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Casio CT-6000: has it phase distortion? (main ICs?)

Casio CT-6000: has it phase distortion? (main ICs?)

2013-09-27 by CYBERYOGI =CO= Windler

The Casio CT-6000 from 1984 was Casios first keyboard with velocity sensitive keys and midi. It also has very versatile accompaniment and can layer sounds. I always thought it was based on Consonant-Vowel-Synthesis (crossfaded stair waveforms with analogue filter, like MT-65), but some people claim it was based on phase distortion. The first official PD preset keyboard (marketet as such by Casio) was its even bigger successor CT-6500, which (how silly is this!) had no velocity sensitive keys anymore. I yet haven't bought a CT-6000 (takes much space), but it seems to be a true technical milestone.

- What are the main ICs?

If CT-6000 has sound ICs "NEC D931C", then it is definitely consonant-vowel. In oppsite to this, the phase distortion IC in my CZ-101 is "NEC D933D".

Are anywhere PCB photos online?

- Is the percussion semi-analogue or sample based?

The sound quality on YouTube wasn't high enough to identify this.


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Re:: Casio CT-6000: has it phase distortion? (main ICs?)

2014-08-08 by cowindler01@...

I have studied schematics of the Casio CT-6000 (which I bought later) and now I doubt that it has phase distortion. But it indeed contains the missing link between the famous Casio sound ICs D931C (MT-65 consonant-vowel) and D933D (CZ-series phase distortion).

The Music LSI "NEC D932G" (64 pin zigzag DIL) was only used in Casio CT-6000 and likely the direct successor of D931C. It communicates with the CPU through 8 input and 4 output pins, has 17 bit audio and additional 14 control output pins for external filters, mixing ratio, stereo chorus and the like. The velocity sensitive highend midi keyboard contains 3 of these unique sound ICs; each is wired to an own DAC with different fixed analogue filter (each 3 control lines). The outputs are mixed; in chord mode the 3rd sound IC is used for chord only, else all 3 are layered as main voice. I suspect that in classic Consonant-Vowel manner the mixing ratio between multiple differently filtered sound ICs changes with keyboard velocity. The existence of so many switchable filters seems to disprove the rumour that CT-6000 was a secret unofficial first phase distortion instrument. The high timbre quality rather results of 17 bit DAC resolution and complex analogue post-processing through filters and a costly 3 line stereo chorus. Even its unique percussion generator IC HD61701 (54 pin SMD) routes some outputs through 2 external filters to shape timbres.

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