Bontempi ES 3100, ES 3200, M325, Antonelli DEK-2350

Bontempi ES 3100, ES 3200, M325, Antonelli DEK-2350 (small monophonic keyboards with rhythm)

Bontempi ES 3100

This small monophonic Bontempi keyboard has 4 sounds and 12 blip rhythms, but neither volume nor tempo control. The case is cyan with violet and pink buttons; apparently this tablehooter was designed as a cheaper version of the Bontempi ES 3200.

The sound style has many similarities with Casio VL-Tone 1, although the ES 3100 sounds harsher due to digital aliasing noise.

main features:

32 midsize keys
monophonic
built-in small speaker (sounds thin and harsh)
4 OBS preset sounds {piano, harpsi, organ, strings} (selected by slide switch)
12 quasi- OBS preset rhythms {disco, samba, rhumba, swing, bossanova, tango, beguine, rock, waltz, march, slow rock, 8 beat} selected by "rh. select" button + keyboard keys
neither volume nor tempo control
simple sequencer {clear, record, reset, one key play}
main voice is made from squarewave with different pulse widths + volume envelope. It has audible aliasing noise.
percussion = 2 squarewave (?) blips {low, high) + snare made from shift register noise
CPU "TAI 4589A, 100384B, MON32H, RCA Z 840" (28 pins).
demo melody ("For Elise" with waltz rhythm, cycles through all sounds)
neither power supply nor sound output jacks

eastereggs:

PCB has unused contact pads for a volume control slide switch (that would need additional resistors) and tempo +/- buttons.
Every rhythm can be also selected by its corresponding key in a different keyboard octave.
The sequencer contains random notes when switched on (and after demo?); some of them are outside the keyboard range.
Pressing "reset" and "clear" simultaneously and releasing the "clear" key last makes the sequencer play the recorded melody automatically in a loop.
Pressing multiple buttons simultaneously plays strange tones and demo tune variants with partly varying volume.
Moving the preset sound slider with held keys plays notes louder.
Pressing "one key play" button during demo steps the demo faster forward. Holding it down, plays the demo with half speed (rhythm speed stays normal).
=>There are likely various keyboard matrix eastereggs available.

notes:

This instrument plays quite loud and has no volume control. My specimen was also missing the knob of the sound select switch. On the type label sticker at the bottom stands "MODEL ES 3100/ M" and "SER No H4850286".

The preset sounds seem to be made from squarewave with different pulse widths. The "piano" is a static waveform with decay envelope; "harpsichord" is the same with a harsher waveform. "organ" sounds harsh and has a slow attack phase (badly imitating a metal pipe organ rank). "violin" has the same envelope but sounds duller. All preset sounds have the same fast, weak vibrato (about 6Hz).

The rhythms are made from high blip, low blip and a snare made from shift register noise. They resemble very much Casio VL-1, but sound fatter and a bit more natural. Possibly there is more analogue circuitry involved, because the blips knock woody (resembling woodblock and clave hits?). Also the rhythm patterns are different. Unfortunately there is no tempo control.

The sequencer behaves bizarre and was likely intended to play the sequence only step by step with the "one key play" button and not automatic by itself. The "reset" button restarts the sequence from the 1st note. I still could not find out what the "clear" button was genuinely intended to do, since I don't have the manual. I only found out that the instrument makes many semi- random note sequences and strange tones when multiple buttons are pressed together.

This eBay photo shows a version with volume slider (to the upper right) and 9 buttons.

This instrument exists also in a version with volume slide switch and tempo buttons (seen on eBay). Possibly it was genuinely a Bontempi ES 3200 with wrong type label and cyan instead of grey case, but bizarre is that also the control panel writing seems to differ from my ES 3200 (watch the world lengths). Thus it possibly might have even different hardware inside.

Antonelli DEK-2350

This keyboard is technically identical with the Bontempi ES 3100 (without volume control) and differs only in the case design, which is blue with slanted instead of strait sliders. Apparently Antonelli simply re-sold Bontempi hardware; even Bontempi's characteristic "made in Italy" logo with the rastered Italian boot still exists at the case bottom of the DEK-2350.

Bontempi ES 3200

This instrument has grey case and features volume and tempo controls, but it is technically identical with the Bontempi ES 3100.

different main features:

volume slide switch (6 steps)
tempo +/- buttons (16 steps)
AC- adapter jack

notes:

The rhythm tempo can be set very low, but not really high. While the model name on my ES 3100 is directly printed on the plastic case, the ES 3200 has a shiny plastic sticker for this. On the type label sticker at the bottom stands "MODEL ES 3200/M" and "SER No L1030353".

A polyphonic variant with a similar case and 50 sound bank was released as Bontempi ES 3300 (which has awful digital aliasing distortion and absurd distorting percussion).

Attention: After dismantling these instruments, they can be only successfully re-assembled in a zero- gravity environment ;-) because always either the plastic buttons or the PCB falls out depending on its actual position. To prevent this, use a strip of adhesive film from outside to hold the buttons in place while closing the case.

Bontempi M325

Also this blue toy keyboard with Mickey Mouse picture is based on the Bontempi ES 3200 hardware class, although it lacks the sequencer by omitted buttons.

different main features:

volume slide switch (5 steps)
no sequencer

Fortunately this one has a volume control and thus doesn't torment the ears so badly like the ES 3100, and also the speaker seems to sound slightly less harsh. The missing sequencer buttons can be certainly re-added as a keyboard matrix eastereggs.

*removal of these screws voids warranty...*

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