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901b tracking

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901b tracking

Postby Rarecomponentadsr » Thu Oct 26, 2017 10:44 am

One of my three 901b clones doesn't track properly. All three are identical in components but although replacing P2 I'm still getting the problem that I run out of turn on the P2 in the problem 901b. I get sync on the upper end of the keyboard but it's way out at the bottom and there's no more turn of the P2 left to bring the tracking in. I'm not sure if that run out is at the DC end or ground end of the P2 as I use a multi-turn.

I'm wondering if there's an alternate component switch that can be used to solve it or perhaps different value P2 ?
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Re: 901b tracking

Postby noddyspuncture » Thu Oct 26, 2017 6:05 pm

I also fitted multi-turns to my original R.A.Moog 901b's... as well as my own 901b clone.

As the point here is getting them to track each other, what I did was to shift them all back (or forward) the same way - I was aiming for my multi-turns to be all set midway. So check which end it is running out at... (I am assuming they are all wired the same way..?) and turn them "all" back the other way..?

I did this with mine and it just changed the 'range' in which they were working.
The only drawback might (or will) be is that you'll need to recalibrate your 901a to compensate..!?

Hope all that makes sense...?

Cheers,
Tom
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Re: 901b tracking

Postby Rarecomponentadsr » Thu Oct 26, 2017 7:36 pm

Thanks for those ideas. I actually did that with the first two which worked fine ..but this third one is a rogue.
As the first two work fine I don't want to mess with the 901a ...
I guess it could be Q7 ...maybe an odd frequency compared to the other two.

Just wondered if anyone had had this problem.
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