[sdiy] ARP Solina/String Ensemble help?

[Eric Frampton]

Hey y’all -

I’m back at my never-ending Solina project, and am down to one last (big) issue.
This is a Series 33, so 1975-ish with the Gate and Trigger jacks in the back and the Chorus switch on the front.

When I play a key, I hear not only the selected waveform from the key, but also some or all (hard to tell) of the other keys droning quietly in the background. If I play multiple keys, the droning is louder. The drones follow the VCA envelope.

If I scope the output for the highest gate chip for the highest 10 notes, and play the top C and work my way downward, I get the waveform for the C down to D# (as you’d expect), then silence/no waveform, then starting at the G (G2?) that is the top of the bass/cello section, I start getting lower amplitude waveforms all the way to the bottom C.

For troubleshooting, I removed and socketed the two highest gate IC's. If I remove those and do the same test, I get silence on those top 10 notes (as you’d expect), then no added waveforms at all going down the keyboard.

The added waveforms I’m hearing seem to be from the main Gate board, and not the Bass board, based on pitch. They show up in all four 4’ and 8’ sounds (viola, violin, trumpet, horn) but not in the Cello or Bass - those two seem to be fine.

i’ve got trimmer on the Gate board adjusted for 15V. If I lower it (say, to the point of voices not starting to speak), the drones are still there, they’re just lower in volume.

Here’s a link to the schematics: https://manuals.fdiskc.com/flat/ARP%20Solina%20Schematics.pdf

any ideas?

thanks,
e

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