Roland JX-3P Modifications -------------------------------------------------------------------------------- Modifications Since the JX-3P is mostly analogue in the sound creation and quite simple digital, there may be done a lot of modifications to the JX-3P. I hope I will soon write more detailed informations, for the moment you will get some short explanations. The most modifications are put to the schematics, you find on this site. Tune the VCF: set the JX3P to measuring mode (hit Tape Memory, hold ProgKey 5 and hit Tape Memory again); select programm B2; set resonance to maximum, the keyfollow to minimum; play the lowest key and raise the cutoff frequency to a value that results in a tone around 200 Hz; save this Program. If you now hit any key you will see the last 6 LEDS (prg 11 to 16) display, which voice is played. LED 11 is the voice closest to the power supply, LED 16 is the voice closest to the boarder of the main board. Now play the lowest voice and adjust with the VR 102, 202, ... 602 the VCF Frequency of the corresponding voice by ear or by a tuning meter. Adjust resonance: Most of the JX-3Ps are set to a moderate resonance behaviour. The usage of the VCF as Sinus oszillator is not guaranteed. This can be achieved by changing the setting of the resonance with the VR 103, 203 ... 603. I suggest to tune first the VCF cutoff frequencies of all voices and then continue with the resonance of the voices. This can be controlled by ear or by an oszilloscope. I used my ears. Add tuning for the control amount of VCF control voltage I did not try this, it is only my suggestion to the courageous ones. The tracking of the JX-3Ps VCF chip is quite linear, but the voices may differ among each other. The amount of the tracking is determined by R109, 209 ... 609. If you replace this by a resistor 39k in series with an variable resistor of 10k, you should be able to adjust the tracking. If you try this please tell me the results. Split chorus for the use as separated effects unit: This has to be done on the switchboard. cut the line between C5 and R19/R22. This break will be the input to the chorus. Add a plug for this input at the rear side of the shelf; the plug should have a switch. If nothing is plugged in the broken line should be connected here. If a cable is plugged in the signal of the cable should be connected over a 10k resistor to C5. If you need a separated output for the chorus, simple connect two plugs to R21 and R23. Chorus speed: I removed the brilliance function and am using the brilliance pot for the chorus speed. Simply replace R43 by a 100k resistor in line with the pot VR1. Stereo voice separation: This is only senseful if the Highpassfilter is removed from the signal. It has to be done on the main board. Build a copy of the circuit around IC1, C1 and R7. Leave R1, R2 and R3 (the output resistors ov the single voices) on the original circuit and move the R4 to R6 to the new circuit. Connect the output of the new OpAmp (pin 1) to pin 3 of the connector CN1 (the former brilliance line) or do a new wire to the switch board. On the switch board you have to breakup the line between R19 and R22. Connect the signal from the new OpAmp (pin 3 on CN1 from main board or new wire) to R19. Add two resistors with 10k which mix the both signals together to feed the chorus input. Replace the Highpass by additional programmable noise: The detailed description should be taken from the schematics. The principle is: use the VCA, that builds the high pass filter as normal VCA for the noise source. Normally the noise is switched in TR18 by the signal from pin 7 of IC 31. This switching has to be removed: I simply removed TR 18. The VCA circuit is handdrawn on the schematics. As the last step you have to remove in each voice R132, (R232, R332, ... R632) from the connection to R137 (R237...) and connect it to pin 3 of IC103. External control voltage input for VCF This input already exists in the form of the brilliance pot. If you use the pot for the chorus speed simply connect a plug to the line which comes from CN1 on the mainboard. If you wish to increase the amount of the modulation, you have to reduce the value of R110, R210, ... to R610 in each voice. I did not do this until now, but a value of 10k to 100k might be ok. Other modifications will come soon.