toy guitar with great blip rhythms & accompaniment

This electronic toy guitar has instead of strings a row of 15 yellow "keys", those basically correspond to the white keys of a monophonic keyboard, except that (in guitar mode) the tones are only played when the big, yellow, flat "lever" is pushed up or down, which provides a halfway guitar-like feeling. (Pressing multiple keys plays the highest pressed note, pressing no key plays the lowest note - like on a real monophonic string instrument.)

In "rhythm" mode notes can be played to one of 15 rhythms. In "demo" mode the instrument plays by each yellow key a preset e-guitar loop. In "ABC" mode the instrument plays rhythms with accompaniment, and the player controls the pitch/ key of the accompaniment with the yellow keys, while the yellow lever plays a drum roll. The employed blip percussion resembles Hing Hon EK-001.

main features:

• 15 "keys" to play 16 monophonic notes (no black keys)
• yellow, flat lever to trigger notes (with no yellow key, the lowest note is played)
• 15 rhythms {country, rhumba, rock 1, rock 2, rap, disco, march, tango, swing, ballad 1, ballad 2, slow rock 1, slow rock 2, waltz 1, waltz 2}
• rhythm tempo {+, -} buttons
• demo button (plays per key 1 e-guitar loop so long the key is pressed)
• "ABC" (accompaniment) button
• "dual" button to enable/ disable chorus effect
• "TIM" button to select 4 e-guitar timbres
• LEDs for "power", "tempo" and 2 for the 4 "TIM" modes)
• "stop" and power on/off button
• volume slide switch (3 steps)
• sound generator based on digital waveforms (monophonic main voice with chorus)
• blip percussion based on squarewave + shift register feedback noise:

• base (low click),
• cowbell (high squarewave),
• hihat, snare (shift register noise)

• The CPU contains a time slice DAC, which outputs polyphony channels time multiplexed as a comb-shaped signal that is turned into analogue waveforms by a capacitor. The output frequency intermodulates higher notes and gives them an unusual glassy timbre.
• CPU= "Holtek HT3630A" (unmarked COB, PCB is labelled "MG1530A-3")
• DC voltage controllable clock oscillator
• neither sound output nor power supply jacks

These are the 4 red status LEDs (covered by differently coloured caps). An idiot had pushed them in and crushed the contacts inside.

modifications:

• pitch, 2 different distortions and volume control potentiometers added.
• pitchbend sensor touch contact added.
• cinch sound outputs, speaker mute switch & AC adapter jack added.

notes:

Strange is that the yellow edge of the fret board is a separate blue plastic parts with a row of holes (one per key) covered by only a yellow sticker. Possibly the manufacturer planned here a row of key lighting LEDs or similar, but the feature was not implemented in this instrument. The CPU is an old variant of My Music Center technology; although it has no percussion samples, it employs the same strange bit stream DAC with DC controllable clock oscillator.
 

circuit bending details The SoundWaves MG-1530 is based on a single chip CPU (unmarked COB, PCB label "MG1530A-3") with resemblance to My Music Center. I later identified this CPU by a datasheet of 1997-12-04 as Holtek HT3630A "Funny Guitar", which is an application of the "2 Channels Ad-lib Micro®" microcontroller HT3630. It has 2K*14 bit ROM, 96 byte RAM, 2 channel static waveform "ETS" synth with 8 waveforms (7 bit, 64 steps, ADSR) and 4 channel blip percussion generator. These percussions {base, hihat, cowbell, snare} are implemented in hardware and have no software parameters. (They are triggered by setting each their bit in a register; 'cymbal' has to additionally set the 'hihat' bit.) When I bought this instrument, an idiot had pushed in the LED caps (solder joints torn off) and crushed the silicone contacts under all round buttons; because the shafts under the buttons are hollow cylinders with slightly sharp rims, they hat punched out the center contact of the silicone rubber switches like a cookie by a cookie mould. Thus I had to dig the pieces out of the cylinders, fill the cylinders with hotglue and glue the pieces back into place =>buttons work again. pitchbend, volume control & distortion Like in My Music Center, the resistor controlled clock oscillator can be easily modified with potentiometers and touch sensor contacts for pitchbend. When clocked down, also here the pulses of the time slice DAC transform into strange tekkno bleep patterns. 3 additional pots at the single transistor amplifier control analogue volume and distortion.   caution: I only have this old schematics and no good documentation of my modifications. The parts in green were added by me. This is my pitchbend sensor rail made from silvered wire. In the middle these rails are held by eyes of thinner wire.

An almost identical looking toy guitar with violet and blue case was released by Simba together with a lousy toy mini- keyboard in the "Music Set" (product number 683 0506). But this guitar contains totally different hardware based on the great Simba 683 3149 toy keyboard. Unfortunately it sucks because this CPU was not designed for a guitar case and thus lacks sharp keys and 2 of the drumpads etc. (its big yellow lever is simply wired parallel to one of the keys). At least the great tribal rhythms and POKEY sounds are still there.
 

removal of these screws voids warranty...
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