ARP Omni 2

Tantalum Capacitors in the Arp Omni 2
Tantalum Capacitors in the Arp Omni 2

This one belongs to Jeff Zeigler, a great musician who also runs the studio Uniform Recording. The ARP Omni 2 is a synth where a lot can go wrong, but it has a very, very repetitive internal architecture so it’s often the same problems over and over– bad logic ICs and bad tantalum capacitors (blue circles in photo above).  That doesn’t mean it’s easy to fix though!

The widely recommended approach is to replace all of the tantalums with new electrolytics, as I did here.  This is a miserable and tedious process because the PCBs on this synth are really fragile.  These are really the worst I have ever worked on.  They are double-sided, and the traces, instead of being etched from the substrate of the board, are just adhered somehow to the top surface, and they tear and lift very, very easily. A lot of the components have to be soldered on both sides because the traces are not connected through the board.

very dirty Arp Omni 2 sliders
nasty dirty sliders

Work done: replaced 100+ tantalum capacitors and electrolytic capacitors with new electrolytics.  Thoroughly cleaned everything including insides of pots/slider pots, lubricated sliders with silicone.  Replaced several 4000 series CMOS logic ICs and a couple comparators to fix some envelope and voice issues.  Reflowed solder on jack board.  Replaced all key bushings and leveled keyboard.  Cleaned key contacts and buss bars, reattached a couple of key contacts that had fallen off or were about to.

This synth was made in 1978 and it has a lot going on.  There are like 7 or 8 PCBs, separate AR for every key for the string voices, and dozens of CMOS ICs to control all the switching, divisions, envelopes, etc.  The notes are all generated from a single Colpitts oscillator with a huge adjustable inductor.  They used to go for a couple hundred dollars but now they are worth a lot more, and it’s worth knowing that it takes many, many hours to fix one up.

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