D Sonic DP207 Coil Information

[TheGrateOz]

Hello Gents,
A friend has brought his broken (and unwound) DiMarzio D Sonic DP207 humbucker for repair. By reading DiMarzio's site, it seems they are mismatched coils. Has anyone measured these coil individually? Thanks for any information in advance. You guys all rock.

[dpm]

I just so happen to have one in front of me

south coil (bar coil) 7k dc resistance, 3.37H @ 100Hz - coil is far from full so I'm guessing 44awg
north coil 5.25k dc resistance, 2.64H @ 100Hz - coil almost full so 43 or 42awg?

[TheGrateOz]

Thank you, DPM!

[dpm]

No problemo. I just coincidentally had pulled one out of a guitar so it was right here

[TheGrateOz]

Out of curiosity, what are you using to measure the inductance?

[dpm]

Tonghui TH2821A LCR meter

[Joe Gwinn]

Tonghui TH2822 series LCR Meters may be suitable for measuring pickup inductance

Tonghui TH2821A LCR meter

The one-page summary of the TH2821 series meters was uninformative, and I was unable to download the "operations manual" from Portable LCR Meter, so I downloaded the TH2822 series data instead, as the TH2822 appears to be the successor.

I just read the 8-page datasheet downloaded from Portable LCR Meter for TH2822 series, and it does look plausible for measuring the inductance of guitar pickups.

As has been discussed many times before, the problem is that many handheld LCR meters are unable to accurately measure low-Q (high D) inductors such as guitar pickups.

Some models will test at 10 KHz (TH2822A,B) and 100 KHz (TH2822B only). While it is unlikely that these frequencies are useful for pickups, as this is above the resonant frequency of most pickups, there is no harm in trying either.

I have no idea how convenient it is to use this meter. Three measurements per second may be slow.

Later, I found an online copy of the TH2821A manual from 2005. The instruments appear similar, but I was not able to tell if it would be plausible for use on guitar pickups.

[dpm]

Joe, this one measures at 100Hz, 120Hz, 1kHz and 10kHz. When measuring similar pickup designs the measurements taken are comparable to those published by makers or posted as measured by other meters. The TH2822 look like an improved version, with USB output and a sexier case.

[Joe Gwinn]

Joe, this one measures at 100Hz, 120Hz, 1kHz and 10kHz. When measuring similar pickup designs the measurements taken are comparable to those published by makers or posted as measured by other meters. The TH2822 look like an improved version, with USB output and a sexier case.

That sounds about right, from the similarity of the descriptions. The acid test is to concoct a variable-Q inductor consisting of an iron-cored audio transformer winding (other windings being open) and a 50K pot in series. Measure the inductance at 1000 Hz while varying the series resistance using the pot. The indicated inductance should not vary much until the series resistance is around the reactance at 1000 Hz or greater.

If the LCR meter is not suitable, the effect will not be subtle - a 2 H inductor will soon be reported as 50 H. Many were perplexed until this effect was understood.

[TheGrateOz]

Hey Joe, I love saying that....
What do you think of the Amprobe 37xr-a for measuring inductance?

[TheGrateOz]

Here's a link to the specs

[TheGrateOz]

Amprobe Test Tools

I guess the link would be nice

[Joe Gwinn]

Hey Joe, I love saying that....
What do you think of the Amprobe 37xr-a for measuring inductance?

Well, for inductance of transformer coils, maybe OK. For measuring guitar pickups, maybe not so stellar. The specs are not that great, and the critical part does not make sense, and may be in error.

From the manual:

INDUCTANCE
Ranges: 4mH, 40mH, 400mH, 4H, 40H ( 3999 counts ) (Auto/Manual ranging ) Resolution: 1 μH Accuracy: ±(5.0 % rdg + 30 dgts) -- For values of Q <= 7
Test frequency: 1 kHz on 4mH, 40mH ranges, 200 Hz on 400mH to 40H ranges.

There are a number of striking problems.

First, pickups are audio devices, not 60 Hz power transformers, and so we are interested in the inductance measured at 1,000 Hz, not 200 Hz, and the frequency cannot be selected independently of the inductance range.

Second, an accuracy of +/- 5% of reading is woeful. It should be more like 1% or better (less).

Third, the part about "For values of Q <= 7" is most likely backwards, as the higher the Q the easier the measurement. I think they meant to say that to achieve the 5% accuracy, the Q must exceed 7, and no accuracy at all is stated for Q below 7. Well, most pickups do not have such a high Q, and I bet the measured inductance values will be wildly in error.


There are better choices.

[TheGrateOz]

Thank you so much Joe.

Do you have a favorite or recommended model?

[Joe Gwinn]

Thank you so much Joe.

Do you have a favorite or recommended model?

The Extech LCR Meter 380193 (about US $200) has been validated to work correctly with pickups, and is what most people use. This is what I have.

Where are you? Oz? The Land Down Under I suppose. If the Extech isn't easily available, there may be others. Use the acid test mentioned above before buying.

By the way, it's useful if you put your general location (city and country) in your User Profile.