[sdiy] 1980s Casio keyboard modification instructions in a PDF

[Ullrich Peter]

Hi Robin!

>I finally scanned my 1981 booklet which gives instructions on
>modifying the Casio M10, MT-30 and MT-40.  It also mentions how to
>get a higher quality sound output from the VL-5.
>
>  http://www.firstpr.com.au/rwi/casio/

Thank you very much for this interesting info!

I wonder if there is a difference in the schematics between you MT-Series Casios and the CT-Series.
I had a look at the CT-320 and CT-620 Service Manuals I bought years ago and I think
they have similar circuits. And yes they also use the uPD931c melody circuit.
And they also have the ladder network DAC but with an "bit compensator" circuit and a 
sample&hold circuit after the DAC circuit. The bit compensator circuit was casios way of getting 
rid of some of the "time lag noise" as they call it caused by the accuracy of the resistor ladder 
network and the response speed of the buffers.
The circuit allow you to add the positive or negative phase of the MSB.

Did you have a look at the MT-series schematics?

Ciao
Peter

http://www.ullrich.at.tt