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August 20, 2009 - 7:48am
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Demagnetizing a 'phono cartridge
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Hi, Jdurrett, welcome!
You ask a fascinating question.
I don't have a definitive answer.
There are reviewers who actually do it for every album side they play.
Other people say at the start of each listening session.
Yet others say every 40 hours, etc...all the way up to hundreds of hours!
It is also cartridge dependent, with some perhaps not requiring it at all. (Of course, MM cartridges are at risk for damage if this is done.)
I'd say to keep track of how many LP sides you play until you notice a decline in sound quality, then demagnetize (degauss) at some number of sides less than that, because we can sometimes be slow to pick up on a small change until it has become much larger. So, how about....the number of plays until you notice a difference minus 20% as your routine interval?
Keep in mind that some people say there is a limit to the number of times degaussing a cartridge is effective, too.
There is controversy, so I do not wish to be pedantic. This should be an interesting conversation!
welcome again.
Interesting video:
Cheaper than you think to do it!
I've seen this before -- is that actually going to demagnetize a cartridge? I was also under the impression that (as you alluded to above) demagnetizing a MM cart wasn't a good idea.
Anybody try this particular tweak?
I must be missing something here. Demagnetizing a device that uses magnetics as its bases of operation.
Maybe if I remove that damn magnet from my speaker it will sound better too.
Are you old enough to recall demagnetizing tape recorder heads?
Question, then. What did the OP hear the benefit of?
i use a mm cart. i recently bought a grounded record brush. in the instructions, it recommended simply pulling along both sides of the cart. rear to front. the maker's theory is that the real enemy is "static electricity". i probably had about 200 hours on the cart at the time and had never done anything to it. instant, non-subtle difference. much quieter and with the lower noise, every other sound jumped out. the brush was $39. i have not heard tweaks in the hundreds of dollar range make that big a difference. live and learn.
That makes sense to me, and the referenced video above may be simply removing built-up static. Pretty cool.
Yes, I remember demaging tape heads which is the equivalent of demagnitizing the coils in a phono cartridge. Demagnitizing the tape is not so good, as is demagnitizing the magnets in a phono cartridge. Maybe the magnets in the phono cartridge aren't affected by the demag process. Only the coils. Or are they? Maybe the magnets were too powerful and the demag process put them at a closer to optimum level than the manufacturer did. I don't have any of these issues with my piezo cartridge.
Buddha,
I just looked at this video. What the person did is to connect the two channel's coils in a cartridge together, effectively in series. Then the vibrations from the moving magnet (or moving coil in the magnetic field) from playing an LP generates a varying signal to the coils. The link to demagnetizing is that the signal goes up and down in level, and may have some demagnetizing effects.
Usually tape head demagnetizers has to be operated as an increasing sinusoidal field and then gradually reduced to zero amplitude so that the hysteresis loop is gradually brought back to zero. This is usually a constant level signal that is activated far from the tape head, then slowly brought from that distance toward the tape head and very close to it, then gradually and slowly removed to a far distance before switching off.
How a continuously varying signal that does not drop back to zero slowly (music on the LP) can do this is not clear to me. Also the frequency of the amplitude variations and the zero crossings happening so quickly in music does not seem to satisfy the idea of gradually ramping the signal up and then down to zero. Maybe one possible change or improvement is to add a high-valued potentiometer to the circuit to slowly bring the signal level up from zero and then down to zero while the record is playing.
The demag circuit in the video conceivably resembles a transformer where the primary winding (MM) is generating a magnetic field (music signal) in the secondary winding (coils) but the secondary is shorted. You know what happens if you short a secondary in a power transformer. In this case, the signal levels and power is low, but the short circuit would be much lower resistance than a preamp input load, and one cannot draw more current to the primary even if the secondary is shorted.
I have not done any calculations to see what this means in practical terms. Maybe someone has already looked into this.
You don't want to use this on a moving magnet cartridge as it will demagnetize the magnet. On a moving coil cartirdge it will demagnetize the coils.
What about the MC cartridge coils demagnetizing the magnet, or are there too few coil turns to generate enough of a field?
The effect is temporary..and the cart will need to be demagged again after about 50-100 hours of use.
If one is a MC cart user and is serious about fidelity..then owning a MC demagger is actually -- mandatory.
Enough people. MM and MC cartridges both have coils and magnets, it's just a difference in if the coils or the magnets move. They both have magnets and coils. Demagnetizing the magnets would be a bad thing.
Don't know if a demagnetizer can affect the magnets.
Do the coils use an iron core because the copper or silver wire coils are not magnetic and can't become magnetized or demagnetized. I think that the relevant question is do cartridges use ferrous materials that can become magnetized and can demagnetizing effect the magnets?
As I reacall, the silver or copper are not magnetic materials, but may have slight effects. I could be wrong on this without checking the books first. I doubt a MC cartridge would use any iron moving with the coils which would increase the moving mass hence the inertia.
I use a Han-D-Mag (the same one i use to demag my MCI and Otari 1" 8 track and 1/2 in 2 tracks..
Let's just say that I'm likely to have bit more information at my back and wind in my sails on this one, with regard to the understanding of the molecular considerations surrounding affects on the wire than most folks would.
As I stated above, it's a consideration of note when using a low output MC cartridge and even the MC transformers.
One should consider demagging their MC transformers as well.
for example, it is well known that measuring the coils on a MC cart can blow the coils or cause an effect that is very much like the issues of sonic quality (ie, a noticeable degradation of sound quality) created before demagging (ie, a used MC cart that needs demagging) and then the cart needing to be demagged.
Demag those transformers. The same issue with measuring the MC transformers is there as well. don't measure them or you might create a stilted unidirectional hysteresis in the core of the transformer. Load the INPUT of the transformer with a value that represents the loading of the cart you are using (eg, 40 ohm cart-use a 40 ohm resistor) when demagging it (demag from the transformer output end, just like demagging a MC cart-you fire into the cart-you fire into the transformer) and this will 'theoretically' create a clean electromagnetic residual in the transformer core that will represent a clean and even hysteresis effect that is reflective of and for the given cartridge.
You dig?
Of course, take this info, go to the given transformer manufacturer, and go to the separate cart manufacturer and see what they say--FIRST--before attempting any of this. I take no liability on myself if you damage anything while attempting these things.
The lower the output of the given MC cart and the lower the impedance rating of the given MC transformer... the more notable the effect of the MC cart and MC transformer demagging, in general.
Same-same for low impedance microphone transformers is therefore inferred, obviously.
You can also then..demag entire circuits, but you'd better really know your stuff at that point. Mixing high level AC electromagnetics with active circuits can be a recipe for disaster.
I would say that once every 2 weeks seems to be the norm from a lot of audiophiles and other sources out there, dealers, magazines, etc. But, AJ Van den Hul of his cables fame, has an interesting take on it, that can be found on his vdH cable site, under the articles section, and in the phono faq he provides. He claims that it does more bad than good, but after hearing my set up with the demag, it is hard to ignore. But to get a an alternate viewpoint, I would recommend checking out all of his faq's online, but keep in mind his English is not so hot from the Dutch translations, and his views can be sometimes pretty heady. FYI.
I suspect that AJ may be alluding to the potential to demagnetize the given magnets that are in use, or similar. I'd have to read it. I tried to find his stuff that relates to this subject, once, but found it difficult to peruse. I'll try again.
So what about demaging the output iron core transformers on a tube amplifier?
Well, let's see, they're supposed to have balanced DC run through the bifilar-wound primary, right?
What about demagnetizing the plastic parts of electronics, as well?
What's good for LP's should be good for gear!
I was trying to figure out a way to demag my CDs and Records. I also want to demag my speakers. I hope you all figure it out.
Key here is "supposed to have balanced DC run through bisexual primary". We all know that there is no balanced DC. Good thing that no AC audio signals pass through the transformer. Just waiting for the aftermarket nonferrous transformers.
Funny, even the 1950's era tube amps I started out with would allow one to ensure balanced DC.
Balanced drive, too.
My goodness, you can even do that with a pair of Type 33 triodes or a 6V6 pair (no G or GT).
You look like you've been dead for 14 years?
(I actually accidentally got to go to his funeral, kinda...come to CES and I'll pour ya a glass of vino and regale you with the tale.)
____________
Anyway, back to the topic...with how few 'winds' there are to some MC cartridges, is it not possible that these poor, few, coiled wires could become magnetized and alter their behavior?
(No agenda in the question, actually curious about this.)
I'm not actually sure. I would hope not, it would suggest that the magnetic structure was a bit odd, and that something was providing enough field to magnetize it.
I'd worry more about damage from overcurrent demag systems, mechanical damage, etc, from the demagger.
But I do not know, and my cheap-*** (as the frog would call it, I suspect) Shure doesn't seem to have any such problem. It does, however, soon find itself in need of a stylus. Bigger problem.
(I found I had one stylus in the freezer, that bailed me out for a while...)
To magnetize a coil it must be a coil made with ferrous wire and it must have a DC current passed through it.
These guys make or sell 92 different Shure replacement styli.
The V-15 models are getting rave reviews.
I have not yet heard them, as my V-15 is holding up nicely.
Ah, like an LP!
This technique is MONEY! Because my friends- it's free and works. Check it out. Worked for me and a commenter was a cart dealer and mentioned he's used it for years.
http://www.youtube.com/watch?v=1TkJ_wwkbNA
One could magnetize the core the coil is wound around, of course, if it's ferrous.
But you'd have to have something applying some 'H' to it.
Buddha that tweak worked well with my Benz MC Gold. Imaging and focus greatly improved. I had never demagnatized this cartridge. I was listening to Willie Nelson's "American Classic" and his image was so solid that I thought I could sneak behind and trim his hair.
You obviously realize that the coil will have to be wound around a ferrous core for a cartridge to work. But your H plane vs E plane argument applies to radiated waves.