MKS-40 Chorus PCB


Overview Roland added a fixed ON/OFF chorus ensemble effect to the Jupiter 4 as it only has one VCO and sounds a little thin. The circuit design has a fixed speed LFO driving a stereo pair of BBD delays (512 stage MN3004), with the second delay 180 degrees out of phase to the first one. The original version used CMOS clocks but was replaced at some point with MN3101 clocks and the BBD output signal was muted when OFF. This improved the signal to noise ratio.

This was the first time Roland used a BBD based chorus in a polysynth, although they had started using BBD’s in the Boss CE-1 of 1976. The design delivers a fixed chorus speed and depth, which Roland expanded in follow on analog synths with variable times and depths. The MN3004 can provide a delay time up to 25ms, but I am not sure what clock speed Roland used in the JP-4, and the actual delay time. In the 172 module Roland used the same MN3004 but with only 7ms of delay which is flange effect not chorus.

MKS-40 Design I have a couple of NOS MN3004’s, so one option is to build the Chorus PCB with these and see what the delay sounds like. However these chips are obsolete and expensive. A good alternative is to use the MKS-30 chorus design which is also fixed in speed and uses the MN3009. This chip has been remanufactured and is readily available but is only 256 stages but I am hoping it will provide a good chorus sound. The MN3009 appeared in many Roland analog synths in the early 1980’s, including the Juno 106 and JX-8P.

For the first prototype I have gone with the MKS-30 chorus design but with the final VCA stage being based on the JP-4 design with BA662’s.

 

 

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