Winds To Resistance Formula?

[automan]

Hi guys. I am new to the pickup building game. I am curious if there is a standard formula where x winds of y wire = z resistance. For example, does 7000 winds of 42 AWG wire always = 8k? Not that it would = 8k, but does it always equal some amount? Do I need to just wind 1000 winds of each wire I use, then check the ohms. Then take that ratio and use it to figure out the amount of winds I need to get desired resistance? I imagine I would need to do this with each magnet type I want to use and make sure they are fully charged before running my tests.

What do you guys with way more experience think?

[belwar]

The ammount of tension you put on the wire changes the resistance slight, but if you want to have a rough estimte then use Zieglers Calculator

http://pickups.myonlinesite.com/serial.php

I had to tweak the resistance slightly as I wind really tightly but after I did it worked perfectly.

[David Schwab]

Don't worry about the resistance at all. I just wind by turn count. I check the resistance when I'm done to make sure there wasn't a short, but I never wind to a certain resistance.

The resistance is a product of the length of the coil and the diameter of the wire. So you can do 5,000 turns with different bobbins and wire gauge and get different readings. Higher tension stretches the wire which then reduces the diameter.

[Mark Hammer]

The resistance does not give the tone or output. The number of turns, wire gauge, insulation thickness, topography of the coil, tension, and magnets do. Yes, there are certain "benefits" to be had by what comes along for the ride when the coil resistance is lower or higher, but quite frankly many of those can evaporate in a cloud of smoke when:

a) the volume control is turned down a bit,
b) the pickups are adjusted wrong
c) the string gauge is changed
d) the winding tension and/or scatter is different
e) the magnets are different
f) the cable from guitar to next stage is longer or shorter

and you can stick in g, h, i, j, k, l, etc in there.

That being said, magnet wire usually does come with specs for how many ohms per line foot. If you were just unspooling one long wire you would be able to easily tell the resistance by the length of how much you had unspooled. Unfortunately, because the outside diameter of the coil is a constantly changing thing (as the coil starts to build up in thickness), the length of a single turn at the start is not the same as the length/circumference of a turn near the end. As you can well imagine, that makes calculating resistance purely on the basis of number of turns a little tricky, and also a little different depending on the shape of the bobbin/coilform. On a tall thin coilform, last turns may be very close in DC resistance to first turns, but on something flat and wide like a Jazzmaster, they may be quite different.

That being said, many repair-bench people will often go with a rule of thumb of just a tad over 1-ohm per turn when you're at the outside of the coil. That assumes one is using a fairly standard-dimension coilform. One would not use such a rule of thumb if dealing with, say, a dual-rail coil or an 8-string lap-steel coil.

[automan]

Thanks for the answers, guys! Let me state some of my assumptions on how certain factors affect the tone and let me know if I'm on the right track. It seems like the thinner the insulation, the more microcracks in that insulation would turn the coil into a capacitor rather than an inductor. I have read here that this increases the high end tone. I also assume that tighter coils would increase this capacitance since it would stretch the wire and insulation.

What I dont understand is how the shape of a bobbin can affect the tone. Say I take a P90 bobbin and wind it about half way to the edge of the bobbin with 5000 winds with 43 AWG plain enamel. I have seen threads here (I have been lurking for several months) that would indicate that if I trimmed off the part of the bobbin that wasnt used, the pickup would sound different because the shape of the bobbin has changed. I just cant wrap my head around how that would be possible. But then again, I dont understand just yet why people use smaller gage wire other than to fit more wraps on a bobbin.

Please forgive and noobness on my part. I am just getting into this and trying to soak up as much as I can.

BTW, one more question. If I wound a two 3 pole bobbin and put them side by side in a strat single coil cover, if the poles were flipped and reverse would on one of them, would it still be humbucking? I assume it would, but dont yet know how a north up would react directly next to a south up in such close proximity.

[Mark Hammer]

No problem. We were all noobs at one time.

Think of it this way. How much influence does a magnet have on something farther away?

Think of it this way too: Does the shape and size of an antenna affect the reception in terms of what it picks up relative to other things?

If what comes out of the coil is a function of what moment to moment fluctuations in the magnetic field do to the coil, then it stands to reason that if one has some turns relatively farther away from the magnet (by virtue of the bobbin being flat and wide), the magnet will have a different sort of influence on those turns.

As well, the coil is an inductor, and the inductance is a function of the gauge, # turns, and spacing of those turns. Much like the inductor coils you'd find in a classic transistor radio, change the shape/parameters of the coil and you pick up different things (more specifically, you are more sensitive to some parts of the audio spectrum than others).

Starting to gel?

[chevalij]

What I dont understand is how the shape of a bobbin can affect the tone. Say I take a P90 bobbin and wind it about half way to the edge of the bobbin with 5000 winds with 43 AWG plain enamel. I have seen threads here (I have been lurking for several months) that would indicate that if I trimmed off the part of the bobbin that wasnt used, the pickup would sound different because the shape of the bobbin has changed. .

I think you've got this part confused. When people talk about the shape of the bobbin, they're basically saying the shape of the coil. If the bobbins is short and wide, the coil will be short and wide etc.

[automan]

AHH :facepalm: I get you.

If I made a 2 string stick, would each pole individually one north up and one south up with the south reverse would and put them directly beside each other, would that work as a hum bucker? Would it kill the field to have them so close together with opposite poles up?

[David Schwab]

AHH :facepalm: I get you.

If I made a 2 string stick, would each pole individually one north up and one south up with the south reverse would and put them directly beside each other, would that work as a hum bucker? Would it kill the field to have them so close together with opposite poles up?

Yes, it would work like a humbucker. You may get some signal drop out as you bend a string from one coils to the other.

You can also use the same polarity magnets, and have one coil out-of-phase, but that wont mix well with other pickups, so all the pickups would have to be the same. That might help with the drop out in the middle, but I don't know, because I haven't tried it.

[automan]

Does having reversed magnets and wired in phase also act as a humbucker?

[David Schwab]

Does having reversed magnets and wired in phase also act as a humbucker?

The coils have to be out of phase to cancel out the common mode signals.

With a regular guitar humbucker, the reversed magnets puts each coil out-of-phase with the strings, and then the reverse phased coils puts the strings' signal back in-phase, but keeps the hum out-of-phase, so it cancels out when you sum the two signals.

[Zhangliqun]

Hi guys. I am new to the pickup building game. I am curious if there is a standard formula where x winds of y wire = z resistance. For example, does 7000 winds of 42 AWG wire always = 8k?

Keep in mind also that the outer turns will be longer than the inner turns so there is no x-ohms per turn formula. This is especially true with P90's because the coil is so wide.

That said, I'm one of those Philistines who goes by DCR rather than turn count.

[RedHouse]

Wire does have an Ohms-per-length (ft/yard/mile etc) value which can be calculated but the trick is ...having a formula that takes onto account the varying length-per-turn because the bobbin (as was said prevoiusly) ...varies as the bobbin get filled.

IIRC, one of our members here has a calculator page that can achieve a decent accuracy, though I didn't save any link to post.

IMHO...I concur with DavidS, wind to a turns count, checking Ohms more as a control variable, develop your winding as a pattern-with-turns-count then you will make more consistant pickups and be able to reproduce good winds more easily when you find them. If you sweat the DCR you can be all over the place because it will vary with ambient temperature, and specially when you wind the coil it's DCR isn't the DCR you will get after the coil rests a while.

[salvarsan]

Wire does have an Ohms-per-length (ft/yard/mile etc) value which can be calculated but the trick is ... having a formula that takes onto account the varying length-per-turn because the bobbin (as was said prevoiusly) ...varies as the bobbin get filled.

It's not a trick. It's tedious math. (heh)

There is an equally good estimator using the average winding length.

I say equally good because all the estimations need to assume a regular
winding pattern and fill factor. *Still, when you remember that magnet
wire specs can vary more than +/-5%, any of these calculators can
make a good estimate of windings count from DC resistance and coil
dimensions.

IIRC, one of our members here has a calculator page that can achieve a decent accuracy, though I didn't save any link to post.

Hmm.


Maybe you mean this one:
Coil Estimator


-drh