Roland Super JX-10

Analog monster width 12 voice polyphony, 24 oscillators

A few images from two repair jobs

Some people seams to dispute Roland’s marketing buff telling us Super JX (MKS-70/JX-10) are two JX-8P in one instrument. Reason are they prefer the sound from JX-8 over Super JX which imply there are differences on the hardware. And after reading Eric Persing ‘s comment on the self-oscillating filter in Super JX I got curries to find out the difference in circuit.

Initial findings show differences around the filter chips. Several changes around control functions but as these also are under software control the most interesting parts to look at seems to be the load and filter frequency caps on pins 6 (Load), 10 (C4), 11 (C3), 12 (C2), 13 (C1). Cap value for C1, C2 and C4 are identical on all units, leaving pins C3 and Load to investigate.

Interestingly we find that the MKS-80 from rev5 also use the same IR3R05 Filter/VCA chips and none of the subjects use identical values as it turns out.

Filter difference between JX-8P and JX-10
Filter values
C3 pin 11 Load pin 6
JX-10 220pF 1K5/10uF
JX-8P 10nF 3K3/10uF
MKS-80 rev5 10nF 3K3/47uF
The JX synthesizers employ a four-pole lowpass filter, which rolls high frequencies off at a rate of 24dB per octave. There is a slight difference between the maximum resonance amount setting in the JX-8P and the JX-10. When pushed to its upper limit, the filter in the JX-10 will oscillate producing a sine wave, but this effect is not possible on the JX-8P. Eric Persing, Keyboard Magazine Oct 1986

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DCO explained: https://www.youtube.com/watch?v=mqY6cVJS9fo

First MIDI upgrade for JX-10 with technical information: http://www.colinfraser.com/jx10/jx.htm

Firmware 3.xx/4.xx: http://www.vecoven.com/superjx/superjx.html