(analogue squarewave keyboard with bizarre sound, accompaniment & programmable analogue rhythm)

This strange analogue instrument looks (besides slightly larger drum pads) almost exactly like the digital Letron MC-3 (see there) and has many similar functions, but it contains totally different hardware and makes a lot of bizarre sound glitches. Possibly it was an obscure predecessor of the latter, I therefore describe here only the differences to my Letron keyboard. The main difference to the MC-3 is that the HBATEC is only 2 note polyphonic and employs real analogue percussion (that can be nicely modified).

different main features:

• main voice polyphony only 2 notes  (a keyboard flaw truncates held notes during fast play, only 1 note with accompaniment)
• 8 instead of pretended 12 OBS preset sounds {piano, piccolo, clavichord, oboe, banjo, accordion, harpsichord= clavichord, organ= accordion, dulcimer= piano, xylophone, guitar, clarinet= oboe} (Of the 12 buttons 4 are only doublets wired parallel to cheat the customer.)
• 8 OBS preset rhythms {rhumba, tango, march, disco, pops, 16 beat, bossanova, waltz}
• rhythm tempo can be set to ridiculous high speeds (>300 BPM?); at this speed accompaniment timing gets very inaccurate and all kind of sound glitches happen.
• no vibrato button (instead the button is "sustain off", while the normal "sustain" button is "sustain on")
• no separate e-bass sound. ("Manual bass" activates the organ chords mode when rhythm is running, which can't be done on the Letron.) All chord/ accompaniment tones are plain squarewave.
• The hardware contains only 1 digital IC: the CPU "R335, KZ 283, LIL9217ASIC, 9024  IW" with 28 pins, made by the well known brand "Zilog" (creator of the famous "Z80" 8 bit homecomputer CPU, another instrument with a Zilog CPU was the Superb Sound EK-922). The sound generator uses analogue capacitor envelopes and all accompaniment voices have own pins. This CPU makes nice analogue distortions and seems to have a VERY bizarre concept of implementing the 2 note polyphony. The first pressed key not only causes the generation of a squarewave tone, but also changes a sort of internal subclock speed (about up to 10%?) depending on which note is played (apparently as a correction term to fine tune the note due to an otherwise too coarse internal frequency lookup table or something similar). When a 2nd key is pressed, the CPU though has to generate a difference frequency to the previous note regarding the changed clock speed, which causes all kind of weird intermodulation distortions those are especially audible when the capacitor envelope of one note has faded silent while its tone generator still sounds through the 2nd note with a ring- modulation- like effect until the CPU finally shuts down the silent note completely. The keyboard matrix signals, rhythm speed and a zillion of other things though wobble around in bizarre ways by the changing clock speed. Despite the CPU itself is crystal clocked, also various short, howling glitches get audible when additional keys are pressed due to the CPU determines by the relative key position order which tone should be played by which oscillator; though a tone played by the 1st one may suddenly jump to the 2nd when a lower note key gets pressed; especially in accompaniment mode (where 3 voices exist for accompaniment) this is very audible.
• keyboard matrix uses a special algorithm with keys wired by diodes in both direction (2 keys per each 2 lines) to save IC pins. It is also multiplexed with the percussion trigger outputs.
• analogue percussion uses transistor noise:

base & tom	= quite dull analogue drums (with decay trimmer pot)
open/ cl. cymbal	= transistor noise with different capacitor envelopes
snare	= tom + cymbal simultaneously

(These analogue drums have not the pressure of a TR-909, but they knock not bad.)

• demo melody = "Blue Danube" (a waltz with fast changing sounds)
• no battery alarm
• way less LEDs (small red round ones)
• yellow, flimsy nylon carry bag with red text "HBATEC INTERNATIONAL"

eastereggs:

• 8(!) additional OBS rhythms found
• alternative to these a rhythm bank switch button to select them through the normal 8 rhythm buttons.
• arpeggio on/ off (very cute and cheesy doodling squarewave). The CPU has an own sound output pin for it which is even already connected through an own resistor to the accompaniment pot.( =>Apparently this mainboard was designed to be equippable with different control panel PCBs.)
• rhythm mute button. 1 press mutes rhythm percussion (accompaniment stays on), 2nd press stops also accompaniment. Muted rhythms can be continued by pressing the corresponding OBS rhythm button.
• 2 similarly behaving buttons those turn accompaniment, demo and custom drummer function off (their buttons/ LEDs get completely inoperative), switch the main voice into a monophonic mode, distort the main voice slightly and change the sound envelopes of all preset OBS sounds. (The "banjo" in this mode doesn't ring anymore and gets inaudible unless many keys are pressed rapidly ( <=ultra- short envelope?). The "piccolo" turns into a music box.) Sometimes (when keys are hold down during button press?) the keyboard ignores releasing keys, i. e. all notes toot until another key is pressed. When the strange buttons are pressed again (or the other one?), the instrument switches back to normal behaviour. (I don't know where this mode is good for; possibly it was an IC test or the CPU should communicate with an external IC or anything similar, or it is just a buggy IC function that was once intended to do something more reasonable.)

modifications:

• voltage regulator added.
• all above described buttons added.
• smaller resistor added to make accompaniment louder.
• separate pots and mute switches for the 3 accompaniment voices added. -volume pot for arpeggio added.
• for both analogue drums each 1 pitch and one envelope length pot added. -analogue hihat volume/ length pot added.
• 2 distortion pots for the analogue rhythm added.
• sensor contact input for the hihat noise transistor added.
• sensor contact outputs for the 3 accompaniment voices and arpeggio added (each connected with their mute switch case or potentiometer nut).

Here you see the row of knobs I have added.

The brass coloured bar is the sensor contact. Blue knobs control the drum envelopes.

notes:

My theory is that either 2 different companies independently(??) imitated a 3rd this way looking brand product keyboard, or (likelier) the manufacturer had first designed the HBATEC hardware with its 28 pin "Zilog KZ 283" CPU for an older instrument, then started to develop the Letron MC-3 and already produced many plastic cases for the new model, but by a technical problem he couldn't finish the new model's ICs in time and though built the old hardware into the new cases, which would explain the pre- moulded LED holes and duplicate sound buttons etc. Strange is also that the manual booklet of my HBATEC (some pages are missing) describes instead an instrument of the name "HBATEC DX", which seems to be rather identical with my MC-3 (e. g. the "500 Miles Away From Home" demo melody is mentioned there). Even more mysterious is that even a 3rd instrument Fujitone 3-A with the same case design was made, which technology and behaviour is extremely similar like the HBATEC, but it has even a few less functions (e.g. no organ chord mode), only a mono amplifier and is based on a 40 pin CPU "KZ381" with the strange brand label "Angeltone". Either this was a predecessor of the HBATEC, or it was even a successor that attempted to replace the Zilog brand CPU (bought from an external company and thus possibly expensive) with a re-designed CPU made by the instrument manufacturer, but he omitted some functions because he didn't manage to get them to work in time. (On the box of my Fujitone 3-A is even a photo of an instrument with the same case but no brand label and button names corresponding to the MC-3.) Later I found the Elta KE-3 toy keyboard, which contains another Zilog CPU with 40 pins and similar main voice sounds (but no percussion), and the case photo on its box shows an Angeltone brand label. Thus it might be that Angeltone was the genuine designer of all these "KZ" keyboard CPUs.

The main voice sounds of the HBATEC are made from squarewave with different pulse widths and generally resemble much the Letron MC-3, but it features a "banjo" with a (rather slowly) ringing mandolin effect and uses more different octave settings (e.g. "piccolo" has a very high pitch). The harsh "clarinet"/ "oboe" sound matches rather the latter name and is harsher than the MC-3 timbres. Also the "xylophone" is a quite harsh sound with the same timbre like the "guitar" - only with shorter envelope. The "harpsichord"/ "clavichord" otherwise uses a dull 1:1 pulse ratio and should be better named "music box" or "cowbell" or "celesta"; also the "banjo" uses this timbre. Like on MC-3, also here the OBS sound select buttons can be abused for realtime sound changes, although the HBATEC always restarts the envelope of held notes when any of these (and various other) buttons are pressed. A little nasty is that this instrument employs a "last note priority" scheme in that when (without accompaniment) 2 simultaneous notes are played and a 3rd key is accidentally touched (e. g. by pressing a key before completely releasing another one) the first of the 2 previous notes is shut off to play the note of the newly pressed key. This can be unpleasant when 1 key is hold down with the left hand in the intention to play a continuous bass tone while the right hand shall play a monophonic melody to it, because an accidentally touched 3rd key during this can stop the bass tone which is quite confusing, despite it may help a lot to train discipline to hit keys more precisely. Especially annoying is that also by very fast play the instrument truncates the note of a held key to re-use its channel to keep the release phase of a previous note played with the other hand. (Some small Casio and Bontempi keyboards have a similar flaw.)

If you want an easily playable squarewave instrument, then one with MC-3 hardware is certainly better suited to fulfil this need; also its 4 note polyphony are an argument for it. But the HBATEC is (IMO) the more interesting beast - simply because its behaves so bizarre in many ways and one can do so many strange sounds on it. It also seems to sound somewhat warmer (almost a Minimoog- like timbre?), while the Letron is more like a C64. The HBATEC is also way more fascinating for circuit bending due to its analogue hardware and the lots of separate sound output lines of its CPU.

Unlike the MC-3, the HBATEC has lots of funny sound glitches and in organ chord mode the tone pitches seem to be quite off when chords are played. There is also always a low tooting hum present, which gets higher for some seconds after a note is played. (Don't worry, the famous historical Hammond organ also featured a well known background hum.) The rhythm tempo of the HBATEC can be set so high that the rhythms turn into a drumroll. Particularly with rhythm volume muted, in this state the accompaniment patterns (especially with arpeggio) start to sounds much like the famous arpeggiator effects known from C64 homecomputer musics. The modified drum section of my HBATEC can create a variety of strange analogue percussion, from tom- tom and base drums or congas up to metallic stuff like (sort-of) gongs and triangles, and when drum decay is set too long, it results in howling self- oscillation. (The point where this happens is very depending on the actual drum pitch and distortion settings.) Also the hihat input sensor contact makes lots of funny tweeting or squelching sounds when touched. Its much fun to create tekkno- like musics on it by cranking the drum sounds knobs while the rhythms plays. (Remember: there is even one programmable rhythm pattern available.)

At eBay I once saw a keyboard "Damff Intertone" which had the same case like the HBATEC, but was claimed to be 4 note polyphonic. I am not sure if both are genuinely technically identical, or if the Damff Intertone was just another variant of the Letron MC-3. At least the button field on the blurred photo looks extremely like the HBATEC. Either a direct predecessor or direct successor of the HBATEC was the Fujitone 3-A (not to confuse with Fujitone 3A). Unlike the widespread MC-3 instruments, these 2 keyboards seem to be generally very rare; I only saw one original HBATEC keyboard on eBay yet. Someone spelled it there "HBA TEC" (in 2 words); im am not sure if it was just misspelled or really a different variant, because I also saw a variant labelled HBA International, which has the same case but apparently contains MC-3 hardware (according to button writing). Also the HBATEC DX (described in my manual) seems to be an MC-3. A common and easy to find successor of the HBATEC hardware class (with same great analogue drum section and 16 OBS rhythms) is the Angeltone DM-380, which can be cheaply found on German eBay. Also a different "HBATEC" keyboard was released with MC-3A case (and likely MC-3 hardware inside, see there), which also had no model name.
 

removal of these screws voids warranty...
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