TESTRON® CL-60910
squarewave keyboard with warm C64 sounds & great accompaniment
Elta KE-4

Testron CL-60910

This instrument sounds very similar like the Letron MC-3, but has a much warmer timbre and a wonderful responsive and versatile programmed automatic accompaniment.

The case is bronze colour and has the German label "ELEKTRONISCHES KEYBOARD" ("electronic keyboard"). It was also released as Elta KE-5, Elta CL-6091, Electronic Sports Collection ESC KE-5 and Waltham WE-88. A black case version was released as Plantron DP88, Pantera PM88 and Eastec ER-460 (seen on eBay).

(Note: This keyboard sounds great, but don't buy one of these so far your only intention is to get a keyboard with faithfully imitated natural instrument sounds. Remember, this is a squarewave instrument and though many of its sounds sound not even remotely like what is written on its buttons, though bought with wrong expectation it may disappoint you.)

main features:

TESTRON®, model:CL-60910

modifications:

notes:

Unlike Letron MC-3, the Testron CL-60910 always uses a piano- like envelope for chords. Depending on the rhythm volume slider position, the chord distorts at the beginning, which creates a warm sounding sort-of dull fading "wah- wah" filter envelope. The accompaniment has very interesting arrangements those vary depending on how many chord keys are pressed, and it does not restrict you to play establishment's standard chords. Thus e.g. the "country" accompaniment can make great disharmonic horror/ thriller music by pressing adjacent keys.

When rhythm is off, this instrument also provides a sort-of key split feature; in "manual bass" mode you can play a monophonic e-bass on the left (accompaniment) keyboard section and the 3 note polyphonic main voice on the rest, while in "fingered chord" mode you can play a 3 note polyphonic piano sound to the left, and the monophonic main voice to the right. The vibrato is unusually fast. Unfortunately all tones of this crystal clocked instrument are detuned by about -0.75 semitones and there is no trimmer to adjust tuning. Like with many old keyboards, the 12 OBS sound buttons can be also pressed while keys are held down without stopping their notes, thus theoretically they may be usable as a realtime sound control for arpeggiator- like timbre changes. Unfortunately the CPU polls the buttons only with about 4 Hz, which makes them respond much slower and less precise than in MC-3, and also the silicone rubber buttons are a bit awkward to press quickly.
 

circuit bending details

The Testron CL-60910 is based on the CPU "NEC D7507CU 234" (crystal clocked @ 1 MHz) with sound IC "Yamaha YM2163". The CPU is made by NEC, who also manufactured most of the early Casio keyboard ICs. The sound IC sounds and looks like the Letron DSG-MC-3 and even has the same pinout and sound output assignment.

The CPU appears to be a "NEC 7507H" (40 pin SDIL), which is a 4 bit microcontroller with internal 2KB ROM and 64 byte RAM, clockable with 4.19 MHz (identified in "NEC Single-Chip Microcontroller Data Book" of 1990).

The pcb has a strange logo.
Because the instrument is detuned by about -0.75 semitones, it would make sense to replace the crystal with an LC oscillator to make it tuneable.

bass & chord volume controls

Install 2 potentiometers (each 47k lin) to control bass and chord volume. Important is to wire them in series with the given resistors (cut a trace for this). Don't choke the signal current by shorting AC- wise against ground because this would destroy the unique warm analogue timbre of this wonderful instrument. Thus I kept the left pin of both potentiometers unused and cut their carbon track at that end to set the volume zero without pulling against a fixed voltage.

I unfortunately made only very coarse and incomplete documentation of the wiring, thus see PCB back photo for details.

Apparently the direct successor of this instrument was the Elta KE-6. A possible predecessor was the ABA-88.

Elta KE-4

This is a simplified and shorter variant of the Testron CL-60910. The main model plate of my specimen is missing and there is only the brand name Elta and a small paper sticker "HS4242/89" at the bottom; the "/89" likely indicates that it was released in 1989. On eBay someone told me that his type plate under an identical looking instrument was "Model: KE-4 Musical Keyboard Power: USE 6xC-SIZE (UM-2) Batteries AC ADAPTOR DC 9V 300mA  HS2163/89." The "HS2163" may hint that this model initially had the sound IC Yamaha YM2163. Later on eBay I saw one with box, telling the official model name Elta KE-4.

This instrument has only each 8 preset sounds & rhythms, but the same lovely accompaniment like the Testron, although the bass sounds less impressive since it uses here a very similar squarewave timbre like its main voice. Likely here a separate bass sound filter was omitted to cut cost; also the sound chip is not genuine Yamaha anymore.

different main features:

HS4242/89

eastereggs:

 removal of these screws voids warranty...    
WarrantyVoid
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