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Re: I wired up a dummy coil...


 
5/7/2003 2:34 PM
Steve A.
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Re: I wired up a dummy coil...
SK:  
 
For the heck of it I tried wiring up the dummy coil in parallel, and the sound is way too bright and there is a very noticeable drop in volume.
That doesn't sound right to me...sounds like it was out of phase
 
 
    Well, I can recheck it after work today, but I did reverse the lead going to ground and it was hum-cancelling so I didn't bother flipping the dummy coil over.  
 
    I was thinking of trying a dummy coil with 4 taps at 2k, 4k, 6k and 8k(full). That way you could dial in different amounts of humcancellation/compression in a series linkage, one of which might work well for the cleaner sounds. On a single pickup LP Jr, I could wire up two push-pull pots to be able to select between different taps or no dummy coil at all.  
 
    I'll let you know what I come up with. Thanks!  
 
Steve Ahola
 
5/12/2003 3:24 AM
Steve A.
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Well, I tested it again...
I said:  
 
For the heck of it I tried wiring up the dummy coil in parallel, and the sound is way too bright and there is a very noticeable drop in volume.  
 
SK said:  
 
That doesn't sound right to me...sounds like it was out of phase.  
 
    Well, with the dummy coil wired in parallel the sound is about as bright as a strat bridge pickup... I guess that is something that I can live with. It might be a good idea to wire up a tone cap and series resistor which would be engaged when the parallel linkage is selected.  
 
    I soldered in some mini-alligator clips so that I can quickly switch between stock, dummy-series and dummy-parallel— it seems like it would be a pretty cool mod for a single pickup LP Jr. (Well, I still need to figure out the switch wiring!) I think that practically everybody would prefer the stock P-90 sound (and response!) but the dummy coil linkages would allow the guitar to be used in environments with a lot of RF noise, or alternately for special effects (extra compression or extra treble).  
 
    BTW the parallel linkage sorta sounds like Freddy King in the 60's, before he changed the spelling of his first name and stopped playing surf music. I'd seen a picture of his LP with P-90's... one or two of the knobs were removed so the he could not accidentally change the settings. It makes me wonder if he might have had the neck pickup converted into a dummy coil! (Another foundless rumor started here at AMPAGE... ;) )  
 
    Thanks for your post! I probably wouldn't have even bothered testing out the parallel linkage a second time (darn those late night sound checks when you don't want to crank up your amp and wake your neighbors! :( )  
 
Steve Ahola  
 
P.S. I am getting some multi-tap P-90 dummy coils wired up for me so that I can try them out in strats... maybe even teles. Something like 6k/7.5k/9.5k/12k to cover all bases.
 
5/27/2003 7:06 AM
Steve A.
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More tests on LP Jr Dummy Coil...
    Well, I routed out the pickup cavity deeper so that I could put the dummy coil under the Gibson P-90 on my single pickup guitar. After shielding the cavity with copper foil tape the tapped dummy coil was slightly too thick to fit... :(  
 
    So I ended up using a 8.4k coil from a 1995 Epiphone P-90 (Sam Sung stamped on the baseplate). I also borrowed the Alnico (5?) bar magnets from the Epi pickup and put them in the Gibson P-90 which came with ceramic magnets. With the Alnico magnets the pickup sounds brighter and cleaner, with less of that "Bad-To-The-Bone" sound I was getting with the ceramic magnets. However, adding the dummy coil in series with the Alnico P-90 thickens up the sound a bit and adds some compression... IMHO it's a better combination than the ceramic P-90 with the dummy coil, which would get a bit muddy, especially if you backed off the guitar volume control.  
 
    Decisions, decisions! I'm going to wire up a switch to toggle the dummy coil on and off, but I wish I could toggle the magnets as well... ;) For the single pickup on my LP Jr, I think that you can get a fuller range of sounds with the ceramic magnets— crank it up for a lot of mids and back it off for more trebles. But it sure sounds sweet with the alnico magnets in there. [I have a two pickup LP (Jr) Special which will be getting P-90's with Alnico magnets and the tapped dummy coil on the back, like on the Gibson Blueshawks.]  
 
--Thanks!  
 
Steve Ahola  
 
P.S. Shielding the pickup cavity significantly reduced the hum and noise with the dummy coil disconnected- I test for hum by turning on the TV which is a few feet away. There is still some 60hz hum with the TV on, but it got rid of most of the higher pitched crap. So why would shielding on the bottom of the pickup cavity reduce noise coming from the top of the pickup??? Maybe the added shielding allows the RFI energy to be bled off to ground...
 
5/30/2003 2:50 PM
Steve A.
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Alnico or ceramic... or both!
    With the Alnico 5 magnets and with the dummy coil switched off, the P-90 in my LP Jr. is a tad brighter than I'd like (with the dummy coil switched on it sounds pretty good!) Perhaps Alnico 2 bar magnets would be the "Goldilocks" solution for me, but as a test I just tried replacing the magnet closer to the neck with a ceramic one. I figured that the magnetic field from the ceramic magnet would sense the middle part of the strings with more of the fundamental while the field from the alnico magnet would sense the part of the strings closer to the bridge with more harmonics.  
 
    Unfortuneately it was too late to crank up my guitar so I'll have to wait until after work tonight to give it a real test, but at low volumes it sounded pretty good.  
 
    Any thoughts on this dual magnet arrangement would be appreciated! I have a hunch that the ceramic magnet might eventually cause the alnico magnet to lose its strength. And maybe I should have tried it with ceramic magnet on the bridge side of the pickup...  
 
--Thanks!  
 
Steve Ahola
 
5/30/2003 5:07 PM
SK
In a p-90 arrangement and poles opposing the Ceramic will DEFINITELY eventually degrade the alnico magnet.  
Also, you probably went the wrong way with the magnet swap, you want the side you want to emphasise with the stronger magnet, either way, in that arrangement it'll be minor I think.
 
6/3/2003 8:09 PM
Steve A.
email

SK:  
 
In a p-90 arrangement and poles opposing the Ceramic will DEFINITELY eventually degrade the alnico magnet.  
 
 
    Thanks for the warning! I got the ceramic magnet out of there FAST... ;)  
 
    I got pretty good results with an A5 bar magnet on the neck side and an A2 magnet on the bridge side of the single dog-ear P-90 in my LP Junior- the weaker magnet on the bridge side kept the tone from getting too bright. But I ended up going back to the stock ceramic magnets because in this guitar they seem to give the widest range of tones depending on your guitar pot settings and picking dynamics.  
 
--Thanks!  
 
Steve Ahola
 
6/4/2003 10:30 PM
SK
Ceramic magnets really get a bad rap. They are just magnets after all...I think it's mostly because they are typicly used when trying to get a HOT pickup which means combined with thinner guage wire and overwinding. One of my most popular pickups is ceramic magnet based, It's also what I have in my main guitar...
 
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