Hantek 1833C LCR meter, great for pickups

[Joe Gwinn]

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.

Many people on this group will want those explanations.

[Helmholtz]

Many people on this group will want those explanations.

So you don't have the second page anymore?

Here's a link to the full book:
https://worldradiohistory.com/BOOKSH...ndbook-1-A.pdf

See pp. 922/923.

[Antigua]

One thing to keep in mind is that when these pickups are modeled in LT Spice with provided values, the resonant peaks based on the L and C from the LCR meter agrees with the bode plots created with the USB oscilloscope, so if the value are off, it must be by a rather small amount.

[Joe Gwinn]

One thing to keep in mind is that when these pickups are modeled in LT Spice with provided values, the resonant peaks based on the L and C from the LCR meter agrees with the bode plots created with the USB oscilloscope, so if the value are off, it must be by a rather small amount.

That's good to know.

While LT Spice is very useful, it assumes lumped-parameter circuits, and thus cannot directly describe eddy current effects. Or for that matter, distributed capacitance. So we must approximate.

[Helmholtz]

Eddy current effects require extended equivalent circuits for simulation, see Zollner's book "PotEG" (complete translation available from the GITEC website).

Did anybody try "Terman's method"? .

[Antigua]

Actually, eddy currents in pickups have been modeled very well too, https://www.tdpri.com/threads/physic...2#post-8528357 The curve matching of actual observed eddy currents and a three part transformer model had a very high degree of agreement. This user TeleTucson was enormously helpful, but this seemed to have been the extent of his interest in guitar pickups.

Similarly with the capacitance, whether it's conceived as lumped or distributed, since the actual impedance plot matches the LT Spice model, it becomes a distinction without a difference. The capacitance is kind of a triviality anyway, for practical purposes, myself and others add 470pF in parallel to simulate line capacitance, and that causes the inductance to become even more dominant. I think the Hantek's C measurement is good to have, but it's also incidental. I'd like to work out a measurement technique for eddy currents losses, since that can help 1) determine the loss caused by particular pickups covers, 2) determine whether a 250k or 500k set of pots is more appropriate for a given pickup in order to get a good resonant knee.

[Joe Gwinn]

Actually, eddy currents in pickups have been modeled very well too, https://www.tdpri.com/threads/physic...2#post-8528357 The curve matching of actual observed eddy currents and a three part transformer model had a very high degree of agreement. This user TeleTucson was enormously helpful, but this seemed to have been the extent of his interest in guitar pickups.

That LT Spice model is equivalent to adding another series resistor to model the eddy-current loss. The problem is the use of a fixed resistor - real eddy currents are in 3D, and respond to the 3D arrangement of various materials. If you measure the effect in a particular setup and use that value in LT Spice, you will get reasonable curves. But when some physical detail changes, the old value will also change, so another direct measurement is needed. Nor is the effect of eddy currents on inductance modeled by adding resistance. But this process does yield reasonable approximations.

Similarly with the capacitance, whether it's conceived as lumped or distributed, since the actual impedance plot matches the LT Spice model, it becomes a distinction without a difference.

Follows the same rule, sorta. Changing the physical arrangement of the windings can change the self-capacitance, an effect not modeled by lumped-parameter models. So, we measure and approximate.

The capacitance is kind of a triviality anyway, for practical purposes, myself and others add 470pF in parallel to simulate line capacitance, and that causes the inductance to become even more dominant. I think the Hantek's C measurement is good to have, but it's also incidental.

I'll grant that pickup capacitance is very often dominated by cable capacitance, but the question was how to measure pickup self capacitance in isolation.

I'd like to work out a measurement technique for eddy currents losses, since that can help 1) determine the loss caused by particular pickups covers, 2) determine whether a 250k or 500k set of pots is more appropriate for a given pickup in order to get a good resonant knee.

Q1. We already have a way to do this, measure the series AC resistance and also the series DC resistance, and subtract the DC value from the AC value. The resulting excess resistance will be due to total eddy current loss (so long as there are no shorted turns, which will dramatically increase the excess loss).

Q2. LT Spice can already answer this question, given measured values of eddy current loading, pickup self-capacitance, and cable capacitance.

[Mike Sulzer]

Other than with a series resonant circuit, in a parallel resonant circuit capacitive and inductive reactances are not simply additive.

PU impedance is essentially represented by a parallel circuit of self-capacitance and inductance in series with the DCR.
Sometimes more elements are necessary for a representative model, but the rest of the circuit is always shunted by the capacitance.

As capacitive impedance drops with increasing frequency (and inductive impedance increases), total impedance at HF is dominated by the capacitance as with all parallel resonant circuits.
When the PU impedance curve eventually drops with -6dB/octave (or -20dB/decade) at high enough frequencies, impedance is almost purely capacitive and the capacitance value can be calculated from the asymptote.
With this method actual inductance doesn't matter.

"PU impedance is essentially represented by a parallel circuit of self-capacitance and inductance in series with the DCR." That implies that the pickup impedance goes to infinity at resonance; that is, at resonance the voltage across a sensing resistor in series with the pickup would go to zero, implying zero current. The highest I have measured is about 10^6 ohms, which seems about right for the coil resistance in series with the coil only. Of course, there must be some resistance in series with the capacitor, but I think this is not so simple.

[Helmholtz]

"PU impedance is essentially represented by a parallel circuit of self-capacitance and inductance in series with the DCR." That implies that the pickup impedance goes to infinity at resonance...

No, as the DCR is in series with the inductance (maybe my phrasing was ambiguous).
The impedance at resonance is ideally given by Zr = L/(DCR*C), ignoring Eddy losses.

As seen from the load/LCR meter, the capacitance always shunts the rest of the impedance. So if the frequency is high enough, the shunt capacitance dominates the PU impedance.
As soon as the impedance drops with -6dB/octave, the impedance is purely capacitive. The -6dB/octave impedance slope actually defines a capacitance.
The capacitance can then be determined from any point on the tangent/asymptote.

[Mike Sulzer]

No, as the DCR is in series with the inductance. The impedance at resonance is ideally given by Zr = L/(DCR*C), ignoring Eddy losses.

As seen from the load/LCR meter, the capacitance always shunts the rest of the impedance. So if the frequency is high enough, the shunt capacitance dominates the PU impedance.
As soon as the impedance drops with -6dB/octave, the impedance is purely capacitive. The -6dB/octave impedance slope actually defines a capacitance.
The capacitance can then be determined from any point on the tangent/asymptote.

OK, I misread what you meant. You are saying what I have always assumed. But I do think that there must be some resistance in series with the capacitor. I do not see how it could be perfect, but it might be small enough to not be important. Can the meter that measures at 100 KHz also give a resistance value simultaneous with the measurement of C?

[Helmholtz]

Can the meter that measures at 100 KHz also give a resistance value simultaneous with the measurement of C?

Yes, just measured a strat PU. Series AC resistance @100kHz measures as 1.1K. The reactance of the 100pF calculates as 16kOhm.

Capacitance/impedance phase angle reads as -87°.

[Mike Sulzer]

Yes, just measured a strat PU. Series AC resistance @100kHz measures 1.1K. The reactance of the 100pF calculates as 16kOhm.

Capacitance/impedance phase angle reads as -87°.

Thanks. So, yes, it can be ignored for many purposes

[Helmholtz]

Thanks. So, yes, it can be ignored for many purposes

Well, the series R raises absolute impedance by 0.2%.

[Joe Gwinn]

Well, I've been quiet for a reason. Brad Burt (Classic Amplification) lent me his Hantek 1833C for testing, just as he did with a DE-5000 unit in 2015, with my results to be published on this forum.

The pickup under test is an no-name Telecaster Bridge singlecoil unit, having six alnico magnets and a copper-plated mild steel baseplate, forbon bobbin plates, and no cover, with Rdc = 6.306 kilohms.

Just measuring the self-inductance is SER mode yielded the correct answer for 100Hz and 120 Hz, but gave no answer (a row of dashes) for 1000 Hz and above. Various displays did or did not work as one went through the test frequencies. One thing that always worked was the R-X option (AC resistance, and signed reactance, in kilohms), so I was able to take a full set of data. The 120 Hz and 1000 Hz inductances were within a half percent of the venerable Extech 380193. This is well within the error bands of the two instruments, and so are equivalent for all practical purposes.

Reduced all the R-X data, mathematically converting to Ls (below resonance, about 10 KHz), and Cs (above resonance). The inductance was very stable, and reproduced the Extech values where available. The apparent self-capacitance varies quite a lot when well above resonance, ranging from 120 pF and 174 pF, a ~50% range. I assume that this is due to eddy currents interacting with distributed capacitance somehow, but don't really know. I have plots, but have not figured out how to post them.

Burt mentioned that there was a notice saying that one should update the firmware in the 1833C, and sent me the files. Long story short, I could not install the firmware updates either, stopped by the fact that the instrument's USB interface does not quite work.

We don't know if the USB interface is unreliable in general, or he just got a busted unit. But the users manual implies that connecting to the USB interface may be a bit random: "If the device is not identified, please repeat step 2." I also tried to operate the 12833C from my computer using the software provided for the purpose. This also failed, for lack of connection to the unit.

Anyway, the 183C seems to be working correctly electrically, but the firmware isn't doing it justice, and the USB interface does not work.

Not knowing the reason for the 50% variation, I don't trust the capacitance measurements above resonance.

Summary: The Hantek 1833C has promise, but needs work. It may be best to wait a year or two, and let Hantek finish their job.


Who else has a 1833C unit? What is their experience?

[Helmholtz]

The apparent self-capacitance varies quite a lot when well above resonance, ranging from 120 pF and 174 pF.

What capacitance do you get using "Terman's method"?

BTW, Eddy currents don't influence capacitance.