Is it possible to accurately describe the tone of magnets and/or pickups?

[Antigua]

Do you have positive evidence that stronger fields/closer PU distances increase the amplitudes of the higher harmonic relative to the fundamental?

Yes, http://guitarnuts2.proboards.com/thr...-string?page=2 and http://guitarnuts2.proboards.com/thr...scrollTo=82326

Looking back at those threads, the difference made is rather subtle, it's not as though raising the pickups causes the guitar's output to jump an octave or two. But also, there is beating in the harmonics, and the rate of beating would vary depending on the degree of string pull. This research isn't conclusive, the testing should be conducted multiple times with multiple guitars in order to establish trends, but there's an enormous time cost in that. I was hoping that maybe someone with a background in physics might come along and explain what was being seen with the string pull and explain it well enough that further testing might not be critical to gain an understanding of how pickup height effects tone. What I can say for sure is that the effects are complex enough that they can't be summed up with simple adjectives.

Another fact that rarely gets mentioned, and is probably never noticed, but raising one pickup effects the tonal outcome of the others, as it disturbs the movement of the guitar string from the perspective of all of the pickups. That being said, it also seems to be that the way in which a pickup disturbs the string movement is most apparent from that pickup, for example, a bridge pickup's magnetic pull excites higher level harmonics, and the bridge pickup also receives more higher level harmonics due to it's position, and the the same is true for the neck pickup and it's interference and reception of lower harmonics, which would contribute to the mutual effects of pickup height being difficult to notice.

[Mike Sulzer]

I disagree. The primary current is determined by the loop EMF, the loop resistance and the loop inductance. This primary current is the magnetizing current of the transformer.
Secondary signal current stepped up with the (inverse) turns ratio of around 10000 will further increase the primary current as with any transformer. Secondary current cannot decrease primary/magnetizing current.

If the magnetizing current in the transformer with the single turn primary has a significant effect it would be most at low frequencies, decreasing at higher frequencies. The effect would be to load the single turn pickup at low frequencies, causing a decreases in bass response. Obviously, there is a frequency below which this effect becomes important, but I think it is low enough so that it does not matter for guitar frequencies. Or do certain models of these pickups have a distinct lack of bass?

[Helmholtz]

If the magnetizing current in the transformer with the single turn primary has a significant effect it would be most at low frequencies, decreasing at higher frequencies. The effect would be to load the single turn pickup at low frequencies, causing a decreases in bass response. Obviously, there is a frequency below which this effect becomes important, but I think it is low enough so that it does not matter for guitar frequencies. Or do certain models of these pickups have a distinct lack of bass?

Yes, I also expect a lower cut-off frequency depending on the ratio of loop DCR to loop inductance. The reflected secondary current will help to shift the cut-off to lower frequencies, meaning that the cut-off frequency will depend on secondary load. I did not have a chance yet to measure an Alumitone.

I tend to view the Alumitone as a voltage transformer: The primary circuit consists of a (zero impedance) voltage source (EMF) in series with the DCR and the loop inductance. This primary circuit is also the primary winding of the transformer which steps up the EMF by say 10E4. It as well steps up (reflects) primary impedance by 10E8. A realistic primary inductance of say 50nH will thus be reflected to 5H at the PU's terminals, a value in the typical range of "normal" PU's. Together with the self-capacitance of the secondary winding of the transformer, a typical parallel resonance results.

[Helmholtz]

Thanks for your reply.

Both effects observed are quite interesting. I have great respect for your experimental creativity and agree that digging deeper would require enormous efforts. After all, these are small second order effects, which always are much harder to quantify than the obvious ones.

Getting back to your post #86:

So it's a given that higher harmonics decay faster, I think we can all agree that any change that shifts energy to higher harmonic levels will therefore result in a net loss of sustain. IIRC, in my own testing I found that putting the magnetic closer to the bridge (or the nut) promoted a transfer of energy to higher harmonics than if you place the magnet over the middle of the string, for much the same reason that if you pluck the strings by the bridge, you also get higher harmonics. Therefore it might be that increased magnetic pull at the bridge could reduce sustain more than magnetic pull elsewhere, by shifting the energy into higher harmonic levels that experience greater mechanical damping within the guitar strong.

If the same magnetic pull produces stronger additional string damping at the bridge position than at the neck position, this in fact points to a damping effect that increases with frequency. It rather excludes PU vibration, but eddy currents (theoretically even in the string) and string hysteresis losses come to my mind. If the magnetic pull actually shifts the string vibration spectrum to higher harmonics, I cannot exclude increased losses by a higher average string bending rate either.
I don't feel able to speculate about which effect might be the dominant one at this point.


From a practical point of view, it seems that all the observed, detrimental effects more or less vanish, if the PUs are adjusted so that no audible "wolfetones" are perceived. And this is what most players intuitively do and many manuals recommend. Except if someone goes for a somewhat rougher sound

[Mike Sulzer]

Yes, I also expect a lower cut-off frequency depending on the ratio of loop DCR to loop inductance. The reflected secondary current will help to shift the cut-off to lower frequencies, meaning that the cut-off frequency will depend on secondary load. I did not have a chance yet to measure an Alumitone.

I tend to view the Alumitone as a voltage transformer: The primary circuit consists of a (zero impedance) voltage source (EMF) in series with the DCR and the loop inductance. This primary circuit is also the primary winding of the transformer which steps up the EMF by say 10E4. It as well steps up (reflects) primary impedance by 10E8. A realistic primary inductance of say 50nH will thus be reflected to 5H at the PU's terminals, a value in the typical range of "normal" PU's. Together with the self-capacitance of the secondary winding of the transformer, a typical parallel resonance results.

I think that there are two separate inductances that have to be considered: the inductance of the pickup (the conducting loop), and the inductance looking into the primary of the transformer. When you look into the secondary, you see approximately the two in parallel. To determine the pickup low frequency response, you need the individual values.

[Antigua]

I measured the values of Alumitones http://guitarnuts2.proboards.com/thr...nalysis-review , it does have an unusual bode plot compared to other pickups.

[bbsailor]

I measured the values of Alumitones http://guitarnuts2.proboards.com/thr...nalysis-review , it does have an unusual bode plot compared to other pickups.

Have you looked at the wire size wound on the two coils under the frame? Since they are wired in parallel, each coil has about 5000 Ohms of wire.

Since these pickups are passsive and have a similar output range of other traditional passive pickups, they must have about 15000 turns in each coil but in parallel so it must equal a 1 to 7500 turns ratio. There is one big difference and that is the closeness of the primary string loop to the string compared to vertically distributing the 7500 turns of AWG 42 over one half inches of bobbin height with the lower portion of the coil receiving less induced voltage than the top section. With the Alumitone design, all the equivalent wire turns are in a stronger induced field area only to be offset by the losses involved in real transformers vs ideal transformers.

If you look at where the laminated transformer cores intersect with the aluminum frame you will see that this is a summary point where the current from the two string loops have a common junction and can form a humbucking design when two magnets are under each string.

Just think how how consistent these designs can be made by stamping out the frames in mass production with the only important variables being the accuracy of the turns count on the underlaying coils and the magnetic consistency.

Joseph J. Rogowski

[Helmholtz]

I measured the values of Alumitones http://guitarnuts2.proboards.com/thr...nalysis-review , it does have an unusual bode plot compared to other pickups.

Thanks for the interesting info!

[LtKojak]

Just think how how consistent these designs can be made by stamping out the frames in mass production with the only important variables being the accuracy of the turns count on the underlaying coils and the magnetic consistency

Is it not like the Fluence p'ups are made?

[Helmholtz]

I think that there are two separate inductances that have to be considered: the inductance of the pickup (the conducting loop), and the inductance looking into the primary of the transformer. When you look into the secondary, you see approximately the two in parallel. To determine the pickup low frequency response, you need the individual values.

Yes, the secondary winding inductance acts in parallel (ignoring leakage) to the reflected inductance of the primary. If it's big enough, this won't change much.
I figure that low frequency response improves with lower primary loop DCR.

[gmaslin]

There were so many great posts in this thread but the one by Mike Sulzer on page one is the one I think I'll address. Even though the magnets don't have a "sound" measurement they can still be classified for being amenable to a type of sound. Magnets have relevant parameters:
1. field strength in gauss
2. field permeability/saturation and
3. field uniformity/pattern
and each can be manipulated to induce a particular type of electrical signal.

This is all a complex and interactive science but knowing what you have in measured magnet specs is the first thing you need to know before you start manipulating the wires used, the winding patterns and all the other physical things you can change before you introduce the electronics of the instrument and that opens another completely different can of worms. I'm sure I'm not the only person who experienced a set of pickups that sounded awesome in one strat and just mediocre on another one of the same era.

You can probably get most any kind of sound from any kind of magnet if you have sufficient control over all the other options. The key is how far you have to go to get it. If you classify the magnets for tried and proven paths to a sound, you might achieve your goal of classifying magnets for a type of sound.

I did some work on resonance experiments which pissed off lots of folks on "TheGearPage". You guys can look those up under "gmaslin" if anyone is interested. I think I did a pretty good job explaining what makes some guitars lively and resonant but you can draw your own conclusions.

[David King]

Now wouldn't an alnico magnet also have internal eddy currents and therefore a damping action or is the material's conductivity too low for that to be an issue? Could different alnico formulations have different conductivities that might affect those eddy currents?

[LtKojak]

Now wouldn't an alnico magnet also have internal eddy currents and therefore a damping action or is the material's conductivity too low for that to be an issue? Could different alnico formulations have different conductivities that might affect those eddy currents?

This and the fact of a magnet being isotropic or anisotropic are topics not so much discussed anywhere, although I think there are important factors in what a magnet "sounds like".

[Helmholtz]

Now wouldn't an alnico magnet also have internal eddy currents and therefore a damping action or is the material's conductivity too low for that to be an issue? Could different alnico formulations have different conductivities that might affect those eddy currents?

Eddy current losses in alnico are low because conductivity is relatively low. This is why strat PUs show a high (unloaded) resonance peak.

I collected some data from magnet literature regarding the specific resistance of some alnico grades. There is some variation (+/-10%) between different sources. Below are average numbers:
A2: 65 (µOhmcm)
A3: 60
A4: 70
A5: 50

Higher specific resistance means lower losses.
Eddy losses also depend on the magnet volume exposed to the AC field, i.e. bigger magnets produce more losses.

[Mike Sulzer]

Here are a couple of plots comparing the impedance of the same coil with Alnico and steel cores. Of course the Q of the pickup is first limited by the resistance of the wire, and so the cores can only make so much difference. Alnico gives a narrower peak, but the major differences show up when you "unparallel" the capacitance and compare with what the low frequency measurement of the coil would predict at higher frequencies without frequency dependent losses from induced currents in the cores.

Eddy current losses in alnico are low because conductivity is relatively low. This is why strat PUs show a high (unloaded) resonance peak.

I collected some data from magnet literature regarding the specific resistance of some alnico grades. There is some variation (+/-10%) between different sources. Below are average numbers:
A2: 65 (µOhmcm)
A3: 60
A4: 70
A5: 50

Higher specific resistance means lower losses.
Eddy losses also depend on the magnet volume exposed to the AC field, i.e. bigger magnets produce more losses.