DC Variations That Are Really Frustrating!

[jrdamien]

So I've been winding pickups for awhile now. I'm in Minneapolis. The weather and temperature is all over the place. I mention this because it's the only thing I can think that's attributing to these maddening aberrations.

I wind a coil to 5400 turns of 42 single poly. Same wire I've been using for years. Same technique. Same speed. Same tension. Same relative tpl (I hand wind so tension and tpl are unknown but my technique hasn't changed any).

So 5400 turns regularly nets me 4.20 resistance for a humbuckering total of 8.4. I mean regularly. Like this is my go to wind.

The last 4 I've done came out as they should but then resistance has dropped on all of them to 8.13, 8.0, etc., all under 8.20.

Anyone care to suggest what might be happening? I'm so frustrated by it I'm not thinking straight.

[the great waldo]

Hi JrDamien

I get the same problem sometimes, wind a pickup at night dc reading well different next morning. I think temperature makes a big difference on the readings (try warming or cooling the pickups to see the change) also I have noticed quite a discrepancy with different rolls of wire.

Cheers

Andrew

[jrdamien]

Hi JrDamien

I get the same problem sometimes, wind a pickup at night dc reading well different next morning. I think temperature makes a big difference on the readings (try warming or cooling the pickups to see the change) also I have noticed quite a discrepancy with different rolls of wire.

Cheers

Andrew

Temp. for sure but can different roles of wire really account for this? This could be one explanation because all these are off of one new roll.

[the great waldo]

Hi JrDamian

More than likely the new roll has a slightly different dc resistance per meter. It's always good to measure the dc resistance of a few meters from a new roll and also half way down the roll as well as rolls can be inconsistent. I tend to wind by turns and nt resistance, although most customers ask for a particular resistance. It helps to explain to them the problems that can be encountered with wire.

Cheers

Andrew

[jrdamien]

Likewise I only wind by turns. But it was still enough of a difference and I'd never encountered it before...

So what accounts for varying resistance in 'just' wire?

[the great waldo]

Hi Jr

If you think about the thickness of the wire it's not hard for it to stretch or to have a slightly different diameter 10% on a piece of copper wire that is 0.063 mm in diameter isn't much in size. It's the same story with fretwire. When I started making guitars in the early 70's you could easily buy good quality nickel silver fretwire that would last for 10 years or more before needing a refret, now it's almost impossible to find hard Ns, fretwire only the stainless stuff seems near. I would imagine the reason for this is penny pinching (profit) So the manufacturers use soft material in order not to wear out the dies that the fretwire is pulled through and save money. That's how it is these days!

Cheers

Andrew

[Joe Gwinn]

If you think about the thickness of the wire it's not hard for it to stretch or to have a slightly different diameter 10% on a piece of copper wire that is 0.063 mm in diameter isn't much in size.

All true. Winding warms things up as well. The temperature coefficient of copper is significant, 0.0068 per degree C, so if one has a 10,000-ohm coil at 20 C, at 21 C, it will be 10000 + (0.0068)(10000)= 10,068 ohms.

If one lets the fresh-wound coil temperature stabilize, then the remaining variation will be due to stretching, tension, and manufacturing variation in the wire. Life is easier if one winds to a turns count, and ignores the resistance unless it is grossly off.

It's the same story with fretwire. When I started making guitars in the early 70's you could easily buy good quality nickel silver fretwire that would last for 10 years or more before needing a refret, now it's almost impossible to find hard Ns, fretwire only the stainless stuff seems near. I would imagine the reason for this is penny pinching (profit) So the manufacturers use soft material in order not to wear out the dies that the fretwire is pulled through and save money. That's how it is these days!

Given the cross-section shape of fretwire, it is rolled from round wire using steel rollers with shaped grooves. This process may need to be done in stages. The round wire feedstock is usually drawn. The act of rolling (or drawing for that matter) always work hardens the wire, so if it is soft, someone is intentionally annealing the wire after drawing/rolling, perhaps to make it easier to install in a slightly loose slot.

Nickel silver is a kind of brass. For comparison, one can order yellow brass wire and sheet in three hardness grades, being full hard, half hard, and soft, the difference being the degree of annealing during the manufacturing process.

[the great waldo]

Hi Joe

I'm sure fretwire manufacturer's aren't going out of their way to make life any easier for guitar makers. I did read somewhere a while ago that frets could be work hardened by burnishing after final polishing with a burnishing steel, any thoughts on that ?

Cheers

Andrew

[Joe Gwinn]

I'm sure fretwire manufacturer's aren't going out of their way to make life any easier for guitar makers. I did read somewhere a while ago that frets could be work hardened by burnishing after final polishing with a burnishing steel, any thoughts on that ?

It should work, but it may be a lot of work. Or, use stainless steel fretwire.

[David King]

When I get a low resistance reading my first instinct is to suspect an internal short. On some of my early winds I remember the resistance would jump around significantly and would always end up being higher after potting.
Look for possible abrasion of the insulation in your wire path and drop your tension to the lowest practical setting.

[jrdamien]

So let me ask you all this very basic but important question:

What's the sonic difference in .10 or .20 change in resistance? Say I have a humbucker that I know all other factors of (like the one's that are troubling me) but instead of the resistance being 8.4 it is 8.13 or 8.10 or... These don't seem like significant differences to me and I don't hear an audible difference, but what factor of resistance makes an audible change in a coil?

[David King]

That's a great question and I do not know the answer yet. Some of my coils were coming in 1kOhm or more on the low side and I expect that besides the lowered output the shorted sections of wire would potentially suck some treble away due to those pesky eddy currents. A tapped coil would be an easy way to estimate what the effects might be.

[salvarsan]

All true. Winding warms things up as well. The temperature coefficient of copper is significant, 0.0068 per degree C, so if one has a 10,000-ohm coil at 20 C, at 21 C, it will be 10000 + (0.0068)(10000)= 10,068 ohms.

Minor correction: copper's resistivity coefficient is 0.0068 ohm-meters but the resistance coefficient is 0.393%/C.

The 20 ->21C change produces a 39.3 ohm increase in a 10k coil.

In Fahrenheit degrees, a 4.6 degree change produces a 1% resistance change, 100 ohms in a 10k coil.

[Mick Bailey]

Hi Joe

I'm sure fretwire manufacturer's aren't going out of their way to make life any easier for guitar makers. I did read somewhere a while ago that frets could be work hardened by burnishing after final polishing with a burnishing steel, any thoughts on that ?

Cheers

Andrew

Burnishing does harden the surface very slightly and gives a much better finish in that it closes the minute scratches left after the final polish. It's a technique used a lot in clock making to improve bearing surfaces - a pivot file has two filing faces and two burnishing faces. There are also tapered burnishers to dress pivot holes. The value of burnishing frets depends on the particular alloy and existing state of work-hardening. It shouldn't be necessary if the wire is good to begin with.

[LtKojak]

So let me ask you all this very basic but important question:

What's the sonic difference in .10 or .20 change in resistance? Say I have a humbucker that I know all other factors of (like the one's that are troubling me) but instead of the resistance being 8.4 it is 8.13 or 8.10 or... These don't seem like significant differences to me and I don't hear an audible difference, but what factor of resistance makes an audible change in a coil?

You just have to forget to think about DC values.

The smallest audible difference I've registered with people with "golden ears" is 2%. We're talking TURNS here, mind you.

HTH,