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Alembic Club » Alembic Basses & Guitars » Archive through May 25, 2005 » Difference between the neck and bridge jazz Activator pickups « Previous Next »

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Username: 90k6259

Post Number: 4
Registered: 5-2005
Posted on Tuesday, May 03, 2005 - 4:38 pm:   Edit Post

The bridge pickup of a 4 string jazz Activator set is an exact fit into the neck position cavity of a Carvin XB75 with the 5w neck...
MY question... Is there a difference between the neck and bridge pickup constuction, of the jazz activator pickups to accommodate the proximidy of the pickup to the bridge?
Such as string excursion and other factors I may not of thought of.
Thanks for your knowledgeable replies.
This forum is great isn't it :-)
Username: mica

Post Number: 2411
Registered: 6-2000
Posted on Tuesday, May 03, 2005 - 4:56 pm:   Edit Post

The only difference between the neck and bridge pickups is the physical size of the shell to match the original routs. The bridge pickup is slightly longer, but the coil is the same in each.

Is the bridge cavity on your Carvin longer than the neck cavity?
Username: 90k6259

Post Number: 6
Registered: 5-2005
Posted on Tuesday, May 03, 2005 - 5:55 pm:   Edit Post

Hi mica,
Welcome back! Hope all went well with the kittens!
To Answer your Question... It is my understanding that Carvin jazz pups are all bridge size.. mine measures 3-11/16"...The cntr. to cntr. string spacing over the cntr. of the neck pup measures 2-11/16".. Will my Activator bridge pickup work?..I have an MM in the bridge position..It measures 4" because of the 3/4 spacing at the bridge... I would love to have a fat boy installed in a similar caseing if posible...
Senior Member
Username: bob

Post Number: 423
Registered: 11-2002
Posted on Tuesday, May 03, 2005 - 9:53 pm:   Edit Post

No, you can't have a FatBoy in the same casing. They use a larger magnet, which fully occupies the AXY casing.

Yes, I concur with your understanding that Carvin pickups are jazz bridge size, for both neck and bridge. Mine also measure 3-11/16", though it happens to be on a four string, and I thought they had wider ones for 5 and/or 6.

The key question is whether the coil is wide enough to properly register all your strings, within reasonable excursion, as you suggest. This is apparently not easy to answer, and might involve some testing, but for starters I suggest you provide the total distance across all strings, at the bridge position (which will be wider).

If that works, then you might be able to negotiate, at modest expense, an Activator set that has two pickups with the same housing size. If the bridge will work, the neck will be no problem.
Username: jetbass79

Post Number: 18
Registered: 2-2005
Posted on Wednesday, May 04, 2005 - 1:06 am:   Edit Post

I think the fundamental problem is that there is no direct replacement pickup that Alembic makes with a Musicman pickup cover. I could be wrong but I do not recall the Musicman shape being offered as a replacement pickup from Alembic (though it might be a cool idea for those who want to "Alembicize" their Musicman basses).

It might be possible to put a Fatboy 5 (or AXY5) in the rout but it might look funky because of the tabs that Carvin humbucker has -- akin to a Musicman but not the same as a 5 string Musicman pickup. The Musicman 5 string does not have the tabs that its four string counterpart does.

My guess is that string spacing concern is rather erroneus because I assume Alembic pickups have ceramic bar magnets so a 5 string pickup would work with most any 5 string spacing and the issue here is the fact that Alembic does not offer a pickup shaped precisely like the Carvin Musicman-style pickup, but I have been wrong before.
Username: jetbass79

Post Number: 19
Registered: 2-2005
Posted on Wednesday, May 04, 2005 - 1:12 am:   Edit Post

Ooh...one more thing I should clarify. The Carvin Jazz pickups are all the same size, even for 6 strings. This is because of the beauty of ceramic bar magnets -- you don't have the string sensing issues like you do with traditional Jazz pickups that have two alnico-5 polepieces for each string.

Carvin 6 string basses tend to be on the narrow side but not so bad as to say they don't play well for fingerstylists or slappers, but they don't have a 3/4" spacing like a Fender Precision Bass, for example.
Username: 90k6259

Post Number: 13
Registered: 5-2005
Posted on Thursday, May 05, 2005 - 2:15 am:   Edit Post

Hi John,
Thanks for all the great info. Your right I had forgotten about the ceramic bar in Alembic pickups. the Alembic jazz pick up I have, is for a four string and although the caseing fits nicely in the location, I wasn't sure if the pickup inside the caseing would span the spacing of my five at 2-11/16" outside string cntr. to outside string cntr.

I see that in the list of pickup shape options at the pickups page. they list custom shapes as an option.. so It may be able to happen.
Username: dfung60

Post Number: 81
Registered: 5-2002
Posted on Thursday, May 05, 2005 - 4:39 pm:   Edit Post

A couple of comments:

1) If you want to see if the Activator you have is sufficiently wide, you need to get some magnetic viewing paper. This is a pair of transparent pieces of plastic bound together with oil between them. Fine iron filings are suspended in the oil. When you hold the viewing paper over the top of the pickup, you'll see an image of the magnetic structure of the pickup appear. You can get this at a kid's science supply store or you can buy one from EMG (I'll admit right now that I've never seen one in a science store before and it no longer appears on EMG's website, but I'm sure you can order one by calling their customer support line).

You want the magnetic structure to cover the full width of your strings plus a little more so the entire range of excursion of the string is over the magnets. You want to check this with the pickup installed too. Some pickups have guts much smaller than than the cover would make them appear and they're not always centered under the top. If you don't have full coverage of the string excursion by the magnets, your outer strings will definitely sound gutless. It makes a HUGE difference! This is partly why a Fender pickups have 8 polepieces - it widens the magnetic field so you don't get volume fluctuations when the string is swinging. The original P-bass had only 4 polepieces and the strong transient fried a lot of those ancient old bass amps.

2) The Fender Jazz basses produced in Mexico also use the bridge pickup in both positions, so this is a common cost cutting measure these days. The Mexi Jazz has pole pieces instead of bars, so it's really non-optimal but saves them a couple of pennies in production since they don't need to stock two different pickup models.

3) Having the same pickup saves Fender (and presumably Carvin) a couple pennies but it is at a cost to the player. Leo was a pretty darn clever guy when he first started building these things. The Jazz Bass pickups are single coil which is simpler to make and has extended high end compared to a humbucker. But they pick up a lot of buzz and hum. So, on the Jazz, Leo inverted the magnets on one of the pickups and wound it in the opposite direction. Without getting all nerdy on you, the result of doing this is that you get the full single-coil tone from the pickups but when both pickups are on, the hum is cancelled out just like a humbucker. If you use the same pickup in both positions, the tone will sound the same, but there will be no hum cancellation.

I believe the Activators (and EMGs too) are a stacked humbucker so they'll be quiet at all times. On a regular Jazz with the trick pickups, it is quiet when both pickups are on but will buzz when you use just the neck or bridge.

Incidentally, the two halves of the P-bass pickup use the same trick which is why they don't hum but are still pretty bright.

The coolest implementation of eliminating hum is (not suprisingly) on the Series bass, where there's that third dummy coil mounted flush between the two pickups. It has a precisely wound coil but no magnets and exists only to cancel the noise from the Series single coil pickups. This is the most expensive way to do it, but this gives you that beautiful pure single coil tone with no noise and it works with any combination of pickups.

David Fung

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