIDI Ultimate project is a fully-featured analogue synth with a performance comparable to many commercially available instruments. The Kit is available on www.soundtronics.co.uk The MIDI Ultimate is an evolution of the musicfromouterspace.com (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 Synthcube.com 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".

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.

PSU

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.

Matched transistor pairs Q101/Q102, Q201/Q202 and Q301/Q302 with tempco resistor in-between

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

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.

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.

https://www.soundtronics.co.uk