The Casio HT-3000 is the full size keyboard version of the MT-700 with 20 preset solo sounds, 10 accompaniment sounds and 20 accompaniment patterns (beat + bass + chords). Additionally, 30 sounds can be programmed and 20 accompaniment patterns can be stored, so it's almost a workstation without a sequencer.
Like in subtractive synthesizers, the sound synthesis consists of a digital controlled oscillator (32 waves including noise) with LFO (5 waveforms), an analog filter (VCF) with cutoff, resonance, ADSR envelope and a corresponding amplifier section (DCA) - also with ADSR envelope and ensuring chorus effect. All 18 parameters can be altered and stored via jogwheel. 2 separate, individual sound syntheses are available for the solo sounds (upper tone) and accompaniment sounds (lower tone), which can be combined in split mode. From the 15 iconic drum sound samples. (lo-fi samples like from the Casio SK-5 / 8 / 200), you can create and store up to 20 own beats with customized bass and chords (with sounds from the lower tones).
The most interesting thing is the analog filter called JRC 2090D, which was also built into the cult devices MT-400V/CT-410V and the flagship synthesizer Casio HT-6000. This low-pass filter with a slew rate of approx. 24 dB sounds very peculiar and quite good. However, it's only adjustable in 32 steps with the digital jogwheel control, resulting in audible frequency steps, and, moreover, it wasn't laid out to be self-oscillating. So I furnished the resonance and cutoff filter inputs with individual control voltages, which can be adjusted by 2 pots.
The result is astonishing. Fluent cutoff controls and resonance up to complete self-oscillation are now possible. All in all, the machine is now a real digital MIDI synthesizer with analog filters, comparible to a Korg DW-8000 or Poly 800, with unique filters, fast envelopes and 2 real-time controls.