[sdiy] Free SSM2044, SSM2056 chips for pickup and one question about single supply VCAs

[hannes.janetzek at gmail.com]

Hello - now that I have your attention I would like to bring up the sad
topic of the numerous synthesizers covering in 80s home-organs that are
daily thrown in the trash by their inheritors.
Ok maybe this is a specific southern Germany problem where it appears every
second home had a Hohner organ which outlived their role as status symbol
by now.. In the US these model were sold as Wurlitzer Omni 3000-6500 - not
sure if these are regularly in classified for pickup as well.

My interest in these devices is mainly in their MEG sound-generator for
which I'm currently writing an interface library. As this starts to work
out nicely I wanted to throw in the filter boards and was very surprised to
see that all the VCAs and most of the mixing is powered with ground to 12V.
Has anyone an idea what could be the reasoning or advantage of this
approach? (I'm very much a beginner on the analog electronics side)
The schematic is on page 35 and all boards I've seen use the BA6110 version:
https://www.synthxl.com/wp-content/uploads/2020/08/Hohner-Symphonie-D98-Service-Manual.pdf
Page 24-29 for the sound-generator - if you are curious.

Regards
Hannes
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