Casio GZ-5 (mini keyboard with MIDI-out)

This concrete coloured Casio cucumber of 1995 (embossed case date) was likely the world smallest MIDI keyboard with integrated sound and speaker. But it has only 10 preset sounds, no rhythm, and despite Casio gladly called it a "midi master keyboard", even the MIDI playability is very restricted since it not only lacks velocity but even the pitch and modulation wheels are fake and only behave like buttons instead of sending intermediate analogue values.

In MIDI mode the internal sound is disabled and the preset sound buttons control MIDI parameters. 2 slide switches set the velocity and keyboard octave range with each 6 steps, but really annoying is that the pitch & velocity wheels have only 1 step (like a button switch). The internal sound mode is not interesting at all; there are only 10 preset sounds (taken from Casio SA-1) and no rhythm; unfortunately even the octave and velocity slide switches don't work here; only pitchbend works and the modulation wheel adds a vibrato.

(Note: This keyboard is not worth to buy for its internal sound unless you want the pitchbend, vibrato and 4 note polyphonic mini keys; other SA-series keyboards sound is more versatile. The GZ-5 was mainly interesting for laptop musicians or mini keys freaks those wanted to use MIDI, but even for this it is nothing great, thus do not pay too much. Nowadays many more useful small USB controller alternatives exist.)

main features:

serial: R004120T

eastereggs:

  • demo "Wake Me Up Before You Go-Go" (by Wham!)
  • 9-step pitchbend wheel

    • notes:

    The manual includes a warning that is truly absurd regarding the size of this thing: "Do not crawl on top of the instrument. Particular caution is required in homes having small children. This may cause the instrument to tip over and break resulting in injury." Likely the text block was copied from a fullsize e-piano or organ and would have been rather appropriate to bulky Yongmei tablehooters of youghurt cup grade plastic (like this), those for sure would shatter if anybody climbs or leans onto them.
     
    The pitchbend and modulation wheel of this instrument are a similarly bad hoax like the scratch disc of Casio Rapman RAP-1, because they contain no analogue potentiometers but only mechanically simulate button presses on silicone contacts (on and off). At least their value range can be adjusted by entering numbers (press "bend sense" + number + "enter"). Casio really should have added real analogue controls here, since these fake wheels disqualify this self-claimed "MIDI master keyboard" far more for serious use than the lack of velocity sensing keys. Bizarre is that the keyboard matrix was indeed prepared for a contact row with some intermediate steps. The PCB is based on classic SA-series single-chip hardware.

    In "internal" (sound) mode only the pitchbend range can be adjusted among 4 depths; press "bend sense", type a cipher between 0 and 3 for the number of semitones per direction and press "enter" (i.e. 0=off). The pitchbend always glides quite fast when the wheel is moved. The modulation wheel adds a 6Hz vibrato so long it is pressed. The 10 OBS preset sounds are simply a subset of Casio SA-1; "e. piano" corresponds to its "elec piano", "organ" to "jazz organ", "e. guitar" to "elec guitar", "e. bass" to "elec bass", "brass" to the famous tooting "brass ens.", "flute" to "quena", "synth-lead" to "synth-reed". (If you like the vibrato sound style of this thing, also watch out for the fullsize MIDI keyboard Kawai PH50, which has plenty more of such sounds with genuine continuous pitchbend and modulation control through a joystick.)

    Like midsize SA-series keyboards (see Casio SA-21), the main voice is 4 note polyphonic and hisses less than those 2 note polyphonic mini keyboards, and like there the volume control and preset sound selection does not change held notes, which can be used for live play tricks; here even the buttons don't play disturbing click noises. But the very limited count of preset sounds and the total lack of rhythm makes the internal sound source quite useless. This was obviously an annoying marketing decission because the demo song easteregg reveals that the SA-series100 ToneBank sound engine is still intact and wasn't removed to make the MIDI functions fit. Even when it were more expensive; a fully functional SA-1 with MIDI- out, MIDI- in, working octave switch and real analogue pitch and mod wheels would have been much more fun than this crippled thing. For a highly compact laptop MIDI keyboard the large speaker section and bulky case of the GZ-5 only wastes space, thus the GZ-5 is not really good for anything. The SA-1 case was smaller and slimmer.
     

    hardware details

    The Casio GZ-5 is based on the SA-series CPU "OKI M6387-A23". The midi-out port is read on CPU pin 19.

    keyboard matrix

    The GZ-5 matrix has diodes because unlike other Casio mini keyboards it is 4-note polyphonic. Despite same CPU the layout strongly differs from SA-series, which hints that the software was made from scratch to fit the midi routines. The fake pitch and modulation wheels only simulate button presses and hence have no analogue inputs.

    This matrix is based on the Casio GZ-5 service manual. I haven't analyzed it by myself, so there may be still unknown eastereggs.
     
    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
    demo
    -
    stop
    N.
    '0'
    N.
    '1'
    N.
    '2'
    N.
    '3'
    N.
    '4'
    out 4
    26 KO4
    -
    -
    enter
    N.
    '5'
    N.
    '6'
    N.
    '7'
    N.
    '8'
    N.
    '9'
    out 5
    25 KO5
    -
    demo glitch
    demo halt
    volume
    +
    volume
    -
    bend sense
    midi ch.
    control
    out 6
    24 KO6
    PB.
    -4
    PB.
    -3
    PB.
    -2
    PB.
    -1
    PB.
    +1
    PB.
    +2
    PB.
    +3
    PB.
    +4
    out 7
    23 KO7
    -
    -
    -
    -
    -
    -
    -
    modulation
    out 8
    22 KO8
    -
    -
    V.
    ff
    V.
    f
    V.
    mf
    V.
    mp
    V.
    p
    V.
    pp
    out 9
    21 KO9
    M.
    internal
    M.
    midi out
    T.
    C6
    T.
    C5
    T.
    C4
    T.
    C3
    T.
    C2
    T.
    C1
    out 10
    20 KO10

    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.
     

    legend:
    "o"
    		 = keyboard key
    underlined
    		 = function needs locking switch (i.e. stays active only so long the switch is closed)
    N.
    		 = cipher buttons
    M.
    		 = mode switch
    V.
    		 = velocity switch
    T.
    		 = octave switch
    PB.
    		 = pitchbend wheel
    orange
    background     		 = easteregg

    eastereggs:

    A button wired to KO4->KI0 plays the demo song of Casio SA-1, which is a nice rendition of "Wake Me Up Before You Go-Go". The fact that it can play this indicates that almost the whole sound engine of the CPU was left intact. I had expected that Casio removed most of it to free rom space to make the midi mode and many note frequency lookup tables for implementing pitchbend fit. So apparently it was an annoying marketing decission to cripple the user interface to only 10 preset sounds and no rhythms. There is still a stop button at KO4->KI2 that here only stops the demo. Bizarre is that connecting a switch KO6->KI2 halts the demo while closed (notes are held, envelopes keep decaying normal). Connecting KO6->KI1 distorts and garbles the demo in strange ways. Apparently this messes up the track syncing of the internal sequencer, so it e.g. plays wrong rhythm, but when it doesn't crash entirely, the music continues normal after a while when it starts the next internal pattern of the song, which hints to its internal structure.

    To my surprise, the pitchbend matrix row supports 8 steps (4 in each direction). Apparently Casio had originally planned a kind of 9 position rotary switch (center position open) and cancelled it to cut cost. Also the row of the modulation wheel looks like designed for supporting more, but in "internal" (play) mode I found none. I did not search in midi mode, so there may still unknown midi eastereggs.

    Once I triggered a glitch mode where the modulation wheel sounded a fast repeating bassy click, so there may be a hidden feature to assign it to different tagets than vibrato. The same click also sounds when closing more than 1 contact in the velocity or octave switch, so it is likely an error signal.

    Another keyboard in grey ugly concrete building design was Antonelli 2381.
     

     removal of these screws voids warranty...    
    WarrantyVoid
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