(keyboard with key lighting, barcode reader & analogue rhythm)
This keyboard from 1984(?) was Casio's first instrument with
key lighting feature ("melody guide") and was likely intended as competitor
to the Yamaha PC-100. Unlike with
modern such keyboards, not the keys itself but a row of tiny LEDs above
the keys flash up to teach keyboard playing. But while the PC-100
had its songs stored on so-called "PlayCards" with magnetic tape
strips, the MT-70 employed an optical barcode reader pen (Casio
MS-1) to scan in the songs from special barcode song books into the
internal sequencer memory.
(photo from eBay, showing my
specimen)
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But although the barcode for one song can take 2 pages, the complexity of the barcode musics is quite limited, because unlike the complex multi- track arrangements on Yamaha's PlayCards or on Casio's later ROM- Pack cartridge keyboards (see e.g. PT-82), the sequencer memory of the MT-70 can only store one monophonic main voice track together with the default accompaniment selecting from only 7 standard chords. A wooden fullsize key version of this instrument was apparently released as Casiotone 501.
The sequencer can be also programmed by live play and then stepwise edited by hand (forward and backward), but it is not possible to store any instrumentation or rhythm changes, nor to playback plain "organ" chords without rhythm from it; besides notes and chords the sequences can only store 2 loop points for refrains and their repeat points - that's all. Entering sequences with chords is very awkward, because chords are entered and edited only stepwise in a different mode, in which the main voice stays muted and only the current note number is displayed on the LCD. I read that some people found also the barcode pen very awkward and difficult to use, but I had no problems with it; with some training it is easy to scan in an entire page within 10s. When a line is scanned wrongly, a drum sound indicates this, and on the LCD you can read which line needs to be re- scanned. Important is only to hold the pen a little tilted, and because it contains no own light source, it may need proper ambient light to work.
All main voice sounds consist each of 2 mixed digital sine(?) waves with different volume envelopes. This sound generator was apparently optimized to simulate organ and flute tones, because everything else sounds very unnatural on it; the timbres are quite hollow, a bit harsh and bass notes tend to turn very dull. Likely it was intended as a direct competitor to the digital waveforms of the Yamaha PC-100 and should proudly demonstrate the end of the squarewave era, but since it sounds quite thin (very dull bass), it was certainly no great success and thus later Casio keyboards (e.g. the great CT-410V) returned to squarewave based timbres. The MT-70 has only one fixed organ timbre for chords and also its analogue percussion sounds rather thin, thus all together the MT-70 sounds quite plain home- organ- like, and this not necessarily in a positive way. But at least it features an unusual arpeggio and some unusual main voice sounds those (by my knowledge) do not exist on any other Casio midsize keyboard.
In opposite to many other early Casio keyboards, the case of this one is not white but light grey. The original German retail price in a German Conrad catalogue from 1986 was 799DM (about 400€).
The main PCB is vertically divided into 2 halves those are interconnected with ribbon cables. The left PCB contains apparently no digital components at all, but only the analogue percussion with 3 trimmer pots for snare, base and woodblock decay. On the LCD daughter board are 2 small ICs "MN12528, 37" (28 narrow pins) and "TC50H001" (16 pins). (I haven't analysed this instrument further yet.)
Interesting
for playing is that the 10 semi- OBS sound preset buttons can be also rapidly
pressed while keys are held down, which switches the sound or retriggers
the envelope of the already selected sound without any noticeable delay,
thus by rhythmically pressing these buttons many arpeggiator- like timbre
changes can be created, though this button field can be regarded as a realtime
sound control. (OBS sound buttons on most other Casio keyboards respond
rather slow.) The left half of the LCD always shows a picture of the sound
preset button layout, and black squares in it indicate the currently selected
button + "select" button status. (Apparently
Casio intended here
to simulate the intuitive visibility of locking switches with non- locking
ones, but in reality theses tiny black squares far away from the corresponding
buttons are rather confusing; a set of LEDs directly at these buttons (like
done with the sequencer controls) would have been more instructive. Later
Casio (like with CT-410V ) also returned to locking push buttons
instead.)
On the MT-70 only flute and organ presets sound fairly realistic, and even these resembles rather undistorted Hammond organ timbres. The "piano" consists of something like a plain sine wave with decay envelope, thus it features the likely dullest bass range ever heard on a so-called piano; possibly it should imitate an e-piano, but it resembles rather a dull Hammond organ bass with envelope, thus it is no wonder that after power- on the MT-70 selects the "pipe organ" as default sound instead. The "tibia" and "full tibias" are also organ (pipe?) timbres. The "celesta" resembles a music box, and its bass range rather a steel drum. Both "jazz organ" sounds are the same dull Hammond timbres, while the 2nd one begins with a more percussive key click. Also the "wood wind" sound resembles a Hammond timbre with a dull percussive click. The "chorus" is also just a plain pipe organ timbre, which perhaps may resemble a "vox humana" pipe organ rank, but has only very vague similarity with a human chorus. Otherwise the "synth brass" on the same button indeed sounds quite much like a synthesized human "wah" voice (although particularly the bass range is extremely hollow and resonant). The "wah brass" instead is no human voice nor anything brass- like, but yet another Hammond organ timbre; unfortunately it starts with a dull percussive click that sounds wrong particularly during polyphonic play. Likely Casio confused some sound names here when they designed the front panel. The "cosmic flute" is an electronic organ tone that starts with a percussive click (like a xylophone) and crossfades from a high to a medium octave sine wave. The "funky" sound resembles very much a steel drum and consists of a medium octave note rapidly followed by a high octave note with each a decay envelope. (You get almost the same sound by selecting the "piano" and then playing a 1 octave higher note rapidly followed by a 2 octave higher one. Interesting is that this sound has (by my knowledge) absolutely no relation to funk music, and that on other (later?) (e.g. CT-410V or MT-60) Casio keyboards instead different sounds with the names "funny" and "funny fuzz" were released, those all may have been the result of a successles attempts to program a "funky" e-bass sound, although none of these sounds like one. The "banjo" sounds rather hollow and resonant; the "xylophone" is a much duller version of it and sounds unnatural. The "vibraphone" is otherwise one of the more realistic timbres. The "synth bells" plays within 0.5s 3 notes (octave 0, octave +2, octave +1) on a sine wave timbre with decay envelope, thus it resembles a short arpeggio fragment. The "chime" is a brightly clanging metallic sound; high notes resemble a triangle, but the bass range sounds rather like telephone touch tones. This sound consists of 2 partial tones with 5 notes distance those have the same percussive decay envelope, and like "synth bells" it is great for new age music. 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 same sound engine like the MT-70, but with far more variations has also the early digital synthesizer Casiotone 1000p, on which the envelope and 2 timbre components for the individual sounds can be selected from each 10 variations (i.e. 1000 sound variations). The sine wave sound engine was apparently also employed in the ancient fullsize wood case keyboard Casiotone 701, but I only asked by e-mail about the sound preset names and couldn't listen to these yet to confirm this.
The accompaniment is similar flexible playable like the Testron one, and thus also accepts any disharmonic note combinations and not just those few ones that establishment has defined as "chords". But unlike later Casio keyboards (e.g. CT-410V or MT-60), the MT-70 features only a single fixed timbre (an organ tone with some sustain) for chords and accompaniment, thus also when played without rhythm, the rhythm switch can not be used here to select the chord section timbre. The arpeggio of the MT-70 behaves quite unusual, because when in fingered chord mode only one key is pressed in the chord section, the instrument plays the arpeggio track not continuously like other keyboards do, but fades it in and out and thus chops the chinking arpeggio note stream into separate bursts of notes (like if someone would slowly turn an imaginary arpeggio volume knob up and down again, synchronized with the rhythm bar speed). Only when more than 1 key is held down, the arpeggio plays continuously; the only other keyboard I know with this behaviour is my Casiotone 1000p, on which the arpeggio pattern can be even programmed by hand. With the MT-70 I also miss independent volume control knobs for the individual accompaniment voices.
My MT-70 came with a musical lesson book containing a stack of barcode score sheets for these 14 songs. In the ancient home computer magazine "Your Spectrum" (Issue 4, June 1984) was an article about connecting a Sinclair ZX Spectrum home computer with the barcode reader input of a Casio VL-5. This article contains a BASIC program and many technical details about the data format of the Casio barcode song books, and it says that the same program works also with the MT-70. The article can be found here.
Technically the closest relative of the MT-70 seems to be the Casiotone 701, because this large wooden instrument from 1982 with 61 fullsize keys had the same melody guide key lighting feature with barcode pen and sequencer (I saw this on an old Casio advertisement flyer). Someone e-mailed me that it is indeed based on the same CPU and sound chip type (although 3 instead of 2 sound chips) like the MT-70. This is quite unusual because the Casiotone 701 had instead of the LCD a red 3 digit "memory step" LED display and a different set of 20 sounds and 16 rhythms those were both selected through a set of locking push buttons and a bank select switch (8+1 for rhythm, 10+1 for sounds), and also the 2 rhythm names those share each button switch are different from those on each slide switch position of the MT-70. (He told me that 2 DAC ICs "AM6012PC" (12bit, 22 pins) had died in his specimen. I don't know if these often fail by ageing or wear - the modern replacement type for them is "Analog Devices DAC312".)
Another instrument with LCD and sequencer was the Casiotone 7000
(seen on eBay) which had a large beige metal case with 61 fullsize
keys, 12 rhythms (6+1 locking buttons) and programmable stereo chorus effects.
Like the MT-70 it had an LCD display and 20 semi- OBS sounds selected through
non- locking buttons, but it had no key lighting and employed a complex
sequencer that could save its data on audio cassettes. But according to
the rhythm names and most preset sound names it seems to be rather based
on the Casio CT-410V hardware class.
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