At the time the Maplin synthesizer systems 3800 and 5600 were developed, also a design for a 600 note sequencer was published in the Maplin electronics magazine february-march 1982.
I found the original article on the website bygonebytes.co.uk, run by a guy who tried to build this sequencer himself. He writes: “The Maplin 600 Note Sequencer was designed to compliment the Maplin 3800 and 5600 synthesisers and back in the early 1980’s it was a kit I would liked to have built but it was far too expensive. At a cost of £125 I decided to build my own sequencer as documented on the Maplin 3800 page, however, I did buy the constructional details leaflet with the possible aim of building it some time in the future. “
The documents and pictures in this post are kindly reproduced from www.bygonebytes.co.uk.