CASIO - electronic musical instrument
Casiotone MT-52
keyboard with versatile semi- analogue rhythm & accompaniment

This keyboard from 1985 (service manual date) has semi- analogue sound and semi- analogue percussion with versatile "Super Drums" rhythm slide switches and accompaniment. The coarse multipulse squarewave timbres sound nicely cheesy.

The general behaviour of this instrument has many similarities with Casio MT-500, but the percussion is semi- analogue instead of sample based and it also lacks the drumpads and drum trigger inputs. Also the timbres have a coarser multipulse squarewave- appeal that sounds less noble but nicely cheesy. The original German retail price of the MT-52 in a German Conrad catalogue from 1988 was 299DM (about 150€). Also a white version was made.

Due to the many similarities I only describe here the differences to MT-500.

different main features:

eastereggs:

modifications:

notes:

The speaker of this thing sounds quite thin and has the same unpleasant midrange resonance like Casio PT-30. The MT-52 main voice sounds coarser and more squarewave- like than Casio MT-500; it seems to be based on the same sound engine like Casio CT-410V (without its VCA). The timbres have a characteristic buzzy bass range. "piano 1" is a usual filtered squarewave piano, while "2" is brighter with short sustain. "harpsichord 1" is bright and thin (like expected) while "2" sounds duller with knocking attack and rather resembles a harp. "elec. guitar" sounds bright with mild attack and delayed vibrato. "jazz organ" is a dull Hammond organ timbre. "flute" sounds like a metal flute with delayed vibrato. "trumpet" sounds a little oboe- like with delayed vibrato. "celesta" has a semi- metallic timbre with percussive attack. "pipe organ" attempts to be a metal pipe organ rank, using a sonorous multipulse squarewave timbre, but this one sounds thin and by its high octave setting no really low notes can be played. "violin" sounds ok with delayed vibrato. "synth. reed" is a muffled envelopeless plain squarewave timbre with weak delayed vibrato. All vibratos have 6Hz. Depending on the selected preset sound, the sustain switch adds sustain or reverb to the sound, but sounds those already contain internal sustain ("piano 2", "celesta") simply ignore it.

Also the percussion sounds much like CT-410V. Despite only 8 preset rhythms there are plenty of variations adjustable because each has 2 rhythm variations and like with MT-500 there are 4 Super Drums switches those switch 4 percussion tracks among 3 variations each. Annoying is that also here the individual percussion tracks can not be muted individually. The patterns differ from MT-500 but the accompaniment also here accepts non- standard chords, and they are even programmed more versatile; e.g. "slow rock" contains an arpeggio that plays the more notes the more keys are held down in the accompaniment section. Also the fill-in pattern has accompaniment. The bass and chord voices employ nicely sonorous multipulse squarewave, that is less muffled than with MT-500.
 

hardware details

The Casio MT-52 is based on the same hardware family like MT-65 and CT-410V. While the main voice sound IC "NEC D931C 011" is the identical, the accompaniment CPU "NEC D930G 020" here has a different software number to handle Super Drums. But despite semi-analogue percussion, the relatively small PCB is much simpler, well accessible and has a clear straight forward design like made for circuit bending.

E.g. the 4 discrete analogue percussion envelope circuits form a well visible rectangular section and have each a trimmer for adjustment. This is what Casio considers the official percussion decay settings (fall time between first and 2nd last positive peak, found in MT-52 and CT-320 service manuals).

percussion trimmer duration circuit abbreviation
base drum BD VR3 (CT-320: VR1) 13ms +/- 10% B.D
snare SD VR4 (CT-320: VR3) 8ms +/- 10% SD.N & S.D
low conga LC VR5 (CT-320: VR5) 80ms +/- 10% L.C
high conga HC VR6 (CT-320: VR4) 40ms +/- 10% H.C
rimshot -   R.S.
cymbal/hihat -   CYM H.H.

Trimmer VR1 tweaks the supply voltage (should be +5V). Trimmer VR2 is bit compensation for linearity of the main voice DAC.

A fixed lowpass filter (same like MT-65) modifies the main voice timbre. These are the filter switch outputs of the D930 CPU shown in MT-52 and CT-320 service manuals.
 
preset sound:
IO-1
 IO-2 IO-3
piano 1
H
H
H
harpsichord 1
 
 
 
elec. guitar
 
 
 
jazz organ
H
H
 
flute
H
H
 
trumpet
 
 
H
piano 2
H
H
 
harpsichord 2
 
 
 
celesta
 
 
 
pipe organ
 
 
 
violin
 
 
 
synth. reed
 
 
H

keyboard matrix

I haven't analyzed this keyboard matrix by myself, but only read the service manual and schematics of MT-52 and CT-320, thus there may be still unknown eastereggs (it has strong similarities with MT-500 and some with MT-65/ CT-410V). Locking switches were found in schematics.
 
51 KI1
50 KI2
49 KI3
48 KI4
47 KI5
46 KI6
45 KI7
44 KI8
 
CPU pin
in 1
in 2
in 3
in 4
in 5
in 6
in 7
in 8
in / out
 
o
C1
o
C#1
o
D1
o
D#1
o
E1
o
F1
 
 
out 1
52 KC1
o
F#1
o
G1
o
G#1
o
A1
o
A#1
o
B1
 
 
out 2
53 KC2
o
C2
o
C#2
o
D2
o
D#2
o
E2
o
F2
C.
casio
C.
fingered
out 3
54 KC3
o
F#2
o
G2
o
G#2
o
A2
o
A#2
o
B2
 
 
out 4
55 KC4
o
C3
o
C#3
o
D3
o
D#3
o
E3
o
F3
 
 
out 5
56 KC5
o
F#3
o
G3
o
G#3
o
A3
o
A#3
o
B3
 
 
out 6
57 KC6
o
C4
o
C#4
o
D4
o
D#4
o
E4
o
F4
 
 
out 7
58 KC7
o
F#4
o
G4
o
G#4
o
A4
o
A#4
o
B4
 
 
out 8
59 KC8
o
C5
 
R.
start/stop
R.
synchro
O.
sustain
 
 
 
out 9
60 KC9
O.
piano
O.
harpsichord
O.
elec. guitar
O.
jazz organ
O.
flute
O.
trumpet
O.
select
 
out 10
61 KC10
C.
bass/chord II
C.
bass/chord III
R.
cymbal II
R.
cymbal III
R.
conga II
R.
conga III
R.
snare II
R.
snare III
out 11
71 KC19
R.
rock
R.
16 beat
R.
bossanova
R.
slow rock
R.
select
  
R.
base II
R.
base III
out 12
70 KC20

The 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. Super Drums slide switches default to "I" when no other place selected.
 

legend:
"o"
 = keyboard key
underlined
 = function needs locking switch (i.e. stays active only so long the switch is closed)
R.
 = preset rhythm
O.
 = preset sound ('orchestra')
C.
 = chord
orange
background 		 = easteregg (unconnected feature)

An MT-52 version with 49 fullsize keys was released as Casio CT-320 (released in a brown and a gold metallic case variant).
 

 removal of these screws voids warranty...    
WarrantyVoid
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