Hantek 1833C LCR meter, great for pickups

[Antigua]

If you still have the PU from post #25, why not re-measure it with the Hantek?
Also using Termans method for reference would be a good idea. Should be easy using the Velleman Bode plotter and a few caps.
I see a chance to stop this seemingly never ending discussion about C-measuring methods and the "real" C.

I don't understand what the debate is about though. What specifically stands in doubt?

[Antigua]

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So the theory revolves around extra resonances. This can be seen most clearly in a phase plot.

This below is not a phase plot, though the meter is capable of producing one, and I still have the pickup. But before going through the trouble I'd wonder what about the plot below is ambiguous? How else would you get a second and third rise and fall of impedance?

The ratio of the inductances is easily estimated, if not the actual inductances in H. Basically, it's the square of the turns ratios. So for ten turns (eyelet loops) and ten thousand turns (main winding), the ratio of turns is a thousand, and the inductance ratio is a million. So, the main coil dominates. It would take very good equipment to even see such an effect by measuring inductance.

I'm getting a little confused as to what's that issue, but if you have two inductors in series of difference L*C values, then you see two resonances because the parasitic capacitance crosses the individual coils, and they resonate together as well as independently. This is seen when measuring humbuckers, a primary resonance relates to the sum inductance of the coils and half the capacitance, but a second resonance appears in relation to the specific L*C of the coils themselves, and the second resonant frequency of the individual coils matches approximately with the "split" resonance. To me this just looks like the same thing, but the resonances are far apart. You might be right that the eyelet inductance is too small to make a blip under 100kHz, I don't know. I could try making eyelet inductors to test it.

I'm doing several guitar projects this weekend, I have some awesome piezo bridges I'm messing with, and I just got a Fishman Fluence and Sustainiac, so I don't mean to be lazy with testing, but I have a few things on the burner.

[Antigua]

Here's a demo case, I found a "Bootstrap" brand pickup they call the "Golden Ale bridge", in my parts drawer, and it demonstrates an apparently bad capacitance measurement at 100kHz:

40kHz - 139.65pF
50kHz - 135.38pF
75 kHz - 148.77pF
100kHz - 74.28pF

74pF is about half of the value measured at the other test frequencies. This bode plot up to 100kHz shows a large spike right at 100kHz for this particular pickup:




Here's a plot up to 500kHz:




Here's the 100kHz plot with phase, it looks like a mess.







Now I'm checking to see if the Hantek's C values agree with L and f...

The 100Hz Ls measure of this pickup is 3.34H, the resonant peak appears to be 7.14Hz based on the plot above. Using this http://www.sengpielaudio.com/calculator-XLC.htm , the C from L and f is 0.000149 uF or 149 pF, note that is very close to, and at the upper end of the three capacitance measurements that were in agreement from the Hantek. The capacitance of the oscilloscope device is in the area of 10pF, so if suppose the true capacitance is 139pF, that comes near median of the three measurements that were apparently accurate.

[Helmholtz]

I don't understand what the debate is about though. What specifically stands in doubt?

See post #2.

[Antigua]

See post #2.

Well hopefully post #33 will resolve that, unless there also exists doubt about the Ls inductance measurement at 100Hz.

[Helmholtz]

.., unless there also exists doubt about the Ls inductance measurement at 100Hz.

Well effective PU inductance typically drops with increasing frequency by Eddy effects.
So if you calculate C from the main resonance peak, where L is lower than at 100Hz, results for C will be too high.

With Terman's method, varying inductance will show as a curved line.

[Antigua]

Well effective PU inductance typically drops with increasing frequency by Eddy effects.
So if you calculate C from the main resonance peak, where L is lower than at 100Hz, results for C will be too high.

With Terman's method, varying inductance will show as a curved line.

So we're not only calling into question the C of the Hantek or the DE-5000, but both the L and the C?

[Helmholtz]

So we're not only calling into question the C of the Hantek or the DE-5000, but both the L and the C?

C-meters evaluate the impedance at the measuring frequency. At high enough frequency, the impedance of a PU is purely capacitive, shown by a straight -6db/octace slope.
So PU inductance doesn't matter here.

Inductance matters when the measuring method is based on resonant frequency.

[Antigua]

C-meters evaluate the impedance at the measuring frequency. At high enough frequency, the impedance of a PU is purely capacitive, shown by a straight -6db/octace slope.
So PU inductance doesn't matter here.

Inductance matters when the measuring method is based on resonant frequency.

In general though, the inductance measures the same well below resonance, and capacitance measures the same well above resonance. 100z is used for the inductance because of eddy currents in pickups with steel parts, but measuring a pickup without steel, such as a Strat pickup, shows nearly the same inductance as 100Hz or 1kHz, One the flip side, the capacitance measures about the same to 40kHz up to 100kHz. You're saying there's an ambiguity here somewhere, but I'm not seeing it.

[Helmholtz]

You're saying there's an ambiguity here somewhere, but I'm not seeing it.

I was only referring to the C value calculated from the resonance frequency.
Of course the frequency dependance of L varies and depends on the materials used in the PU or cover.

Generally I think the C measured at 100kHz with an LCR meter is good enough - except if the measuring frequency hits a secondary resonance.
In this case the multiple frequency Hantek looks like a problem solver.

[Antigua]

I was only referring to the C value calculated from the resonance frequency.
Of course the frequency dependance of L varies and depends on the materials used in the PU or cover.

Generally I think the C measured at 100kHz with an LCR meter is good enough - except if the measuring frequency hits a secondary resonance.
In this case the multiple frequency Hantek looks like a problem solver.

I'm not familiar with Terman's method, and from googling I can tell it's not something I would figure out quickly, so for what it's worth, here is the same Bootstrap pickup measured without added load, and with parallel load of 4.7nF. The added capacitance reduces the resonant peak from 7.05kHz down to 1.27kHz.

[Helmholtz]

Terman's method can be seen from Fig.28 in the attachment.

It means adding increasing value caps in parallel with the PU and measuring the resultant resonant frequencies (fres). Then plot the 1/(fres)² values over the cap values in pF.

I'm sure J.Gwinn can provide additional advice.

[Joe Gwinn]

Terman's method can be seen from Fig.28 in the attachment.

It means adding increasing value caps in parallel with the PU and measuring the resultant resonant frequencies (fres). Then plot the 1/(fres)² values over the cap values in pF.

I'm sure J.Gwinn can provide additional advice.

That's right. I think I was the original source of that pdf, but where is the second page?

[Joe Gwinn]

This below is not a phase plot, though the meter is capable of producing one, and I still have the pickup. But before going through the trouble I'd wonder what about the plot below is ambiguous? How else would you get a second and third rise and fall of impedance?

It looks like there are two extra resonances around 150 KHz. A phase plot will locate the resonances precisely - in a low-Q inductor like a pickup, the resonance peaks don't tell the full story.

I'm getting a little confused as to what's that issue, but if you have two inductors in series of difference L*C values, then you see two resonances because the parasitic capacitance crosses the individual coils, and they resonate together as well as independently. This is seen when measuring humbuckers, a primary resonance relates to the sum inductance of the coils and half the capacitance, but a second resonance appears in relation to the specific L*C of the coils themselves, and the second resonant frequency of the individual coils matches approximately with the "split" resonance. To me this just looks like the same thing, but the resonances are far apart. You might be right that the eyelet inductance is too small to make a blip under 100kHz, I don't know. I could try making eyelet inductors to test it.

At this point, we are trying to figure out why we get those implausible self-capacitance values, and one theory is that those extra resonances are the culprit. My instinct is that they are irrelevant, but we don't yet have enough information to nail it down.

I'm doing several guitar projects this weekend, I have some awesome piezo bridges I'm messing with, and I just got a Fishman Fluence and Sustainiac, so I don't mean to be lazy with testing, but I have a few things on the burner.

Life.

[Helmholtz]

That's right. I think I was the original source of that pdf, but where is the second page?

I copied the page from the book, which I had downloaded many years ago, because it contains a lot of essential info on tube amps.
I think the next page mainly explains how to read inductance from the slope.
The figure should be self-explanatory.