Mattel - BeeGees Rhythm Machine

monophonic toy keyboard with melodic POKEY rhythms

This rare toy keyboard from 1978 (embossed case bottom copyright) has 3 nice melodic squarewave rhythms with crunchy POKEY hihat. The monophonic main voice is a simple clarinet tone.

The rhythm patterns are fairly complex and rather constitute a monophonic fixed- key accompaniment, but they can be set to only 3 speeds. Turning volume louder distorts the conga envelope from a percussive sound into a rather constant squarewave toot, which is nice for tekkno. The manual of the instrument contains score and lyrics for several songs of the rock band BeeGees.

main features:

20 small mini keys
built-in small speaker (on case bottom)
monophonic main voice
3 OBS preset rhythms {disco, latin, pop} (rather fixed- key accompaniments)
tempo button (cycles through 3 steps & rhythm stop)
volume knob
main voice is a clarinet tone made from plain squarewave with soft attack volume envelope.
percussion is made from 3 squarewave congas {low, mid, high} + grainy hihat(?) made from low shift register noise. The complex patterns have 32 steps.
CPU= "SSI 251, 1072-9439, D 7928" (22 pin DIL)
tuning/ transpose knob (about 1.5 octaves)
headphone jack

eastereggs:

So long any single preset rhythm button is held, the instrument plays the low conga in a loop. Holding 'disco' + 'pop' plays the hihat in a loop. Holding any other 2 preset rhythm buttons mutes the rhythm (plays silence in a loop). There are also some other rhythm glitches explained below.
turning volume louder distorts the conga envelope and makes it less percussive.

notes:

The case of this small instrument is only barely bigger than a VHS video cassette. The speaker is facing down in the case bottom and there are no pods to make the sound come out, thus a carpet muffles it a lot. To prevent this there is a small flippable wire stand to lift the rear end of the instrument (very recommended to save the 9V battery). There is a weak high pitched static beep in the speaker, which is likely a key matrix interference and doesn't change with the volume setting. But it is only audible when you hold your ear close to it. The tiny keys press on foil contacts and feel rather like pocket calculator buttons because they move only about 1mm. While the keys are pushed up by a still intact smooth foam neoprene mat, the blue buttons were held up by a block of dark foam rubber that is crumbling apart by ageing. Unlike in other toy keyboards of its age, there is already a digital single chip CPU inside on an surprisingly empty PCB, and the CPU even seems to have independent clock oscillators for main voice and rhythm because the tuning knob does not change rhythm tempo or pitch. The CPU has 2 unused pins, thus there may be hidden eastereggs. (I haven't analyzed the hardware closer yet.)

The monophonic main voice is a quite nice sounding clarinet tone, that even has a slow attack phase (but no vibrato etc.). The tuning knob can transpose it by about 1.5 octaves.

The 3 preset rhythms are made from a POKEY- like low shift register noise hihat and 3 squarewave congas those are very melodic and rather resemble the synthetic "xylophone" sound of other squarewave keyboards. The low conga resembles the base drum on Hing Hon EK-001. The patterns are complex and have each 32 steps; I would rather consider them monophonic fixed- key accompaniments (resembling Casio MT-40) than normal rhythms. The rhythms do not change their pitch and speed with the tuning knob but tempo can be only set with the tempo button, which cycles through 3 speeds and rhythm stop.

The preset rhythm buttons switch the rhythm after 1 step (i.e. almost immediately) and there are various strange glitches those permit fill-in- like live play tricks. So long any single preset rhythm button is held, the instrument plays the low conga in a loop. Holding 'disco' + 'pop' plays the hihat in a loop while holding any other 2 preset rhythm buttons mutes the rhythm (plays silence in a loop). Interesting with the POKEY hihat loop is that you can well hear how the shift register waveform changes its timbre every beat. Rhythms are started with either their OBS buttons or with the tempo button. But the tempo button apparently only sets the tempo to zero when it stops a rhythm, because the next press on the tempo button does not start the pattern from beginning but from where it stopped, and after power on it starts no rhythm at all because none was selected yet. Pressing any button (while none is held) apparently restarts the internal rhythm tempo oscillator when it was previously halted with the tempo button. Thus when you stop the rhythm with the tempo button while any rhythm buttons are still held, you can not restart the rhythm until you first release all buttons.

Other small keyboards with great POKEY rhythm are the Hing Hon EK-001 and the Creatoy keyboard.

*removal of these screws voids warranty...*

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