we discovered that our standard Neutricon (Avalon) to DIN13pin cables do not work with the Roland VG-99!
the VG-99 has a smarter 13pin input than the other such guitar synthesizers and polyphonic effects: it mutes the main output if the pin 8 (synth volume) is not connected – probably to make sure that there is not noise if no input is connected at all.
so we need to add a resistor to the cable:
about 2MOhm from pin 8 to ground (the connector housing) works with the VG-99.
probably better (to make sure it works with future gear) is to use two resistors:
47kOhm from pin 8 to ground and 18kOhm from pin 8 to pin 14 (+7V)