Jackson's primer on pickups, circa 1985

[timtam]

I just came across this pickup primer from Jackson Guitars, from 1985 (!). It was buried somewhere rather inaccessible on the internet. It's now on a free PDF download site.
pdfhost.io/v/rd81la2Cg_images

It's only 17 pages long, but goes into more detail on pickup parameters than anything I have seen from guitar manufacturers or pickup manufacturers, almost 40 years later. I'm guessing it has errors, but it's a decent effort for the time. Its main interest is perhaps historical rather than technical (its font is very reminiscent of the first HP dot-matrix printer I had in the mid-1980s !). The primer was presumably written by Paul Gagon, who had just joined Jackson in order to design their American-made pickups, after 5 years of pickup R&D at Fender.
www.charvelusa.com/jackson_pickups.html
"After Grover and I had defined what our line of pickups would be, we hit the road and visited our Charvel/Jackson dealers all along the west coast from Seattle Washington to San Diego California. We conducted clinics we called “Jackson Pickups…..what you should know.” These clinics allowed music store owners to bring in their customers so they could ask us questions about how pickups work and why they sound the way they do. During this adventure, I realized just how little most players really understood about the most important part of an instrument's sound: the pickups."

It seems that not much has changed for most players. And the current guitar/pickup manufacturers are largely responsible for that dismal state of affairs; for failing to provide comprehensive information on how pickups work, backed up by full specs on their pickup products.

[nienturi]

May 22, 2022 0:28:47 GMT -5 timtam said:

I just came across this pickup primer from Jackson Guitars, from 1985 (!). It was buried somewhere rather inaccessible on the internet. It's now on a free PDF download site.
pdfhost.io/v/rd81la2Cg_images

It's only 17 pages long, but goes into more detail on pickup parameters than anything I have seen from guitar manufacturers or pickup manufacturers, almost 40 years later. I'm guessing it has errors, but it's a decent effort for the time. Its main interest is perhaps historical rather than technical (its font is very reminiscent of the first HP dot-matrix printer I had in the mid-1980s !). The primer was presumably written by Paul Gagon, who had just joined Jackson in order to design their American-made pickups, after 5 years of pickup R&D at Fender.
www.charvelusa.com/jackson_pickups.html
"After Grover and I had defined what our line of pickups would be, we hit the road and visited our Charvel/Jackson dealers all along the west coast from Seattle Washington to San Diego California. We conducted clinics we called “Jackson Pickups…..what you should know.” These clinics allowed music store owners to bring in their customers so they could ask us questions about how pickups work and why they sound the way they do. During this adventure, I realized just how little most players really understood about the most important part of an instrument's sound: the pickups."

It seems that not much has changed for most players. And the current guitar/pickup manufacturers are largely responsible for that dismal state of affairs; for failing to provide comprehensive information on how pickups work, backed up by full specs on their pickup products.

Thanks for your share. I've never seen it before. It's even more detailed what aftermarket brands presented.

[ms]

Section 8 is about magnets.  It has four definitions in the first paragraph.  These contain incorrect information.  Here are three links that contain better information:

byjus.com/jee/ferromagnetic-materials/
en.wikipedia.org/wiki/Remanencehttps://en.wikipedia.org/wiki/Remanence
en.wikipedia.org/wiki/Maximum_energy_producthttps://en.wikipedia.org/wiki/Maximum_energy_product

[ms]

Section 9 on shielding (and also on hum bucking, although this is not in the title) contains many errors.  They follow from the misconception that both shielding and humbucking reduce hum from "electromagnetic fields".  Shielding reduces hum from electric fields, while humbucking reduces hum from magnetic fields.  A propagating electromagnetic wave (radio, tv, cell phones, etc.) has both kinds that oscillate together.  This is not usually a problem for guitars because the frequency is so high and guitars do not efficiently "detect" the modulation on the wave.

Section 11 on single coil versus humbucking says that the major difference in sound is a result of harmonic canceling from sampling one versus two regions on the string.  This is a real effect but minor, and only affects the lower frequency strings. The relevant harmonics are high number and out of the bandwidth of the system on the higher frequency strings.  Humbuckers sound darker because they have higher inductance.  Well, not all single coils have lower inductance; for example, a P-90 has high inductance.  The myth is that a P-90 has good high frequencies because it is a single coil pickup, but it does not.

Also, stacked hum buckers do not have cancelled bass.  There is some loss in output level from coupling between the coils at all frequencies.

[stratotarts]

It's stated in that document that Q should be defined (so I suppose measured) at the resonant frequency. I usually consider it that way, but I'm aware that it's not quite right, you can measure it at any frequency. Some people talk about Q at some standard frequency, for example 1.0kHz. The difference and the discussion should be about why, and what exactly you are trying to measure, describe or specify. I have personally avoided using the term, instead talking about peak amplitude because it's the effect that I believe will be most audible. If you have a polar plot you can calculate Q at any frequency, but it's meaningless without the reason and context. For comparative purposes you do have a good rationale for using a standard frequency other than the resonant, but it's a different purpose, and the two values are closely related anyway.

It's amazing that so many people (who also pose as experts) get shielding wrong. Or, only partially right. Even Bill Lawrence's published treaties start off on the right note but seem to go sideways and miss the simple well known (to engineers anyway) difference between magnetic and electrical field interference. Quite a few "experts", like the late Bill L. did, continue to claim that aluminum blocks magnetic interference well. It does not. If it really did, you would see it performing that function in all kinds of crucial professional electronics going back 100 years now. But you don't. There is only mu-metal but even it doesn't act as a simple block.

A big factor in the inaccuracy of published information in the field is the effect of the isolation of designers from information carefully protected from any public view for proprietary reasons. The only reason that has significant cracks in it now, is that the internet exists and people have more chance to view a lot more and a lot more varied information.

[stevewf]

May 22, 2022 0:28:47 GMT -5 timtam said:

www.charvelusa.com/jackson_pickups.html

An excerpt from the first paragraph from the above-linked page:

Most of the Jackson employees that were hired to wind pickups were women.
This is because women have a greater tolerance for this very meticulous process.
Men generally have less patience for a process such as winding pickups.


Struck me to where I had to post this before continuing reading.

[ms]

Mar 5, 2024 2:32:38 GMT -5 stevewf said:

May 22, 2022 0:28:47 GMT -5 timtam said:

www.charvelusa.com/jackson_pickups.html

An excerpt from the first paragraph from the above-linked page:

Most of the Jackson employees that were hired to wind pickups were women.
This is because women have a greater tolerance for this very meticulous process.
Men generally have less patience for a process such as winding pickups.


Struck me to where I had to post this before continuing reading.

That was 1985. Still a lot better than what would have been written in 1965.

[stratotarts]

I can attest to that because in 1965 or very close to that, I was a kid interested in electronics and overheard that a friends's mother was a coil winder in an transformer factory. I considered that a bit awesome and asked her about it. She got angry, her face turned red and she told me not to tell anyone else.

[gckelloch]

Regarding the effect of Al shielding on SC pickups, I have experimented extensively with Al shielding and can confirm Bill L's statements (to an extent). He recommended placing a thick reusable Al pie tin behind a SC pickup across from an electromagnetic noise source to hear the difference. I did so and the noise reduction was quite apparent. I then placed a ~7H GFS P90 on my desk and recorded the noise captured enclosed in two such Al pie tins and without them, making sure the attached wires, jack, and pickup orientation remained consistent. Here is the result:

drive.google.com/drive/folders/0Bx0CnqsQz_uYblRTLTQwam5FS2s?resourcekey=0-HmA9RFQMWz4AYmvFTPpD2Q&usp=sharing

You can see most noise reduction occurred in the midrange. Perhaps it would be shifted higher with a lower L pickup?

He claimed there is some reduction in the harsher upper-midrange of typical Strat inductance level pickups with 0.015~o.025" Al shielding without affecting the highs. My b4 and after recordings of 0.015~0.025" range of Al shielding revealed it to be mostly true. However, a test conducted by someone I can't recall at the moment showed a 0.063" thick Al Strat pickguard produced a -2db shelf above ~1kHz when an electrical signal was sent through a typical S-type pickup. I assume there is less loss of high-end with 0.015~o.025" Al shielding, but I have no specific data.

Bill L. also claimed here: "At about .250 thickness your single coil will be as quiet as a hum bucker, but you also lose about 60% output and about the same amount of highs."

www.billlawrence.com/Pages/All_About_Tone.htm/TeleLovers.htm

Not sure what HB pickup he referred to, or what 60% output translates to in dB's. I assume .250 means 0.250". Although he was of European descent, he tended to use imperial measurements. "When in Rome..."

Here's some more data on shielding types:

alexkenis.wordpress.com/2016/03/17/guitar-pickup-theory-5-shielding-hum-cancelling-and-flux-concentrators/

[ms]

What is an electromagnetic noise source? You need to test with electric and magnetic fields separately for useful consistent results.  But getting rid of electric fields is easy. A thin metal shield is adequate, so there is really nothing to learn there.  Magnetic fields are harder.

[stratotarts]

Bill L. was very smart and observant. But he lacked the engineering background to understand the experimental rigour that is needed to really verify or invalidate theories. He never published enough details in his experimental techniques to give them any scientific validity. Largely, what he did do with those investigations is to confirm the more obvious (to an engineer) aspects, and to somewhat steer people away from really wacko theory and pickup folklore.

The main experimental risk, is that magnetic and electric sources must be isolated so you don't attribute results from one phenomena to the other, which may not be the root cause.

Errada's lab had a very carefully constructed magnetic field generator, it was a large tube with field windings around it. By turning the field currents on and off, he was able to isolate the magnetic from the electric field effects. That is what it takes to be sure.

[gckelloch]

I see. I am aware that he did not have secondary formal education, but he did tell me he published some of his work in Germany, including a book on magnetism, and that he was at odds with the scientific community regarding a physics theory for which he advocated called something like the "exemption principle", which involved the laws of physics breaking down under certain circumstances. He mentioned inside a black hole as an example. Mind you, this was just from a phone discussion over 10 years ago. Some generally accepted physics theories are being challenged now due to recent evidence. Of course, that's not an argument for whatever Willi L Stich (Bill L) was promoting.

My understanding is that the paramagnetic Aluminum disturbs, rather than blocks, the magnetic flux around the coil. I wouldn't know how to go about isolating magnetic and electrical sources. By electrical sources, do you mean only that which travels through the wiring to a given device? All I can do is show the results of my tests. I can't say whether Al affects the magnetic or electrical signal or both, but it does affect the sound the pickup produces.

ms, there was another thread in which I thought you were saying the distance of the coil from the flux lines emanating from the strings does not affect the output, and that Herr Stich was wrong in stating that the lower half of a typical Fender SC height coil contributed more to noise than was worth to the output. I replied to your criticism, but you did not further clarify. Did either of us misinterpret the other's statements?

There's another shielding test from the same cat as b4. Perhaps it is of some use?

alexkenis.wordpress.com/2016/04/13/guitar-pickup-theory-7-effect-of-pickup-cover-material-on-tone-and-noise/

[antigua]

So if I slide a sheet of mu-metal between the strings and the pickup, the sound should go dead quiet? I can try it, I have some stashed away in a tote with experiment supplies. If it fails, then I think the idea that it or aluminum can block magnetic noise is off the table, and vice versa. From what I've read, in order for a conductor to cancel magnetic waves, it needs to be several inches thick, thickness depending on the frequency, and then all that is really happening is that eddy currents are repulsing the magnetic wave. 

[ms]

Mar 6, 2024 17:27:18 GMT -5 gckelloch said:

There's another shielding test from the same cat as b4. Perhaps it is of some use?

alexkenis.wordpress.com/2016/04/13/guitar-pickup-theory-7-effect-of-pickup-cover-material-on-tone-and-noise/

"The hum bucking configuration will cancel out some of the lower harmonics to a degree, but the upper harmonics will still make it through."

This is not useful, except to suggest looking at everything else he writes very carefully.

[stratotarts]

Mar 7, 2024 0:59:48 GMT -5 antigua said:

So if I slide a sheet of mu-metal between the strings and the pickup, the sound should go dead quiet?

Maybe. I'll be honest and tell you I don't know what is special about mu metal. But, with respect to aluminum (or plated copper as we see in cheap covers) the situation with eddy currents is comparable when a sheet is placed nearby, except that if it is behind the pickup it is far away from the string field and so has minimal effect. But yes, a small part of the same effect.

However the string field and an external interference field are not of the same character. A conductor in the near vicinity of a string field has induced voltage in opposite directions, which only create eddy currents (and therefore somewhat block the field variations) when there is a low resistance path through the conductor which connects the induced regions. This is just the well known effect of lossy covers.

But, a uniform alternating external field does not excite regions of the conductor in different directions, because the field lines are uniform. A voltage is induced by Faraday's Law. However in this case the voltage differential is also uniform across the conductor and therefore there are no regions with opposing voltages, and no current will flow. Thus, there is no diminuation or blocking of the external field.

This is why I think the attributes of aluminum as a material that will block interference, must be mistakenly attributed to magnetic interference when it is really electrical. It's the lack of experimental rigour that made that mistake possible. Also I think, a sketchy understanding of electromagnetism, in fairness it's pretty weird stuff.

Also, it's unlikely that a plate could "disturb" the field. It's recognized that such materials are transparent to externally applied magnetic fields. I explained why there is no (or extremely minimal) electromagnetic interaction, so you can't look there (unless you want to debate that specific point). Simply put, there isn't any specific theory that would predict it. I'm open to suggestions, but I haven't encountered any that are fully fleshed out.

Installations of mu metal that I have seen, fully enclose the shielded object, perhaps that accounts for a difference... we do know that steel will concentrate magnetic field lines, but it is far from magnetically transparent.

[stratotarts]

Mar 6, 2024 17:27:18 GMT -5 gckelloch said:

By electrical sources, do you mean only that which travels through the wiring to a given device?

No, I'm talking about the dynamic electrostatic fields that exist in the (mostly technological) environment. You are sensing them every time you touch the disconnected end of a guitar cable that's plugged into an amplifier. The BZZZZZZZZT. You can tell that it's electrostatic (high impedance) in nature, because if you ground some other part of your body to the amp ground, you have created a medium (~2k to ~500k ohm) impedance path that short circuits the signal.

Another bit of evidence from this, if you connect the plug tip to a much larger object, the capacitance between the electrical source and the input is greatly increased, which greatly increases the buzz. The operation of a capacitor is fundamentally electrostatic, it's an electric field displacing electrons that are held captive in the plate conductors.

[ms]

Mu-metal has very high permeability.  There are really two separate things happening here:
1.  Currents excited in the "shielding" metal by the B field of the string produce a field that the pickup detects.
2.  Currents excited in the pickup coil (especially at and near resonance) cause a magnetic field that induces current in the "shielding" metal that causes a field induces voltage in the coil.  This is like an extension of the damping caused by the metal cores of the pickup.

[gckelloch]

Thanks, guys for replying to my questions. I don't fully follow the explanations, but I get the gist of how the two noise types differ, and there's no way to tell how much of either type influenced the result in my graphs. That might explain why Cu tape pickup cavity shielding in some YT videos I've seen did reduce the noise of the SC pickups.

I will say that I do think Willi L Stich was aware of noise type differences, although some of his articles are a bit confusing, or can even appear contradictory. There may have been some translation issues with his partner Becky when she wrote them, as well as the effect the cancer and treatments had on his ability to concentrate around 2010. He was sometimes confused during our phone conversations then-- one time not even recognizing who I was after we had already talked several times. He did distinguish between noise types in this article stating that only humbucking coil designs will "...neutralize external magnetic fields.":

www.billlawrence.com/Pages/Pickupology/External%20Interference.htm

That and the fact that his hum-canceling and Micro-Coil pickups incorporate Cu-shielding lead me to believe he was aware that shielding did not reduce EMI (if that's the correct acronym). Unfortunately, the last sentence of the "For Tele Lovers" article I linked to was misleading. Maybe it was meant to refer to rheostat "hum-buzz" from the previous paragraph? It makes no sense that he would intentionally contradict himself, but I've seen it happen in a few other articles.

[stratotarts]

Yeah, but one reason why the Micro Coils have less noise is in the small internal radius of the coils. The larger the radius, the more inductance all other things being equal, and also a reduced degree of coupling to external magnetic fields. I'm not sure if Bill came to that with a full understanding or by experiment but it certainly works that way. I know of no other designer that recognized that opportunity and leveraged it. At the end of the day, he was doing the right things to minimize the noise - both electric and magnetic - at least in the Micro Coils and I think with the others too.

EMI is a general term that could apply to either electrostatic or magnetic interference. It can also refer to interference from electromagnetic waves, but as ms mentioned, it's not applicable in this case.

The topic is not restricted to pickups. Many, many electronics devices have needed some kind of protection from external fields and so the field is pretty full of solutions. For example, toroidal inductors, which offer exceptionally good isolation from external fields and also contain their internal fields from outside circuits very well. Some early humbucking pickup patents reference existing patents for humbucking transformers, inductors and so on that were for general electronic use. It was not a new idea.

[antigua]

Mar 8, 2024 8:31:57 GMT -5 stratotarts said:

Yeah, but one reason why the Micro Coils have less noise is in the small internal radius of the coils. The larger the radius, the more inductance all other things being equal, and also a reduced degree of coupling to external magnetic fields. I'm not sure if Bill came to that with a full understanding or by experiment but it certainly works that way. I know of no other designer that recognized that opportunity and leveraged it. At the end of the day, he was doing the right things to minimize the noise - both electric and magnetic - at least in the Micro Coils and I think with the others too.

EMI is a general term that could apply to either electrostatic or magnetic interference. It can also refer to interference from electromagnetic waves, but as ms mentioned, it's not applicable in this case.

The topic is not restricted to pickups. Many, many electronics devices have needed some kind of protection from external fields and so the field is pretty full of solutions. For example, toroidal inductors, which offer exceptionally good isolation from external fields and also contain their internal fields from outside circuits very well. Some early humbucking pickup patents reference existing patents for humbucking transformers, inductors and so on that were for general electronic use. It was not a new idea.

The Lace Sensor also seems to be low noise because of the very small coil located right near the top of the pickup, and the ferrite magnet probably invites less noise than the pole pieces of regular passive pickups. I'm not sure if the Lace Sensor or Micro Coil came first, but the Lace Sensor seems to take the innovation a couple steps further. 

I think EMI and RFI all being used interchangeably is why the difference between electrostatic and magnetic noise isn't common knowledge. But the other reason is that magnetic interference seems to be specific to lower frequencies, because if the magnetic noise is a high enough frequency, it will be blunted by thin shielding. The same shielding that blocks electrostatic noise would block magnetic, and they dont have to be addressed separately in most applications, I would think. 




 

[stratotarts]

It's true. In the 20th century, most interference was from mains frequency. That is low frequency, except where there is arcing or chopping like in a light dimmer. In the latter years, more and more high frequency circuits made their way into consumer and industrial circuits. So there is a much greater range of frequencies that have to be protected.

As the frequency increases, the magnetic and electric effects increasingly interact, which makes it all the more difficult to fix and to explain. Small wonder that there is some confusion.

[gckelloch]

Mar 9, 2024 3:02:31 GMT -5 antigua said:

Mar 8, 2024 8:31:57 GMT -5 stratotarts said:

Yeah, but one reason why the Micro Coils have less noise is in the small internal radius of the coils. The larger the radius, the more inductance all other things being equal, and also a reduced degree of coupling to external magnetic fields. I'm not sure if Bill came to that with a full understanding or by experiment but it certainly works that way. I know of no other designer that recognized that opportunity and leveraged it. At the end of the day, he was doing the right things to minimize the noise - both electric and magnetic - at least in the Micro Coils and I think with the others too.

EMI is a general term that could apply to either electrostatic or magnetic interference. It can also refer to interference from electromagnetic waves, but as ms mentioned, it's not applicable in this case.

The topic is not restricted to pickups. Many, many electronics devices have needed some kind of protection from external fields and so the field is pretty full of solutions. For example, toroidal inductors, which offer exceptionally good isolation from external fields and also contain their internal fields from outside circuits very well. Some early humbucking pickup patents reference existing patents for humbucking transformers, inductors and so on that were for general electronic use. It was not a new idea.

The Lace Sensor also seems to be low noise because of the very small coil located right near the top of the pickup, and the ferrite magnet probably invites less noise than the pole pieces of regular passive pickups. I'm not sure if the Lace Sensor or Micro Coil came first, but the Lace Sensor seems to take the innovation a couple steps further. 

I think EMI and RFI all being used interchangeably is why the difference between electrostatic and magnetic noise isn't common knowledge. But the other reason is that magnetic interference seems to be specific to lower frequencies, because if the magnetic noise is a high enough frequency, it will be blunted by thin shielding. The same shielding that blocks electrostatic noise would block magnetic, and they dont have to be addressed separately in most applications, I would think. 




 

The Lace Sensors came out long b4 the Nd-powered Micro-Coils (which has much better S/N than the AlNiCo version). Judging from the relative coil sizes and DCR values, The MC's have thinner wire. Willi told me it was 0.044mm by Elektrosola. That would make it 46AWG from their tables. The L is brought up by the high permeability pole screw bushings (possibly permalloy or 440 stainless). The Q isn't much lower than a typical AlNiCo pole pickup, but some SPL's I took running white noise through a 2.8H bridge MC and a 2.8H L200SM with a 190pF cable and 110R load into a 1M input show the high-end of the MC extends out further than the L280SM, although the L is the same.

drive.google.com/drive/folders/18dYvn3nRfY4I9GScPZgxNKBzd84Ajtur?usp=drive_link

I guess that's the difference in Q width resulting from the thinner wire, and/or something in the magnetic circuit?

Can't say if the S/N noise is better than the Lace Sensors, but I think the output of an Nd MC at the same distance as a Sensor is probably higher due to the effect the high permeability (permeable, permeance?) core has on the flux lines from the string. Judging from the relative coil sizes and DCR values, the MC's likely also have much thinner wire. I haven't owned a set of Sensors, but my understanding is the Steel shielding on the outside spreads the magnetic field from the center out such that they need be up close to the strings for good output, which severely limits the dynamic character a player might prefer for a given output or string action setting. Lowering a Sensor or better output balance up the neck would then sacrifice more S/N than other designs. They also don't have the adjustable poles that allow the MC's better fine-tuning per string and position, and they are just a bit more expensive. Granted, it takes hours to set all the MC coils and pole heights to taste, but it's worth the result for me. After all that, I hesitate to recommend the Nd MC's due to an issue with the recent pole screws not being magnetic-- likely switched by the manufacturer without notice. The pole screws should also be snugged with something like screw thread tape so they don't wind around from vibration or picking stroke hits. As of this writing, I don't know if the screws have been replaced with the correct ones, although I found some suitable black-oiled hex head 1209 Steel screws that work on a recent "defective" T set without significantly affecting the Q.

As evidenced in my DI recordings, the stock set of Ceramic-powered Steel-core pickups in my Rhondo SX guitars have notably stronger output at the same string distance from the pole tops than the A5 pole pickups of about the same L (~2.3H) in my Agile ST-625EB, yet the flux strength at the A5 pole tops felt much stronger with a screwdriver pull-off test. Those SX PUP's even sounded higher output than my Nd MC's, but the MC's sound more "dynamic", and are supposed to be more sensitive to smaller vibrations, which I attribute to the thinner wire coils up close to the strings. Incidentally, doesn't grounding pickup poles eliminate any potential noise contribution? AFAIK, all Wilde pickup chassis' are grounded, and humbucking magnetic circuits are balanced. I'll hand the flight controls back over to the OP now.

[stratotarts]

The proximity to the poles gained by the thinner wire, also improves the efficiency. Refer to Zollner's EM simulations of steel pole pickup string fields.