I have 2 RUBIN Systems for acoustic guitar available. It works for Nylon and Steel both.
It can drive Midi or Modeling devices by 12 pin (Neutrik) to 13 pin (cable is there), and Standard systems as well by a jack.
The preamp is mounted inside the guitar on the back, you can reach through the soundhole. volume pots for each string.
2 soundhole controls: Volume and synth vol.
The systems were installed by Rolf himself in 2013, and never went in serial production.
I have all the drawings, photos… on request I will give you more information.
As they were pre-serial production, its a thing for the experienced technician,
who is familiar with Rolfs works…
For my purpose the systems were too sophisticated,
so I removed them. The sound was fine, very balanced and full bodied with all the possibility to drive Midi/Synth…
Some problems with ground noises, but that came from the PU and Matthias knows to fix that easily.
With a special PU glue.
I am happy to hear from you, and answering your questions.
All the best. Daniel