tuning, osc 1 pitch wandering

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nato
Posts: 6
Joined: Mon Jul 26, 2010 8:42 pm

tuning, osc 1 pitch wandering

Post by nato » Tue Jul 27, 2010 1:59 am

I'm completely new to Moogs so I bought a used LP from a music store last week to learn more. (This LP is a few years old I think, no USB, gray/black, "Little Phatty (R) analog synthesizer".) I'm very impressed by the sound but I have noticed a tuning problem that has persisted after the calibration sequences. After being powered up >1 hr, I still have a very uneven osc 1 pitch. The problem is most pronounced at the "calibration preset" tone (osc 1 only). The tone is uninterrupted but the pitch wanders broadly, 50-60 cents at 16', several semitones at the 2' setting. The pitch varies unpredictably, sounding like a gnat buzzing or a tea kettle on high notes. When I zero "osc 1 level" and listen to osc 2 alone, it is the even tone I expect. This behavior is consistent whether I've set the LP to "auto tune" or fine tune. I am making no other changes to the panel. This wavering of osc 1 sometimes goes away which is encouraging but then returns suddenly with a seemingly random panel change and no setting change will correct it again. This happens whether I listen through the headphones jack or through the audio out. The preset light has not changed to red when I hear this sound (though my preset light sometimes turns red on its own). My question: does this sound like a factory repair candidate? Is there something else I can try first?

Sir Nose
Posts: 1024
Joined: Sat Sep 20, 2008 11:15 am

Re: tuning, osc 1 pitch wandering

Post by Sir Nose » Tue Jul 27, 2010 10:51 am

It sounds like you hit everything on the normal try this 1st checklist. I would run a calibration one more time if you haven't already, make sure it is performed in the same order as stated in the manual. There could be signal coming from the pitchbend wheel causing the fluctuation. Check to see if OSC 2 also drifts, turn OSC 1 all the way down, tune OSC 2 and see if it drifts. Does it drift tune up and down the keyboard or does it drift for a single frequency held over time?

It does sound like a repair job though. Before you look into getting it repaired, email moogsupport, they will have a more comprehensive checklist. They have helped many people at home to avoid having to send in their instrument. If you have to send it in anyway you may want to consider CV out mod while it's there, depending on your needs.

nato
Posts: 6
Joined: Mon Jul 26, 2010 8:42 pm

Re: tuning, osc 1 pitch wandering

Post by nato » Tue Jul 27, 2010 9:14 pm

Thank you for the response. This is an exceptional forum! To answer your questions: 1) it drifts around one frequency but I don't know what frequency it will be until I turn it on. The C keys on the calibration preset have on different days sounded G#, Eb, a very flat F (too far from C to be corrected with fine tune). When I keep the LP on the calibration preset but bring down Osc 1 level and turn up Osc 2 level, the Osc 2 tone is always an even C. I'll rerun the calibrations and if that fails email moogsupport. If there's any generally useful news I'll post it. Thanks again!

dlearyus
Posts: 195
Joined: Wed Nov 08, 2006 7:55 am
Location: Canada

Re: tuning, osc 1 pitch wandering

Post by dlearyus » Wed Jul 28, 2010 12:37 am

this couldnt be related to a grounding issue could it?
seems that one has mystifyed alot of people in past
as it manifests itself in all kinds of intermittent weird
effects.
just a thought before rushing into repairs etc.

Cheers,

DL

Sir Nose
Posts: 1024
Joined: Sat Sep 20, 2008 11:15 am

Re: tuning, osc 1 pitch wandering

Post by Sir Nose » Wed Jul 28, 2010 7:48 am

Definately make sure the outlet the LP is plugged into is grounded. With OSC 1 drifting on one frequency, while OSC 2 is stable, it sounds like a repair job.

tript
Posts: 39
Joined: Sat Oct 31, 2009 12:04 pm
Location: below deck

Re: tuning, osc 1 pitch wandering

Post by tript » Wed Jul 28, 2010 8:33 am

this sounds like a grounding issue.

nato
Posts: 6
Joined: Mon Jul 26, 2010 8:42 pm

Re: tuning, osc 1 pitch wandering

Post by nato » Wed Jul 28, 2010 9:10 pm

Thank you for the responses. I tested my outlet and it's definitely grounded (as it should be). I've been in touch with moog support so I think this LP will be traveling soon. I'll give the CV out mod some thought.

praxisaxis
Posts: 91
Joined: Tue Mar 23, 2010 1:31 am
Location: Brisbane, Australia
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Re: tuning, osc 1 pitch wandering

Post by praxisaxis » Tue Aug 03, 2010 8:01 pm

"My question: does this sound like a factory repair candidate? Is there something else I can try first?"

It sounds very much like you'll have to get it repaired. But perhaps try the factory reset? I guess you have already... I only suggest it because that did away with some minor weirdness I was experiencing shortly after I purchased the instrument.

nato
Posts: 6
Joined: Mon Jul 26, 2010 8:42 pm

Re: tuning, osc 1 pitch wandering

Post by nato » Tue Aug 10, 2010 11:26 pm

Thanks. I also tried a factory reset and that didn't help. I ended up exchanging it for a new LP so I'm not sure what the problem was.

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