Casiotone 401

This was Casio's first keyboard with accompaniment and (so far I remember well) also the world first keyboard with automatic single finger accompaniment.
The Casiotone 401 has 16 unusual, partly incredible dry semi- analogue preset sounds and 16 analogue rhythms; also the bass sounds nicely warm and seems to be based on a triangular wave. Unusual is the "hold" switch, much like the manual fingered chord mode (with chord memory) on newer keyboards, here also the melody voice notes hold until any other chord or key combination is played. The noble designed case is unusually heavy, because it is made of plastic coated steel instead of genuine wood.

main features:

  • 49 fullsize keys
  • built-in big speaker (with reasonable bass)
  • main voice polyphony 8 notes
  • chord polyphony 12 notes
  • volume knob
  • separate accompaniment/ melody volume balance knob
  • tempo knob
  • 16 semi- OBS preset rhythms {rock, slow rock1, swing, bossanova, march1, waltz, rhumba, habanera | rock'n'roll, slow waltz, shuffle, samba, march2, rock waltz, beguine, mambo} (selected through 8 locking button switches + "variation" bank switch)
  • 14 OBS preset sounds {organ, flute, oboe, clarinet, trumpet, violin, cello, piano, harpsichord, celesta, accordion, electric piano, funny, frog} (buttons with each a red status LED)
  • "casio auto chord" switch {off, fingered, on} (manual chord mode with rhythm off)
  • "chord" switch {rhythmic, continuous}
  • chord memory switch (chord stays held after releasing key when on)
  • "octave down" switch (transposes main voice 1 octave down, works only in chord mode).
  • rhythm "fill-in" and synchro buttons
  • switches for vibrato, vibrato delay, sustain, hold
  • main voice timbres based on 2 mixed multipulse squarewave tones with different digital envelopes, those are differently low pass filtered through capacitors. Vibrato modulates CPU clock oscillator.
  • analogue percussion {base, snare, low tom, high tom, open cymbal, close cymbal, woodblock} which uses transistor noise for cymbal and snare
  • complex multi- chip hardware:
    • main CPU= "NEC D773G, K05266, Japan" (64 pin zigzag DIL)
    • accompaniment CPU(?)= "NEC D8049C, M0Z076-049, 084, Japan" (40 pin DIL)
    • IC "NEC D8243C, E01039-005, Japan" (24 pin DIL)
    • ROM(?) "Texas Instruments TMS3615NS, MBS [triangle] 8048" (28 pin DIL, socketed)
    • IC "AMD(?) AM 6012PC, 8050FM" (20 pin DIL)
  • tuning knob
  • mains operated
  • jacks for headphone, line out, aux in, volume pedal, sustain pedal, foot switch
Casio Auto ChordSERIAL NO. 181707, CT-401

notes:

Although on the case back this instrument is called CT-401, but its official name on the front panel was Casiotone 401. All preset sounds are selected through non- locking OBS push buttons with individual small red indicator LEDs; apparently Casio wanted to visually demonstrate here their use of advanced digital technology, since the similar looking OBS rhythm buttons employ still old fashioned locking switches. But all buttons and switches have still the classic 1970th home organ appeal with even different button colours per preset sound group; they all respond easily and feel quite noble. (The controls e.g. strongly resemble those on older Yamaha Electone organs of the A-, B-, C- and D- series.) The speaker grill has still the same style like with the Casiotone 201 (the world first Casio keyboard), although here it is dark brown instead of black. Impressive are also the massive count of 6 jacks on the back. Unfortunately there are no individual volume controls for rhythm and accompaniment (although these can be certainly added). My specimen came with the volume pedal Casio VP-1 and a stylish chromed original Casio keyboard stand.The Casiotone 401 is quite heavy (about 10kg?) because despite its case looks almost perfectly like wood, it is mainly made of plastic coated sheet steel. (Casiotone 201 and 202 were of genuine wood.) In spite of this it is not as robust as it appears, because at the corners of the side pieces (made of pressboard?) the plastic woodgrain tends to peel off. I had to hotglue mine back into place, but this sheet plastic stuff also cracks off easily when accidentally folded to hard. I bought my specimen in very dirty state; the whole case was severely sticky especially at the bottom. I am not sure whether it was fatty kitchen dirt or if anybody had tried to apply furniture wax on the case despite it is not of wood. I removed most of that gunk with a paper towel and vegetable oil (stay away from rubber parts) followed by water with dish washing soap.
The dirty speaker grill had to be removed also for cleaning, because someone spilled cacao or similar on it.
Be careful with the 5 metal lashes with screw holes those hold the rear part of the control panel from inside. With case opened, these lashes are sharp as razor blades and easily damage the panel and PCB traces; with mine a preset sound LED failed by an accidentally cut trace after working on the opened keyboard. After soldering the trace I glued ribbon adhesive tape over the sheet metal lashes to make them less dangerous. After opening, a lot of broken small black rubber rings fell out of the case - likely they belonged under the piano keys somewhere for damping (keys feel a little loose), but turned brittle by oily room air or ozone. The quite complex analogue hardware of this instrument has the size of an old style PC mainboard and contains many discrete components for the analogue percussion. The percussion have individual trimmers for their decay time. The main IC numbers and sounds have some similarities with the smaller Casio MT-40. The power amplifier is a quite big hybrid module. Unusual is that the fingered chord is up to 12 note polyphonic with additional monophonic bass, while the main voice has a polyphony of only 8 notes. (I haven't analyzed the hardware further yet).

Like with the Casio CT-410V, the main voice sounds of the Casiotone 401 consist of 2 mixed multipulse squarewave suboscillators with different pulse patterns and different digital volume envelopes, those are (depending on the preset) muffled by different filter capacitors. Thus both instruments have the same kind of sounds, although unlike the rather dull CT-410V,  many sounds of the 401 have a reasonably bright and partly incredible dry timbre, and when a key is trilled with sustain, each new note here occupies a new sound channel, which produces a great phasing sound and volume increase effect although this eats up polyphony. In the bass range many sounds turn into a more or less buzzy, sonorous purring drone, which is a characteristic style element of squarewave based instruments. These basses can resemble some of the famous POKEY sound effects on Atari XL homecomputers and are very different from the gradually duller and duller growing sine wave bass behaviour of average Yamaha FM keyboard sounds. (For further technical details about this hardware family also see here.)
By the use of simple low pass filters, many sounds play high notes too quite. The "organ" is a slightly dull metal pipe organ timbre, which seems to be a muffled variant of the that classic multipulse sound. The bass range reminds to a wooden accordion. The "flute" is dull and resembles a sine wave tone. As expected, "oboe" is harsher; the bass range resembles a saxophone. The "clarinet" turns thinner during its attack phase. The "trumpet" sounds quite thin and barely recognizable (like with many squarewave based instruments). The "violin" sounds ok (especially with vibrato), while the "cello" is dull and could be also a dull tuba or the like. The "piano" has a too dull bass range; the "electric piano" is the same in slightly brighter. The "harpsichord" sounds ok. The "celesta" is a musicbox sound that sounds unrealistic by a too slow attack phase; the timbre resembles a flute. The "accordion" has a fluttering attack phase (quickly quieter and louder again, more like a violin) and sounds too dull and plastic- like. The "funny" preset is a sort of rough digital slap bass (creaky picked e-bass) which sounds like "ennng!" (possibly it was initially intended to be called "funky", but sounded to artificial for this?). An even harsher variant of this is called "frog" (although it doesn't sound at all like one), which makes a wonderful rough and incredible dry bass noise. When sustain is switched off, all sounds stop almost immediately after releasing the key, and the sound presets itself also contain neither vibrato nor tremolo. The sustain duration depends on the preset sound. The vibrato is quite fast (6Hz) and its intensity depends on the preset sound. When "vibrato delay" is additionally pressed, the vibrato waits 1s before it starts (vibratos affect also sustain); with vibrato off this button does nothing. Very unusual is the "hold" switch, which makes the melody section of the keyboard behave like the manual fingered chord mode on most newer keyboards; the notes of any pressed key or key combination (e.g. chord) are held after key release, and after all keys are released, any newly pressed keys stops the old held notes and instead plays and holds the new ones. Apparently the algorithm of the manual fingered chord with chord memory was re-used for this. Despite there are nicely big semi- OBS preset sound buttons, they are no good realtime sound control since they mute held notes while pressed and cause a delay of about 0.3s after button release before held or new notes will sound again.
The percussion are typical soft analogue home organ drums; cymbals and snare are likely made from transistor noise. The patterns also include beside the usual stuff also a few nice latin rhythms and the "fill-in" button inserts a fill-in pattern (including accompaniment), which depends on the selected rhythm. Unusual is that during rhythm not only the "start/ stop" LED lights up during the first step of a bar, but both the red "start/ stop" and the (at that time expensive?) green "synchro" LED dimly flash during every step. Despite the locking button switches, the semi- OBS preset rhythm buttons switch a playing rhythm only at the end of the bar, which limits their use for realtime play tricks.
Unlike later Casio instruments, the accompaniment here was not yet called "Casio Chord", but "Casio Auto Chord" (abbreviated "CAC"), and it also did not feature yet an arpeggio. But the accompaniment of this historical instrument already accepts any disharmonic note combinations and not just those few ones that establishment has defined to be "chords". Apparently there was already more software behind than with the archaic Antonelli Star 2379, because the bass pattern here only plays its note sequence when it recognizes chord- like key combinations, while it plays only one note during wild clusters or a single key press. Unusual with the 401 is the "chord" switch; when set to "rhythmic", you get the usual automatic bass and chord accompaniment, but when set to "continuous" only the bass plays automatic the note of the lowest pressed chord section key, while all keys of the chord section otherwise are in manual organ chord note like with rhythm off. The accompaniment patterns are made from a monophonic bass line (some with walking bass) and simple staccatos of the current chord (or note combination). The chord voice is a plain squarewave organ tone, while the bass is a dull and warm organ bass tone with sustain that reminds to a dull Roland TB-303 bass and may be made from a triangular wave. With rhythm off there is a manual chord mode (12 note polyphonic!) with bass on the lowest played key. Unfortunately also here the notes always stay within 1 octave, thus it is no real key split. Regard that with this ancient Casio the chord section will not play any sound when the "chord" switch is set to "rhythm" while rhythm is off. With the "memory" switch the current chord is held after key release (with or without rhythm). Moving the "chord" lever switch slowly during rhythm varies the chord volume, which can be also used musically.
A strange Casiotone 401 variant without accompaniment section was released as Casiotone 301 (seen on eBay - likely extremely rare now since I never saw another one). This CT-301 had an identical case beside that it lacks the 4 white switches, the letter row above leftmost keys, the fill-in button and has only 4 jacks. Also the control panel sections are in different order (power switch, 16 preset sound buttons, vibrato switches, 8 rhythm buttons, rhythm start/ stop & synchro switches, 3 knobs) and employ the 2 black toggle switches here for rhythm start/ stop and synchro instead of the missing sustain and hold functions. Also the orange rhythm select switch apparently does something else, thus there are only 8 OBS rhythms.

Casio PT-87

Casio PT-87

This grey cased instrument was a re- release of the PT-82 from 1987. (Inside the case embossed marks for 87 and {5, 6, 7, 8} make me conclude that it was manufactured between may and august in 1987.) Unlike the PT-82, it has the classical pale coloured Casio buttons again.

On this photo from eBayyou see my Casio PT-87 and my PT-82 (below).
The PCB of this specimen contains less discrete components, the shielding aluminium cardboard inlay is gone and the PT-87 has also no headphone jack anymore. The CPU is "HD61703B01, 7D 33". My specimen has a strange defect; when operated with batteries, it sounds distorted and howls, while with a power supply it sounds perfect. Apparently the battery voltage (5 batteries = 7.5V) is too low to operate the circuit properly - possibly a defective voltage regulator drops too much voltage.

modifications:

  • Power supply jack polarity changed and protection diode added (with PT-82 and PT-87).


Casio PT-82 small keyboard with ROM-Pack, key lighting & blip rhythm



Casio PT-82
This keyboard from 1986 has many similarities with the Casio VL-Tone 1 and PT-1, but includes a "melody guide" key lighting feature for music teaching (not the keys itself light up but a row of small LEDs above them) and a ROM- Pack music cartridge slot. Unfortunately this instrument is missing the great built-in synthesizer, sequencer and 3 octave switch of the VL-Tone.



Although the music playback from the ROM- Pack includes wonderful polyphonic accompaniments, the player can play own musics only monophonic with thin and dull sounding blip rhythms. A bit unusual is that this white keyboard has brightly coloured orange and red buttons and red lines while Casio normally preferred pastel colours. Also a red case version of the PT-82 was made. In 1987 it was re-released in grey as Casio PT-87.

main features:

  • 32 mini keys
  • built-in speaker (with unpleasant, loud mid-range resonance)
  • monophonic main voice
  • 8 OBS preset sounds {violin, organ, harpsichord, piano, celesta, trumpet, clarinet, flute}
  • 12 preset rhythms {rock, disco, 16 beat, swing 2 beat, swing 4 beat, samba, bossa nova, beguine, tango, march, slow rock, waltz}
  • volume switch (5 steps)
  • tempo +/- buttons (16 steps?)
  • ROM- Pack music cartridge slot for melody guide and "auto play" (jukebox mode)
  • "melody guide" keyboard play training feature with key lighting (32 red & green LEDs above the keys), 4 levels and automatic rating
  • 2 "one key play" buttons (to step note by note through ROM musics)
  • semi- analogue sound generator similar like VL-1 (only monophonic keyboard play, but additional 4 note polyphonic accompaniment during automatic ROM music play). The digital envelopes (with audible zipper noise) are linear and thus sounds unrealistic because they fade silent too soon.
  • rhythms consist of dull and distorted digital (squarewave?) blips + simple shift register noise {base, low tom, high tom, snare, cymbal}
  • CPU= "HD61703B01, 5L  13"
  • tuning adjustment trimmer
  • headphone and power supply jack



notes:

The PT-82 was likely intended as a technically simplified successor of the Casio PT-80. The speaker has an unpleasant, loud mid- range resonance. The main voice sounds are the same like with the PT-80, but tend to sound a little thinner and harsher. These sounds resemble much a Casio VL-Tone 1; unfortunately they don't include the famous "fantasy" sound of the latter. Although the musics from ROM- Packs play with nicely orchestrated accompaniment, the player can play own musics only monophonic with a simple rhythm and no accompaniment at all. Due to various other "Casio PT" keyboards (e.g. PT-30 or PT-80) had a set of additional buttons to the left of the keyboard to play chords, I searched also for such keyboard matrix eastereggs, but yet found none. The distorted percussion sounds a bit harsh, very colourless, and really thin and boring (like when blip drums from a PT-30 keyboard would have been resampled at an extremely low resolution and sample rate which removes all dynamics). The rhythm patterns resemble the PT-80, but are not identical (e.g. blip instead of popping base drum). Much like with the VL-Tone 1, the harpsichord sound suffers from a too slow attack rate, which makes it unrealistic. In the plastic case of my PT-82 was an embossed mark that seems to be the manufacturing date 86-02-08. The hardware is much simpler than PT-80 and contains far less analogue components; with my PT-82 one of the red key lighting LEDs was faulty and had to be replaced.When the instrument is switched on, it plays a tone scale (8 notes) while a light runs from left to right on the LED chain. The instrument was sold with the Casio ROM- Pack RO-551. The ROM- Pack cartridge employs the same conductive carbonized silicone rubber connector that is used in many LCD watch displays. (I had to clean mine and the contact row on the PCB with isopropanol to make it function reliable.)
More interesting is that the musics from it can be used with "melody guide" training feature, in which a flashing LED (next key) and a lit LED (current key) in the LED chain above the keys teach monophonic keyboard play. It has 4 training levels {1= with light, waits for correct key, 2= with light, no waiting, 3= without light, waits for correct key, 4= without light, no waiting}. After finishing a piece of music, the player can press the "rating" button to see how good he has played. To show this, a sort-of "wheel of fortune" noise effect is played while a light runs multiple times from left to right above the keys. The light turns slower and then stops at a certain key. The better the player has played (less wrong noted and timing flaws), the further right it stops with a short jingle that depending on how good the player was {"* TRY AGAIN"= falling notes, "** FAIR"= very disharmonic clip of "Unterlanders Heimweh", "*** GOOD"= fanfare, "**** EXCELLENT"= different fanfare}. As a sound effect, the rating jingles can be also started by pressing the "rating" button while the mode switch is set to "play" instead of "melody guide". In this case the melody guide level select switch selects which of the 4 jingles is played.





Casio MT-18

(photo taken from eBay, showing my specimen)

 
This brown keyboard is simply the midsize version of Casio PT-80. Thus the main voice is still monophonic despite bigger keys. The specimen I bought even came with the same ROM-Pack RO-551.

different main features:

  • 32 midsize keys
  • better speaker (without disturbing resonance)
  • different CPU= "HD61703A01, 5B 33" (80 pin SMD)

notes:

Very unusual is that the MT-18 contains a different CPU despite the behaviour is identical with the PT-80. Thus I guess that the same CPU core was only re- released in a different package or manufacturing process for technical reasons, while the internal circuit stayed the same. Also the PCB layout and material looks very different. Despite it worked well, I found in my Casio MT-18 an exploded electrolytic capacitor (which I replaced).


Casio PT-80 small keyboard with nice analogue rhythm & accompaniment

Casio PT-80
This keyboard has many similarities with the Casio VL-Tone 1 and PT-1, but includes a "melody guide" key lighting feature for music teaching (not the keys itself light up but a row of small LEDs above them) and a ROM- Pack music cartridge slot. Unfortunately this instrument is missing the great built-in synthesizer, sequencer and 3 octave switch of the VL-Tone.  Like the Casio PT-30, the single finger chord concept of this instrument makes chords selectable by name instead of pressing multiple keys, but unlike the latter it is even more restricted and permits only 4 different chords. Besides the white version, this instrument was also made in red. The original German retail price in a German Conrad catalogue from 1986 was 299DM (about 150€).




(This is an eBay picture; my PT-80 is missing the cartridge lid.)


main features:

  • 32 mini keys
  • 12 key buttons + 3 select buttons for direct selectable single finger chords (only 4 standard chords)
  • built-in speaker with unpleasant, loud mid-range resonance
  • monophonic main voice
  • 4 note polyphonic chords or accompaniment
  • 8 OBS preset sounds {piano, harpsichord, organ, violin, flute, clarinet, trumpet, celesta}
  • 12 OBS preset rhythms {rock, disco, 16 beat, swing 2 beat, swing 4 beat, samba, bossa nova, beguine, tango, march, slow rock, waltz} with piano(?) accompaniment
  • rhythm fill-in
  • main & accompaniment (with rhythm) volume sliders
  • tempo +/- buttons (20 steps)
  • ROM- Pack music cartridge slot for melody guide and "auto play" (jukebox mode)
  • "melody guide" keyboard play training feature with key lighting (32 red & green LEDs above the keys), 2 levels
  • 2 "one key play" buttons (to step note by note through ROM musics)
  • semi- analogue monophonic sound generator similar like VL-1; the digital envelopes (with audible zipper noise) are linear and thus sounds unrealistic because they fade silent too soon.
  • chord sound with fixed timbre (3..4 voice squarewave organ)
  • simple analogue percussion with transistor noise (base, low tom, mid tom, high tom, snare, open & closed hihat}
  • CPU= "NEC D1868G  007, 8441XK, Japan" (80 pins SMD)
  • tuning adjustment trimmer
  • headphone and power supply jack



The PCB has empty solder holes, but unlike Casio PT-30these ones have no printed component names.

modifications:

  • Power supply jack polarity changed and protection diode added.

notes:

The speaker has an unpleasant, loud mid- range resonance. The hardware of this instrument consists of 2 large, stacked PCBs with much analogue stuff. The upper PCB has empty soldering holes for a 16 pin DIL IC, those unlike the rest are not labelled with component numbers. Very interesting is that this instrument contains the same CPU (D1868G) like the (older?) Casio PT-30, but the latter has additionally the small IC "HD B 61914" (44 pins SMD) that communicates with it. First I thought the small IC would be an external program ROM, but I guess that the different 3 following digits of the CPU type number indicate a different internal ROM software.The monophonic main voice sounds much like a Casio VL-Tone 1; unfortunately it lacks the famous "fantasy" sound of the latter. Much like with the VL-Tone 1, the harpsichord sound suffers from a too slow attack rate, which makes it unrealistic.
Although the single finger chord section looks interesting, its capability is very restricted; during rhythm the organ chord is always replaced by automatic accompaniment (like with most keyboards) and it is also generally impossible to play fewer or different tones than a standard 3 or 4 note chord, and unlike the PT-30, this instrument even plays only 4 different chord types and nothing else. With rhythm, once the accompaniment has started (by touching a chord key button), you can not stop the accompaniment again (i.e. pause chords) without stopping also the rhythm.
Rhythms are selected by OBS buttons, and by pressing the button of the already playing rhythm, a fill-in is inserted. The analogue rhythms resemble the Casio PT-30, but additionally they have an unusual popping base drum, that sounds like an exploding firecracker far away. The percussion has an interesting timbre with partly long sustaining white noise "cymbals". The toms seem to be based on squarewave tones produced by the main CPU and muffled by external capacitors.
The instrument was sold with the Casio ROM- Pack RO-551"World Songs", which contains the 4 songs {1= "Unterlanders Heimweh", 2="Greensleeves", 3="Die Lorelei", 4="Old Folks At Home"} and has a "not for sale" notice. All these  musics have a great and complex orchestrated arrangement. The ROM- Pack cartridge employs the same conductive carbonized silicone rubber connector that is used in many LCD watch displays. More interesting is that the musics from it can be used with "melody guide" training feature, in which a flashing LED (next key) and a lit LED (current key) in the LED chain above the keys teach monophonic keyboard play. It has 2 training levels {1= keeps playing, 2= waits for correct key}. With the "cancel guide" button the LED row can be switched off, thus the same 4 variants like on the later Casio PT-82 exist. But the PT-80 does neither include the great "rating" feature of the latter. When the instrument is switched on, it plays a tone scale (8 notes) while a light runs from left to right on the LED chain.
A likely direct successor of the PT-80 was the technically simplified Casio PT-82 (which unfortunately misses the chord buttons and has boring blip drums).



Casio PT-50 small keyboard with nice analogue rhythm, accompaniment & ROM-Pack

This was the only Casio keyboard with ROM-Pack slot but no key lighting; instead it can load the ROM-Pack musics into an internal sequencer, and with the optional Casio TA-1 module it can even save them on audio cassettes. Even a RAM-Pack cartridge Casio RA-1 was made for this thing to save sequencer data - I never saw any other Casio keyboard designed for using it.

Despite this keyboard looks almost like a twin of the Casio PT-30, there are many small differences. 3 of the 8 preset sounds are changed, the chords and bass timbre is different and also the rhythm set is completely different and includes fill-in. Even the LCD has different segments and shows e.g. a "J" for major chords. Also the sequencer of this thing was changed and is horribly awkward like with Casio MT-70, because it apparently neither can record note lengths in realtime nor melody and chord together, thus everything has to be entered in different modes step by step. But by the general similarities I only explain here the differences to the PT-30.

different main features:

  • 8 OBS preset sounds {piano, harpsichord, organ, violin, flute, clarinet, trumpet, celesta}.
  • 16 preset rhythms {rock, rock'n'roll, disco, 16 beat, samba, latin rock, bossa-nova, beguine, tango, march, waltz, rock waltz, slow rock, ballad, swing 2beat, swing 4beat} made of analogue percussion + bass & piano accompaniment (contains no arpeggio).
  • tempo +/- buttons (19 steps, counts 1..20)
  • different editable sequencer (no realtime recording, terribly awkward!)
  • transpose buttons (12 semitone steps)
  • different LCD display shows pressed keys and chords (only important for the sequencer)
  • ROM-/ RAM- Pack slot (but no key lighting/ melody guide feature)
  • demo button (plays musics from the inserted ROM-Pack when present)
  • multi-chip hardware:
    • CPU= "NEC D1868G 004, 8314EK, Japan" (80 pin SMD)
    • 2x SRAM= "HD  B, 61914, 3D, 23" (44 pin SMD)
serial F015914


eastereggs:

  • To mute only the accompaniment but keep the rhythm running, keep the sequencer memory empty and press the "one key chord" button.

modifications:

  • Power supply jack polarity changed and protection diode added.

notes:

Like the Casio MT-800, this instrument came with the ROM-Pack RO-201 and has to load ROM-Pack musics into its internal RAM (takes a few seconds) before it can play them. This is also valid for the demo melody, which doesn't play with ROM-Pack removed (shows error "E -") despite the melody keeps playing when the ROM-Pack is removed while the demo is playing. The hardware in the small PT-50 case is even more crowded than in the similar looking Casio PT-30, because between panel and analogue PCB it contains even a 3rd intermediate PCB for the digital ICs. But fortunately this daughter board at least makes the CPU behaviour a bit easier to examine since you don't need to take out the panel PCB (with a hand full of loose buttons flying around) to access it. Also the LCD here is held by a sheet metal bracket that didn't exist in the PT-30. (I haven't examined the hardware further yet.)
Some preset sounds differ from Casio PT-30: The "organ" here has neither vibrato nor sustain, the "violin" and "flute" here lack sustain also. The sounds "horn", "fantasy", "mellow" of the PT-30 were replaced with "clarinet" (has no vibrato), "trumpet" (like "horn" without sustain) and "celesta" (like "harpsichord" with sustain and 1 octave higher).The manual organ chord voice lacks the dull organ bass component and instead everything plays an octave lower, which sounds cheaper and more squarewave- like. In opposite to the PT-30, here you can trill around on different chord type buttons while holding a chord note key. (The PT-30 ignores further chord type button presses, thus you have to also release and press again the chord note key before you can choose another chord type, which was bad for comparing how different chords sound.) With rhythm, the bass voice has here a low, sonorously buzzing, decaying squarewave timbre with sustain, that reminds to an e-bass, but is also a little brassy. The rhythms set is very different from PT-30 and unfortunately lacks the nice arpeggio styles. But instead the rhythms now have each a fill-in pattern with accompaniment. Annoying is that the rhythms don't start immediately anymore after selecting them, but you have to press the "start/ fill-in" button, which always begins with a 4 step snare lead-in before starting the rhythm itself. Also the pattern restart trick of the PT-30 can not be used here by the lack of "chord change" buttons.

Casio RAM-Pack RA-1I finally found on eBay the mysterious RAM-Pack cartridge for the Casio PT-50. It is named Casio RA-1 and can store apparently only one song. You can even save any ROM-Pack song from the internal PT-50 sequencer memory to it, which is correctly loaded back including the obligato voice.
I first hoped that it would be possible to compose own musics on the PT-50 (or even PC through the TA-1 tape interface) and play them on other ROM-Pack compatible Casio keyboards. However unfortunately the RA-1 seems to be incompatible with normal ROM-Pack keyboards; they ignore it like when the ROM-Pack slot was left empty.
The RA-1 contains a 3V lithium button cell "BR-2016"; the manual claims it would last only 1 year, but longer with RA-1 inserted into the keyboard. (This can make only sense so far the keyboard contains batteries.) However in PC mainboards the same kind of "CMOS" memory backup batteries last about 10 years. For battery replacement you have to open the cartridge; first remove the slider, then unscrew the 2 tiny screws underneath.
To analyze the hardware closer, I needed to take out the PCB itself. But the only screw holding it was jammed in so tightly, that its flat soft iron head refused to be moved and only crumbled apart by any serious attempts of loosening it. Thus I had to drill it out; unfortunately the thin drill I used suddenly bent away by too much force, which made my heavy household drill machine violently crash down into the PCB, resulting in a PCB crack that damaged a lot of traces - arrg! Fortunately by my Casio KX-101 nightmare repairs I was more than experienced enough to patch them together again.
The hardware is made of 2 identical SRAM ICs "HD B 61914". Interesting is the pin assignment; the left side of the 1st RAM exactly corresponds to the pinout of the ROM-Pack slot, the traces are 1:1 connected with its top side pins and with the left side of the 2nd RAM. To top row pins of RAM 1 are all wired to +Vs. Almost all pins of the down side of both ICs are shorted with each other. To the right side only few pins are used (apparently for control purposes), while many others are shorted too. I assume that the top pin row of the 61914 IC is likely NC (internally not connected) and thus simply connected in a way that makes it easiest to route traces from other pins underneath it on the single sided PCB.
Casio used the same IC also as internal SRAM in the PT-50, the PT-30, and a similar looking HD C 61914 in the KX-101.
The ROM-Pack implementation of this keyboard is very different from all my other Casios and a little unobvious. To select a song, press the "R/MT" button once ("R" appears in the LCD), then type the 2 digit song number with the rightmost keys and press "play", which copies the song into the internal RAM (takes some seconds) and plays it. (Pressing "R/MT" twice displays "MT" and apparently tries to load the music file from a cassette through the optional Casio TA-1 module.) Unlike a ROM-Pack, the RAM-Pack RA-1 ignores the selected song number, because it apparently holds only 1 song. The "demonstration" button plays all musics from the inserted ROM-Pack in a sequence, starting with the first. The 2nd melody voice (obligato) of ROM-Pack musics plays a bit too quiet on my PT-50. (Warning: Playing any ROM-Pack musics overwrites and thus deletes the actual sequencer contents.)
Unfortunately I have no manual for this thing, but this is what I found out. Press "chord" and then "play" to play only the chord track. Press "melody" and then "play" to play only the main voice. To delete the sequencer contents hold "record" and press "clear". To record your own melody into the sequencer, hold "record" and press "melody" to enter melody recording mode. Play the melody note by note (press "reset" to quit). Afterwards the note lengths must be entered separately, and also chords can not be recorded together with the melody. :-[  (No joke! The PT-30had no trouble with that.) To enter the note lengths, press "play" in melody recording mode and step with the right tempo through the melody using the "one key play" buttons until the melody ends (or press "reset" to finish). When no note lengths are entered, the melody plays with tremendous speed. To record chords works similar, but hold "record" and press "chord" for the chord recording mode. To enter chord lengths (not necessary when you played right), press play in this mode and step forward with the "one key chord" button. To edit the sequencer contents, enter the melody or chord recording mode again and step through your track with the "for" button. Any new played notes or chords are inserted at the current position. The "delete" button deletes the last played note/ chord from the track. After edit press play in that recording mode and correct the note lengths with the "one key play" and "one key chord" buttons again. (Note: ROM-Pack musics contain beside melody and chord voice a 2nd main voice called "obligato"; unlike melody and chord, this additional voice can apparently not be edited in the sequencer.) To save the actual sequencer contents on a RAM-Pack, press "R/MT" once and then "save".

Like the Casio PT-30, the PT-50 has an expansion cartridge slot for the Casio TA-1 tape memory interface to save the sequencer contents, thus it might be possible to save with this thing ROM-Pack music data on cassettes or upload them to a PC for further analysis or even sound emulation. Unfortunately you can not play them through the RAM-Pack RA-1 on other ROM-Pack keyboards, because the RA-1 is incompatible with them.
 


Casio PT-30small keyboard with nice analogue rhythm & accompaniment

This keyboard has many similarities with the Casio VL-Tone 1 and PT-1, but unfortunately it is missing the great built-in synthesizer and 3 octave switch of the VL-Tone. Interesting is the single finger chord concept of this instrument, which makes chords selectable by name instead of pressing multiple keys.



The instrument has only a monophonic main voice with 4 channel chords, but it features 18 nice rhythms made from analogue percussion with quite special sounding white noise cymbals. There is also an editable sequencer. A dark grey version of this instrument was released as Casio PT-31.

main features:

  • 31 mini keys
  • 12 key buttons + 9 select buttons for direct selectable single finger chords
  • built-in speaker with unpleasant, loud mid-range resonance
  • monophonic main voice
  • 4 note polyphonic chords
  • 8 OBS preset sounds {piano, harpsichord, organ, violin, flute, horn, fantasy, mellow}.
  • 18 preset rhythms {waltz, ballad, swing, enka, 16 beat, rock 1..3, disco 1..2, bossa- nova, samba, arp. 1..6} made of analogue percussion + bass & piano accompaniment (partly with arpeggio).
  • tempo +/- buttons (19 steps, counts -9..9)
  • 3 sliders for main, chord & rhythm volume
  • sequencer (with edit features, 8 song memories, battery backed-up)
  • 2 "one key play" buttons (to play or edit sequencer contents note by note)
  • transpose buttons (-9..+3 semitone steps)
  • LCD display shows pressed keys and chords (only important for the sequencer)
  • semi- analogue monophonic sound generator similar like VL-1; the digital envelopes (with audible zipper noise) are linear and thus sounds unrealistic because they fade silent too soon.
  • simple analogue percussion with transistor noise (low tom, high tom, snare, open & closed hihat,??}
  • chord sound with fixed timbre (3..4 channel squarewave organ + monophonic bass organ voice)
  • multi-chip harware:
    • CPU= "NEC D1868G  001, 8319EK" (80 pins SMD)
    • SRAM= "HD  B, 61914, 3F, 33" (44 pins SMD)
  • expansion cartridge slot at the bottom (for cassette saving module)
  • tuning trimmer
  • sound output & power supply jack


It would be a hell job to search for matrix eastereggs inside this nasty hardware design.

On the PCB there are some empty holes where an additional logic IC was planned.

eastereggs:

  • To mute only the accompaniment but keep the rhythm running, select an empty sequencer memory or "edit" and press the "one key chord" button.

modifications:

  • Power supply jack polarity changed and protection diode added.

notes:

At least with my specimen of PT-30 the speaker has a very unpleasant, loud mid- range resonance and some keys squeaked badly when pressed (I lubed them with thick silicone oil to fix them). The hardware of this instrument consists of 2 stacked, large PCBs with much analogue stuff. Unfortunately the SMD CPU sits at the rear side of the control panel PCB, which makes this instrument extremely awkward to analyse because the buttons and silicone contacts tend to fall out and the LCD with its fragile plastic foil cable can easily break or get dusty inside during measurement attempts at the CPU. (I didn't dare to analyse it further yet, but at least made some PCB photos.) The CPU is of the same "D1868G" series like in Casio PT-80, but the following 3 digits are different and it communicates with an additional small IC "HD B 61914". First I though the small IC would be an external program ROM and the CPU would be the same. But because my PT-50 contains also a D1868G series CPU and 2 identical "HD B 61914" ICs, and the latter are also used in the RAM-Pack RA-1, I conclude that the 61914 ICs are SRAMs for the sequencer, and the numbers "001" and "007" at the end of the CPU type "D1868G" instead indicate that both CPUs contain different software in their internal ROM.
Although the single finger chord section looks interesting, its capability is very restricted; during rhythm the organ chord is always replaced by automatic accompaniment (like with most keyboards) and it is also generally impossible to play fewer or different tones than a standard 3 or 4 note chord, thus this instrument forces the player only to play tone combinations those its programmed musical dogma regards as a chord. A little confusing is also that it ignores further chord type button presses when a chord note key is held, thus you have to also release and press again that key before you can choose another chord type, which is bad for learning by direct comparison how chords sound. But despite all this the PT-30 has some interesting sounds; generally the tones are a bit harsher than my Casio VL-1, and unique is that the "mellow" sound (a sort-of vibraphone) has a vibrato envelope that turns faster while fading silent. The "organ", "violin", "flute" and "horn" all include short sustain and a 6Hz vibrato. "fantasy" is (similar like on VL-1) a high synth flute timbre with longer sustain and 6Hz vibrato (that also turns a tiny bit faster during sustain?). Its a pity that the PT-30 has neither the famous VL-Tone ADSR synthesizer feature nor real polyphonic play. Much like with the VL-1, the "harpsichord" sound suffers from a too slow attack rate, which makes it unrealistic. I also discovered that when shitshot by battery wiggling it sometimes makes other sounds than the built-in presets, much like my VL-1 does.
The analogue rhythms have an interesting timbre with partly long sustaining white noise "cymbals". The toms seem to be based on squarewave tones produced by the main CPU and muffled by external capacitors. But at least my PT-30 specimen has not the strange popping base drum of the technically similar PT-80. The manual organ chord mode plays a sort of thin metal pipe organ rank timbre layered with a warm and dull organ bass and a small dose of sustain. The accompaniment with rhythm simulates a kind of piano and e-bass sound using these waveforms with decay envelope. The 2 "chord change" buttons almost immediately restart the current rhythm pattern on each a different step, which can be used as a sound effect.
The sequencer works quite similar like with Casio VL-Tone 1. To record or edit anything in the sequencer contents, switch the power switch to "record". You can now simply play keyboard (including chords) and everything is recorded. Press "memory play" to listen to it. To change the note lengths, play the melody with the "one key play" buttons in the correct tempo. To delete the last heard note or chord press "del.". Use the arrow buttons "<", ">" to step back and forward (notes and chords sound alternatingly to ease deleting). Any now played notes or chords are inserted at the current position. With the "chord change" buttons you can step the value of a currently displayed chord up and down. To delete the entire song, press "clear". The sequencer supports 8 songs; to switch between songs, press "memory" followed by one of the black keys "M1".."M8". I have no manual for my PT-30, thus there may be still hidden features I don't know. E.g. you can select "edit" here, which in "play" mode simply behaves like an empty memory and in "record" mode mutes the keyboard. The arrow buttons are labelled "save" and "load", which likely refers to the optional TA-1 expansion module to save sequencer data on audio cassettes. Likely you have to set the power switch to "MT", select a song memory and press "save" or "load" to save or load data from cassette.

Here you see the open expansion cartridge slot at the bottom of my PT-30. At the back you see 2 plugged holes labelled with "memory in/ out"; the expansion module Casio TA-1 could be inserted here for saving sequencer data on audio cassettes.To the left of it you see the pitch trimmer for tuning the instrument.



Casio TA-1 (tape storage cartridge for sequencer data)I now finally got the occasion to buy the very rare Casio TA-1 cartridge ("Tape recorder interface for CASIO electronic keyboard"), originally packaged with manual and connection cable.


Unlike my expectation it is not just an empty "pay additional luxury" dongle plug with a few jumper wires or cheap resistors inside to fool customers, but it contains indeed 2 ICs, a clock crystal and some discrete components soldered on 2 small PCBs. The ICs are "HD 43530, 3A13" (44 pin SMD) and "KIKN61S, 2N3111" (10 pin COB).






The manual mentions in the specification:

Output terminal:
Output impedance: 1.6 kOhm
Output voltage: 2.5 - 4.5 mV
Input terminal:
Input impedance: 55 kOhm
Input voltage: 2.5 - 50 V
Data recording format:
Kansas City standards

I don't know if "Kansas City standards" is anything documented or just a fancy name for a proprietary data format. I also yet haven't tested to save and load data with it. By my knowledge only the Casio PT-30 and PT-50 have a cartridge slot for the TA-1, but possibly also others exist; in the TA-1 manual there is no list of compatible keyboard types included.

Here you see the TA-1 cartridge inserted into my Casio PT-30.

An interesting fact is that Casio first advertised this tape saving feature as "MT" (for "magnetic tape") and later(?) named their entire midsize keyboards series "MT-..." despite none of them included a tape interface. Later Casio named a midsize toy keyboard with built-in stereo cassette player Casio TA-10, which also has no sequencer functions.

Interesting is also that the Casio PT-30 case has a groove at its upper rim; possibly this style element was inspired by the PlayCard slot of theYamaha PC-100 to suggest that this keyboard had similar capabilities. The key position dots on the LCD might have been intended as a cheap key lighting replacement, although I could imagine it terribly awkward to use them this way by an expansion module.
A likely direct successor of the PT-30 was the Casio PT-50, which case layout looks almost identical but has a ROM-Pack music cartridge slot (without key lighting) in the upper right corner and the strange case groove is gone. It could not only save sequencer data on cassettes (using the optional TA-1), but even on very obscure RAM- Pack cartridges those look like ROM-Packs but are certainly as rare as the TA-1. In detail there are many small differences between PT-30 and PT-50; e.g. some sounds and especially the entire rhythm set is different.
Also the rare ghettoblaster Fisher SC-300 Stereo Composer likely contained on its top a detachable Casio PT-30 (with different case style resembling Casio PT-50).


Casio PT-20

(photo from eBay, showing my specimen)

This tiny instrument seems to be just a downsized Casio PT-30 and sounds very similar. (I haven't examined the hardware yet.) Unlike the latter it is missing the LCD, the cartridge slot, some of the sequencer buttons, the transpose buttons and 2 high note keys (thus also the "arp. 6" rhythm). Instead of separate rhythm and chord volume sliders it has only a combined slider. Its small case resembles the Casio PT-1. The original German retail price in a German Conrad catalogue from 1986 was 199DM (about 100€).

The likely most advanced member of this hardware family was the ultra- rare keyboard boombox Casio KX-101 (37 mini keys, chord button pad, complex sequencer that saves data on audio cassettes), which was even 4 note polyphonic.