OSC SYNC mod for Behringer Neutron

A description of how I modified my Behringer Neutron synthesizer, adding circuitry known from the Prophet 5 rev3, allowing for a much cleaner OSC SYNC sound than the Neutron's native one. An added flip-switch on the front panel now allows me to toggle between the Neutron's harsh default sync and the smooth, modded behavior that is also heard in the Behringer Pro-1.

Inspiration / Must-Reads

• This Reddit from the guy who once published this mod (but then completely removed it from the web):
  https://www.reddit.com/r/synthesizers/comments/9h5aem/behringer_neutron_sync_mod_by_some_clever_guy/
• electricdruid's fantastic article on the 3340 VCO:
  https://electricdruid.net/cem3340-vco-voltage-controlled-oscillator-designs/
  I used the sync circuit from the Sequential Prophet 5 Rev.3 scheme in that article.
• This discussion on Gearslutz:
  https://www.gearslutz.com/board/electronic-music-instruments-and-electronic-music-production/1199238-behringer-neutron-semi-modular-182.html

Sound demo/comparison of native vs. modded OSC SYNC

See this YouTube video.

Requirements

The whole circuit is extremely inexpensive. I had old, used SMD components lying around, so it cost me nothing except for the €1 flip switch from Amazon.

• BC859 PNP transistor
  (because I had one at hand; the other guy used a BC858, and the Prophet scheme suggests a 2N4250)
• resistor 10k
• resistor 47k
• cap 100nF
• cap 200pF
• 1 flip switch (3-pole, ON-ON)
• you will also want enough shrinkwrap at hand

Full description in a single image

Disclaimer

• Modifying your Neutron will void its warranty.
• This repo is a pure "works for me" description of how I modified my Neutron.
• I am NOT a professional electronics engineer, and I do NOT guarantee correctness or harmlessness of anything.
• You alone are responsible for damages you do to yourself or your device.