Casiotone M-10 (semi- analogue keyboard)

This keyboard from 1980 was one of the very first polyphonic midsize instruments made by Casio. It has only 4 preset sounds and a vibrato switch, but by an easy modification it can be upgraded to 23 preset sounds.

This keyboard belongs to the same hardware family like Casio MT-30 and thus sounds and behaves very similar.

main features:

eastereggs:

notes:

Unusual is that the speaker is placed at the case bottom; obviously Casio tried out here yet another of their strange early speaker constructions known from their VL- series (see Casio VL-1, VL-10 and VL-5). However with older fullsize keyboards this placement was not that uncommon (see e.g. Bontempi HF222). In 1980th there was a Casio keyboard modification manual available, with instructions how to upgrade the M-10 with up to 23 preset sounds, because it is technically almost identical with Casio MT-30 (see there) and the preset sound slide switch is basically nothing else than the "tone memory" switch of the latter. But the CPU has a different software version inside, because the preset sound order (and thus the 4 default sounds) differ from the MT-30.
 

circuit bending details

The M-10 is the smallest polyphonic first generation Casio keyboard. Its NEC D773G CPU is an early member of the D77xG family and was also used in the serious fullsize Casiotone 401. Although the CPU outputs 14 bit audio, the DAC is a simple 12 bit construction to cut cost. The filter cutoff is controlled through CPU pin 46 to 750 Hz {piano, flute} or 820 Hz {violin, organ}.

I even got the Casiotone M-10 service manual from 1980. Although it tells nothing new (and of course keeps silence about all those mythical hidden eastereggs), this ancient manual gives a nice introduction into the the general basics of sound synthesis. So there are diagrams of multipulse bit sequences for all active pins sent to the DAC during violin, flute and organ preset, which reveals a bit about the early Casio way of thinking.

This text is only a brief overview and mainly meant for hardware comparison. The M-10 has been detailedly researched by Robin Whittle in his technical bulletin "Modifying the Casiotone Instruments" from 1981, which is very recommended to read if you want to upgrade this instrument. It e.g. explains mechanical details, how to upgrade the poor DAC and bankswitch to missing keys.

keyboard matrix

I haven't analyzed the M-10 by myself, but Robin Whittle explained it with many technical details including keyboard matrix. While the layout is generic for D77xG CPUs (see there for additional info), here are the D773G preset sound names for each key (based on Robin Whittle).
 
sounds:
(aSound)
 = a Casio M-10 preset sound name
aSound
 = a Casiotone 401 preset sound name
'aSound'
 = an additional sound named by Robin Whittle
16 SI-1
17 SI-2
18 KI-1
19 KI-2
20 KI-3
21 KI-4
22 KI-5
23 KI-6
24 KI-7
 
CPU pin
S in 1
S in 2
in 1
in 2
in 3
in 4
in 5
in 6
in 7
in / out
 
 
 
o
C1
o
C#1
(organ)
o
D1
(violin)
o
D#1
(piano)
o
E1
'slow harpsichord'
o
F1
'fast harpsichord'
o
C5
piano
out 1
 33 KC-1
spread scale
pedal sustain
o
C1
o
G1
'trumpet2 / mystery2'
o
G#1
o
A1
o
A#1
o
B1
o
F#1
'st.ensemble / mystery1'
out 2
 31 KC-2
O.
memory set
O.
memory set (silent)
o´
C2
o
C#2
o
D2
o
D#2
'triangle wave'
o
E2
'square wave'
o
F2
o
C2
out 3
 30 KC-3
O.
tone memory 1
O.
 tone  memory 2
o´
C2
o
G2
o
G#2
o
A2
o
A#2
o
B2
o
F#2
out 4
 29 KC-4
O.
tone memory 3
O.
tone memory 4
o
C3
o
C#3
o
D3
o
D#3
o
E3
o
F3
o
C3
out 5
 28 KC-5
O.
vibrato
O.
vibrato mild
o
C3
o
G3
o
G#3
o
A3
elec. piano
o
A#3
frog
o
B3
funny
o
F#3
out 6
 27 KC-6
O.
vibrato slow
O.
sustain
o´
C4
(flute)
o
C#4
accordion
o
D4
harpsichord
o
D#4
violin
o
E4
trumpet
o
F4
celesta
o
C4
'thin violin'
out 7
 26 KC-7
octave down
hold
o´
C4
(flute)
o
G4
'repeat'
o
G#4
organ
o
A4
flute
o
A#4
cello
o
B4
oboe
o
F#4
clarinet
out 8
 25 KC-8

The keyboard matrix input lines are active-low, i.e. react on GND, thus any functions are triggered by a switch in series to a diode from one "in" to one "out" pin.
 

legend:
"o"
 = keyboard key
"o´"
 = strange behaving key doublet
underlined
 = function needs locking switch (i.e. stays active only so long the switch is closed)
O.
 = preset sound ('orchestra')
orange
background 		 = easteregg (unconnected feature)
grey
background		 = unconnected doublet

Matrix eastereggs are selected by each a locking switch in series to a diode at the following CPU pins:

  • memory set

    • CPU pin 16->30
    Like with Casio MT-30, this switch assigns a different preset sound to the actual preset sound slider position by pressing a keyboard key. This way you can access 23 preset sounds. Because many of these are outside the keyboard range, you need to add bank switches to exchange key matrix lines. Robin Whittle's bulletin explains an elegant method to do this.
     
  • memory set (silent)

    • CPU pin 17->30
    This does the same like the normal 'memory set', but omits sounding a demo note.
  • mild vibrato

    • CPU pin 17->27
    This vibrato has less depth.
  • slow vibrato

    • CPU pin 16->26
    There is already a diode wired at the vibrato switch that has to be disconnected and wired through a switch to get a  faster vibrato.
  • sustain

    • CPU pin 17->26
  • pedal sustain

    • CPU pin 17->31

    You may connect a sustain pedal here. It holds all notes until pedal release (or running out of polyphony).

  • hold (pedal)

    • CPU pin 17->25
    This holds all notes (like stuck keys), but unlike 'pedal sustain' new notes stop old ones. It was likely intended for chord memory.
  • octave down

    • CPU pin 16->25
    This makes the instrument play an octave lower.
  • spread scale

    • CPU pin 16->31

    This makes a slightly different chromatic tone scale.

  • dissonant howl

    • CPU pin 18->29, 18->30
    These strange C2 key doublets use a different sound channel than their normal versions and change pitch and timbre when held or trilled during play of other notes; it also depends on vibrato and other settings. Sometimes each strange key press plays the note in different octaves.
The CPU supports in total 49 keys, thus 17 lower note keys can be added as matrix eastereggs.

Attention: I haven't tried out these eastereggs, thus I don't know if they are correct.

The Casio M-10 was (as far I know) the only first generation Casio keyboard with an "M-" name prefix. Only much later in early 1990th they released their "Casio Club" keyboards M-100, M-200, M-300, those were simply re-releases white versions of their sample based SA-5,SA-35 and SA-40.
 

 removal of these screws voids warranty...    
WarrantyVoid
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