DCR & Indcutance on wind of same turns

[kayakerca]

I need some more education here. . .

I would 2 Strat style single coils, both to 8,100 turns. Only two differences. First, the wind was the wire tension. On the first I set the pull force created by the felt tensioner to ~ 35 grams and on the second ~ 40 grams. Second, the first wind was done with a round traverser cam producing wire buildup at both ends of the traverse and the second wind was done with a heart shaped cam with has a slight build up in the centre area of the traverse.

Here is how the coils measured after the fact:

- #1 - DCR = 6.10K; Inductance = 2.42
- #2 - DCR = 5.96K; Inductance = 2.44

I would have thought that if anything, a tighter wind would have the potential of increasing the resistance through pull force stretching and resultant thinning of the wire.

Any thoughts on what might cause the difference in the DCR would be much appreciated. Also didn't think where the wire built up would affect the DCR.

Just trying to learn. . .

[big_teee]

Hi Jim:
I've been following your winding build thread.
Very interesting, and can tell you have enjoyed the journey.
Just a guess here, on the difference in DCR of the two coils.
The first with less tension, would probably have more feet of total wire, for the same turns.
The second would be tighter, so maybe just a little smaller amount of wire.
It would be a tighter coil, and perhaps why the inductance is higher.
So next question, is how do they sound?
That is what is important to me.
Also, don't forget the tonal effects of bobbin height and coil diameter.
look forward to more of your winding installments.
T

[bbsailor]

I need some more education here. . .

I would 2 Strat style single coils, both to 8,100 turns. Only two differences. First, the wind was the wire tension. On the first I set the pull force created by the felt tensioner to ~ 35 grams and on the second ~ 40 grams. Second, the first wind was done with a round traverser cam producing wire buildup at both ends of the traverse and the second wind was done with a heart shaped cam with has a slight build up in the centre area of the traverse.

Here is how the coils measured after the fact:

- #1 - DCR = 6.10K; Inductance = 2.42
- #2 - DCR = 5.96K; Inductance = 2.44

I would have thought that if anything, a tighter wind would have the potential of increasing the resistance through pull force stretching and resultant thinning of the wire.

Any thoughts on what might cause the difference in the DCR would be much appreciated. Also didn't think where the wire built up would affect the DCR.

Just trying to learn. . .

Jim,

See this link for more discussion http://music-electronics-forum.com/t9362/ .

Consider that the maximum amount or wire or maximum copper is that which fills the wire window of the pickup bobbin with the least amount of air. The outside diameter of the wire includes the wire insulation thickness. The maximum turns per layer assumes a perfectly wound coil with the wire turns laying next to each other and each layer stacked the same way, sometimes called "machine winding". Hand winding tends to spread the winding and add a little more air between the turns and also between the layers. More air also means less wire, less capacitance between turns and accounts for a difference in tone, resistance, coil quality factor (called coil Q) and inductance.

Winding calculations are just an estimate of the amount of wire that will fit in the wire window with fill factors accounting for the variables introduced by the winding techniques mentioned above.

Joseph Rogowski

[J M Fahey]

Dear friends.
First and foremost, let's put our feet firmly on the ground, and call both coils *exactly the same* , the difference is not significant in the real world.
We are with exactly the same turns, 2% difference in DCR, which anyway is the least important parameter, and 0.8% difference in inductance, which would be the most significative one. (and which confirms they are exactly the same).
Both "errors" are smaller than measurement apparatus error.
Finding a difference in sound will owe more to what is expected than to any *real* difference.
I'm sure the difference magnetism passing through them, not forgetting mechanical position errors, will be much larger than that.
Let alone pickup-to-string distance.

Note: I doubt even more, that wire diameter and enamel thickness are that consistent.

[kayakerca]

Hi Jim:
I've been following your winding build thread.
Very interesting, and can tell you have enjoyed the journey.
Just a guess here, on the difference in DCR of the two coils.
The first with less tension, would probably have more feet of total wire, for the same turns.
The second would be tighter, so maybe just a little smaller amount of wire.
It would be a tighter coil, and perhaps why the inductance is higher.
So next question, is how do they sound?
That is what is important to me.
Also, don't forget the tonal effects of bobbin height and coil diameter.
look forward to more of your winding installments.
T

Hi Terry. Haven't talked with you for a bit now. You're right, I really like this journey. This is all very cool stuff. And you gotta be doing it for the love of the game 'cause it ain't cheap to get in! :-)

I like the "more wire" on the first coil thought a lot. It is a lot looser than the second, even visually. I should be able to put my first set in a Strat body this weekend. Just setting up to pot them now!

Update----------

Finished the potting. Put the 4 of them in together for just under 2 minutes (probably a little too long). Looked like a Jacuzzi in that little crock pot for the first minute and a half! Might have been better to do them one at a time which would allow more time to clean off the excess wax. Trial and error, trial and error. :-)

[kayakerca]

Thanks Joseph and Juan for your comments. I like to understand how things are affected, one by the other. Your points are very helpful to me and how I look at things going forward.

[David Schwab]

Put the 4 of them in together for just under 2 minutes (probably a little too long).

That's not too long. I leave my coils in for 10 minutes.

[big_teee]

That's not too long. I leave my coils in for 10 minutes.

Sometimes I get distracted, and leave them 20-30 minutes. lol
He is doing his with vacuum, so I guess he can get by with less time.
T

[SonnyW]

That's not too long. I leave my coils in for 10 minutes.

I always pot mine for 20 minutes, set on a timer. So far never had any issues. I usually have my pot set for about 150 F. Maybe a little overkill, but I don't think that's too long at all. The pickup needs to come completely up to temperature for the wax to soak in thoroughly. I don't use a vacuum on them though.

[kayakerca]

Sometimes I get distracted, and leave them 20-30 minutes. lol
He is doing his with vacuum, so I guess he can get by with less time.
T

I had a look at the Seymour Duncan factory tour video (link can be found in big_teee's resource thread). At about 3:40 into the third video they show them vacuum potting. The technician runs the pump down to about 30" of vacuum and is letting air back in by about 30 seconds after the start and the pickups are coming out of the wax at about the 1:30 minute point. Most of the time from the 30 second point to the 1:30 point is wiping the wax off the leads and separating them to allow her to life each of the 3 blocks of p/u's out one at a time. I also remember reading in a couple of Jason Lollar articles that he vacuum pots from 30 seconds to 2 minutes max (if my memory is correct). Only wish it had a clear so so you could see the vulcano activity created by the vacuum pump drawing the out of that many pickups at one time. The next time I pot, I'll try and see if I can take a little video of the violent eruption when you turn the vacuum pump on.

[J M Fahey]

Nice potting setup.
What mix do you fill it with?
I don't make pickups but sometimes pot some belonging to customers if they are squealing too much with one of my high-gain amps.
Don't have a vacuum pump (now you gave me ideas) so I leave them in around 20 minutes.
I see some odd bubble until almost 10 minutes, and double that for safety.
Do you really pot in under 2 minutes?
Well, if coils only, maybe it's possible, much lower thermal mass.
Vacuum or not I'm worried about cold pickup parts hardening or thickening wax too much for good impregnation.
Note: I pot the full pickup, magnets and all, only take apart covers and spring, etc, of course.

[kayakerca]

Nice potting setup.
What mix do you fill it with?
I don't make pickups but sometimes pot some belonging to customers if they are squealing too much with one of my high-gain amps.
Don't have a vacuum pump (now you gave me ideas) so I leave them in around 20 minutes.
I see some odd bubble until almost 10 minutes, and double that for safety.
Do you really pot in under 2 minutes?
Well, if coils only, maybe it's possible, much lower thermal mass.
Vacuum or not I'm worried about cold pickup parts hardening or thickening wax too much for good impregnation.
Note: I pot the full pickup, magnets and all, only take apart covers and spring, etc, of course.

I mixed the was 80% paraffin wax from the grocery store and 20% beeswax. You can buy a cheap single stage vacuum pump at a place like Harbor Freight for $90, so I thought what the heck.

These were my first pickups and I really was just doing a dry run and just trying to figure out how things go a little better. Next set I will preheat in the oven before potting. But seriously on the vacuum potting, it's like a Jacuzzi running at full speed. It wasn't some bubbles coming out of the coils, it was this violent volcanic eruption for about 30 - 40 seconds and then it started to settle back to the minute and a half point. It was definitely pretty cool to watch.

[jason lollar]

I too would consider pickups with those numbers to be matched coils if the turn count and traverse per layer is the same- youll never get closer than that consistantly!
DC resistance can go all over for various reasons- heries will stay closer to the same number if you have all the other variables under control