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Oscillator shifting, unsteady (see video) on initialize

Oscillator shifting, unsteady (see video) on initialize
« on: April 10, 2019, 07:15:26 PM »
Hi Everyone -
New and happy OB-6 user.  Bought it used off of Reverb a week ago, supposedly in "excellent condition."  But oh man, what is this strangeness (see video)? VIDEO: https://youtu.be/zjE1N1IKeIQ
Oscillators suddenly shifting on an initialized patch. This issue seems to come and go.  Any ideas?  Very concerning. 
Sincere thanks in advance,
Paul

Re: Oscillator shifting, unsteady (see video) on initialize
« Reply #1 on: April 10, 2019, 10:57:05 PM »
Hello Paul, and welcome.

This sort of behavior has been observed by others (myself included) before. It is due to the automatic temperature compensated tuning, which is trying to keep the synth in tune as the circuits inside warm up.
It should not be this obvious though.

From what I understand, the system takes the internal temperature reading several times a second, and looks at a temperature table in memory to know what appropriate Control Voltage to send to the circuits in order to stay in tune.

But sometimes that table might not be reliable (for example if the room you use the OB6 in has a different temperature behavior than the previous owner's room).

One sure way to fix this, but it might take some time to get back to normal, is to erase that temperature table and start from scratch (pressing MANUAL+3), and then by pressing MANUAL+0 (calling calibration routine) each and every time the synth goes out of tune.

After a short while, the observed behavior seen in your video should be a lot less obvious (but not quite completely gone for the first few minutes that the synth is powered up from cold). After that, the tuning should stay rock solid. Well, as rock solid as analog oscillators go.

Anyway, that worked for me and a few others here who had the same issue.
Hope this helps.

Alain.
Minimoog D (vintage), OB6 (Desktop), Oberheim Matrix-6 (MIDI Controller), Prophet REV2-16, DeepMind 12

Re: Oscillator shifting, unsteady (see video) on initialize
« Reply #2 on: April 11, 2019, 09:15:17 AM »
Alain,
I can't thank you enough for taking the time to write that out.  It went a ways toward putting my mind at ease. 

In general, the synth definitely seems to take 10-15 to be totally stable.  That said, the video was taken yesterday after the synth had been on for probably 30 minutes, which was all the more alarming. 

Holding down Manual +3 certainly sends it outta whack, which I suppose makes sense.  I'll try to keep up w. the Manual +0 to re-train it. 

Thanks again for your thoughtful response, Alain --
Paul

Re: Oscillator shifting, unsteady (see video) on initialize
« Reply #3 on: April 11, 2019, 09:42:39 PM »
Alain,
I can't thank you enough for taking the time to write that out.  It went a ways toward putting my mind at ease. 

In general, the synth definitely seems to take 10-15 to be totally stable.  That said, the video was taken yesterday after the synth had been on for probably 30 minutes, which was all the more alarming. 

Holding down Manual +3 certainly sends it outta whack, which I suppose makes sense.  I'll try to keep up w. the Manual +0 to re-train it. 

Thanks again for your thoughtful response, Alain --
Paul

You're welcome Paul.

Hope that everything gets back to normal after the retraining period.
BTW, this solution was suggested to another forum member who had similar tuning issues with his OB6 by DSI (now Sequential) support a while back. And it worked out okay for him (and me too) so there's a high probability that it will also for you.

Keep us posted.

Alain.

P.S. If it fails, there is always the excellent Sequential support team ready to help out.
Minimoog D (vintage), OB6 (Desktop), Oberheim Matrix-6 (MIDI Controller), Prophet REV2-16, DeepMind 12