Casio MT-31
The MT-40's cheaper sibling. Same 22 sounds, same 37 keys, no bass board and no rhythm box.
Polyphony (October 1984, p.42) ran classified equipment-exchange listings for readers buying and trading gear of exactly this vintage.
Overview
The MT-31 is the stripped-down half of a pair, and the period mail-order ads say so bluntly: "Very similar to the MT-40 but without the bass keyboard, auto accompaniment feature and the rhythm box." What's left is a 37-note polyphonic keyboard with 22 preset sounds, vibrato, sustain and pitch control. It runs on batteries or an optional mains adaptor, and it puts out through an integral amp and speaker with a line output jack. Casio's own copy pitched it for solo lines - flute, violin, trumpet, oboe - or chords on organ, piano, banjo, guitar, and claimed a "remarkable quality of sound, especially through an auxiliary amplifier."
The weight shows how little separates the two. The MT-31 comes in at 4.4 lbs. The MT-40, with its 15-key bass board and rhythm section, is 4.9 lbs. Half a pound is the whole difference. The price gap was bigger. Tempus, the Cambridge Casio mail-order specialist, listed the MT-31 at £69 against £99 for the MT-40, and elsewhere quoted an RRP of £79 against the MT-40's £125. Buyers were paying roughly thirty pounds for a bass keyboard and six rhythms.
Portability was the pitch, and the ads lean on it hard: "beautiful, compact, take it with you anywhere." It shipped with an instruction manual. Accessories included the AD-1E AC adaptor at £5.00, a PC-2 hard case at £9.95, and a £10 bundle of free accessories thrown in by Tempus on orders. Nothing exotic.
What the MT-31 Actually Is
The specification is modest but coherent. The 37-note keyboard is polyphonic, the 22 presets cover the usual early-eighties Casiotone spread, and vibrato, sustain and pitch control are the basic shaping tools. The line output jack matters. Casio's own literature says the sound improves markedly through an auxiliary amplifier, which is an admission that the built-in speaker is a convenience, not a monitor. The optional mains adaptor is a separate purchase, so a battery-only owner is running on cells by default.
What the MT-31 does not have is the reason many players bought the MT-40: the automatic bass keyboard, the Casio auto-accompaniment system, and the rhythm box with its fills. Casio built a cheaper board by deleting the arranger features and keeping the voices, and the price list makes the trade explicit. Same sound engine, different amounts of accompaniment bolted on.
For calibration, Casio's common specifications across the Casiotone line at the time included built-in amplifiers and speakers, headphone and external amplification output jacks, and a pitch control on every model. The MT-31 sits at the small, cheap end of that family - well below the CT-101 at £195 and the CT-202 at £275, and only a notch above the VL-1 at £35.95.
Buying and Living With One
Collectors chasing an MT-31 today are usually after the cheapest route to that early-Casiotone preset set in a battery-powered box. The £69 street price from Tempus and the £79 RRP are the numbers for what these cost new. This was a budget instrument, and it should be priced like one on the secondary market. The PC-2 hard case and AD-1E adaptor turn up less often than the keyboard itself, so a complete package is worth more than the sum of its parts.
Practical notes from the period documentation: the MT-31 was excluded from Tempus's free Securicor 24-hour delivery and from their 0% credit offer, both of which applied only to the larger CT models. The MT-31 was treated as a same-day-post item, not a considered purchase. These move cheap and fast, and the ones that survive intact tend to be the ones that lived in a case.
As for sound, the verdict is the one Casio printed: it's fine through its own speaker and considerably better through an amp. The 22 presets are the appeal, not the fidelity.
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