A Q for the pros...

[David Schwab]

wouldnt you be able to use a multimeter against the pole pieces and one of the ends of the coil to find a short? obviously that doesnt find wire to wire shorts.

Yeah, I did that after my readings showed something wasn't right. But even just reading the coil... it came up a lot lower than it should have. I wind this particular pickup to a certain amount of turns, and I know what the DC resistance should be, and they are usually very close. So when I was hundreds of ohms off I knew something was amiss. Then I remembered that I didn't tape them.

Then I checked from the blade to either end of the coil and got a reading.

Only one bobbin out of 6 didn't have a short. They started out as the best three pickups I wound too!

[NightWinder]

I think at some point, you would have.....having shorts in your coils will surely dissapate your bank account fast because of returns, if you ahev a outstanding warrentee. A must in my opinion

[NightWinder]

MAn tape just is too risky!!! I know you forgot to, but seriously, find something else. All it takes is one wire to sneak under there......BOOM!! Makes a shitty risk factor........and since your handwinding, a slight increase in tension near the edge.......

[Joe Gwinn]

How do you use the LCR to spot shorts? I plan on picking one of those up soon.

By measuring the AC resistance. A shorted turn increases the loss in the coil (which makes the pickup sound dead), and the added loss shows up as an increase in series AC resistance.

Not all LCR meters work with pickups, which have very high resistance for their inductance, compared to for instance a transformer or inductor winding.

The test is to wire a 50K pot in series with the primary of an AC power transformer and attempt to measure the inductance of the winding plus series pot. The inductance reading should vary almost not at all as you change the series resistance by turning the control on the 50K pot.

[Possum]

shorts...

Yes its AC resistance that will spot them when nothing else will. I have had a rare coil or two that didn't short to any poles, didn't change the DC resistance but a huge jump in AC resistance showed me that somewhere in the coil the wire shorted on itself. Personally I don't listen to my pickups before they go to the customer, because I get my recipe nailed down, I have all the specs on it written down in stone, when the pickup gets tested before being sent there is a tolerance it has to meet in matching those specs, if it does its a good one. If something is out of whack I wind it over again. I make too many different kinds of pickups to plug them into an amp in any kind of meaningful test guitar. I do have a test guitar but in order to fit every kind of pickup out there in it, its so hacked up it doesn't really sound like a guitar anymore :-) I quit using it for testing after thinking some pickups sounded really dull, but in a real guitar they sounded great.

The LCR meter has really helped me understand coils and pickups better than anything else I think. Nothing is be-all, end-all but I rely on my test gear every day. Another use of the LCR meter is testing a new batch of magnet wire. MWS won't pull specific spools for me so if I get something thats different than I was hoping for I have to wind a new pickup and see what it takes to match my recipes again with the new wire. When plain enamel disappeared for awhile and came back I had to make drastic changes in my winds to match the stuff I used to get. A very useful tool for me....

[soundmasterg]

By measuring the AC resistance. A shorted turn increases the loss in the coil (which makes the pickup sound dead), and the added loss shows up as an increase in series AC resistance.

With my Rickenbacker humbuckers, the AC resistance is up around 19k, and the DC resistance is around 12k. They use samarium cobalt magnets and are bright and harsh on the top end compared to an alnico magnet pickup, but they are also very powerful. When I first measured the AC resistance, I thought that having that number so much higher than the DC resistance could be an indication of a problem, since many other pickups, like a Strat for example, will show a much closer spread between the two measurements.

That brings up a question in my mind. When measuring the AC resistance, how would you know if whatever number you get is high or not? Do you need to already have a baseline reading for a particular coil design to know what will be high?

Greg

[WolfeMacleod]

Wow Wolfe. So you have'nt heard you best seller?

Nope, unfortunately. It started out as a custom build for someone who requested something based on a rewind I did for someone else. After he got it, he sent it to someone else, who refused to send it back. Shit hit the fan, and before I even knew what was happening, I was getting dozens of emails from peopel asking for the exact same thing.
It's been that way ever since. Email I answer at the beginning of the day is scrolled off the bottom of the screen by mid-day, because so many requests are coming in.

Sorry for butting in here as a newby......but was wondereing what you are saying here (or really thinking) Wolfe.?....bearing in mind a comment Jason made in one of his articles ,etc.....
Nigel

I'm not really sure what your question is, but I'll try. Most of the guys I deal with are searcing for that "someting" that me best seller seems to provide. They hear other customers stuff, and then contact me.

I make time to listen to everything I make, I would consider myself lame for not doing so.

Call me Lame!
I'd love to be able to hear everything I did, and used to be able to do it - every single pickup went into a guitar before it was shipped out. Just got too dang busy to be able to do that. I've got the Mercurio Pickup Tester which I need to sort out, so I can do it again.

MWS won't pull specific spools for me so if I get something thats different than I was hoping for I have to wind a new pickup ....

Hmm? I get specific spools pulled for me all the time. My guy knows what I want and will will read off the ohms-per-foot on spools untill he comes up withthe magic number. If the OPF is too low, I can't use it because I have to add more turns. If it's too high, I have to subract turns. There's a +/- that I accept.
The most bizzarre thing about the ohms-per-foot measurment...you'd think that the higher reading OPF would be smalle wire, right? It's not...

[Joe Gwinn]

With my Rickenbacker humbuckers, the AC resistance is up around 19k, and the DC resistance is around 12k. They use samarium cobalt magnets and are bright and harsh on the top end compared to an alnico magnet pickup, but they are also very powerful. When I first measured the AC resistance, I thought that having that number so much higher than the DC resistance could be an indication of a problem, since many other pickups, like a Strat for example, will show a much closer spread between the two measurements.

That brings up a question in my mind. When measuring the AC resistance, how would you know if whatever number you get is high or not? Do you need to already have a baseline reading for a particular coil design to know what will be high?

The first answer is that you measure all your production and keep records. Pretty soon, you'll know when a reading is out of line. You don't really need to understand what the number really means to do this - it's the deviation from the usual values that raises the red flag.

What is AC resistance? It's the sum of DC resistance and eddy-current loading. If you measure the AC resistance of a bobbin full of wire but no metal objects nearby, AC and DC resistances will be equal. This will be true no matter what the inductance. Now, bring a piece of metal nearby. The AC resistance will increase, while the DC resistance is unaffected. How much the ACR increases will vary from metal to metal, and with the size and shape of the piece.

The excess resistance (ACR minus DCR) increases in direct proportion to eddy current loading, and it is this excess resistance that's such a good detector of shorted turns.

You can try this. Take a good pickup and measure its inductance and AC resistance at 1 KHz. Wind a few turns of heavy wire around the pickup and solder the ends together, forming a shorted little winding. The AC resistance will go up noticeably. If the shorted turns are near the magnet, the effect is even more pronounced.

[soundmasterg]

Ok, from what you're saying Joe, it sounds like if you're checking an unknown pickup, rather than something that you have in production where you have a record of what a good one should be, that it may not be as easy to tell if an AC resistance reading is out of line and indicating a partially shorted coil?

Since I'm not winding pickups myself yet, I won't have any baseline readings from anything, though when I do start, the info you've shared will help me get good coils. At this point I'm just checking various pickups that I have (lots of Duncan humbuckers, lots of Rickenbacker pickups, some Strat and Tele, some Duncan custom shop lipsticks, some Adeson Tri-Sonic air coils which are clones of the original Burns Tri-Sonic, etc) and comparing readings with the Extech and a DMM to see how they all stack up against each other. The Rickenbacker humbuckers had a bigger spread between DCR and ACR than some other pickups, but I guess it could be due to the metal in the pickup among other things, and maybe due to the samarium cobalt magnets too? The pickups work and sound fine, so I know with a reasonable certainty that those readings are accurate for them.

Wolfe, it sounds like you need a pickup tester similar to TV Jones's setup!

[Possum]

MWS

Unfortunately I only buy one spool at a time from those guys, I don't actually produce alot of pickups so he refuses to "cherry pick" as he puts it, for my needs. I don't use ohms per foot, I go by the O.D. and there's a production batch thats does some "magic" stuff for certain pickups I make. (Now, I never said "magic" I was channeling Don Mare, sorry....). If I was buying in quantity (or maybe had another sales rep?) I'm sure they'd pull what I need. My business is small and I intend to keep it that way, too many other business irons in the fire at this time in my life.....

[Joe Gwinn]

Ok, from what you're saying Joe, it sounds like if you're checking an unknown pickup, rather than something that you have in production where you have a record of what a good one should be, that it may not be as easy to tell if an AC resistance reading is out of line and indicating a partially shorted coil?

It could be pretty difficult, unless the reading was way out of line with all similar pickups as well. But you would also know that the output was low and it sounded dead.

Since I'm not winding pickups myself yet, I won't have any baseline readings from anything, though when I do start, the info you've shared will help me get good coils. At this point I'm just checking various pickups that I have (lots of Duncan humbuckers, lots of Rickenbacker pickups, some Strat and Tele, some Duncan custom shop lipsticks, some Adeson Tri-Sonic air coils which are clones of the original Burns Tri-Sonic, etc) and comparing readings with the Extech and a DMM to see how they all stack up against each other. The Rickenbacker humbuckers had a bigger spread between DCR and ACR than some other pickups, but I guess it could be due to the metal in the pickup among other things, and maybe due to the samarium cobalt magnets too? The pickups work and sound fine, so I know with a reasonable certainty that those readings are accurate for them.

That's the thing -- take a lot of measurements, and also listen to the pickups. And keep good notes.

As for samarium cobalt magnets, I don't know what their effect on eddy-current loss is. You can try it. Measure a coil with nothing near, then with the magnet as close as possible.

[jason lollar]

I have known wolfe for around ten years and weve been to each others shops and we always agree. I wouldnt have said anything but someone brought up my name and seeing how you can google this I dont want people assuming I approach R+D like wolfe does.
R+D is really important to me.
I want to know what my pickups sound like, I dont advocate having to listen to every stock coil design I make as it comes off the winder because I have a series of tests I do but I do want to know they are consistant with each other and I want to know what it is suppose to sound like in the first place.
We both started off as one man shops and he has an idea what my workload has been for ten years.
I cant imagine making a stock item for a year or two and not having a half an our minimum in that time to put one in a guitar and listen to it but everyone has thier way of doing things so he probably things I am obssesive
I do advocate listening and not relying purely on machinery to tell me what I make. Machines dont tell the whole story

[Wired]

Thanks to all for great responses.

I would love to hear more about eddy currents in pickups. I've a vague idea about heat losses and ineffeciencies in transformers etc (I believe laminated formers are used to help in this area) but I can't get my head around how they apply to guitar pickups. Chris Kinman even has a design with a laminated bobin for the hum cancelling coil. And lace's new pickups onlyhave a tiny coil that looks like a mini transformer at one end.

[Possum]

aaaaah grasshoppppper.....

Tape is actually the ONLY reliable way to stop shorts to the magnets. I've been taping for 3 years or so and never ever had one fail and never had a short to the magnets. You have to use the right tape and it takes practice.....

[kevinT]

You have to use the right tape and it takes practice.....

D. Schwab listed a few tapes that he uses.

Do you recommend a particular tape for this or is it top secret?

Just wondering.....do you leave a little extra tape beyond the edge of where the mags enter the flatwork so that when the wire wraps in the corners it sort of folds the edge of the tape where it lays flat on the flatwork so that it prevents the wire from sneaking behind the tape? ....I hope that made sense.