ARP Omni 1

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ARP Omni 1

Postby moogtard » Tue Jun 25, 2013 5:21 pm

I just accquired an ARP Omni 1. I think the .22 uf tantulum capacitors are frozen open because the viola, violin, 4' and 2' synth sections are all sustianing all the notes nonstop. Is this an easy fix as in targeting the .22 uf caps in the Envelope generator sections? Or do all the caps need to be replaced?
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Re: ARP Omni 1

Postby rhino » Tue Jun 25, 2013 5:31 pm

Don't have a schematic for the Omni 1, but IMHO the probability of ALL caps failing in nil. I'd recomment looking at the decay/sustain circuits instead. BTW, tantalum caps ARE prone to shorting, bu I don't think that's the case here.

EDIT: Check that the decay slider has not failed.
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Re: ARP Omni 1

Postby perfectdefect » Tue Jun 25, 2013 5:46 pm

Caps are a good place to start. If it was mine and knowing what I know as outlined below, I'd try and replace only the problem components for a start -look at Rhino's suggestion above, but that said... I have read tales of sudden destructive failures in Omni's, so maybe a full redo is the best approach. PM me for manual PDF's if you want.

Knowing what I know: I replaced ALL the seventy-some-odd caps in an Omni 2 a few years ago. It also had nearly frozen sliders so I did the Simple Green board soak* thing too, and it worked perfectly after. Really, 100% perfectly! Still does.

I felt empowered so I bought a barely functional Omni 1 and did the same -it remained barely functional after. I had a synth tech work on it and now it's about 90% functional.

Replacing all the caps is about a days work if you know what you are doing and are careful. Will it solve all the problems? Maybe. There are threads here and blog posts and etc where you can get more pointers.

Is it worth trying? Absolutely. For a simple string and synth machine it's really good sounding.

*Simple Green board soak is: you remove the boards with sliders, put them in your shower, spray them down with simple green -especially in the sliders, let them soak for a few minutes then use the shower head pressure to clean them. Lots of c**p comes out. You can find Youtubes of this for other Arp's with the same sliders. Once they are clean you rinse them in distilled water -I did anyway, to avoid hard water deposits then put them in the sun to dry. Try and time it so the sun is shining right when they come out of the rinse. You can also use a spray bottle of rubbing alcohol to 'chase' the water away. Apply fader lube and reassemble when perfectly dry. You might want to do this bath before you recap...

Hope this wasn't too much info...
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Re: ARP Omni 1

Postby synthparts » Tue Jun 25, 2013 9:57 pm

If it hasn't been done yet any Omni really needs to have all its tantalum caps replaced.
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Re: ARP Omni 1

Postby ppg_wavecomputer » Tue Jun 25, 2013 10:59 pm

The Omni is a pain in the arse. As soon as I acquired mine back in 1991, it started beaving in very odd ways very soon. At some point I grew rather tired of this un-funny kind of behaviour (and of its hideous sound)... I was very happy when a collector from Denmark travelled all the way from Kopenhagen to my place, just to collect it.

Never missed it. A godawful piece of junk. Yes, it says "ARP" on its back...

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Re: ARP Omni 1

Postby Steve Jones » Wed Jun 26, 2013 2:54 am

ARP released an important field change order to service techs to modify the power supply with a UZ314 transient suppressor, a resistor and a cap to stop it from blowing up the Omni's CMOS chips with spikes. You should make sure that this has been done if your machine has A series chips, and if not, do it. If you can't find a UZ314 you can sub an SA15A or similar.
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