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Just run the pot to the extremes and the most hollow/square sound will become obvious. Make sure you are plugged into an amp and have it turned up a bit!

The hardest part of tuning on 4 and 2 pole is getting the noise to match the pitch of a note (initial frequency calibration). That one can be tricky but do as the service manual suggests i.e. setting the osc to half and full. I like to do one more step. I toggle through all 8 cards and if the pitch of the noise does not match the other cards, it will stick out like a sore thumb. Repeat on both 2 and 4 pole settings.

Sounds like the button might be going out. Doug @ synthparts can help. Easy to replace them.

Have you found IC #64 yet for the DAC adjustment. It is actually IC 166

CHeck out my blog on my Oberheim experiences. I have some calibration and restoration stuff in there!

https://sites.google.com/site/jlonanostuff/home/oberheim-ob-xa

From: walter bonacci <walterbonacci@...>
To: oberheim@yahoogroups.com
Sent: Tuesday, January 7, 2014 8:57 AM
Subject: Re: [oberheim] Oberheim OBX-a voice tuning specifics

Thanks guys!

Ok, I will start with the power supply and then follow the service manual. Yes I tried it before and the pulse weight was the hardest part... (do you have any tip Searching for the most hollow sound doesn't tell much).

Can I leave the modulation at the end if I disable it

I know I have a problem with -1 octave transpose button (down), sometime it works more often it doesn't... seems to be random.

The light turns on always but the transposition seems to work only in certain circustances, I couldn't realize when, maybe only when I select certain programs... or sometime after clicking it 20 times or moving down from up :/

Is the mod for enabling self resonance on the filters hard to implement

Thanks!

Walter

On Tue, Jan 7, 2014 at 2:42 PM, Les Lambert < les_lmbrt@... > wrote:

I have done it without any testgear at all, but if you don't have a good ear, you're in for a rough ride.
The pulse width adjustments and tracking are particularly hard, and there are many interactions of course.
It all hangs off the accurate adjustment of the power supply as mentioned above, and the bender wheel adjustment is crucial.
Previous answer is the correct one, do what they did at the factory, if you can get the info.
At the time I did it, the info wasn't easily available, and I'd done my OBX a short time before, so felt confident.
Mistakenly some might say. : o

On Tuesday, 7 January 2014, 12:34, James < fl_799@... > wrote:

Walter,

First, download the 1st and 3rd edition of the service manual. First edition is here:

http://launch.groups.yahoo.com/group/oberheim/files/OB-xa%20files/

3rd edition: http://www.synthfool.com/docs/Oberheim/Oberheim_OBXa/oberheim_obxa_service_manual_3.pdf

You don't need a scope to tune the boards. It is very straight forward if you follow the manual.

To do this right, you need to perform the full service. The 5 and 15 volt piece always comes first followed by all of the adjustments on the bender assembly. Once those are finished, then you tackle the cards.For your first time, you might want to plan on 2 hours for the whole calibration.

James

From: walter bonacci < walterbonacci@... >
To: oberheim@yahoogroups.com
Sent: Tuesday, January 7, 2014 5:51 AM
Subject: [oberheim] Oberheim OBX-a voice tuning specifics

Hi,

Someone has the specifics for the voice of an oberheim obxa

I would like to know which trimmer does what.

In theory is it possible to do the tuning by hear and without an oscilloscope

Thanks,

Walter

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1794 Re: [oberheim] Oberheim OBX-a voice tuning specifics