Bontempi HT313 Analogue Synth & Drums SN 02750016

via this auction

"This toy- like keyboard from 1984 has a lot of charm It produces very pure warm analogue tones , it has some very nice Tr606 style analogue drums plus it’s also polyphonic. It’s a synth with circuit bending possibilities. The black acrylic control panel with its green, yellow and red diagrams with funky yellow buttons is a nice piece of cyber age design. This keyboard had a little bit something extra over your other circuit bent standards like the Casio Sk1s etc. as the analogue preset sounds it does sound really decent.

There is a sound on one of the pre-sets that is exactly like the eerie lead lines over the acid bass of Aphex Twins - Green Calx from selected ambient works 1.

Listen here - it's the mellow tones that come in at 0:16 over the squelchy acid line."

"Here's the specs:-

⦁ 4 voice polyphony

⦁ 6 pre-set sounds {organ, clarinet, violin, piano, harpsicord, glockenspiel.} (selected in a sequence by a single button) – All sound nothing like the above but more like classic analogue synth sounds.

⦁ Pre-set analogue drum sounds including bass drum synth and hi hats – all very nice - very electronic sounding – sadly not programmable but you’ll be pleased to hear there is a very proto type hip hop style beat masquerading as a rock rhythm. Very nice for sampling! Slow the tempo right down and you should be able to sample the individual sounds

⦁ Speaker & ¼ inch stereo headphone out jack

⦁ Can run on batteries or power supply (not included with sale)

This Analogue keyboard does have a lot of potential for modifications, the main PCB of the Bontempi HT 313 contains a lot of discrete analogue stuff and seems to be technically similar to a lot of other analogue based designs; there are trimmer pots for main and rhythm voice pitch and vibrato intensity.

The preset sounds style are all pure analogue. The "clarinet" is made from a square wave with delayed vibrato and is warm and musical, while the "glock." (Means glockenspiel?) Is another square wave music box sound made from the same timbre with a sharper decay envelope. The "sustain" button adds a long 3 second sustain to all the sounds adding an almost eerie reverb quality. If you're brave enough to get involved I think you could coax a lot out of this charming little synth!"

You can find demos of a circuit bent HT-313 here.