[sdiy] Niche ACM-1 how's this thing work?

Mike Bryant mbryant at futurehorizons.com
Mon Mar 20 16:10:16 CET 2023

The NatSemi LM1973N used to be fairly popular for this application.  Not as good as the dBX chip but a lot cheaper and smaller.  It was three channel, but there were also one and two channel versions.  Maybe they prototyped an 8-channel version but never released it into volume manufacture.

From: Synth-diy <synth-diy-bounces at synth-diy.org> on behalf of mark verbos via Synth-diy <synth-diy at synth-diy.org>
Sent: 20 March 2023 13:55
To: synth-diy at synth-diy.org <synth-diy at synth-diy.org>
Subject: [sdiy] Niche ACM-1 how's this thing work?

Those of us as old as I am might remember this thing from the 90s. It is patched into the inserts on a mixer and then adds MIDI controlled automation. All the chatter around is about how it is passive, so it has “infinite” headroom, 0% distortion, 0% gain. I got one recently for a low price. I looked inside, eager to know the trick…. Vactrols? Motorized pots? something I don’t even know about? Inside the is a big chip 28pins or something with the label scratched off. Does anyone know what is actually going on in this thing? Is that an 8 channel digitally controlled pot? Just curious.


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