View Full Version : Loudspeaker magnets: magnetizing fixture?

06-28-2005, 05:11 PM
Hello again

a year or so I bought a 2440 with a mis-alignment at the top plate.
Questions arised, how to fix it? demag it or use a hammer? Searching for companies in Norway or Sweden who could possibly demag and re-gauss it after the mis-alignment have been fixed?

It was then I got the bright idea to build my own magnetizer.

Ok, I bought parts from eBay for nothing and read the paper: Methods of Magnetizing Permanent Magnets (by Joseph J. Stupak Jr. 2000).

My magnetizer will be capable to push out 6-8 kJoules in this moment but I could get more out of it if buying more electrolytic caps at the eBay auctions.

When the magnetizer was in the step/level to funktion I made some tests. It worked and the first object to test it to was to demag the bad 2440. Yes, it was a very exiting moment when I easily could lift of the top plate at the 2440s motor.

I fixed it and re-align the top plate, well it was then the real work could take place: constructing of a magnetizing fixture (or two fixtures). But that job was hard to do because I couldnt find any relevant information when searching the internet, so I couldent figure out how to construct the fixture.

Is there anybody (eg. "rbrooks7" and "pelly3s") at this forum who have realy seen a loudspeaker magnetizing fixture or could describe it in words (inductans, ohms, turns etc).

Thanks in advance


06-28-2005, 05:33 PM
Well this won't really help you but there is a picture in one of the JBL Insight Brochures in the reference section. There is a photo with a magnetic assembly in the machine. The caption however will not make you smile. Good Luck on this very ambitious project.


06-28-2005, 05:35 PM
honestly i couldnt tell you a single thing about the one i use at my shop. it was made by a guy who made about 8 of them. i will see if i can find any manuals on it at the shop or anything. pretty strange device though. i can launch a screw out of the thing about 3 feet in the air. mine works off a 220v line and runs it through a bank of about 16 caps which are hooked to a panel with cam locks so i can change polarity. i'll also try to take a couple photos if i can remember. sorry i cant be of too much help at this moment.

06-28-2005, 06:45 PM
I have seen the one they use at Great plains audio. It looks like the one pelly3s describes. :)

06-29-2005, 02:56 AM
pelly3s wrote

i'll also try to take a couple photos if i can remember. sorry i cant be of too much help at this moment.

pelly3s, hope you can post some photos at the Forum. I think not only me have an interest in to see how a magnetizing coil looks like. Would it be possible for you to measure the inductance of the particular coil if data is not available?

Could you tell us, okay -me what is the value of the caps in your machine?
do you know what is the voltage you zap through the coil? Do you use it to all JBL models or do you have different sizes of coils ? I plan to build two different coils. One to suit the bigger JBL models like the 2440/375 and 14-15" cone speakers. And a one to suit smaller models like the LE10, LE8, 077 etc.. Maybe it is not necessary to build two different coils, maybe it will do with only one size coil? Whats your opinion?

Robh3606, thanks for the link. I have seen it befour, many years ago.


Mr. Widget
06-29-2005, 09:39 AM
I know I'd be interested in seeing pics.

Flodstroem, you might want to ask some of these questions to a tech at Orange County Speakers. They also have a magnetizer and may be able to shed additional light on the subject.


06-29-2005, 03:55 PM
the machine has a single coil big enough for any speaker i've put in it so far. I can get about 430volts through it before the caps get a little too warm for my own comfort. there are 24 caps in total. I have to try to remember my camera tomorrow when i go to work. my brain doesnt always work too well. too much time in the recone room sniffing glue

06-30-2005, 03:56 PM
here are some pictures, no values for anything yet though. its a scary looking thing.

06-30-2005, 03:57 PM
just a few more pictures

Mr. Widget
06-30-2005, 04:09 PM
Don't be surprised if you get a visit from the Office of Homeland Security... that thing really looks scary!:applaud:


06-30-2005, 06:03 PM
Hi pelly3s

Photos was fine and I could understand how your machine was build
The construction is not much far from my machine.

I could se the data of the caps and with a litle calculations I can see your machine is capable to zap ca 3 kJoules thru the big coil (Joules=1/2xCxVxV). It also means that my machine have the required output power and beyond that (ca 7 kJoules maximum).

The coil, yes the photos explaind a lot to me and your coil or fixture is not far from my first trial and error-coil.

Becouse of the good photos you posted here it maked me shure to go further and build a real magnetizing fixture.

I could se in the pictures that you could change the charging voltage for different purposes and that the charging power come from the big transformer thru the rectifier bridge. I also noticed the big "ishockey puck" SCR which is the big high power switch to decharge the caps thru the coil.

When my machine is build to a working condition I would like to take some photos to show you forum members how it works.

Thanks for the tip Mr. Widget to contact Orange County Speakers. I wrote to them and if I get any iteresting answer I will post it here.

I agree with Mr. Widget (and your self) that your machine looks a litle bit scary. Look after your self when working with it.

Thanks for all your responce to this subjekt


Maron Horonzakz
07-01-2005, 06:56 AM
That looks impressive. I have a couple of metal clips in my body from a operation. I wonder if that unit would pull them out if I stood too close. Could be dangerous If someone had a metal hip or steel plate in the scull.

herki the cat
12-24-2011, 10:59 AM
For description of a good magnet charger, read the entire post # 28 in Thread: Magnet Recharging Center.

Maron Horonzakz (http://www.audioheritage.org/vbulletin/member.php?257-Maron-Horonzakz) ,Regarding post #12 below; Please note that with the RCA machine described in post #28 Thread: Magnet Recharging Centers you need to keep your hands clear because if the work piece shifts __well, i will skip the gruesome words. herki[Quote/]

12-27-2011, 06:20 AM
See my thread: http://www.audioheritage.org/vbulletin/showthread.php?29464-Refurbishing-a-pair-of-2440

Remagnetization was done at HYAB (http://www.hitta.se/ViewDetailsPink.aspx?Vkiid=JcjJ6eKKowe6bHbBjkgFdg% 253d%253d&vad=hyab) in Bromma Sweden.

aman khalsa
04-08-2012, 07:46 AM
hello sir... i want to make magnetizer like this .. can u pls help me.. how can i start ...:blink:

04-08-2012, 01:52 PM
by Moldyoldy:


aman khalsa
04-09-2012, 07:32 AM
thank u sir ...