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Topic: Magnet 1/2 life? |
Wayne Cox
From:
Chatham, Louisiana, USA * R.I.P.
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Posted 20 Mar 2005 9:57 pm |
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When it comes to pickups and magnets, I don't have the expertise of Rick, Jerry, Jason and many of the other forumites. Nevertheless, years ago I did quite a bit of experimenting and found that certain types of magnets (such as "pole-piece"magnets)that are charged or magnetized in the shop right before the pickup is wound, tend to have (for lack of a better description) "half-lives". I had some pickups made for me by Sho-Bud which were wound to my specifications. They were all different ohms but all sounded great for about 2 weeks. I noticed that the magnets seemed to lose about 20% of their strength in 2 weeks, then another 15% to 20% over the next 6 months. This loss of magnetism really affected the tone of the pickups. Pickups made with ceramic magnets,alnico,and other more permanent materials din't seem to decrease in strength as drastically or as rapidly.
Do any of you have some more reliable data or test results on this anomally???
~~W.C.~~ |
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Rick Aiello
From:
Berryville, VA USA
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Posted 21 Mar 2005 4:48 am
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| Quote: |
| I had some pickups made for me by Sho-Bud which were wound to my specifications. They were all different ohms but all sounded great for about 2 weeks. I noticed that the magnets seemed to lose about 20% of their strength in 2 weeks, then another 15% to 20% over the next 6 months. |
| Quote: |
| Pickups made with ceramic magnets,alnico,and other more permanent materials din't seem to decrease in strength as drastically or as rapidly. |
What were the magnets made of ... ???
Steel has to be heat treated to retain its magnetism ... if not ... it will charge, but rapidly loose its Remnance ...
The "grade" of steel is also very important. Carbon content, alloying components, etc ... all play roles in steel's magnetic properties.
If Cunife (copper-nickle-iron) ... it should have retained its charge, similar to alnico ...
As far as "half life" ... in the "ideal" environment ... a permanent magnet will retain its remnance charge indefinitely ...
But in "real" situations ...
There are "conditioning" aspects of magnetizing permanent magnet material ...
There are "domains" in the magnet which are basically “weak” and will lose their alignment ... so the remnance seen as soon as the magnetizing field is removed ... will be higher than its "resting" charge will be ...
Exposure to heat and external fields will facilitate this phenomenon.
So placing 6 to 10 freshly magged pole piece magnets next to each other in a bobbin ... will bring about this kinda degaussing ...
Permanent magnets do have a property known as their Intrinsic Coercive Force (Hcl). This is a value that describes the ability of a magnet to degauss itself.
Here's a good summary of a Hysteresis Loop
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Aiello's House of Gauss
My wife and I don't think alike. She donates money to the homeless and I donate money to the topless! ... R. Dangerfield
[This message was edited by Rick Aiello on 21 March 2005 at 08:22 AM.] |
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Wayne Cox
From:
Chatham, Louisiana, USA * R.I.P.
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Posted 22 Mar 2005 10:58 am
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RICK,thanks for responding. On this subject I feel like a auto mechanic trying to describe steel guitar licks to Buddy Emmons or Jerry Byrd. Most of my unscientific experimenting was done in the 70's,and my memory of some of the details has faded. For example,I do not remember what the metallurgic content of the Sho-Bud magnets of that time period was. I do remember trying to convince David Jackson to adopt larger diameter magnets (more like the Emmons). My thinking being that when the magnets "settled in",the larger ones would have a bit more strength. I have also forgotten what common pickup wire gauges were being used at that time,however I did discover that the most common gauges did not produce as rich a tone as I wanted to hear. Everyone kept re-assuring me that a few more windings or greater ohms resistance would do it...but it never did. The gauge of the wire actually made an audible difference in tone,even when the specs checked out to be the same as another pickup which was identical except for the diameter of the wire. During that era Sho-Bud made some really nice steel guitars that pleased a lot of people so David wasn't too anxious to go changing the basic components of the instruments. I eventually dropped the whole quest for a Nirvana sound.
~~W.C.~~ |
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Wayne Cox
From:
Chatham, Louisiana, USA * R.I.P.
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Posted 22 Mar 2005 11:24 am
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Bruce Zumsteg also made a few non-standard pickups for me to field test. There was one which came really close to the sound I was searching for. It was a single-coil of wire wrapped around a ceramic bar magnet. The magnetic field was so strong that the pickup sort of turned into a microphone. It had a tremendous tone,in between the outbursts of feedback.
~~W.C.~~ |
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Donny Hinson
From:
Glen Burnie, Md. U.S.A.
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Posted 23 Mar 2005 3:20 pm
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Wayne, how are you determining that the magnets are "losing their charge"? Are you using a field meter? If you're guaging the loss of charge by touching them with a piece of steel, you're robbing the charge. I know of 4 things that cause magnets to lose their magnetism...heat, shock, other magnetic fields (especially AC), and "bleeding". Bleeding occurs whenever a ferrous object is brought into close proximity of the magnet. Strings, picks, or any other iron or steel object brought very close to, or in contact with the magnet will draw off some of it's charge. This degradation can take many decades, but can also happen in an instant if conditions are right.
Good permanent magnets not exposed to any of the aforementioned detrimental conditions will retain their charge almost indefinitely. |
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Wayne Cox
From:
Chatham, Louisiana, USA * R.I.P.
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Posted 24 Mar 2005 8:08 am
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DONNY, back in those days I did not have access to a field tester,gauss meter,or anything scientific except a volt/ohm meter for testing the resistance of the coil windings. It did occur to me that I could be weakening the magnets in the manner you described,so I left a couple of pickups untouched after mounting them and playing through them. The tone change was just as pronounced as in the others after a couple of weeks of being idle. I know it wasn't just my ears changing , because I recorded the sounds and listened again at different times. The change was real. I don't have the tapes anymore as that was many years ago. I am grateful that Carter steels had the presence of mind to record different pickups so that others can here the difference in various major pickup designs without having to experiment as I did. That is a real publick service.
~~W.C.~~[This message was edited by Wayne Cox on 26 March 2005 at 11:24 AM.] |
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Gerald Ross
From:
Ann Arbor, Michigan, USA
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Rick Aiello
From:
Berryville, VA USA
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Posted 24 Mar 2005 10:23 am
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I'm stepping way out of my "comfort zone" here ... and I don't know squat about microphones.
But I always understood that "Condenser" microphones either used an installed battery or a "Phantom Power" source for their "voltage needs" ... no magnets in there.
"Dynamic" microphones use coils and magnets ...
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Aiello's House of Gauss
My wife and I don't think alike. She donates money to the homeless and I donate money to the topless! ... R. Dangerfield
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Gerald Ross
From:
Ann Arbor, Michigan, USA
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