Yamaha MP-1
  world first key lighting keyboard,
first keyboard with score printer

Yamaha PC-100

This Yamaha instrument from 1982 was likely the world first keyboard with key lighting feature. Unlike modern such keyboards, not the keys itself but a row of tiny LEDs above the keys flash up to teach keyboard playing. The musics to be learned are stored on so-called PlayCards, those show the musical score and have a strip of magnetic tape on their lower edge that stores the music data, much like nowadays MIDI files.

This is the instrument in its carry case.
To read the data, the card is simply moved by hand from right to left through a slot on the instrument top, which only takes a second (extremely fast in comparison to that time's homecomputer datasette tapes and diskettes). The PlayCard musics are quite complex orchestrated and contain multiple accompaniment voices; thus they were far superior to the barcode reader approach of Casio's competitor MT-70 and resemble rather the quality of Casio's later used ROM- Pack cartridge technology.

The main voice preset sounds are cold and very bright and resemble simple 2 operator FM sounds; interesting is the cheesy "vibraphone" sound which has slow tremolo. The single finger accompaniment has a nice arpeggio. The rhythms employ blip percussion of quite unique electronic style with semi- metallic hissing cymbals (a bit like Casio SK-1) and may be interesting for tekkno. The original German retail price of the PC-100 was 990DM (about 445€).

main features:

Above the keys are the key lighting LEDs. At the top is the PlayCard slot.
These are the key lighting control buttons. The round knob is for transpose.
This is a PlayCard; much like a MIDI file the data tape strip contains the music data.


I didn't examine the hardware of this instrument closer yet, but I could imagine that there may be a hidden sequencer in it because the hardware used for PlayCard reading and playback (RAM etc.) is basically the same like the one for a sequencer. Possibly the sequencer might even save data onto PlayCards, but Yamaha disabled this to prevent users from accidentally overwriting their precious pre- recorded cards (or to avoid disturbing Yamaha's own PlayCard sale interests). Nowadays these cards are not made anymore; it would be interesting to find out the PlayCard data format to make own PlayCards from MIDI files; beside the main voice, PlayCards contain also accompaniment information, because the PC-100 plays them often with more complex accompaniment than the normal built-in ones. The Yamaha MK-100 had a sequencer that can save its data on audio cassettes; possibly there are technical similarities in the data format. Has anybody more information on this?


This instrument sounds very bright and almost harsh; thus the "harpsichord" is the most natural sound on it. The PC-100 sounds much like when Yamaha attempted to replicate the at that time modern timbre of their digital FM instruments on cheaper non- FM hardware, thus this keyboard sounds extremely different from the rather muffled analogue timbre of my first PortaSound generation's PS-2. The locking push buttons were likely taken from the previous analogue PortaSounds where their multiple contacts had been technically necessary. A nice sound effect of the PC-100 is the arpeggio, which has a harp- like timbre and is a typical element of early 1980th keyboards; most modern keyboards don't feature this chinking and slightly cheesy accompaniment style anymore. The PC-100 was shipped with thesePlayCards. (I haven't examined the hardware yet.)

The "organ" is rather Hammond than church style; it quickly grows slightly duller during its percussive attack phase (likely by crossfading 2 waveforms). The "piano" sounds more like an electric than acoustic one and the bass range strongly resembles a gently picked nylon guitar; "harpsichord" sounds much more realistic. The "trumpet" sounds way too thin and harsh. "trumpet", "violin", and "oboe" have a delayed 7Hz vibrato. "guitar" attempts to be a bright acoustic one. The "vibraphone" has a strong and cheesy sounding 3Hz tremolo, includes sustain and ignores the sustain switch. All other sounds stop almost immediately after key release when sustain is not pressed.

The single finger chord mode employs an envelopeless electronic organ chord timbre, while the automatic accompaniment during rhythm plays a kind of piano chord made from the same waveform with decay envelope, combined with an e-bass. In manual chord mode the variation button toggles between a very bright and a less bright organ timbre or vice versa depending on the selected rhythm. (There are 2 chord timbres in total, those are also used by the accompaniments.)

A fullsize variant of the PC-100 was released in 1983 as Yamaha PC-1000 (49 keys, metallic with dark control panel, case style like Yamaha PS-55 but only 1 speaker, very rare). A white PC-100 variant with slide switches instead of push buttons was later released as Yamaha PC-50 (seen on eBay). 2 variants without PlayCard reader (and no key lighting) were made as Yamaha PS-400 and PS-300 (I read the manual). The black PS-400 had a chord sequencer, 4-bar rhythm variation switch and duet mode. The beige PS-300 (with beige carry case) has far less features; it has only 37 keys and 8 preset sounds and is missing many features like the chord sequencer, chord variation, transposer knob, duet mode and even lacks the arpeggio. (The Yamaha PS-500 looks identical and Yamaha PSS-401 seems to be a golden 44 keys variant of it.) These instruments were likely intended as digital successors of the analogue Yamaha PS-2 and PS-3. Also the Yamaha PS-200 from 1984 seems to be a black PS-300 variant with slide switches instead of push buttons and 3 built-in demo melodies. In 1984 the larger PlayCard keyboard Yamaha PCS-500 was released as successor of the PC-100; it featured 49 midsize keys, stereo symphonic (rotary speaker simulation), fingered chord and warmer sound, but unfortunately has no arpeggio anymore. A small PlayCard keyboard with only 32 keys and squarewave sound was released as Yamaha PCS-30. Later Yamaha released some ROM based key lighting instruments like e.g. the small TYU-30.

Yamaha MP-1

YAMAHA PortaSound mp-1

This keyboard was a close variant of the Yamaha PC-100, but instead of the PlayCard key lighting feature it had as the world only such midsize keyboard a built-in musical score printer.

This printer is a small plotter that draws music notes on a narrow paper strip using a small ball pen. It either prints immediately all played notes, or prints the recorded contents of an internal sequencer. There is also an additional duet mode and much like Yamaha PS-30 it has a stupid "4 bar" button switch that automatically inserts a rhythm fill-in every 4th bar; a manual fill-in button would have been much more useful here. Due to the strong similarity I only mention the differences to the PC-100 here.

different main features:

SER.NO. 018708
The PCB has a grid of empty test solder pads.


My MP-1 specimen is missing the plotter pen, thus I could not test the plotter yet, but the plot head seems to move correctly. The big main PCB is fairly crowded. Interesting is that Yamaha introduced in this hardware class already in 1982 digital mixing of rhythm, accompaniment, arpeggio and main voice, while Casio used analogue mixing until late 1980th (abandoned with Casio MT-540); despite the separate volume sliders are potentiometers, they are polled digitally with each only 8 steps. The instrument even assigns polyphony channels of muted parts to the main voice when a slider is set to zero.

circuit bending details

I haven't analyzed this hardware by myself, but Scott Nordlund made a great hardware analysis of it. This is what he wrote (slightly edited by me):
I just got an MP-1 a few days ago (serial number 017836) and I spent some time checking it out.  Hope you find this interesting:


solder side (surface mount):

  • Oki MSM80C85A: 8-bit CPU, not sure if models like the PS-400 have this or if the YM1034 can handle all those duties, maybe this CPU is just for sequencer?  Also, there isn't a ROM chip, the IG07806 might include this.
  • Toshiba TC5516AFL (x3): 2048 byte SRAM (6KByte total), probably works as printer buffer and sequence memory (might be good for circuit-bending)
  • Hitachi HD44820A71: 4-bit microcomputer with built-in ROM, used here to control the printer
component side:
  • 4558DV: dual op amp
  • 4560D: op amp
  • TL061CP: op amp
  • LA4138: audio amplifier
  • M5232L: voltage detector alarm (low voltage shut-off?)
  • LB1257: 8-channel driver, for printer
  • 4066BP: quad analog switch (audio processing)
  • 4051BP: 8-channel analog multiplexer (audio processing)
  • 4069UBP: hex inverter
  • 50H000P (x2): inverting hex level translator (to drive the DAC)
  • 40H174P (x2): hex D-type flip-flop
  • 40H074P: dual D-type flip-flop
  • 40H368P (x2): inverting buffer
  • 40H373: octal D-type latch
  • 40H139: 4-line demultiplexer
  • 40H032: quad 2-input OR
  • 40H000: quad 2-input NAND
  • 40H374: octal D-type flip-flop
  • YM1034: key/button scanning, controls tone generator
  • YM1019: tone generator
  • IG07806: likely some kind of interface to the RAM, and/or program ROM for the 80C85 ???
  • strange integrated components: SI4Z205IN, and one other I can't see, maybe these work as filters
The DAC is basically just a resistor network, 10-bit I think, I don't know the sample rate.  There are some additional chips that I guess act as sample and hold (4051 and 4066), etc. which is apparently more sophisticated than the DAC configuration that Casio used at the time.  All audio is digitally generated and mixed (main tone, chords, bass, arpeggio, and drums), and output as a single channel, no filters or anything like Casios had, no multiplexing or anything (this is strange- most other keyboards I've seen feature at least some analog mixing for different parts, like the PSS-130, PSS-570, VSS-200, etc., and this was in 1982!  Anyway I had hoped I could add separate outputs for different sounds, oh well..).

Of course there are sliders for individual volumes, but this doesn't work the way you'd think.  The YM1019 sends out a reference voltage that feeds the potentiometers, the control voltages from these are read by different pins of the YM1019 (not multiplexed and scanned like the key matrix).  I had noticed that sounds mute completely when turned to the lowest level, this even intelligently assigns voices- when the arpeggio is on, the upper keyboard part is 3-note polyphonic.  When it's turned low enough, it turns off completely and you now have 4-note polyphony. I also noticed that the chord/arpeggio/rhythm volume sliders only work in 8 steps.  I'm happy anyway that the final volume control is analog.

I messed around with the button scanning matrix and didn't find any eastereggs, though I may not have been looking in the right places.  Unlike most keyboards, it's a bit more difficult to find the matrix lines because it's all on one board, no multiple boards with ribbon connectors like I'm used to seeing.

I don't have a working oscilloscope so testing some of this stuff was a bit difficult.  And of course I couldn't view waveforms directly.  It would be worth looking at the audio output to see what the waveforms look like, but I haven't done this yet. By simultaneously touching the audio amplifier pins and the printer pins, you can hear the printer signals- pretty cool.  Also I noticed that if you similarly "listen" to the RAM chips, the sound varies with the tempo setting.  I also noticed that the keys/buttons are polled at a fairly high rate.  And of course by individually mixing the bits off of the DAC, the sound can become very distorted.

Drum sounds change pitch along with the voices.  I think it's strange how much the drum sounds here resemble FM drums from the OPL2 chip, etc.  I'm sure these older keyboards don't use FM, but I suspect maybe Yamaha used some of their existing technology for primitive digital drums, or maybe they deliberately emulated the sounds for the FM chips (I doubt it).

Question: Can anybody tell me what the original plotter ball pen for Yamaha MP-1 looks like? I want to replicate one.
With my Yamaha MP-1 someone had stuffed a cylindrical lump of tar- like dirt into the tuning trimmer hole. I first thought it was the remain of the plotter pen, but according to the instruction sticker on the plotter lid a ball pen was used for it. Someone e-mailed me that also his Yamaha PC-100 had the same sticky stick in its trimmer hole, and after a close look even at my PC-100 trimmer hole I discovered some black smeary stains from it. Thus it was apparently originally placed there by the manufacturer and not just stuffed in by a kid. Thus likely it was some kind of plug that was originally made of some wrongly mixed or accidentally unvulcanized rubber compound, that turned into pulp after few years. I only know that my Yamaha PS-20 and PS-30 had badly smearing dissolved black foam rubber pods at their case bottom. However I don't understand why anybody should plug a trimmer hole tight with a soft material at all. It might be that the case was painted after assembly (which makes very little sense) and the soft plug thus should protect the electronics against paint, and the manufacturer forgot to remove it.

 removal of these screws voids warranty...    
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