Newly wound pickup coil reading differently after "cooling down"

[Brian W.]

Been noticing it's not a good idea to take an ohm reading from a newly wound coil. It's always noticeably higher than after it's been cooling down for awhile. The coil also seems to tighten up on the bobbin after cooling down, too. I wind by hand [with a sewing machine] so the heat from my hands seems to heat the coil whist winding.

[copperheadroads]

If you are soldering the lead wires before taking a dcr reading ,the heat from the solder gun is what usually creates the higher dcr , if you sand the insulation off & take a reading before you solder you should have a lower & more accurate reading .

[Leo_Gnardo]

What you've observed has to do with the temperature coefficient of conductivity of your wire. Copper is approximately 0.4% per degree (Centigrade or Kelvin). I've noticed differences in coil resistance measurements when measured on my workbench in cold winter ambient temp compared to hot summer temps.

A couple of my customers think pickup coil resistance is an important factor in the sound of their pickups, and this difference in measurements drives 'em crazy. "What's wrong with my pickups ?!?!?" "Aw, they're cold. Or hot. Do they sound good? Get over it."

Wiki here: https://en.wikipedia.org/wiki/Electr...d_conductivity

Go about halfway down the page and you'll find a handy chart of coefficients for lots of popular metals, alloys, and other materials. Copper is second & third on the list, plain & annealed, not much difference.

Also, as we know metal expands when hot, shrinks when cooled. This explains the tightening of your coils as they cool.

[Brian W.]

A few months ago I actually thought my coils were being wound too loose so I put more tension on the wire.......and the wire started breaking. After a couple of days of this I took a close look at the pickups and noticed how much tighter the coils were after they had sat around for awhile. Lesson learned.... it had to be the heat.

[mozz]

As soon as you are done winding the reading will be higher. Let it sit for a hour or two. I have never seen soldering for 1second to bring the reading up.

[Brian W.]

As soon as you are done winding the reading will be higher. Let it sit for a hour or two. I have never seen soldering for 1second to bring the reading up.

There were a couple of times that I took a reading too soon and clipped the wire before it had settled in. A couple hours later I'm left with a pickup with a lower res. then planned.

[Helmholtz]

There were a couple of times that I took a reading too soon and clipped the wire before it had settled in. A couple hours later I'm left with a pickup with a lower res. then planned.

It's number of turns that defines output and frequency response for a given PU design - not exact resistance. Otherwise PU sound would change with ambient temperature.

[Brian W.]

It's number of turns that defines output and frequency response for a given PU design - not exact resistance. Otherwise PU sound would change with ambient temperature.

Understood.
There are plenty of occasions that the temperature & humidity on a particular day would affect the overall sound of the guitar. Cold rainy days sound one way and real hot days sound another. After living in Austin for awhile I was continually frustrated with the change in the guitars' sound from fluctuations in temperature . Of course, the amps must be taken into the equation. Hot temps seemed to sound "better" to me [fuller overall tonality, thicker tones..etc] while real cold made everything go thin and wimpy. This was also evident with acoustic guitars, too. Getting balances in the mix when in a recording studio or on a live stage became a chore.

[big_teee]

Wax potting is a great stabilizer.
Once potted the tension is no longer a factor.
Especially recommend potting on Fender style single coils.
Potting not only makes them less microphonic, it makes the coils more stable.
Keep in mind if you check the DCR after taking them out of the wax pot the DCR will be sky high, until they cool off.
I highly recommend potting pickups.
GL,
T

[Helmholtz]

Understood.
There are plenty of occasions that the temperature & humidity on a particular day would affect the overall sound of the guitar. Cold rainy days sound one way and real hot days sound another. After living in Austin for awhile I was continually frustrated with the change in the guitars' sound from fluctuations in temperature . Of course, the amps must be taken into the equation. Hot temps seemed to sound "better" to me [fuller overall tonality, thicker tones..etc] while real cold made everything go thin and wimpy. This was also evident with acoustic guitars, too. Getting balances in the mix when in a recording studio or on a live stage became a chore.

Yes, temperature & humidity influence musical instruments via contraction and expansion (think truss rod tension) as well as electronics, speaker cones and probably the musician himself.
I even noticed that the weight of my guitars drops from summer to winter by around 40g, because of lowered wood moisture content.

But the influence on PU performance I consider negligible.
To study the effect of a somewhat increased DCR, wire a resistor of e.g. 470R in series with the PU and see, if/how sound changes.

[Brian W.]

Wax potting is a great stabilizer.
Once potted the tension is no longer a factor.
Especially recommend potting on Fender style single coils.
Potting not only makes them less microphonic, it makes the coils more stable.
Keep in mind if you check the DCR after taking them out of the wax pot the DCR will be sky high, until they cool off.
I highly recommend potting pickups.
GL,
T

Yup, I usually pot the coils. Hmm.....why .wouldn't wax potting the coil permanently preserve it in whatever
"stretched" state it was in when the hot wax stabilized it?

[Brian W.]

Yes, temperature & humidity influence musical instruments via contraction and expansion (think truss rod tension) as well as electronics, speaker cones and probably the musician himself.
I even noticed that the weight of my guitars drops from summer to winter by around 40g, because of lowered wood moisture content.

But the influence on PU performance I consider negligible.
To study the effect of a somewhat increased DCR, wire a resistor of e.g. 470R in series with the PU and see, if/how sound changes.

I have done that and noticed a slight difference.
I think anything that heats the pickup coil [and expanding it ] will affect the sound a little.

[Helmholtz]

Yup, I usually pot the coils. Hmm.....why .wouldn't wax potting the coil permanently preserve it in whatever
"stretched" state it was in when the hot wax stabilized it?

Wax/paraffin shrinks when it solidifies and thus compresses the coil. Shrinkage can be reduced by mixing bees wax (20% IIRC) into pure paraffin, but this increases the melting point by 10..15°C. And increased potting temperature might deform plastic bobbins. Also the paraffin somewhat increases the PU's capacitance depending on coil penetration depth. Not saying that it matters, though.

[big_teee]

Before we go into great length about wax potting, there are countless threads and polls here on the MEF about wax potting.
A little research will save a lot of repeated info and posts about wax potting.
https://music-electronics-forum.com/...obbyist/37703-
GL,
T

[Leo_Gnardo]

Understood.
There are plenty of occasions that the temperature & humidity on a particular day would affect the overall sound of the guitar. Cold rainy days sound one way and real hot days sound another. After living in Austin for awhile I was continually frustrated with the change in the guitars' sound from fluctuations in temperature . Of course, the amps must be taken into the equation. Hot temps seemed to sound "better" to me [fuller overall tonality, thicker tones..etc] while real cold made everything go thin and wimpy. This was also evident with acoustic guitars, too. Getting balances in the mix when in a recording studio or on a live stage became a chore.

Let's not leave out the effects of humidity on - paper - speaker cones.

Also, for those who play at altitudes, say Red Rocks up the hill a ways from Denver, air pressure is about 20% lower up there. Fewer molecules per cubic centimeter, foot, furlong, whatever. Speakers sound different. It affects your eardrums too. And you gotta adjust your carburetor. And boil your spaghetti longer. And breathe deeper to get the oxygen you need.