Moog Opus 3 Strings/Chorus

In a Moog Mood? Here's a forum for discussion of general Moog topics.
Post Reply
easterleggs
Posts: 3
Joined: Tue Nov 21, 2006 8:42 pm

Moog Opus 3 Strings/Chorus

Post by easterleggs » Sat Dec 09, 2006 9:15 pm

I've read a lot about the Opus 3 String section being notorious for failing. But what fails? Can anyone pinpoint a component or connection that is likely to fail? I see from the schematics that the Strings run to the Chorus mixer section. The 3080A chorus VCA on my unit is reading correct voltage, but I have no output from the Chorus mixer section (but I do get organ from the other two mixer sections). Thanks!

ARP
Posts: 170
Joined: Fri Sep 30, 2005 5:14 pm
Location: USA

Post by ARP » Sun Dec 10, 2006 1:22 pm

If i remember correctly, the notorious chorus failure is via the Reticon SAD512 chip, I know these were hard to come by years ago..I don't know if anyone has remanufactured them.
"Although they heard the music..they didn't understand the tune"

electrical_engineer_gEEk
Posts: 320
Joined: Tue Feb 10, 2004 12:30 pm
Location: Seattle, WA (new resident!)

Post by electrical_engineer_gEEk » Sun Dec 10, 2006 6:16 pm

mine has a broken TOS divider chip....i can't find one so it sits in my closet in 10 pieces....it's quite sad actually.

easterleggs
Posts: 3
Joined: Tue Nov 21, 2006 8:42 pm

Moog Opus 3 strings/chorus

Post by easterleggs » Sun Dec 10, 2006 8:29 pm

I tested the three SAD512's. They're all reading around 6-7V which seems about right. And aren't these three parallel paths? If one SAD512 fails is it catastrophic to the chorus circuit? Or must all three fail to render it inoperable?

Something simple that is common to both Strings and Organ in the Chorus path is the Strings/Organ mix slider (10K LIN). It's reading 0-150+K while the PAN sliders (10K LIN) read 0-3K. Seems like a 10K slider shouldn't read over 10K...? Stop me if I'm wrong!!!

OysterRock
Posts: 800
Joined: Thu May 26, 2005 8:52 pm
Location: Portland, OR
Contact:

Re: Moog Opus 3 strings/chorus

Post by OysterRock » Sun Dec 10, 2006 11:22 pm

easterleggs wrote: Something simple that is common to both Strings and Organ in the Chorus path is the Strings/Organ mix slider (10K LIN). It's reading 0-150+K while the PAN sliders (10K LIN) read 0-3K. Seems like a 10K slider shouldn't read over 10K...? Stop me if I'm wrong!!!
You are measuring the potentiometer while it is in the circuit. Doing so can give a different value than what it really is due to the surrounding circuitry.

User avatar
CZ Rider
Posts: 586
Joined: Thu Jul 14, 2005 12:13 am
Location: Southeastern, PA

Post by CZ Rider » Sun Dec 10, 2006 11:25 pm

Something simple that is common to both Strings and Organ in the Chorus path is the Strings/Organ mix slider (10K LIN).

Have you tried listening to the mix slider? I would use a small amp with one
end grounded and the other end to probe for audio signals first. See if
there is a signal from the string section and organ section at the mix
slider, and work down from there. I have trouble-shot many a problem just
by listening to the signals at various spots. I generaly use a small 9V amp
with a little 3" speaker. Does the job!
Terry

Jauntimus Prime
Posts: 43
Joined: Tue Jan 02, 2007 6:17 am
Location: Seattle, WA
Contact:

Post by Jauntimus Prime » Tue Jan 02, 2007 6:26 am

That's a great troubleshooting suggestion.

My Opus had an intermittent problem with no output from the chorus section, but in my case the organ/strings mix slider was the culprit -- a replacement and it was 100%. The sliders are known to be fragile, but if your problem is NOT intermittent then I would guess it's a circuitry thing.
"There's a reason digital audio has earned its reputation for sterility, lifelessness, and harshness. Mainly, it's because it tends to be sterile, lifeless, and harsh." [url=http://www.myspace.com/froghollowdaycamp]Frog Hollow Day Camp[/url]

Post Reply