Korg MonoPoly modification – analog white noise

Believe it or not, first revision of Korg Monopoly features a digital noise source with that irritating loop sound. So in response to encountering the digital noise generator with its persistently irritating sound in the initial version of Monopoly, I resolved to craft a genuine analog noise generator as an antidote. My journey commenced with the pursuit of an authentic solution, steering me towards the realm of reverse-biased transistors.

With determination propelling my endeavor forward, I delved into the depths of analog circuitry, seeking to construct a noise generator that harkened back to the essence of the original Monopoly’s design. After thorough research, I unearthed the schematic for the transistor-based White Noise generator utilized in the revised iteration of Monopoly (post the production cycle of May). I didn’t have to search far. The answer was in the service manual of the unit.

You will need a prototype board for this project. They are cheap and forgiving if you make a mistake as opposed to building a custom PCB. This drawing is a showing you how to connect the components, of course you can use any other configuration / layout that you prefer.

Once you build it, it should look something like this:

A good location on where to insert the new board into the unit. I took power from the KLM 356 board (+15V, -15V, GND):

All that was left was to adjust the trimmer to about 4V AC output and connect it to the place of the C11 capacitor on the “old” sound generator. The C11 capacitor must be removed to “disconnect” the old generator from the board. Good bye to annoying digital noise generator that loops all the time. Of course for all the details you will look into the Korg MonoPoly service manual’s schematics which can be found here.

Bill of materials:

  • 3x 10uF/16
  • 1x 1uF/50
  • 1x 4k7 ohm
  • 1x 6k8 ohm
  • 2x 10k ohm
  • 1x 100k ohm
  • 1x 1M ohm
  • 1x 1M ohm trimmer
  • 1x 2N3905 or any other PNP transistor
  • 1x LM4558 or similar
  • all resistors 1/4W

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