E&MM Spectrum Synthesiser Preview

Published on Oct 20, 2019 Reuben Jones

"The E&MM Spectrum is a British DIY synthesizer designed by Chris jordan and released with Electronics and Music Maker magazine in 1981.....

The magazine provided a painted metal faceplate, keyboard assembly, and printed circuits boards. The rest was sourced by the builder using a supply kit provided by the now defunct Maplin Electronic Ltd, UK (see also the Maplin/ETI 3600, 3800, 4600, and 5600S synthesizers).

The synthesizer uses the famed Curtis integrated circuits: VCOs (CEM 3340), VCF (CEM 3320), VCA (CEM 3330), and envelopes (CEM 3310). These chips were used by many companies at the time, including AKAI, ELKA, Ensoniq, Oberheim, Roland, and Sequential Circuits.

Perhaps the closest synthesizer to the Spectrum is the Sequential Circuits Pro~One, both of which use the same CEM chips for VCOs, filter, and envelope; and use a similar two-VCO architecture. However, whilst the Pro~One is known for an extensive modulation section, the Spectrum is very interesting in its own right.

The design makes the most of the CEM 3340 VCOs, with a total of five waveforms, including a SUB square wave. The LFO, with multiple waveforms including random and regular sample and hold (the latter of which produces more defined sequencer like voltages), can be routed in positive or negative polarity to the VCOs, filter, ringmod/noise, and output. The multimode LP, LBP and BP filter is a self oscillating one and can be modulated by the joystick, envelope generator, and the LFO. There are also two sync options, as well as FM, ring mod, and an envelope shaper. The stereo output can also be modulated for panning and stereo FX; and there are eight jacks for external connectivity including CV/Gate in and out, and pre filter in.

In conclusion, I would describe the Spectrum as a drunk and wonky Pro~One. Mine is temperamental, and sometimes has a mind of its own, but when tamed, the Spectrum becomes a very live and organic synthesizer. The tech who serviced it for me said it reminded him of an ARP 2600, and described it as a 'proper synth'. GreatSynthesizers.com describe it as "...a mixture of EMS Synthi, Sequential Pro-One and Roland SH-5" and "one of the most outstanding monophonic analog synthesizers in history".

This audio was recorded directly from the Spectrum in mono, using a TC Electronic Alter Ego delay pedal for some parts. All parts played from the keyboard, or using the LFO to gate the amplifier."