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This page explain how to upgrade an MCV876 to get a 12 bits notes/pitch DAC accuracy...

It is very very simple

(Clic on the picture to enlarge it)

1. The MCV876 pcb is populated as usual excepted DACs. I use MCV876-3CV schematics references here...
   
   
2. This upgrade use a firmware who recognise only 3 DACs even on MCV876-4CVpcbs ( the 4th is simply ignored...)
   
   
3. Auxiliary DACs ( U4 & U5) are classic 8 bits ones like the DAC0832 ( or DAC0831 or DAC0830...)
   But the DAC0 (U3) is now a DAC1231. It is a 12 bit version pin to pin compatible with the good old DAC0832...
   Disclaimer : I have no idea if the DAC1231 is still available and easy to find on the marked... Mine are ceramic version , coming from recycled industrial boards , but still goods :)
   
   
4. To drive U3 correctly a little mod of the pcb is required : usualy legs 19 of each DACs are connected together and then wired to the +5V. Disconnect them of the +5V and connect the leg 19 'bus' to the pin 5 of the PIC chip (J18) with a short piece of wire. (see pictures)
   
   
5. Burn the firmware MCV876-12bits v2.71k into the PIC. It is a special version with a 48 notes table with a 12bits range for tuning ( 0..4096) This interface is mainly destinated to be integrated into a Korg MS10 or MS20 and the gate output is negative logic.
   
   
6. Use the special 12 bits version of the MCV876 PC config software to edit this interface parameters only. Sysex messages are almost identical for all MCV876s, but here the 48 notes table messages are differents because of the 12 bits range.. Polyphonic mode has been removed as well as many other 'unuseful' features here. This improve the overall interface speed and response anyway...

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Installation of the MCV876-12bits into the Korg MS20.

The 12bits Pitch CV & Gate outputs replace the Keyboard CV/Gate IN normalisation on the MS20 panel. Auxiliary DACs are outputed in place of the wheel & push button . The wheel voltage is summed directly with the DAC2 on the interface pcb. The MIDI din plug is placed on the rear panel and the interface psu is picked up on the MS20 motherboard, nearby main voltages regulators.

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