CASIO SA-21 small keyboards with complex lo-fi wavetable sounds
Casio SA-41, SA-8, SA-2, PA-31, KA-20, TA-10

These keyboards all belong to the Casio SA-21 hardware class, which was the direct successor of Casio SA-1 hardware. Sound engine and behaviour are basically identical; the only change was that the newer CPU supports 5 different demos (through 5 OBS buttons) and 5 drumpads. So I only describe here the differences to SA-1.

Casio SA-21

This midsize keyboard from 1992 (embossed case date) is likely the most common of the series. A bit annoying is that volume can not be set lower than ambient volume.

It was also released as Casio SA-25/ SA-38/ SA-39 (seen on webshops/ eBay) and as Realistic Concertmate-460 (seen on YouTube). Also a white SA-21 was made.

different main features:

In opposite to the predecessor Casio SA-20, here the PCB is double sided with one side mainly used for copper shielding to reduce EM radiation. It also has 2 additional pulldown resistor arrays (each 8x 220k) at the matrix lines.

The demos are nice and complex orchestrated although they are quite short (repeating in a loop) and the tune "Twinkle Twinkle Little Star" sounds almost like when the programmer forgot to add the main voice because most of the time plays only the accompaniment and 2nd voice (obligato?); the melody voice appears only for a few seconds as ringing mandolin. On the Casio SA-35 this tune indeed exists complete with main voice and there the main voice can be muted by hand to train playing.

A new case variant of this instrument was released as Casio SA-45 (aka RadioShack CK-480 | different silver metallic case, same features, seen on eBay).

Casio SA-41

This midsize keyboard from 1997(?) came out in India. It is basically a normal SA-21, but with changed demos including 3 nicely arranged Hindi songs.

different main features:

The control panel is printed in funky neon colours and also the hardware has subtle differences. E.g. the PCB here is single sided (no copper shielding) and the CPU has a different software number and is made in Thailand (normal is Japan). On case bottom the "JASRAC" (music copyright) sticker is plain white without number, and next to it is an additional field with embossed US patent numbers. The rear plastic is shinyer than my normal SA-21. The embossed case date is 1993, but its newest demo song seems to be from 1997, so the SA-41 seems to be the latest released classic SA-series keyboard.

Song A is a quite messy and disharmonic arranged short medley of different jingles that sounds like from a trashy 1990th Hindi TV series. I read, in India it is known as a socialist patriotic song against colonialism. Song B sounds like Chinese dance music (somewhere between tango and disco); it is the title song of a Bollywood romance movie from 1997. Song C is a slow and optimistic disco pop tune that sounds like late 1980th platform videogame highscore music; but also this is a movie theme - of the Bollywood thriller Teesri Manzil from 1966. Song D and E are like SA-21.

Casio SA-8

This 2 note polyphonic instrument from 1993 (embossed case date) is basically a crippled Casio SA-21, so I will only describe the differences. It 2 note polyphonic and has only 25 sounds due to omitted cipher buttons.

It was also released as Casio SA-3 in black, white or green. It also came out as Realistic Concertmate-370 (seen on YouTube).

different main features:

eastereggs:

circuit bending details

Casio released many crippled small keyboards based on Casio SA-21. Despite same CPU "OKI M6387-11", they lack many of its features by omitted buttons and keyboard matrix diodes. This is how to re-enable them. This text deals mainly with Casio SA-8, but the principle is always the same.

For general info about the SA-series hardware see here.

keyboard matrix

11 KI0
12 KI1
13 KI2
14 KI3
15 KI4
16 KI5
17 KI6
18 KI7
 
CPU pin
in 0
in 1
in 2
in 3
in 4
in 5
in 6
in 7
in / out
 
o
F3
o
F#3
o
G3
o
G#3
o
A3
o
A#3
o
B3
o
C4
out 0
30 KO0
o
C#4
o
D4
o
D#4
o
E4
o
F4
o
F#4
o
G4
o
G#4
out 1
29 KO1
o
A4
o
A#4
o
B5
o
C5
o
C#5
o
D5
o
D#5
o
E5
out 2
28 KO2
o
F5
o
F#5
o
G5
o
G#5
o
A5
o
A#5
o
B5
o
C6
out 3
27 KO3
'0'
'1'
'2'
'3'
'4'
tempo
+
volume
+
rhythm select
out 4
26 KO4
'5'
'6'
'7'
'8'
'9'
stop
tempo
-
volume
-
out 5
25 KO5
P.
base
P.
snare
P.
hihat
D.
'E'
D.
'D'
D.
'C'
D.
'B'
D.
'A'
out 6
24 KO6
P.
cymbal
P.
agogo
-
-
-
-
-
polyphony 4
[diode]
out 7
23 KO7

All button names were taken from the original Casio SA-21. Unknown function names and in/ out numbers in this chart were chosen by me. The input lines are active-high, i.e. react on +Vs. Any functions can be triggered by a non- locking switch in series to a diode from one "out" to one "in" pin. The SA-21 additionally has 2 pulldown resistor arrays (each 8x 220k) at the matrix lines (likely against EM interferences or capacitance problems).
 

legend:
"o"
 = keyboard key
P.
 = drumpad
D.
 = demo songs
orange
background 		 = easteregg (in SA-8 unconnected feature)

The matrix layout of the M6387-11 CPU is designed in such a way that it would (beside different demo) also work as a replacement for the M6387-01 in the SA-1 and SA-20. In SA-20 possibly the connection between pin 23 and 18 (see "upgrade polyphony") would need to be replaced with a diode to avoid collision with the 'cymbal' and 'agogo' drumpads. The original M6387-01 matrix is almost the same, except that row KO6 contains only doublets of the cipher buttons '0'..'4' and 3 doublets of the 'demo' button; row KO7 is unused. 

eastereggs:

The only 5 available cipher buttons {'1', '2', '3', '4', '5'} of the Casio SA-8 correspond to the buttons {'0', '1', '2', '3', '6'} on the SA-21. It is very recommended to add also the 5 missing buttons to get access to the 75 missing preset sounds buried in its CPU. The 2 demo buttons {'A', 'B'} correspond to {'E', 'A'} on SA-21.

upgrade polyphony:

Technically it is possible to upgrade the SA-8 with the 4 note polyphony of SA-21. To activate higher polyphony, connect a diode from pin 23 to pin 18 of the CPU (permanently or only at boot time). However to prevent polyphony bugs, a diode needs to be wired in series with each key (from an output to an input); soldering 32 tiny matrix diodes to the flimsy multi-layer PCB is not really worth the effort unless you have a special reason to do so.

Casio SA-2

This lousy little tablehooter from 1995 (embossed case date) is an even more crippled version of the Casio SA-8. It has no(!) tempo control, only 2 volume steps, only 16 preset sounds (due to 4 cipher buttons) and no drumpads anymore. A red version of it was released in 1995 as Casio KA-2. A violet version came out in the CasioClub series as M-80.

(Don't confuse the SA-2 with the similar looking Casio SA-5, which is way more versatile and has fantastic tekkno synth sounds.)

different main features:

  • only 16 preset sounds {piano, elec piano, honky- tonk piano, harpsichord, brass ens, warm brass, trumpet, tuba, samba whistle, whistle, quena, flute, strings, warm strings, violin, violin- piano}
  • only 4 cipher buttons
  • no tempo control
  • only 2 step volume slider
  • no drumpad buttons
  • CPU= "OKI M6387-11, 5092301" (30 pin SDIL)
  • only 1 demo: "Choral (Beethoven)" [="Ode to Joy"]
  • no sound output jack

    • eastereggs:

    Very annoying is that this horrible crippled tablehooter has only a mechanical switch for 2 volume steps despite its CPU would support digital volume control. Also the omitted tempo buttons are inexcusable. The SA-2 is certainly good for circuit bending (all the missing stuff can be added by matrix eastereggs, see Casio SA-8), but for not much else. (I would never have bought one of these but found mine in a junk pile after a flea market.)

    Casio PA-31

    Casio PA-31

    Unlike Casio SA-1, this instrument is 4 note polyphonic, has higher tone quality and 4 demo melodies. Unfortunately the digital volume control is gone, which on the SA-1 could be used as a sound effect to change the sample bit resolution and the speed of algorithmic preset sounds (e.g. mandolin ring).
    The special feature of the Casio PA-31 in comparison to other such keyboards is the so-called "voice pad controller", which is simply a set of 8 sound effect buttons those play each a fixed low resolution sample (like drumpads), which pitch can be adjusted with a knob within a bit more than 1 octave.

    different main features:

    eastereggs:

    notes:

    All sounds of this instrument sound cleaner and less harsh than Casio SA-1. I am not sure if the output DAC bit resolution is somehow increased by external discrete components (demultiplexer?), but I think it is just better filtered and not reduced by a digital volume control.

    The "voice pad controller" is implemented by the independent sound IC "OKI M6373-349", which clock speed can be adjusted with the big red knob to change the pitch. Unfortunately the effect pads respond too slow for fast trilled sounds and have only a monophonic sound generator. The low-res effect samples sound quite noisy but not harsh. (I haven't examined the hardware yet.)

    A variant with ROM-Pack, key lighting leds and voice changer (hardware class PT-88) came out as Casio PA-81.

    Casio KA-20

    Casio KA-20

    This quite rare yellow toy keyboard from 1993 (embossed case date) was apparently the model for the widely spread and greatly bizarre sounding My Music Center, because it has many design elements and even some sounds common with it.

    Both have a case with moulded handle opening at the top, 32 keys, 5 drumpad buttons and 4 edge protectors, although My Music Center is typically red with yellow plastic protectors while the violet protectors on KA-20 are of rubber. The percussion timbres of My Music Center sound even like low- res samples of the latter, both include a honky- tonk piano sound and multiple demo tunes, and also the arrangement of the wonderful "Jingle Bells" demo has noticeable similarities with the Casio model (regard the trilled notes) although they are not identical. The My Music Center is also much smaller and has mini keys while KA-20 has a midsize keyboard. An even closer case imitation of it was the Sun Ta Toys SDN BHD 1996, although its "Jingle Bells" is arranged differently.

    Unlike the tinny My Music Center, the sounds of Casio KA-20 are surprisingly clear and even the speaker sounds pleasantly warm and has some bass. The KA-20 uses the same CPU like the Casio SA-21, but has only 16 sounds due to omitted cipher buttons. These are the differences to SA-21.

    different main features:

    eastereggs:

    notes:

    The only 4 available cipher buttons {"1", "2", "3", "4"} of the Casio KA-20 correspond to the buttons {"0", "2", "6", "7} on SA-1or SA-21 hardware. It is very recommended to add also the 6 missing buttons to get access to the 84 missing preset sounds buried in its CPU. (I didn't modify mine because I already own complete variants.) Bizarre is that in the case bottom is a crossed out embossed date table of 1991..93 and (like in its top) a new one from 1993..96.

    Under the key top cover is an unused row of key LED holes, because in 1990 a red keyboard with same case, key lighting (LED row) and ROM-Pack slot instead of the preset sound list was released as Casio - Sound Kids 02 (Casio KS-02). It has 8 OBS preset sounds {piano, harpsichord, violin, organ, flute, clarinet, trumpet, vibraphone}, no rhythms and its 5 drumpads can be switched to effect sounds. Technically it is a relative of PT-88.

    Casio TA-10

    This is basically a midsize Casio SA-8 with built-in stereo cassette player. This is not a cassette recorder despite there is a microphone for singing, and despite midsize keys it is only 2 note polyphonic.

    different main features:

    notes:

    This keyboard came with the German audio cassette "Mein Casio TA-10 Keyboard - probieren, spielen, lernen". With my specimen the cassette sounds detuned against the keyboard and plays a little higher; likely the cheap plastic tape drive runs a bit too fast. The first cassette side musically explains the functions of the keyboard. Then the player shall accompany an imaginary eerie movie scene with the "fantasy" sound.  On side 2 there are 6 German children songs. First it plays a complete version, then followed by only the accompaniment to play to.

    The 6 children songs are:

    1. Alle meine Entchen (="All My Ducks")
    2. H?nschen Klein (="Little Bee")
    3. Es tanzt ein Bi-Ba-Butzemann
    4. Meister Jakob (="Brother John")
    5. Vogelhochzeit
    6. Guten Abend, Gute Nacht (= Brahms lullaby)
    The songs are nice polyphonic arrangements and were likely played on one of the professional Casio workstation keyboards with its automatic accompaniment.
     

    Another member of this hardware class was the oval mini keyboard Casio SA-6 (100 sounds, 5 drumpads).
     

     removal of these screws voids warranty...    
    WarrantyVoid
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