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Fixing a demagnetized pickup.

Benjamin Strange

Benjamin Strange

Commercial User
Dec 25, 2002
9,737
310
49
New Orleans, LA
www.ufodeathcult.com
Disclosures
Owner / Tech: Strange Guitarworks
#1
I'm putting this here because I feel the best minds on TB are in the Luthier's forum.

I just picked up a Ovation Magnum bass, and it's got some electronic problems. The preamp has some issues, which I don't care about as I probably won't end up using it, but... the bridge pickup has got a problem as well. It's an interesting pickup configuration (see here for details: http://www.ovationtribute.com/Catalogues/Magnum Bass Owner Manual/Magnum Bass Owner Manual.html ), where the neck pickup uses 4 individual coils, and the bridge uses two - one for the E and A and another for the D and G. The neck pickup works fine, but when the neck and bridge are used together, the E and especially the A string phase out almost completely. The bridge soloed doesn't have as much of a problem, but the E and A are still a bit weaker than the D and G. When I put a screwdriver on the poles, the E and A have a much weaker magnetic pull on the tool.

What gives here? I've got everything wired up properly, but I have no clue what's going on with the pickup. Can a pickup demagnetize? Could something else be causing these phasing issues? Help me, luthiers - you're my only hope.
 
#2
Also, I've noticed that on the neck pickup (which utilizes 4 individual poles and coils), that the E and A are north polarity, and the D and G are south polarity. I'm not sure if this is normal or not, but it strikes me as a bit odd that there would be two different polarities within the same pickup. Any thoughts?
 
#3
Interesting pickups, you can remagnetise a magnet using a stronger rare-earth magnet. there's a free information sheet over at stewmac.com if you want to check it out.

The fact you've got two different polarity on one pickup could be simply to make it a humbucking pickup like P pickups. So there's nothing to worry about. Only thing is if you are getting phase problems on that one pickup only, there's always a possiblity you migh have screwed the magnet polarity at some point. Maybe your pickups were in close proximity to a stronger magnet at some time? Who knows.

The first thing I'd do is e-mail Ovation and ask about the pickup specs, whether its supposed to have the same polarity or not then you can decide if you need to remagnetise or not.
 
#4
Update: I've taken the pickups completely out of the circuit, and they seem to measure up to reasonable DC resistance. The neck humbucker is about 12K, and the bridge pickup has about 8K for each coil, and 4K when measured together in parallel.

I'm going to try to track down some rare earth magnets and follow StewMacs instructions - hopefully I can get this thing working before this weekend's string of gigs.
 
#5
That's one hell of a geeky bass! Interesting stuff, not much I can add to this thread, sorry.
I think contacting Ovation is your best bet, although support on a 30 year old product, hmm.. Probably the engineers who worked on this are long gone, they might be inclined to give you the schematics. In which case the guy with the Wal pickup off eBay might be interested, the configuration looks vaguely similar.

Best regards,

Jarno.
 

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