Casiotone MT-60 (analogue keyboard with unusual sound & arpeggio accompaniment)

This egg white Casio keyboard has unusual, partly incredible dry analogue sounds and a bizarre and thin sounding accompaniment with analogue drums and arpeggio. It sounds really quite weird, but that makes it unique and I like it. Despite this instrument has the same control panel layout and case like my Casio MT-45, it contains totally different hardware and is likely older, because it contains a lot of discrete components and its sound selection method corresponds to the ancient Casiotone 202.

main features:

The dual colour button style resembles somewhat my Yamaha PS-30; likely both were created in the same era.



The quite complex analogue hardware of this instrument resembles the Casio CT-410V (besides that it has no synthesizer filter) and was apparently a predecessor of it. Like the latter it is divided in an accompaniment CPU and a separate main voice soundchip, although in the MT-60 not only the accompaniment CPU but also the main voice soundchip both poll the keyboard matrix. A benefit from this is that (unlike with Casio CT-410V) the polyphony is not reduced by the accompaniment.

The main voice soundchip D990G was likely a predecessor of the D931C (which is used in the CT-410V). Like with the CT-410V, the main voice sounds of the MT-60 consist of 2 mixed multipulse squarewave suboscillators with different pulse patterns and different digital volume envelopes, those are (depending on the preset) muffled by different filter capacitors. Thus both instruments have the same kind of sounds, although unlike the rather dull CT-410V, most (not all) sounds of the MT-60 have a very bright and partly incredible dry timbre, and when a key is trilled with sustain, each new note here occupies a new sound channel, which produces a great phasing sound and volume increase effect although this eats up polyphony. In the bass range many sounds turn into a more or less buzzy, sonorous purring drone, which is a characteristic style element of squarewave based instruments. These basses can resemble some of the famous POKEY sound effects on Atari XL homecomputers and are very different from the gradually duller and duller growing sine wave bass behaviour of average Yamaha FM keyboard sounds. (For further technical details about this hardware family also see here.)

On the MT-60, the trumpet and mandolin sound more realistic than on CT-410V, and also the sonorous organ and wind instruments are nice, but best are harsh stuff like the harpsichords, and particularly the bright effect sounds are great. When sustain is switched off, all sounds stop almost immediately after releasing the key, and the sound presets itself also contain neither vibrato nor tremolo. The "funny" preset is a sort of rough digital slap bass (creaky picked e-bass) which sounds like "ennng!" (possibly it was initially intended to be called "funky", but sounded to artificial for this?). An even harsher variant of this is called "frog" (although it doesn't sound at all like one), which makes a wonderful rough and incredible dry bass noise. The "cosmic tone" preset is a slowly duller fading spacey synth pad timbre, which begins thin and quiet, and then grows louder while it makes audible use of the crossfading between the 2 subvoices. (On CT-410V it sounds simply like a plain saxophone tone, so far no envelope switches are added.) The "synth brass" is a sort- of trumpet sound which fades quieter and then louder again (sounds nice with sustain and trilled notes). The "funny fuzz" is a sort of picked string, which rapidly fades higher between 2 tones those are 4 notes apart. The "music box" rings at a slow speed of about 1Hz, which creates interesting repeating patterns when multiple keys are held down. ("Chime" is a brighter and not ringing version of it, which sounds like a cute plain squarewave toy.) There is also a ringing mandolin, which rings at a different speed and has a far less buzzy bass than on CT-410V.

To select sound presets, the "mode" switch has to be moved from "play" to "set", which will also assign the selected sound to the current position of the "tone memory" switch. The decaying sounds (e.g. piano) are selected by pressing any of  the white keys, while continuous tones (e.g. organs) are selected by black keys. Very interesting is that the selected sound is played as a hint during the selection key press, but only when the key is held down longer than about 0.2s. (It's a pity that this trick is not used on average toy keyboards, because the delay would make it possible to rapidly select OBS sounds during live performance without hearing the selected sound, and despite easily test the sounds by pressing the buttons slightly longer.) When the "mode" switch is set back to "play", the keyboard behaves normal again (and the "tone memory" switch can select between 4 of these sound presets during play.)

The accompaniment is similar flexible playable like the Testron one, and thus also accepts any disharmonic note combinations and not just those few ones that establishment has defined to be "chords". Unfortunately the chord timbres are very thin and creaky, and this instrument can play only either chords or a monophonic arpeggio. The bass is dull and resembles a triangular wave organ tone with release envelope. With rhythm off, the rhythm slider switches the chord between 3 different and thin sounding organ timbres. Very unusual is that when in fingered or single finger chord mode arpeggio is enabled without rhythm, then the chord section plays instead of bass and chord only the arpeggio (monophonic using the chord timbre). I never found yet any other old keyboard that can play arpeggio without starting a rhythm, but Casio should have at least enabled also the bass, because the thin monophonic arpeggio without anything else sounds so naked - really bizarre - almost absurd, but at least it is great for new age music. (With chord memory off, the arpeggio pattern stops when releasing the chord keys, and without rhythm it always restarts from beginning after pressing a chord key again.) Generally this creaky accompaniment with the trashy, old fashioned white noise home organ drums and tooting bass always sounds a little broken, but this gives the thing also much personality - I love this strange tablehooter.

 I only miss independent volume control knobs for the individual accompaniment voices.


circuit bending details

The complex analogue hardware of this instrument resembles the Casio CT-410V (besides that it has no synthesizer filter). Like the latter it is divided in an accompaniment CPU and a separate main voice soundchip, although in the MT-60 not only the accompaniment CPU but also the main voice soundchip both poll the keyboard matrix. A benefit from this is that (unlike with Casio CT-410V) the polyphony is not reduced by the accompaniment.

The main PCB is vertically divided in 2 halves those are interconnected with ribbon cables. The analogue percussion circuits are on the left PCB and have trimmers for decay time adjustment .

The accompaniment CPU D910G has the keyboard matrix inputs at the top left and most keyboard matrix outputs at the top right. Between both are some drum trigger outputs. At the bottom it has various accompaniment sound outputs. The keyboard matrix input pin seem to be {66, 63, 60, 59, 58, 57, 56, 55}. Matrix output pins are at {49, 48, 47, 46, 44, 41, 39, 75}. (I didn't fully understand the keyboard matrix yet; e.g. I didn't find the lowest bass key input, nor eastereggs.)


I didn't upgrade this instrument (yet...), but I have discovered that connecting pin 76 of the D910G with various keyboard matrix outputs or pin 75 results in very strange, often disharmonic accompaniment timbres and bizarre analogue drum noises. Apparently pin 76 was intended as a serial input to be controlled by an external CPU for generating different accompaniments. Pin 75 seems to synchronize the D910G with the main voice soundchip D990G, and likely also controls rhythm tempo.

Despite the case shape and button layout of the MT-60 is identical with the (newer?) Casio MT-45, the latter contains a simpler PCB with totally different hardware, which features only 8 main voice sounds but a very sonorous and powerful droning accompaniment - the contrast between these unequal twins could not be bigger. Apparently a fullsize key version of the MT-60 was the large Casiotone 403, which had a noble looking brown wood case with the same sound preset names written above the keys, but the rhythm button section like Casiotone 401 (Casio's first keyboard with rhythm and accompaniment, that had 16 semi- OBS preset rhythms). A cheaper 403 variant without rhythm/ accompaniment was released as Casio CT-101.

 removal of these screws voids warranty...    
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