Digisound 80 Modular Synthesiser

The Digisound 80 modular synthesiser sprang to life in 1980. Various modules were released afterwards in the magazines Electronics Today International and Electronics and Music Maker. Charles Blakey was the designer and you could get the kits from his company Digisound who were based near to Blackpool. A lot of the modules were based yet again on the Curtis Electromusic integrated circuits and the modules were very carefully and nicely designed, to be honest they gave you everything you could possibly want from a modular synthesiser, just about every option and control you could ever want was there on the panel and just about any module you could imagine was available and then some more that you hadn’t even thought about! They are also still being used today more than thirty years after most of the modules were assembled. They also conformed to the 1 volt per octave standard so interfacing with other gear was straight forward.

If you wanted to take synthesis to the next level on a budget this was the system for you. I have also spoken to quite a few people who built them and they all tell me how by building them themselves they knew how they worked and while they waited for the money to build more modules they were able to fully explore almost all of the options and interfacing options and were able to experiment much more than if they had just bought a complete system out right.

The modules comprised of the

The 80-1A Power Supply which powered the modules although you could build your own to save a bit of cash for the more serious stuff.

The 80-2 VCO which used the Curtis CEM 3340 and produced six waveforms, it was also configures to be able to synchronise the pitch of its oscillation with another and also featured a soft synchronisation input which further added to its sonic output as well as having a linear frequency modulation input.

The 80-3 LFO also used the Curtis CEM 3340 but running at a much lower frequencies.

The 80-4A Voltage Controlled Mixer was a four input mixer used for combining the output of several modules or mixing together the different waveforms of an oscillator, however as is given away by its title the mixers inputs could be voltage controlled as well.

The 80-5 Processor  is one of those type of modules that doesn’t sound immediately exciting of useful  but its quickly apparent that it enables you to get more out of the other modules and hence the whole system. It contains a lag processor which gives you a glide effect when putting a keyboard derived control voltage for the oscillators and it will of course smooth any stepped voltages that you put through it. There are also various inverters and sub tractors which you can use to combine and split signals in ways that you find you need to do when connecting modules together.

The 80-6 Low-Pass, Band-Pass, High-Pass, Phase-Shifting Filter. This was a 24 decibels per octave filter, you couldn’t switch between the various modes instead it was intended that you built it depending on how you wanted it to function, so you could build four of these filters and build each one as a different type of filter! This filter also included the more unusual option of controlling the resonance by voltage control, again giving you more versatility than most similar designs.

The 80-7A State-Variable Filter came along after the 80-6 and gave you the option of switching between the operating modes of the filter rather than them being hard wired.  It could perform as a low pass, high pass, band pass and band reject. It could also be switched between 12 or 24 dB’s per octave as this was also quite a distinctive difference in filtering

The 80-8 ADSR is a basic envelope generator and functions pretty much like most conventional envelope generators. Perhaps the most notable function is that it equipped with a push button to manually trigger it if you haven’t got it connected to a keyboard or sequencer.

The 80-9A Dual VCA has linear and exponential control voltage inputs as there are subtle differences when used. This module is particularly useful as it has been cleverly designed so not only can you put an audio signal through it in a conventional way in conjunction with an envelope generator to produce the normal sound contours but you can put control signal through it as well as for instance you could route an LFO through it to a VCO to produce vibrato and have an envelope generator control the modulation depth through the duration of the note of the note!

The 80-10 Voltage-Controlled Envelope Generator was a very versatile envelope generator featuring not surprisingly from its title voltage control of the elements of the envelope ADSR. It also featured inverters with attenuators so the envelope contours could be bent and twisted around to your heart’s content. There was also a timer for the delay and retriggering of individual gate and trigger inputs

The 80-11A Dual Ring Modulator was quite a simple module cosmetically, with each of the two devices only having two inputs and an output, however its output was sonically complex, and a traditional ring modulator that was capable of producing many types of bell, gong and metallic tones depending on what was fed into it.

The 80-12 Noise Generator with Sample & Hold was a fairly traditional design generating white and pink noise, it also had a sample and hold circuit which like many designs used with white noise on board to produce random output voltages

The 80-13 External Input Module enabled other sound sources to be used as sound sources for the Digisound system. It also contained an envelope follower, which was a useful device to have as it enabled the control voltage envelope to be extracted from a sound fed into it. There were also a couple of circuits to extract gates and triggers from external sound inputs.

The 80-14 Stereo Power Amplifier is a pretty normal stereo power amplifier 10 watts driving an 8 ohm impedance loud speaker and also includes a headphone output for those times when you’re driving every else insane!

The 80-15 is the keyboard and controller for the Digisound system. It is a digitally scanned keyboard which makes it extremely accurate and also readily interfaced with the microprocessor controlled Alphadac System. You could choose how big your keyboard was from 37, 49 or 61 keys. It also provided octave transposition switching and an x-y controller for pitch bend and modulation.

The 80-16 Dual Resonant Filters module was original published in the February issue of electronics and music maker 1982 and was a very useful addition to the system featuring two individual  band pass and enhanced filtering options. Manual and voltage control was provided for the resonance and the frequency. Resonant filtering wasn’t a very common filter and not available in many other systems.

The 80-17 Reverberation Unit was a solid state device rather than the more normal spring reverb of the time, to be honest this was one thing that wasn’t that good an idea in an analogue system and has since been left behind with modern devices seriously outperforming this on every level.

The 80-18 Multi-function Envelope Generator came to life in December 1981 through the magazine Electronics and Music Maker again; it had three modes that could be switched between. The first was the standard ADSR envelope, the second was a damped piano type attack decay release release envelope and the third was an automatic mode which required a short pulse to start a complete attack, decay and release cycle, this was particularly useful when combined with things such as arpeggiators and sequencers.

The 80-19 Dual VCLFO contained two separate oscillators that were both voltage controlled and sync able so that more complex modulation waveforms could be produced, they also each contained a built in voltage controlled amplifier that could control the level of the modulations produced. All in all a first class LFO.

The 80-20A/B Waveform Multiplier was designed by David Ward-Hunt and not Charles Blakey who designed the other modules, the idea of this module was to provide an effect similar to using multiple oscillators. An oscillator waveform was fed into it and produced six variations shifted in phase that were then mixed back with the original, it also had on board six LFOs to continually alter the phases of the shifted waveforms as keeping the phases static  wouldn’t have produced the chorus type sound.

The 80-21 Voltage Controlled Digital Oscillator came out originally in March 1985, again it was featured in the magazine Electronics and music maker that I subscriber to at the time and waited eagerly each month for its release, i particularly remember this one for the design of this unusual  VCO for that time. The oscillator was analogue in control using a standard CEM 3340 oscillator that many synthesisers did at that time however the waveforms that it produced were digital! It used the oscillator to drive a rom which was a form of pre-programmed memory chip that had voltage levels stored in it so they could be output by using a digital to analogue converter or DAC. This could produce 32 different waveforms which was pretty unusual at that time.

The 80-22 Patcher was designed to enable a preselected voltage to be instantly recalled, it sounds simple but it was one of those devices that could be used in plenty of different ways depending on your imagination! Depending on the options you decided on when you built it and how many units you used this could become a very complex unit and could function as a sequencer for all sorts of control options, it really was limited by your own imagination as they say!

The 80-23 Quad LFO had four independent oscillators all in the same module each oscillator had six switch selected waveforms and individual frequency control although not by an external control voltage [some things had to be sacrificed to be able to get four LFOs in one unit}

The 80-24 Polyphonic Keyboard Controller was an eight note polyphonic keyboard that could output eight separate control voltages, so eight voices could be utilised if you had the hardware! It was also possible to set up splits enabling control voltages to be sent all over the place, a pretty much ground breaking device at the time again.

The 80-25 MIDI To CV Interface  was a sophisticated device that enabled MIDI, which was the new digital music interfacing standard, to connect directly with analogue equipment, it was able to control up to eight analogue synthesisers as well as extract  velocity and after touch to be used as further modulation sources.

The 80 C9 Voice Card was a complete monophonic synthesiser on one circuit board. It contained to VCOs,  2 EG’s and a filter although obviously they were not as versatile or had the options of single modules as again sacrifices had to be made to fit everything on one card, in many ways it reminded me of the voice cards that were in the Powertran Polysynth.  They were designed for the increasing use of polyphony in synthesis. Remember in early days monophony was the only real option but as electronics moved on and the prices started to come down it became feasible to duplicate the analogue circuitry to produce real polyphony, and the voice card was produced at that time to address that issue.

Digisound went on to produce another couple of modules towards there end. The DEV-91 and the ALPHADAC. The DEV-91 was a signal processing board that was based around the CEM3391 integrated circuit which had a VCA, a VCA, an ADSR and a couple of output VCAS all on a single chip!

The ALPHADAC was a seriously complex microprocessor control system for controlling voices, modules, complete synthesisers and just about anything that was connected to it. It contained various real time recording, splitting, arppegiating and complete sequencing and performing capabilities, a complex device to say the least.

The Digisound System was able to do an awful lot of things brilliantly and Charles Blakey was a hugely talented designer who produced many ground-breaking and versatile units that could be built form kits at home that enabled the user to learn and produce results to rival professionally built products at a lesser price.