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Kawai DX-900

Synthesizer Organ - 1982

Blue Book says:

2 49-Key Manuals

13 Pedals w/Sustain & Attack

37 Key Solo Manual

8 Percussion Preset w/Repeat

Upper, Lower, Pedal Drawbars

16 Synthesizer Presets w/Touch Effects

Sound Effects (Wind, Thunder, etc)

Keyboard Selector

Electro Bass Chord III

Auto Rhythm (32) w/Break

Rhythm Cancel Foot Switch

Auto Arpeggio

Knee Lever Sustain

A Different Organ

Different in many ways compared to most analog organs I have heard so far. I was pretty astonished while learning its details. Primarily it uses divider technology, but it starts with using two TOS. They are normally sync'ed to the same phase, but can be split, if one section (Orchestra) needs vibrato.

Drawbar Organ

Let's start with the drawbars. The octave dividers and electronic switches are integrated in one IC. Each tone is filtered by two R/C pairs, i.e. 6 dB/oct which still passes the 3rd harmonic and sounds a bit "clainetish". Why didn't Kawai use 12dB filters? I guess the effort was too high, this tremendeous number of parts (6 big PCBs for switching and filtering) was enough and when the orchestra part of the organ comes into play, the sound difference would be marginal. And the sound of the drawbars can be sent through a real internal Leslie speaker.

Orchestra Organ

This part uses the same ICs for divider and switching, they are also able to form different pulse waves like saw pulse and 10% rectabgle pulse. A common Voltage Controlled Filter shapes the reed sounds, while the strings are supported by a chorus unit. The reeds do have their own slow chorus and sound like two slightly detuned oscillators. And a third chorus unit shape an accordion sound.

The tabs of lower manual is not a copy of the upper manual, it has own circuits to shape singing Ohs and Ahs using 6 separate bandpass filters.

Percussion Sounds

These ICs are used again for the creation of a polyphonic cecay to come up with piano-like sounds. Because it generates also saw pulses the sound of the cembalo tab sounds really good. Vibrato and chiff.

Mono Synthesizer

A real mono synthesizer was integrated. I guess it was the rare model Teisco 100P (or later Kawai S-100P), a brand which was taken over by Kawai shortly before. Short descriptions about this good sounding synth can be found -> here and -> there.

Sound Effects

An outstanding funny addition are the sound effects whis are substantially the synthesizer modules noise generator,  VCF and LFO. The filter cutoff and LFO have their own sliders. This LFO also affects the WahWah-Trumpet of the Upper Orchestra.

The Organ Inside

Lots of parts inside, I would say OVI (Organ Volume Index) by 70%. Highly modular, many big PCBs for the tone generation are placed at the back side, while filters, chorus circuits etc. are on the upper part of the organ. Some PCBs have sockets, but most cables are directly soldered, as well as the ICs.

Extensions

I could not resist and built a digital effect unit into this organ. This time it was a Digitech StudioQuad, which supports 4 physical effect lines which I connected to: 1: Drums, 2: Total Reverb, 3: Monosynth, 4: Percussion Instruments. This changes the sonic experience tremendeously, but it can be switched off also...

Sound examples here.