The Misleading Nature of DC Resistance in Regard to Pickup Coils

CheopisIV

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Time... if you happen to find it, send some my way please ;)
 

ARandall

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Good idea James

Its almost like you need to contact @LtDave32 and get it into a sticky right from the word go. Its important info that really should be to hand - even for more experienced people it is a great resource to have to hand.
 

garybaldy

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This thread needs more attention. This topic is coming up a bunch, lately.

Perhaps I'll do a "version 2" of this thread, which incorporates some audio examples. :dunno:

...just gotta find the time.
Opinion if you don't mind pls.
I'm soon to receive a handwound UK made Dogear P90. It's A3, unpotted , 42awg enamelled wire and nickel silver baseplate, 7.2K. It's supposed to be like the late 40s ones. It's for a laminated jazz box. Do you think it'll cut the mustard?
Cheers
 
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cooljuk

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Opinion if you don't mind pls.
I'm soon to receive a handwound UK made Dogear P90. It's A3, unpotted , 42awg enamelled wire and nickel silver baseplate, 7.2K. It's supposed to be like the late 40s ones. It's for a laminated jazz box. Do you think it'll cut the mustard?
Cheers
:dunno:

Sorry, man. I have no idea. Some simple specs don't always say much about a pickup's voice. That's sort of the point of this thread. I don't think Gibson was hand-winding anything in the late 40's but that doesn't mean it would or wouldn't be a decent pickup. A nice set of A3s in a P-90 can be real nice but they vary from foundry-to-foundry (even batch-to-batch from some).
 

garybaldy

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:dunno:

Sorry, man. I have no idea. Some simple specs don't always say much about a pickup's voice. That's sort of the point of this thread. I don't think Gibson was hand-winding anything in the late 40's but that doesn't mean it would or wouldn't be a decent pickup. A nice set of A3s in a P-90 can be real nice but they vary from foundry-to-foundry (even batch-to-batch from some).
Thanks. Your input is always interesting and educational. Thinking about it, it was a bit of a stupid question, sorry. Also I didn't consider the fact that Gibson would be using machines back then. I hope the A3 is a good one. May be I should ask the winder the source. The pickup is £75 and I dont think the builder is that well known so I'm hoping it's good. The guitar is a budget Chinese, bought during early lockdown and playing it today, the original pup isn't bad!!! Gonna be interesting. Cheers.
Alden AD150 Mine Ebay 26 may 20 299GBP.jpg
 

cooljuk

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Nah, man. No stupid questions. You're good. ...don't worry about what foundry, or likely distributor vendor, the magnets come from. Even if you knew, it wouldn't say anything for sure. Just use your ears! That's really what matters at the end of the day, anyway.
 

cooljuk

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For the winter shoppers, looking at vintage pickups on Reverb... I'm getting a bunch of questions about DCR and referring many to this thread. Might as well bump it.
 

cooljuk

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This is something I wrote in another thread that's a perfect compliment to this thread. Here are a few factors that can alter the DCR of pickup coils independently of the sound. In these examples, even the turn counts of the pickup don't change, but the DCR can chance significantly.

Coil Patterns:
If the wire falls onto the bobbin unevenly, forming more of a cone shape, with the bulk of the wire piled up on one end, then the average length of a single turn on that bobbin will be much longer than on a more evenly wound bobbin, as more of the wire is piling up on top of itself making longer loops. Two otherwise identical coils will have significantly different DCR but sound similar. It could even be that the cone shape coil has less turns and sounds brighter, both because the turn counts are less and also because the bulk of the coil is closer to the strings, and this brighter sounding coil made of the same materials would have the higher DCR. The "cone" could also be a barrel shape (wide in the middle) or an hourglass (wide at both ends) and have a similarly misleading DCR. Coils that have a uniform shape, but are made with heavy scatter will do the same, increasing the length of every turn and building a physically wider coil as a neatly wound one, for the same turn counts/wire/bobbin/etc.

Coil Turn Count Offset in Humbuckers:
Consider a humbucker with 10,000 turns evenly distributed on both coils. Let's just say everything about the bobbins, wire, and coils is identical. Let's say it's 8k Ohms total. What if you keep everything identical in another humbucker but distribute the total turn counts differently. Let's put 7,000 turns on one coil and 3,000 turns on the other. The output will stay the same. The turn counts are the same. The DCR will be much higher. This is because the length of wire it takes to go around the already piled up layers on the 7,000 turn bobbin for the last 2,000 turns is longer, now traveling around an already laid down 5,000 turns, than it was on the previous pickup where that same wire only had to travel a shorter distance per turn around only 3,000 turns piled up. So two identical pickups with the same bobbins, wire, and total turn counts, but the second humbucker has a much higher DCR. ....and it will also be the brighter sounding one, due to the heavy coil offset. DCR will mislead you, once again, even with unrealistically precise materials and everything else being identical.

Ohms/Foot Ratings:
The stated resistance per foot of a given spool of wire is taken from a single sample off the end of that spool. Not an average of the whole spool, and is not consistent along the length of the entire spool.

Differences in Tolerance:
The NEMA standard for magnet wire tolerances, of both copper core thickness and insulation thickness, is at least four times tighter today than it was in the 1950s. Vintage wire (or modern wire produced to looser standards, which can be had) will have a wider range of variation.

The Start Lead Jumper:
The way original P-90s and PAFs were made, there is a black plastic insulated stranded lead, about 1mm wide and up to about 7in long (although the length varies), wrapped around the inside of the bobbin, before the coil is laid over it. There is also the bulk of a solder connection of this plastic insulated stranded jumper lead to the fine coil wire, which is then tapped off, also adding to this bulk between the bobbin and coil. The way that this extra bulk sits under the coil is a bit unique on every pickup and changed both the internal shape of the coil, as well as the length of wire needed to pass around the bobbin each time. This will vary both the voice of the coil and the DCR of the coil, and not really in predicable ways, as they size and shape changes, as does where this mass ends up laying inside the coil.


These are a few variables I see seldom, if ever, discussed. I have intentionally left out different wire types and gauges, different magnets, steels, and other materials, as well as different bobbins and construction designs. Those are more commonly discussed. I decided to stick to just coils and of the same bobbins and wire type/gauge, for the point of getting the gears turning away from the commonly understood stuff. Any of the variables I listed in the body of this post can cause two coils, that are by all practical means "identical", to have different DCR, different voicings, or both and absolutely in opposite directions than expected. Higher DCR coils, which are otherwise identical, can very much sound brighter and/or have lower output, while lower DCR coils of identical design and materials can sound darker and/or have more output. Sometimes, by very obvious amounts. We aren't talking about little differences that take "golden ears" to hear.
 

TM1

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Has anyone taken into consideration the fact that the wire used in the 50’s & early Sixties was different than modern wire? Wire 50-70 years was full of impurities. Modern wire is almost pure copper. The impurities in the wire will make each coil sound slightly different.
 

cooljuk

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Well, I mentioned the differences in core and insulation size tolerance in the post above, as I've been able to measure that, myself. I don't know how I could quantify how pure the copper in 50's magnet wire used to be and what, if any, effect that would have on the sound of a pickup, independent of other factors, though.

I'm not saying the copper purity is or isn't different, or that it does or doesn't influence the sound. I don't know. I'm just not sure how that theory could be tested / quantified.

I've definitely used spectrometry and microscopy in research and I know, when looking at samples of old wire, the insulation can be in very poor condition and the wire can be oxidizing. Even with spectrometry, how could I know what impurities were originally in the wire what impurities are just a result of oxidation? ...and, if from oxidation, at what time did they come to be present? Before the 60's or 70's when classic rock songs were recorded? Later in the 90's or 2000s? After that? How could I determine what those impurities do to the sound of a pickup?

Honest questions, all of them. If there's a way to test for and prove any of that, I'll be more than happy to do it, contribute to it, participate in testing of it, etc.

I know there are other winders who preach this theory of copper impurity in magnet wire being a contributing factor to the sound of old pickups. If I'm remembering right, one even presented that theory in my PAF book with Mario. I didn't contest it, as I don't know one way or the other. I don't think these guys who have this theory have actually quantified it or it's effect on sound, though. I think it's just a running theory. ....but, hey, maybe I'm wrong and, if I am, please clue me in! I hope I always keep learning new stuff about vintage gear.
 

Michael Matyas

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As I read these MLP forums daily, I realize that some of us spend more time reading these et. al. forums than actually sitting down and playing a favorite guitar and amp; (myself included). Perhaps it has to do with affluence that exists today and the generous amounts of leisure time many people have. I do believe that there are a certain number of people (more than we all realize) who are so busy making a living as a professional guitarist that they have no spare time to indulge studying the current state of the technical side of equipment in all its manifestations.

Guitar playing today (compared to the days I started playing) is an industry in itself. There have always been the major guitar and amp manufacturers in it to make money. It has evolved strictly in a business sense to almost a "science" with many small entities producing variation of advanced products, hence, the myriad discussions on DCR, ohms, watts, and miliamps; all associated with the process of obtaining our favorite artist's tone.

Yes, it is all good and for a purpose, I suppose; otherwise I'd cease my regular reading of all forums dealing with guitar and equipment. I just get a bit concerned sometimes that the actual "magic" of playing an original and exciting style of guitar is fading into the background.


Classicplayer
Thank you for your thoughtful post. My New Year's resolution this year is to dust off the classical, the dreadnought and the jazz box and try to give them their due. Happy New Year and God bless!
 


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