Getting it home, it sounded very much like a poor man's DR-55-claves, open and closed high hats, snare and kick and that's it, but all voices were nice and punchy.
On the back was a label which made it appear that it had been part of the holdings of an educational institution-presumably in the US given the date format from when it entered inventory in 1980 - T. something College of the Arts?
The label is interesting for a couple of reasons-firstly, it dates it from the brief period when analogue synths were moving into the consumer space before the Casiotone onslaught, and indeed the quirky design brings to mind Paul Schreiber's recollections of how he was told to design the Moog Concertmate for Radio Shack around the same time. For example, they required all line outputs be on phono jacks for connection to domestic hifis-as is the case here. It has a 2.5mm start/stop footswitch input that screams "dictation machine"-and indeed it was sold bundled with a plain-looking footswitch that just reeked of typing pool anti-chic, and was probably excess stock from a Realistic dictaphone.
Secondly is what appears to be the college's intended use of it-a "tamura". In South Asian music, an electronic tampura or tanpura box is an electro-acoustic accompanist for live acoustic musicians (it was originally invented in India in 1979). When I got the Realistic home and turned it on I was surprised-the built-in speaker is loud-really loud, easily sufficient to accompany a small acoustic performance. In these days, when we are conditioned to expect inbuilt speakers in portable instruments are usually toys or at best sufficient for personal practice, this came as quite a surprise.
There was also something else that was really loud-a continuous tone that would not stop unless the input power voltage was dropped to 4.5V. Fortunately the schematic was not hard to find online. It appeared that the "tuned" voices (bass drum, claves and snare) were produced by the "pinging" of four pole single-transistor hipass filters generating tones from decaying feedback from the collector, and the emitter of each transistor is connected to a trimmer which sets the gain on the collector resistor and therefore controls feedback. Could it be that one of the voice trimmers was out of alignment and feeding back too much so that the sound never decayed?
Time to open it up!
The biggest surprise is that the speaker takes up almost half the space inside the instrument. The rhythms are driven by a Sanyo preset rhythm generator chip called the LM8972 (bottom left of the main board). Many other devices used this, and many of them used a remarkably similar circuit to this one, but in stomp box format (such as the Sound Master Rhythm 1). Transistors were all the bog-standard NPN 2SC1815 except for the reverse-biased noise generator, which was a 2SC1923, presumably because it was noisier! Note the big red inductor-a single transistor LC cymbal noise filter is a big part of the DR55's sound, and a similar circuit technique is present here too.
Any way, to work. After all the effort it was almost anticlimactic. A slight twist on one of the trimmers and the droning stopped, with the snare now decaying nicely!
I tried turning the noise trimmer, and it did modulate the level of the noise source pretty effectively.
So to wrap up, it's a fun instrument with a powerful voice that is hamstrung by its limited rhythm selection. Also its primitive RC power bypassing puts the sensitive analogue circuitry at the mercy of interference from the digital circuitry, so that even when stopped a very faint ticking is audible from clock interference "pinging" the clave circuit. Nonetheless, it has great potential as a sound module. Adding trigger inputs would be easy as it already has pulse extractors on all voices, likewise adding individual outs, with plenty of room in that huge case.
Another thought-remember those pedals based on the same circuit we mentioned earlier? Thanks to prominent Youtubers featuring them, they are now quite expensive, although they offer very little of the customisation potential of this unit due to their cramped size. This one on the other hand seems to have slipped under the collectors' radar courtesy of its odd appearance and the Realistic brand name and thus is undervalued accordingly. But then again, so was the Moog Concertmate synth once upon a time, for exactly the same reasons...
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