multi-gauge wire humbucker question

[belwar]

I'm trying to remember the answer to this question, but for the life of me I cant remember it...

If you were making a basic side-by-side coil humbucker with two different gauge wires (i.e. slug 43awg, and screw 42awg) what gives you the maximum hum cancelling? Is it equal number of turns on each coil or equal DC Res?

I remember dimarzio used to have a patent on multigauge pickups, but i think its expired now. Did anyone ever get a nasty letter from them about it?

bel

[David King]

Equal turns will get you very close but it's really turns * area and the area of a 43 coil might average ever so slightly smaller than a 42 coil.

[belwar]

this may sound stupid, but can you define "area"? Do you mean the total volume taken up by the wire? Total surface area on the wire? How would I even begin to calculate something like that?

[David King]

Mmm, I would define it as the area that fits inside the coil from what I understand. So presumably you would measure the area of the middle-most layer of wire in the coil. If your coil "A" starts being 1/4" x 2" and finishes at 1/2" x 2.25" your average coil size would be 3/8" x 2.125". The "A" coil area would be 0.797" multiply that by 5000 turns to get coil x turns of 3985.
If you know that your coil "B" is 43 awg and is say 5% smaller than coil "A" you might want to add 5% more turns to coil "B" or 5500 turns.

[belwar]

Hmm interesting. Seems totally unscientific. Ill try it. Hey so you remember the name of that crazy expensive solder we were talking about recently? I will cant find the discussion for the life of me

[big_teee]

I was of the understanding that equal amount of turns of each would give best Hum Canceling.
I make one all the time, full screw coil with 42 SPN, and fairly full slug coil of 43 SPN.
It hums a little but not bad. I'm sure it would be quiter if both coils were equal.
Makes a good hot pickup.
T

[David King]

Hmm interesting. Seems totally unscientific. Ill try it. Hey so you remember the name of that crazy expensive solder we were talking about recently? I will cant find the discussion for the life of me

The wonder solder? It should pop up in a search, I scabbed it onto some totally unrelated discussion. God knows what but search anyway.

[copperheadroads]

Is it this thread ?
http://music-electronics-forum.com/t24670/

[Mike Sulzer]

The law of induction works on the time varying magnetic flux for any closed path. That is, what matters in effect is the time varying flux through each turn, with all of them added up. So, if all the turns had the same amount of flux passing through them, it would just be the total number of turns that counts. And that's not such a bad approximation for a pickup with cores because the cores concentrate the flux more to the middle of the coil, and the varying size of the turns is less important than it might be.

(If the flux is constant throughout the loops, the area of each loop times the number of loops is very accurate. This is a very goo approximation in some cases)

(To be very accurate, you integrate the spatial varying time varying flux over each loop and add the results. We do not have accurate enough measurements or predictions to do it exactly.)

[fieldwrangler]

So, do we think that the quietest practical (although not particularly appealing) setup in a situation with two different wire gauges (same # of turns) would be to use the same core material in both coils and then add a small resistor to the heavier gauge coil to match resistance?

Well... after running out of the house immediately after posting this it occurred to me that this kindof kluge would only apply to the parallel configuration, so... in the immortal words of Gilda Radnor - "Never Mind!"

Bob Palmieri

[David Schwab]

I do equal number of turns. You can also alter that for different tones.

[Alan0354]

number of turns govern the inductance, not the gauge of the wire. You need to match the number of turns as long as the two bobbin is exactly the same. If the cross-sectional area in the middle of the coils are different, then all bets are off. Good example is the Suhr noise cancelling coil. It has much less turns but with a big loop, it can cancel noise with much fewer turns because the center area is much bigger and can sense much more magnetic flux.

[belwar]

Ok now that makes sense! Thanks. Your suhr reference was perfect.

[Joe Gwinn]

I was of the understanding that equal amount of turns of each would give best Hum Canceling.

It is not the number of turns, it's the area-turns count. That is the basic rule, absent any nearby iron. The "area" is that bounded by the turn in question. In practice, we use the average area of turns, and multiply by the turns count, and it's close enough.

Note that the inductance is not the issue, it's the area-turns product, which controls the voltage generated by a coil immersed is a uniform changing magnetic field. The difference is that the inductance varies as the square of the turns count, while the area-turns count varies linearly with the turns count.

[big_teee]

It is not the number of turns, it's the area-turns count. That is the basic rule, absent any nearby iron. The "area" is that bounded by the turn in question. In practice, we use the average area of turns, and multiply by the turns count, and it's close enough.

Note that the inductance is not the issue, it's the area-turns product, which controls the voltage generated by a coil immersed is a uniform changing magnetic field. The difference is that the inductance varies as the square of the turns count, while the area-turns count varies linearly with the turns count.

If you had 5000 turns 42 and 5000 turns 43 is that equal in Hum reduction?
I usually do highly mismatched coils and hope for the best.
T