The Spectrum Synthesiser was featured in the magazine, Electronics and Music Maker, it was in the first few issues of the magazine if my memory serves me correctly in early 1981, I also went on to build this synthesiser as well although a lot more work was involved as it had a lot of components on quite a few printed circuit boards and a lot of wiring to the numerous controls on the quite complex front panel.
Once again those stalwart high street electronic component suppliers Maplin produced the kit however it wasn’t complete as you had to fabricate the wooden and aluminium parts of the case yourself, all you got in the kit was the front panel.
You also had to obtain the CEM integrated circuits yourself. These were the famous Curtis Electromusic integrated circuits that were specifically made for synthesiser applications and were also used in the Sequential Circuits Pro One and Prophet Five, Roland SH101, MC202 and Jupiter’s and the Oberheim OB8 and OBXA among quite a few others so already you can see it was among quite a high pedigree of synthesisers.
The picture below shows the oscillators, noise generators and ring modulator section of the front panel
In terms of similarity it was probably closest to the Sequential Circuit Prophet One. It had two voltage controlled oscillators that could produce all the main waveforms but could also be used together producing frequency modulation and two different modes of synchronisation [were the pitch of the oscillators is held together] were all sorts of extra harmonics and twisted waveforms could be produced. The output from these versatile oscillators was then mixed with the noise generator and ring modulator into the filter, which could be switched to be a low, high or band-pass filter.
The picture below shows the filter and envelope generators section of the front panel
The Spectrum Synthesiser also contained two full ADSR envelope generators and a large range of modulation options due to its flexible switching. When I constructed the synthesiser in 1982 it cost about £200 which for what you got was quite a lot of synthesiser for your money. Also it complied to the 1 volt per octave standard so interfacing was a breeze and mine happily combined with a Roland MC202 micro composer and a Sequential Circuits Prophet One.