Pickup theory question

[bbsailor]

Salvarsan,

Since you are open to other explainations, consider this. The grounding of the blades adds distributed coil capacitance and lowers the pickup resonant frequency compared to those blades free floating. The free floating blades also pick up noise and cause the pickup coils to be more sensitive to induced noise carried within the blades. Grounding the blades and the strings offers one of the most common noise reduction techniques.

Joseph Rogowski

[salvarsan]

I'm really tired of the totally bogus specs, if they can even be called that in our business. This pickup is hot; this one is clean and low output... The microphone and loudspeaker industries have both agreed upon a standardized set of tests, and thus sensitivity and noise specs actually mean something. The pickup industry is totally insane. Nobody agrees upon color codes for wires... wind start and end ... clockwise vs. counterclockwise winding. Magnetic polarity...

If you accept 'comment' to mean "fume, rant, invectivate, splutter, and bitch",
I used to comment about this very lack.

Practical observation: no one talks about it if no one listens.

There is a reluctance (cough!) to embrace more science in the pickup-building craft.
IF there was ever a modest amount of support for a standard test suite for pickups,
then there would already be one.

What would you test for?

[salvarsan]

If it was as simple as hanging an extra ~500pF across the output, it probably would have been done.

Find a Barden pickup vendor and have a look at the construction.
Much of this was hashed out in the July 2004 PMF on Ampage.org.

[David Schwab]

This is an interesting observation. Can a strong neo change the tone of a pickup, or do we have to look at the whole system in order to see what is happening?

A neo is essentially a nearly perfect source of magnetic field; it is not affected significantly by other magnetic material. [That is, its permeability is low, only about 2% larger than a vacuum.] It is also cheap and you can get it in a wide variety of sizes., and so it is the ideal material to use in new designs.

So how does it make a pickup muddy sounding? I do not think that there is any way it can, directly. I think what is happening is that a few hundred Gauss is plenty to cause string pull, subtle or not depending upon various factors, such as the height of the string. The magnet is affecting the vibration of the string, not affecting the tone of the pickup directly.

But this is not something that neo does; it is something that a strong field does; neo and other types of magnets can do this. It is more useful to classify according to cause rather than the type of material.

OK, what happened was this (and this has happened on more than one pickup design I was working on). I wound a dual blade Strat size pickup. It's the pickup in that Tele test clips I posted. I had wound it in the range of a clean sounding humbucker. I'd have to find my notes to be specific, so I will generalize for the moment. I believe it was wound to about 7K in series.

I used two low carbon steel blades. It's listed as 1008-1010. First I tried a C8 magnet, the size you find in these pickups; 1/4" x 1/4" x 2.3". That sounded pretty much like any of these dual rail pickups. Then I used a neo 1/4" x 1/4" x 1". That was very bassy sounding. In fact it was so bassy sounding that I had to switch the wiring to parallel to get a useable tone from it. It wasn't that the highs were missing, it was just too much low end. Switching that neo for a very small one instantly improved the tone. Now the lows and highs were in balance. It made a nice jazz sounding pickup, but wasn't as snappy as I wanted. Then I rewound the pickup with less windings, which is the one you heard in the test. Now it's about 5.5K in series.

One thing I notice about the large neo magnets is that the field is very wide; much wider than the pickup. I wonder if that has anything to do with this effect. Otherwise I don't have any ideas why. I doubt the neo was strong enough to saturate the blades.

[David Schwab]

In changing the magnet material from Alnico to ceramic or samarium cobalt or neo, you're also changing the resistance of the magnet and thus the eddy current performance; and of course, you're changing the inductance.

That makes sense. I'm sure even between alnico types that the inductance must be different when the pickup is measured as a whole.

[Mike Sulzer]

That makes sense. I'm sure even between alnico types that the inductance must be different when the pickup is measured as a whole.

The difference in inductance resulting from using two different types of Alnico is probably less than the difference resulting from taking out the magnet. I tried that; see above. The location of the resonant peak changed by about 3%. This is a very small effect.

[Mike Sulzer]

OK, what happened was this (and this has happened on more than one pickup design I was working on). I wound a dual blade Strat size pickup. It's the pickup in that Tele test clips I posted. I had wound it in the range of a clean sounding humbucker. I'd have to find my notes to be specific, so I will generalize for the moment. I believe it was wound to about 7K in series.

I used two low carbon steel blades. It's listed as 1008-1010. First I tried a C8 magnet, the size you find in these pickups; 1/4" x 1/4" x 2.3". That sounded pretty much like any of these dual rail pickups. Then I used a neo 1/4" x 1/4" x 1". That was very bassy sounding. In fact it was so bassy sounding that I had to switch the wiring to parallel to get a useable tone from it. It wasn't that the highs were missing, it was just too much low end. Switching that neo for a very small one instantly improved the tone. Now the lows and highs were in balance. It made a nice jazz sounding pickup, but wasn't as snappy as I wanted. Then I rewound the pickup with less windings, which is the one you heard in the test. Now it's about 5.5K in series.

One thing I notice about the large neo magnets is that the field is very wide; much wider than the pickup. I wonder if that has anything to do with this effect. Otherwise I don't have any ideas why. I doubt the neo was strong enough to saturate the blades.

That is definitely a bizarre result. Can you demonstrate the increase in bass over other magnets by injecting a signal with a coupling coil?

[Rick Turner]

The problem with using a signal coil to inductively couple a signal to a pickup is that it isn't a string. This is what I keep hammering about... There is a complex dynamic 3 dimensional interface between string(s), coil(s), and magnet(s). The field has a shape of varying density in 3 dimensional space. The string is "X" distance from what? The top of the magnetic structure? The string is passing through a flux field, has induced magnetism from the permanent magnet, and is also changing the static field by means of oscillation. The coils turns are in there somewhere too.

To really get down on this whole thing, you'd also have to do some experiments in which the relationship between magnet and string remained constant, and the shape, height, and aperture of the coil changed.

And once again, I believe if you want to isolate the effects of magnet/coil interface from the coil inductance and frequency response, you'd have to do this with low impedance coils that have resonance way beyond 20 kHz (no big deal) and whose physical size is carefully monitored.

I also think you've got to use real strings at real tension to get a handle on this. Either driving the strings with a controlled pluck (magnet wire loop pull) or perhaps with an E-bow would work. You'd also want to have the reference of a good piezo pickup, and a lot could be learned by having a piezo at each end of the string mounted at 90 degrees to one another so you could see string phase vector response.

I've got to build that test rig I designed. The thing was called "Project Pythagoras", and the monochord is to be fully adjustable for string length and tension, string after length and break angle at each end of the string, with a movable platform to carry and test magnetic pickups at various places along the string, pickup height adjustment, piezo pickups at each end of the string, various string pluck or drive devices also adjustable along the string length, etc. It is designed to stand vertically so gravity does not affect string motion. It will be built out of sand filled aluminum tubing (3 pieces) with movable platforms with a hole running down the center of each platform through which the string will stretch. The idea is to make it as non-resonant as is reasonable, and as free from flexture as possible.

With such a device, it should be possible to standardize many now-ethereal factors re. pickups including output from a standard string pluck, and hopefully allow quantifying some of these effects that seem to be present, yet have not been adequately described. We don't even have a proper spec for absolute phase of pickups yet. We're in the dark ages.

When (and if) I get around to building Pythagoras, I'll publish the design under Creative Commons protocol. I'd just like to see some rudimentary standards adopted, and beyond that, I'd like to have a real way to test pickups that involves real world conditions...strings...not just drive coils, gauss measurements, and inductance figures. That stuff is handy, but it clearly does not tell us all there is to know about how a pickup sounds.

Like I say, I'm all for the science, but not if it's telling me what to hear. I want to have the science to explain what I hear, and it doesn't yet. The science of measuring pickups is inadequate at this time.

The fewer variables in any of this, the better.

[ScottA]

The difference in inductance resulting from using two different types of Alnico is probably less than the difference resulting from taking out the magnet. I tried that; see above. The location of the resonant peak changed by about 3%. This is a very small effect.

This may be true when the magnets are external to the core of the coil, but when the magnets are in the core, there are much more significant effects.

When AlNiCo is the pole piece, the inductance of a pickup with AlNiCo2 is about 2x that of AlNiCo5, and the ratio of the resonant frequency Al2/Al5 ~ 0.7.

Also, as a reference, the inductance with AlNiCo5 is only about 1.5x the coil by itself.

[ScottA]

The problem with using a signal coil to inductively couple a signal to a pickup is that it isn't a string. This is what I keep hammering about... There is a complex dynamic 3 dimensional interface between string(s), coil(s), and magnet(s). The field has a shape of varying density in 3 dimensional space. The string is "X" distance from what? The top of the magnetic structure? The string is passing through a flux field, has induced magnetism from the permanent magnet, and is also changing the static field by means of oscillation. The coils turns are in there somewhere too

....

Like I say, I'm all for the science, but not if it's telling me what to hear. I want to have the science to explain what I hear, and it doesn't yet. The science of measuring pickups is inadequate at this time.

The fewer variables in any of this, the better.

It's funny. You are expressing somewhat of a disdain for science, yet you are outlining a very scientific approach to the problem.

I would say that I think there is quite a bit more that can and should be done in terms of fundamental understanding of pickup response with "basic" measurements like frequency response and AC electrical measurements.

But the approach of controlling, minimizing or eliminating variables is absolutely key. I think a controlled actuator of the kind you are describing is critical as well.

[Mike Sulzer]

This may be true when the magnets are external to the core of the coil, but when the magnets are in the core, there are much more significant effects.

When AlNiCo is the pole piece, the inductance of a pickup with AlNiCo2 is about 2x that of AlNiCo5.

Also, as a reference, the inductance with AlNiCo5 is only about 1.5x the coil by itself.

Right, you do need to use the correct Alnico to get consistent frequency response in single coils. If I remember correctly, A2 gives a weaker field than A5, but has a higher permeability. The higher permeability makes the coil more sensitive to the vibration of the magnetized string than A5 for the same level of string magnetization. So you expect to get similar output levels the same distance from the string since A5 magnetizes the string more. However, with A2 you can put the pickup closer to string without too much string pull, and so you expect a higher output if you do this. [This is the answer to the question I asked Peter before he retired from the conversation at the top of this discussion.]

[Rick Turner]

I do not disdain science; I disdain those who wrap themselves in cloaks of science and clearly miss reality. I know there are things we can hear that do not show up in the science so far presented in audio. I remember the time when transistor amps were considered perfect by the scientists and solid state audio designers...all because the techs were falling all over themselves to proclaim lower and lower numbers for THD. Then TIM and slew rate were discovered to have much more of an audible impact on the quality of the sound. Whoops... The scientists had been wrong...because they were emphasizing one range of measurements that really didn't explain what people with trained ears were hearing.

And in this discussion...frankly, I'm amazed that anyone would want to test for magnet differences with the masking effects of coil resonance and limited bandwidth being in the way of the tests. Wouldn't a scientist want the most level playing field possible so the variable (in this case, the magnet type and strength) could be observed in as uncolored a manner that could be devised?

I think that there may very well be very audible differences among magnets as used in pickups...differences that go beyond simple output. Some of those differences will be found to be "Stratitis"...string pull that creates false nodes on vibrating strings. Some may be due to inductance changes...but we can eliminate that issue by using low Z coils. As for the remainder of the changes...if there are any...let's have a good way to understand them...or put the matter to rest and prove that it's just inductance and string pull.

But so far, the science has not been adequate. Science needs skepticism in order to stay honest. Science needs to reduce experiments to the simplest possible with as little "noise" in the test procedure as possible. Science needs to look at one factor at a time without any other confusing issues in the way. If state of the art science cannot adequately explain what people hear, then it may be time to improve the science and not rest upon it as truth until observation and measurement are in better agreement.

[Mike Sulzer]

I do not disdain science;
........

A Science needs skepticism in order to stay honest.

Skepticism is part of science; every scientist knows that and practices that. (Well, not the ones bought out by the oil industry, etc.)

[Mike Sulzer]

And in this discussion...frankly, I'm amazed that anyone would want to test for magnet differences with the masking effects of coil resonance and limited bandwidth being in the way of the tests. Wouldn't a scientist want the most level playing field possible so the variable (in this case, the magnet type and strength) could be observed in as uncolored a manner that could be devised?

If you want to find the reason for certain effects in a certain environment, you do not change that environment, you keep it the same while testing. You are assuming you already know what the cause is, and you are guessing as to what might best show up that effect.

[Rick Turner]

Mike, you try your tests...masked as they might be by the incredibly screwed up frequency and phase response of high impedance coils...and I'll (eventually) try mine. I already know that removing coil response better reveals some very interesting tonal variations that are not attributable to inductance and coil resonance. I'd love to quantify those differences free of the straitjacket of high impedance pickups so the magnetic differences become more obvious...if there are any. I don't want to hear about coil inductance when it comes to assessing magnet differences...for this particular kind of test. I think you want a reductionist solution to this whole issue. If it doesn't fit your textbook understanding of Maxwell, et al, then it doesn't exist. I'm skeptical of that world view. I want a finer resolution look at the issue. And that doesn't mean that I reject Maxwell, etc....I just think that there's another level...or two...that you may not be looking at because of some learned and entrenched prejudice against trusting ears. This is not the first time you and I have disagreed about ears vs. incomplete science. I'm not yet satisfied that you've addressed what many musicians hear...differences separate from simple voltage increase or diminuation induced in pickups when you change magnets. I think the tonal change might very well be real and not be attributable to changes in inductance.

Don't forget the three blind men each describing the elephant. Don't be blind to the bigger picture.