Casio SK-2100, SK-200, SK-100, Hohner PK60 [SK-200 hardware]

CASIO SK-2100
Casio SK-200
Casio SK-100
Hohner PK60

keyboard with lo-fi sampling & accompaniment

The SK-200 variants were Casio's late ambition of following the foil keypad hype of early 1980th - a trend that became popular with Yamaha DX7 and adapted by the visionary Casiotone CT-6000, but soon was abandoned because it made musical instruments less intuitive and hard to use without staring at the panel - a nuisance that nowadays returned with the touchscreen craze (that can end deadly when part of automobiles). The foil buttons of Casio at least are a little raised and have tactile dome switches underneath to mitigate the trouble.

Casio SK-2100

This bulky keyboard from 1986 (service manual date) is the fullsize version of Casio SK-200. It was the biggest instrument of its series, combining a lo-fi sampler similar like Casio SK-8 with additional consonant-vowel preset sounds and accompaniment.

The sampler can store up to 4 short samples and can not be used on full keyboard length but only for either the lower (chord) or upper (melody) section or replace drum samples of the rhythm. The stairwave sound engine uses a variant of the low-end consonant-vowel chip found in MT-88. The accompaniment has a bass with simple staccato chord patterns. At least the chord preset sound is selectable. There is also a sequencer and programmable rhythm pattern with accompaniment.

main features:

49 fullsize keys
built-in stereo speakers (a little dull)
main voice polyphony 8 notes stairwave or 3 notes sampling
upper voice polyphony 4 notes
12 OBS "lower" preset sounds {piano, vibraphone, celesta, jazz organ, pipe organ, trumpet, flute, violin, elec. guitar, funky clavi, synth. ens., synth. sound}
10 OBS "upper" preset sounds {piano, vibraphone, celesta, jazz organ, pipe organ, trumpet, elec. guitar, funky clavi, synth. ens., synth. sound}
4 OBS sample preset sounds {conga, piano, vibraphone, horn}
20 OBS preset rhythms {rock 1, 8 beat 1, 16 beat 1, disco 1, pops 1, swing, slow rock, samba, bossa nova, waltz, rock 2, 8 beat 2, 16 beat 2, disco 2, pops 2, funk, reggae, salsa, beguine, march}
lo-fi sampler (up to 4 low- res samples, with tuning, reverse & loop function)
6 selectable preset envelopes (usable only for samples)
4 OBS sample select buttons
4 sample pads (not usable for internal percussion)
fingered & single finger chord & accompaniment
tempo +/- buttons (40 steps?)
synchro & fill-in button
simple sequencer (polyphonic record/ playback of chord, melody 1 (2000 notes), melody 2 (with samples, 1000 notes), no edit)
programmable rhythm pattern (with fill-in, chord, bass)
volume sliders {main, bass, chord, rhythm, samples}
sample based sound generator for 4 voices + rhythm, stairwave sound generator for other preset sounds & chords
stereo chorus
complex multi-chip hardware:

CPU= "HD61702A04" (100 pin SMD)
sampling CPU= "OKI M6283-02" (100 pin SMD)
percussion IC= "OKI M6294-03" (28 pin DIL, 16KB ROM)
sample ROM= "NEC D23C256EAC 012" (28 pin DIL, 32KB)
sample SRAM= "HMS-62256LP-15" (28 pin DIL, 32KB)
common RAM= "uPD4464C-15C" (28 pin DIL, 8KB)
stereo chorus: BBD= "MN3207" (8 pin DIL, 1024 steps), clock= "MN3102" (8 pin DIL)

battery backed-up memory
auto power-off
tuning knob
jacks for AC- adapter, volume pedal, line out, line in, microphone

notes:

Despite a large sampling keyboard may sound exciting, this is still rather a tablehooter and far less interesting than Casio FZ-1 and similar serious samplers. The sampling features are just like SK-8, and also the consonant-vowel stairwave preset sounds are too dull and belong to the less interesting of its kind. The sampler does not support full keyboard length and thus always activates split mode with stairwave for "upper" section. If you wonder why there is a dedicated upper/lower "tone" and "rhythm" button to the left of the panel despite everything is OBS; they seem to be only for seeing the currently selected sound & rhythm on the LED row/column matrix. It is unknown why for the "upper" (chord section) preset sounds 'flute' and 'violin' are not available, and why Casio didn't combine upper/lower into only one preset sound button row since the rest is the same.

The sampling microphone of SK-2100 is detachable on a spiral cable and even has volume control with LED bargraph to avoid distortion.

hardware details

The Casio SK-200 (and SK-2100) contains complex multi-chip hardware with much analogue stuff. It is built around the main CPU HD61702A04 that produces stairwave sounds and controls the sampling CPU M6283-02 which controls the percussion IC M6294-03.

Because my own SK-200 is a wreck (flickering LEDs, no sound, missing keys and speakers), I could only examine my Hohner PK60. I didn't get far with this complex hardware, so this description is mainly based on the Casio SK-2100 service manual.

The common RAM uPD4464C-15C stores sequencer data and has a system exclusive area shared between both CPUs. The sampling RAM HMS-6225SLP-15 stores the samples. The sampling ROM uPD23C256EAC-012 contains preset samples, percussion data and envelope data for sampled sounds.

Like in other SK-instruments, the sampling CPU needs 4 external VCAs for analogue envelopes. But because one channel is hardwired for bass, sample playback here is only 3-note polyphonic (even when bass is not in use).

The sampling CPU M6283-02 has an interesting model select function. According to service manuals, in SK-100 its input pin 84 is wired to ground, while in SK-2100 it is connected to its output pin 61. Likely this sets the installed amount of RAM and count of samples (SK-100 = 16KB for 2 samples, SK-2100 = 32KB for 4 samples).

The stereo chorus is a phase shifting delay circuit with plenty of analogue stuff, using a 1024 steps BBD IC MN3207 clocked by IC MN3202. Its LFO has 1.25Hz.

The upper and lower main voice preset sounds are routed through each a fixed low-pass filter, which cutoff frequency and gain is switched by the CPU. The lines F1..F4 are latched by a 75HC175 from CPU pins KO1..KO4 during rising edge of pin FC7. Lines F5..F8 are latched the same way during rising edge of FC6. (In this table "X" means hi.) In schematics both filters are identical beside that upper melody has an additional 470k pullup resistor before the 33k output resistor.

upper melody lower melody

preset sound filter gain filter gain

F1 F2 F3 F4 F5 F6 F7 F8

piano X X

vibraphone X X X

celesta X X X X X X

jazz organ X X X X

pipe organ X X X X X X X X

trumpet X X X X

flute X X

violine X X X X

elec. guitar X X X X X X

funky clavi X X X X X X

synth. ens. X X X X X X X X

synth. sound X X X X X X

In Casio SK-100 hardware the lower melody filter is simplified because its preset sound or chord stays always 'piano' and so has no latches for different modes.

keyboard matrix

The keyboard matrix is polled only by the main CPU. Although there is much demux going on, at least the matrix looks less insane than in MT-800. The main CPU uses its address-/databus and some other lines (including KI8, LO8) to control the sampling CPU. The LEDs are latched in 2x 74HC174 from pins KO1..KO12 during rising edge of a clock pulse on pin LO11, with LEDs wired against inverted LO12, LO13. The tempo LEDs are controlled by pins FC1, FC2 directly. The sampling level indicator LEDs of SK-2100 are not part of the matrix but controlled by an IC LB1403N.

This matrix is based on SK-2100 service manual. I didn't analyze it by myself, so there may be still hidden eastereggs.

40 KI1 41 KI2 42 KI3 43 KI4 44 KI5 45 KI6 46 KI7 CPU pin

in 1 in 2 in 3 in 4 in 5 in 6 in 7 in / out

o
C1 o
C#1 o
D1 o
D#1 o
E1 o
F1 C.
manual out 1 83 KO1

o
F#1 o
G1 o
G#1 o
A1 o
A#1 o
B1 C.
split out 2 84 KO2

o
C2 o
C#2 o
D2 o
D#2 o
E2 o
F2 C.
fingered out 3 85 KO3

o
F#2 o
G2 o
G#2 o
A2 o
A#2 o
B2 C.
single finger out 4 86 KO4

o
C3 o
C#3 o
D3 o
D#3 o
E3 o
F3 P.
sample 1 out 5 87 KO5

o
F#3 o
G3 o
G#3 o
A3 o
A#3 o
B3 P.
sample 2 out 6 88 KO6

o
C4 o
C#4 o
D4 o
D#4 o
E4 o
E#4 P.
sample 3 out 7 89 KO7

o
F#4 o
G4 o
G#4 o
A4 o
A#4 o
B4 P.
sample 4 out 8 90 KO8

o
C5 R.
tempo + R.
tempo - R.
fill-in R.
start/stop power
on power
off out 9 91 KO9

OU.
piano OU.
vibraphone OU.
celesta OU.
jazz organ OU.
pipe organ OU.
trumpet OU.
flute out 10 92 KO10

OU.
violin OU.
elec. guitar OU.
funky clavi OU.
synth ens. OU.
synth sound SA.
sample 1 SA.
sample 2 out 11 93 KO11

SA.
sample 3 SA.
sample 4 out 12 94 KO12

OL.
piano OL.
vibraphone OL.
celesta OL.
jazz organ out 13 66 LO1

OL.
pipe organ OL.
trumpet OL.
elec. organ OL.
funky clavi OL.
synth ens. OL.
synth sound R.
rock 1 out 14 67 LO2

R.
8-beat 1 R.
16-beat 1 R.
disco 1 R.
pops 1 R.
swing R.
slow rock R.
samba out 15 68 LO3

R.
bossa nova R.
waltz R.
program 1 R.
program 2 R.
rock 2 R.
8-beat 2 R.
16-beat 2 out 16 69 LO4

R.
disco 2 R.
pops 2 R.
funk R.
reggae R.
salsa R.
beguine R.
march out 17 70 LO5

SA.
sampling SA.
sampling long SA.
effect select SA.
rhythm S.
rhythm pattern S.
bass pattern S.
chord pattern out 18 71 LO6

S.
play S.
chord S.
melody 1 S.
melody 2 (sample) OU.
upper tone OL.
lower tone R.
rhythm out 19 72 LO7

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

R. = preset rhythm

OU. = preset sound upper

OL. = preset sound lower

C. = chord

P. = pad

SA. = sampling

S. = sequencer

orange
background = easteregg (unconnected feature)

grey
background = unconnected doublet

During sampling, the CPU transmits data directly to the RAM and therefore disables key common signals KO0..KO9 which makes the keys inactive.

Interesting is that the same strange slave CPU architecture was also used in a sampling keyboard by Yamaha, namely the VSS-200, which main CPU XD716A0 handles the longer keyboard and high polyphony non-sampling (FM) preset sounds, but controls a whole VSS-30 CPU YM2416B for sampling (which there can even resample the FM for adding synth effects).

Casio SK-200

This was Casio's longest midsize SK-series sampling keyboard.

My SK-200 is an incomplete wreck. See Casio SK-2100 for features and hardware.

different main features:

49 midsize keys
no separate bass volume slider
internal microphone with neither volume control nor bargraph.
no volume pedal jack

Casio SK-100

This keyboard from 1986 (service manual date) is a crippled mono variant of Casio SK-200. By lack of upper tone select button, the chord section keys in split mode only use 'piano'.

My SK-100 specimen is braindead, so I can't test it.

different main features:

49 midsize keys
mono speaker
no stereo chorus
no "lower" (chord) preset sounds
only 10 preset rhythms {rock, 8-beat, 16-beat, disco, pops, swing, slow rock, samba, bossa nova, waltz}
2 instead of 4 samples
only 2 OBS sample select buttons
only 2 sample pads
no music sequencer (only pattern/chord memory)
hardware changes:

sampling CPU= "OKI M6283-02GS" (100 pin SMD)
sample SRAM= 2x "uPD4464C-15L" (28 pin DIL, 8KB)
common RAM= "uPD446C-2,3" (28 pin DIL)

no volume pedal jack

eastereggs:

most features from SK-200 keyboard matrix addable (AFAIK except 4 samples because of less RAM.)

Hohner PK60

This is the Hohner variant of Casio SK-100 (see there), which has different preset sounds & rhythms due to changed rom and CPU software versions.

different main features:

changed 12 OBS preset sounds {piano, vibes, celesta, jazz organ, church organ, brass, jazz flute, synthe strings, e. guitar, clavinet, synthe, dist synthe}
changed 10 preset rhythms {disco, 8 beat, 16 beat, rock, march/ polka, swing, slow rock, samba, bossa nova, waltz}
hardware changes:

CPU= "HD61702A06" (100 pin SMD)
sampling CPU= "OKI M6283-06" (100 pin SMD)
sample ROM= "NEC D27C256C-15, sticker "H139")" (28 pin DIL, 32KB PROM)

notes:

I got this keyboard with bad battery leak damage causing matrix shortcircuits, so I had to thoroughly cleaned it. But key groups keep failing by corroding keys PCB traces. When I dumped the rom, I tested what happens with rom removed. You can still play on keys and switch through preset sounds, but instead of rhythm there is a fast ticking noise (speed depends on selected preset rhythm) and complex things like sampling crashes. So instead of accompaniment there was only a hanging note, but simple key split works. I.e. most of the software is inside both CPUs, those software numbers differ from those Casio SK-100 counterparts.

*removal of these screws voids warranty...*

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