prototype testing of hum canceling P-90 design

[big_teee]

You guys take all this stuff Way to serious.
Lighten up and have Fun!
Terry

[David Schwab]

You guys take all this stuff Way to serious.
Lighten up and have Fun!
Terry

I think most of us ARE having fun.

[big_teee]

I think most of us ARE having fun.

You Could Have FooLed Me!
T

[Steve Conner]

I'm an engineer, what is this "fun" of which you speak?

Mike seemed to say that the sensitivity of a coil to hum depends only on the turn count, loop area etc. I (and David) pointed out that it also depends on how much iron you put in it, as the iron concentrates the field through the coil.

I expressed this as "sensitivity and inductance are the same thing", as they are both functions of exactly the same variables: turn count, loop area, amount and permeability of iron. This is probably wrong, as you could make two inductors, one with a rod core and the other with a toroid core. They could have the same inductance yet the rod would be much more sensitive to hum, as the toroid has a closed magnetic circuit.

The most important point is that you can make two coils of quite different sizes, shapes, turn counts, and still have them buck hum, by balancing the variables in the sensitivity equation. Probably best done by trial and error.

[big_teee]

I'm an engineer, what is this "fun" of which you speak?

Does that mean you get to blow the whistle when you herd the train down the tracks?
I didn't realise that Calling each other Names was fun to an Engineer, but I'm not an engineer!
Have fun guys, go back to the name calling if you like.
Rock On!
Terry

[David Schwab]

I'm an engineer, what is this "fun" of which you speak?

Mike seemed to say that the sensitivity of a coil to hum depends only on the turn count, loop area etc. I (and David) pointed out that it also depends on how much iron you put in it, as the iron concentrates the field through the coil.

I expressed this as "sensitivity and inductance are the same thing", as they are both functions of exactly the same variables: turn count, loop area, amount and permeability of iron. This is probably wrong, as you could make two inductors, one with a rod core and the other with a toroid core. They could have the same inductance yet the rod would be much more sensitive to hum, as the toroid has a closed magnetic circuit.

The most important point is that you can make two coils of quite different sizes, shapes, turn counts, and still have them buck hum, by balancing the variables in the sensitivity equation. Probably best done by trial and error.

You can see if you wind some pickup coils, that pickups with low inductance cores, like ceramic magnets, or air, have less output than pickups with steel cores charged by the same magnets and wound the same. So you have to balance the two when you are designing pickups.

So it's not hard too see that the bottom smaller coil with more steel is closer matched to the top larger coil with less steel, and also with a shield. I think it was Joe had pointed out once that you don't need total noise cancelation to make the pickup sound quiet.

The two times I tried out those DiMarzio stacks, I found them to be very quiet. They were on a guitar with a humbucker at the bridge, and I detected no extra noise switching from each pickup, and while having them run through a high gain patch. The output was good also.

Here's a quick recording I did with a customer's guitar I assembled. It's an old Kramer Nightswan body fitted with a Gibson scale bolt on neck.

All the guitar tracks are the Virtual Vintage Solo Pro at the neck position. It's normally a bridge pickup, but he had a Duncan Invader at the bridge.

Bass Head

[Mike Sulzer]

So it's not hard too see that the bottom smaller coil with more steel is closer matched to the top larger coil with less steel, and also with a shield.

I think what Joe said about the shield is the important thing. Since inductance goes down so fast with decreasing turns count, I think the extra steel is not is not enough to make the sensitivity the same as the top coil without the shield. The shield must reduce the sensitivity of the top coil to hum without affecting the sensitivity to string vibration so much. I think this is possible because the hum source is not too close, so its field strength is not changing much over the length of the coil. The field of the string vibration decreases a lot over the depth of the pickup, and therefore the sensitivity of the top coil is not affected a lot by a shield that comes part way up around the sides.

[David Schwab]

I think what Joe said about the shield is the important thing. Since inductance goes down so fast with decreasing turns count, I think the extra steel is not is not enough to make the sensitivity the same as the top coil without the shield. The shield must reduce the sensitivity of the top coil to hum without affecting the sensitivity to string vibration so much. I think this is possible because the hum source is not too close, so its field strength is not changing much over the length of the coil. The field of the string vibration decreases a lot over the depth of the pickup, and therefore the sensitivity of the top coil is not affected a lot by a shield that comes part way up around the sides.

I agree. For a hum bucker, you want both coils to pick up hum. So the top shield partially reduces the noise in the top coil. It's also a steel shield, and is grounded, so it takes care of both magnetic and electric field noise, unlike a copper shield.

So the bottom is not as sensitive as a matched coil, but then the top is not as sensitive either.

I said this back in post #45:

You have to remember that the top coil is shielded. It's a magnetic shield, and it's also grounded. The bottom coil is not grounded or shielded. Therefore the top coil is already less sensitive to noise. It's all a balancing act, and it works very well.