[sdiy] Beyond bending: clock sweeping Korg MSM6235 etc

[Benjamin Tremblay]

My plan here is to add MIDI triggering to the Korg DDM-110 and -220, and MIDI pitch bend. 
I will use 4066 switches for the drum keys and to change the routing of the drum voice clocks so that a neutral pitch bend position produces a perfect 250khz clock signal. 

If the switch matrix was bigger I would use a crosspoint switch. I may be able to simply poke values into the latches used in the control board but the 4066 seems like a safe way to isolate old and new logic. 

Interesting compendium of early 80s consumer-grade  drum machine voice chips here. I bet much of this would work with some of the Casio things... I have a Casio HT-700 so could try (or rip out the drum chip for fun).
https://acreil.wordpress.com/2017/10/18/casio-and-korg-drum-ics/
Casio and Korg drum ICs
acreil.wordpress.com








> On Sep 4, 2024, at 12:22 AM, Benjamin Tremblay via Synth-diy <synth-diy at synth-diy.org> wrote:
> 
> I’m too tired to write coherent thoughts but I will clarify asap.
> 
> The Korg drum voice chips are clocked at 250khz so divided down from a 4mhz clock using a binary counter. 
> 
> First of all, you can use the other outputs to run the drum voice chips at powers of 2 higher speeds which is neat.
> 
> I remembered in college I got my DDM-110 super duper drums to sweep playback pitch using a knob or control voltage. I could sweep it from 2x speed down to low grinding crunchy oblivion. 
> 
> How did I do it? 
> 
> I’m not totally sure how it works, but if I disconnect the MSM6235  clock inputs from the D output of the binary counter, reconnect these to the C output (500khz)  and run a capacitor (less than 10nf) from the binary counter D output to a 250K potentiometer and the back into the clock input pin on the counter….
> (I think that makes sense) you can sweep from 500khz way down. Something about any output pin on the counter feeding back into the clock input via an rc circuit seems to slow the clock without slowing the speed of the main CPU. 
> If I connect the drum sound chips to the A output of the binary counter (2mhz) and connect my “sweep” pin to output D it’s a very wide range but the audio playback sounds distorted like the clock is a staircase wave. 
> Anyway I thought I would write this down and share with anyone interested in these chips used in the MR-16 etc. I will try this with the PSS-50.
> Ben
> 
> Benjamin Tremblay
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