Cryogenic treatment of guitars warning

[eschertron]

Variable reluctance is a derived concept. It works fine, but it is far from the physics, and makes the physics harder to understand. How does something "perturb" the permanent field? Only by another field; and fields add. The permanent field need not be from the pole piece. Suppose you replace the pole piece with one with the same permeability and conductivity but no permanent field. You can then make the pickup work by holding a magnet over the strings. You must use a magnet to magnetize the string, one way or another. (Of course the string retains very little permanent magnetism when you remove the magnet, but the magnetization can be permanent or temporary; it matters little.)

I understand that the permeability of the string is different from free air and that is what alters the magnetic field. You're telling me that this change in the field lines is an observed effect, and not the physics model. I'll step into the lion's den and ask for links to further info, knowing that the introduction to Maxwell's equations in 2nd-year physics class was what changed my career path from rocket scientist to programmer!

[ScottA]

I think there are two separate mechanisms through which the string vibration couples in to the pickup.

In one, the string is a magnet, moving with respect to the coil. In this mechanism, the magnetic field of the pickup is not important except that it magnetizes the string.

In the second, the string is a permeable material in the field of the pickup. The field associated with the pickup is concentrated in the permeable string relative to the air that surrounds it. As the string moves, it drags these field lines with it, causing the field to effectively move in relation to the stationary coil.

This second mechanism may seem insignificant if you consider an unwound high E string, for example. But consider a bass string. Here the mass of the string associated with the pickup is comparable to the mass of the pole piece. I don't see any question that this is a significant part of the sensing mechanism.

[salvarsan]

Soft steels do not magnetize permanently - by definition, magnetically soft materials are easily magnetized and demagnetized. Steels which are physically soft are also magnetically soft. As you lower the carbon content of steel, they become physically softer and magnetically softer. You can make a cheap permanent magnet out of steel - load it up with carbon and heat treat it for high hardness.

Right. The terms "soft" and "hard" ferromagnetism are not binary, but indicate segments of a continuum. Otherwise remanence and permeability figures would not be published for soft magnetic materials.

Coercivity examples

430 stainless is 160 Amp-turns/meter and 2 Oersteds
0.10% carbon steel and 150 A/m = 1.9 Oe
1.0% carbon steel is 600 A/m = 7.5 Oe
Alnico 2's coercivity is 45,000 A/m = 560 Oe, two orders of magnitude higher.
C5 ferrite coercivity is 190,000 A/m = 3500 Oe

The remarkable thing is that in guitar pickups, 0.10% carbon steel slugs sound different from 0.18% slugs.

[salvarsan]

...And "I don't see how it can make a damn bit of difference, honestly." is not the kind of statement that accompanies an open mind,

True, dat.

< insert embittered vindictive caustic profane exhortation here >.

This exhortation, in more elaborate forms, may involve someone, their mother, and the horse they rode in on.

[ScottA]

With pole pieces, it all about permeability.

It's actually mostly about eddy currents.

[Mike Sulzer]

The first one, the string is a magnet, accounts for all the applied time varying field through the coil if you include the fact that the magnetization of the string varies (by a small amount) as the string vibrates because the permanent field varies in intensity in space. There is only one thing happening in the string: the partial alignment of the atomic currents in response to an applied field from the permanent magnet. This creates a magnetic field; this magnetic field passes through the coil where it causes some alignment of the atomic currents in the pickup cores, and finally this total time varying flux (field times area, or more accurately, integrated over area) passing through each turn of wire in the coil induces a voltage around it (law of magnetic induction from Maxwell's equations), and the voltages of all turns add.

You can describe this process in various ways, but it is simplest to keep the description of what happens in the string as simple as possible since it is explained by one physical process, and it is most convenient to account for the response of the pickup cores as due to permeability.

Note also that closed magnetic circuits, or those with just a small gap, can be solved easily with the variable reluctance method since the flux is contained in a path analogous to a wire circuit for electrical effects. Pickups, on the other hand, are open circuits with small pieces of magnetic material and large open spaces completing the circuit. They can be solved by solving differential equations, such a FEMM can do for some simple cases.

I think there are two separate mechanisms through which the string vibration couples in to the pickup.

In one, the string is a magnet, moving with respect to the coil. In this mechanism, the magnetic field of the pickup is not important except that it magnetizes the string.

In the second, the string is a permeable material in the field of the pickup. The field associated with the pickup is concentrated in the permeable string relative to the air that surrounds it. As the string moves, it drags these field lines with it, causing the field to effectively move in relation to the stationary coil.

This second mechanism may seem insignificant if you consider an unwound high E string, for example. But consider a bass string. Here the mass of the string associated with the pickup is comparable to the mass of the pole piece. I don't see any question that this is a significant part of the sensing mechanism.

[Mike Sulzer]

It's actually mostly about eddy currents.

Both matter, and it is often the case that the losses that determine the Q of the resonant circuit are more a result of eddy currents in the cores than the resistance of the coil. On the other hand the permeability of the cores can alter the inductance by as much as about a factor of three, thus having a strong impact on the frequency of the resonance. Yes, both are important.

[Diablo]

Copper can't be transformed by cryo?

Effect of cryogenic treatment on thermal conductivity properties of copper

OK, this is mainly about thermal conductivity, but change is change.

Cryogenic Treatment of Materials: A Cryo Central resource from the CSA

and:

Machine Tool Cryogenic Treatment : Texas-Machine Tool International

Note that this is about reduction of residual stresses, and I would imagine that drawing magnet wire does induce stresses in the copper.

or:

Machine Tool Cryogenic Treatment : Texas-Machine Tool International

My point is that there are reports of change to copper with cryo treatment. I'm not saying whether these changes are good or bad for pickups, but rejecting the possibility of change without doing the testing is a rather Luddite-like reaction to scientific curiosity.

I don't believe this report about the effect of cryo treatment on OFHC copper. They did two things - cryo treatment and then temper at 300F. Why would anyone assume it was the cryo treatment that caused the effect?
It's obvious that it was the tempering process that annealed out the dislocations, just like it has been doing for hundreds of years in metals heat treating.

[big_teee]

I'm curious to see what the -300 does to pickup solder joints?
Like the solder of the eyelets on a strat single coil?
In the OP they had a sealed pickup failure, wonder if it could have been the solder?
T

[the great waldo]

Hi T

I've got a feeling that the coil might have got damaged by the different rates of contraction of the copper winding and the potting resin. I have not dissected the pickup so this theory is just a guess. Maybe someone at Seymour Duncan can chirp in and let us know if the blackouts are waxed before potting or whatever ?

Cheers

Andrew
Ps. Could do with some cryogenic treatment myself today 36 deg. C in the shade today, and not much cooler in the workshop.

I'm curious to see what the -300 does to pickup solder joints?
Like the solder of the eyelets on a strat single coil?
In the OP they had a sealed pickup failure, wonder if it could have been the solder?
T

[Chuck H]

The magnet powers the pickup. I'll fight to the death on this one.

I think it's interesting that this silly truth was singled out for a nit pick. It's sort of like the way a woman responds when she's unhappy about being wrong. She'll try to find a way to make the person who's right wrong about something else to make herself less small. Apparently even open minds can be small ones. Usually it's a woman though.

The argument that the string powers the pickup is a semantic jab at best (and designed specifically to make me wrong, which I'm not). The interruption of the magnetic field is certainly the greatest contribution to the signal from the pickup. And even if you believe it's the magnetized string that is energizing the signal via inductance to the coil, where do you suppose the string gets it's magnetic charge? Any AC POTENTIAL in the pickup is only there because of the magnet. No matter what. So the magnet powers the pickup.

Saying the vibrating string powers the pickup instead of the magnet is like saying that internal combustion engines are power by explosions instead of gasoline.

[Rick Turner]

Mike, your comment:

"Note also that closed magnetic circuits, or those with just a small gap, can be solved easily with the variable reluctance method since the flux is contained in a path analogous to a wire circuit for electrical effects. Pickups, on the other hand, are open circuits with small pieces of magnetic material and large open spaces completing the circuit. They can be solved by solving differential equations, such a FEMM can do for some simple cases."

The small gap issue is what I was referring to with regard to the Roland hex synth pickups. I do believe that when you get them to within 1/16" of the strings, you're starting to look at variable reluctance with the strings completing a magnetic circuit with two time variable flux gaps.

And Diablo, there's one way to find out if cryo affects DCR of copper wire, and that is to test it rather than just rejecting it based upon what? Tests that may not find what we might find? I have a feeling that few have actually tested DCR before and after with thousands of feet of magnet wire, and those who have aren't chiming in here and they haven't published anything that I can find. As we've discovered, there are more than one pickup maker using cryo. They must feel that it's worth it unless you think it's just marketing bullshit. But we're going to find out a few things...one way or another, as I keep saying. If the results show no changes or if the changes are not audible, I don't really care; there will be one less process upon which to spend money, and I/we will have definitively learned something. That's a lot different from projecting preconceived prejudices on something.

Re. the issue of permeability and eddy currents...they are intimately connected. The higher the electrical resistance is of a material, the lower will be the eddy current losses. Apply that to magnetic materials in pickups, and you have permeability pretty much figured out.

[The Dude]

The magnet powers the pickup.

I'm no pickup maker, but this seems obvious to me. You can talk into a guitar pickup and hear it through an amp. Or,..........maybe my tongue is creating a magnetic field?

[Chuck H]

The lynch pin the any contrary argument is that there is absolutely no AC potential without the magnet.

[Rick Turner]

This is getting hilarious.

There is absolutely no AC potential in a pickup. There is not even power in a pickup...there is a force (magnetic), but no power unless you want to go with the tin hat perpetual motion machine crowd. The AC comes from a vibrating magnetically charged string and it's alternating cyclic motion. The magnetic force must be modulated in order to generate power. Strings and pickups basically make up an alternator...yeah, just like in your car...an alternator. Another example...there was and is no power in the giant generators that Tesla put in at Niagara Falls. With the generators just sitting there, they had no power at all. The power was provided by falling water. The generators transformed the power of falling water in to electrical power. The mechanical energy of one moving thing or substance is transformed into another form of energy/power.

Is there power in a loudspeaker? Hmmm, a coil and a magnet, just like a pickup...or a dynamic mic. But no power; that comes from the amp or from vibrating air in the case of the mic.

How many of you have put an air core coil under a string and then held a magnet over the strings to listen? Or touch the strings with the magnet right above the air core coil to magnetize the strings? I think I can count a couple of hands in the air, Mike's being one, Salvarsan being another, and probably a few more. This is an experiment that we did at Alembic in 1974, for God's sake. This knowledge is so old it ought to be in the Old Testament.

Just thinking about pickups and how they work can lead even intelligent people down many a dark, un-illuminating alley. It's really easy to think they work in a particular manner, even make decent pickups, and be utterly wrong about your concepts. Why? How? Because of no actual experimentation...no scientific testing. I made good pickups before I really knew shit about them, but I got into the whole controlled experiment system working with Ron Wickersham and learned a lot. That was one of the threads that became the beginning of Alembic...rigorous testing and charting what we did.

And I have to say, it continues to blow my mind that people can be so vocal and vehement about things they have not personally tested.