Whats going on here.. Inductance / Zero Phase Resonance Question

[belwar]

Ok,

I've been taking some measurements of a Bass Pickup this morning. The pickup is an 8 coil humbucker. The top row of 4 coils are in series together, as is the bottom, then the two sets are put together in series . Coming out of the pickup is 5 wires..

Wire1 : Start of Coil Set 1
Wire2 : End of Coil Set 1
Wire3 : Start of Coil Set 2
Wire4 : End of Coil Set 2
Wire5 : Common ground wire (grounding the poles, keeper, and magnets)

I used the Extech LCR meter to measure inductance and Q and the two frequencies, using the serial setting. First off, considering the pickup has ceramic magnets, the pickup has a very high inductance! .. Second off, the inductance changed quite dramatically between the two frequencies, AND changed again when I added the common ground into the mix! Also, I measured the resonance frequency using both the Peak response and zero phase method and obtained dramatically different results, and different results again when I add in the common ground!

So my questions are as follows:

1) Why the dramatic change in inductance between the two frequencies?
2) Why does adding the common ground change the results for both inductance, and resonance?
3) Which method of the resonance frequency measurement is providing me with the correct number?

Here are the direct readings of the scope, DMM, and LCR meter.. (Signifigant digits not calculated)

Inductance @ 120hz,Coils Only, No Common ground:18.008 Henries
Inductance @ 1000hz, Coils Only, No Common ground: 15.303 Henries
Inductance @ 120hz, Coils + Common Ground: 17.99 Henries
Inductance @ 1000hz, Coils + Common Ground: 16.132 Henries
Q @ 120hz, Coils Only, No Common ground: 0.6944
Q @ 1000hz, Coils Only, No Common ground:2.425
Q @ 120hz, Coils + Common Ground: 0.6891
Q @ 1000hz, Coils + Common Ground: 2.212
Zero Phase Resonance Freq without common ground: 3010 hz
Zero Phase Resonance Freq with common ground: 2400 hz
Peak Response Resonance Freq without common ground: 4552 hz
Peak Response Resonance Freq with common ground: 2429 hz

Bel,

EDIT: All resonance measurements done with a 1 Megaohm Resistor between the signal generator and pickup.

[frankfalbo]

Because you didn't put in the crystals.

[belwar]

I *so* need to see that movie.

Dont you have non-boutique pickups to make?

[salvarsan]

I used the Extech LCR meter to measure inductance and Q and the two frequencies, using the serial setting.

Try the PARallel setting on the Extech.


The CircuitGear 101 network analysis mode will give you the impedance plot and phase shift directly. *If there is a resonance peak, then you will see zero phase there too.



Drive the pickup through a SERIES 1.5k resistor.
Hook the A channel across the resistor+pickup.
Hook the B channel across the pickup.
Go to the network analyzer menu.
Set the frequency range at 100Hz to 10kHz.
Banzai!


-drh

[David Schwab]

I've been taking some measurements of a Bass Pickup this morning.

So I take it you got the pickup?

[belwar]

So I take it you got the pickup?

I sure did! I figured it was best to get the pickup measured as much as possible before cutting any of the metal.

Anything you see of interest here?

bel

[David Schwab]

Anything you see of interest here?

Yeah, the time machine! 1982 would be fun....

Oh, the pickup...

Was that the inductance for the row of coils in series? Or a single coil?

[belwar]

... actually my avatar refers to time travel, so there you go! :>

per salvarsanarium (or however they heck you type that)...


Here are the Parrallel measurements
Inductance @ 120hz,Coils Only, No Common ground:56.10 Henries
Inductance @ 1000hz, Coils Only, No Common ground: 17.871 Henries
Inductance @ 120hz, Coils + Common Ground: 56.34 Henries
Inductance @ 1000hz, Coils + Common Ground: 19.40 Henries
Q @ 120hz, Coils Only, No Common ground: 0.6830
Q @ 1000hz, Coils Only, No Common ground:2.341
Q @ 120hz, Coils + Common Ground: 0.6891
Q @ 1000hz, Coils + Common Ground: 2.212


per David Schwab

Row 1:
Serial Setting
Inductance @ 120hz, 4 Coils Only, No Common ground:9.634 Henries
Inductance @ 1000hz, 4 Coils Only, No Common ground: 7.916Henries
Inductance @ 120hz, 4 Coils + Common Ground: 9.638Henries
Inductance @ 1000hz, 4 Coils + Common Ground: 8.054 Henries
Q @ 120hz, Coils Only, No Common ground: 0.7347
Q @ 1000hz, Coils Only, No Common ground:2.396
Q @ 120hz, Coils + Common Ground: 0.7333
Q @ 1000hz, Coils + Common Ground: 2.314

Parallel Setting
Inductance @ 120hz, 4 Coils Only, No Common ground:27.54Henries
Inductance @ 1000hz, 4 Coils Only, No Common ground: 9.298Henries
Inductance @ 120hz, 4 Coils + Common Ground: 27.57 Henries
Inductance @ 1000hz, 4 Coils + Common Ground: 9.560 Henries
Q @ 120hz, Coils Only, No Common ground: 0.7347
Q @ 1000hz, Coils Only, No Common ground:2.395
Q @ 120hz, Coils + Common Ground: 0.7333
Q @ 1000hz, Coils + Common Ground: 2.313


Row 2:
Serial Setting
Inductance @ 120hz, 4 Coils Only, No Common ground: 9.640 Henries
Inductance @ 1000hz, 4 Coils Only, No Common ground: 7.916Henries
Inductance @ 120hz, 4 Coils + Common Ground: 9.635 Henries
Inductance @ 1000hz, 4 Coils + Common Ground: 8.044 Henries
Q @ 120hz, Coils Only, No Common ground: 0.7274
Q @ 1000hz, Coils Only, No Common ground:2.387
Q @ 120hz, Coils + Common Ground: 0.7274
Q @ 1000hz, Coils + Common Ground: 2.312

Parallel Setting
Inductance @ 120hz, 4 Coils Only, No Common ground:27.83Henries
Inductance @ 1000hz, 4 Coils Only, No Common ground: 9.308Henries
Inductance @ 120hz, 4 Coils + Common Ground: 27.91 Henries
Inductance @ 1000hz, 4 Coils + Common Ground: 9.550 Henries
Q @ 120hz, Coils Only, No Common ground: .7259
Q @ 1000hz, Coils Only, No Common ground: 2.387
Q @ 120hz, Coils + Common Ground: 0.7252
Q @ 1000hz, Coils + Common Ground: 2.310

Do you want me to un solder one coil and measure that david?

matt

[Possum]

....

Well you left out some important information like DC resistance of each coil and AC resistance readings. Usually when there's a big difference between 120hz and 1khz readings it means there's alot of metal in there and/or the use of fine wire.....

[David Schwab]

A lot of metal for sure! Four small coils in a "coil set". About 2.4K each, if I remember right.

[Joe Gwinn]

... actually my avatar refers to time travel, so there you go! :>

per salvarsanarium (or however they heck you type that)...

[snip]

Do you want me to un solder one coil and measure that david?

matt

A diagram or two would be useful.

Unsoldering one coil so we can seen the four inductances would be useful: A alone, B alone, A+B, A- B.