Seymour Duncan SMB-4A inductance?

[dincz]

I'm modelling some preamp designs for use with this bass pickup and need to know the coil inductances. My cheap LCR meter reads 2H per coil. Is this close?

[Joe Gwinn]

I'm modelling some preamp designs for use with this bass pickup and need to know the coil inductances. My cheap LCR meter reads 2H per coil. Is this close?

What make and model of LCR meter are you using? They do differ, and not all kinds can handle low-Q inductors like a pickup.

Although 2 H per coil isn't an uncommon value.


PS: Where in the world are you? It helps us to answer many kinds of questions. Please update your user profile to give at least the country, or country and nearest big city.

[dincz]

The meter is a Vichy DM4070 and supposedly works at 1kHz. I realise it's not necessarily accurate on low-Q coils but was hoping someone might have a reliable figure.

[Joe Gwinn]

The meter is a Vichy DM4070 and supposedly works at 1kHz.

Well, I couldn't find user manual or specifications, so I cannot assess it, but at US $30 or so, one has to wonder.

The standard here is the Extech model 380193 handheld LCR meter, but this is more like US $200, so perhaps a test of the DM4070 is in order.

The basic test is to connect an iron-core inductor of a few Henrys in series with a 50 Kohm pot, and measure the inductance. If the indicated inductance goes crazy when the 50 Kohm pot in turned up (increasing the resistance), the LCR meter is hopeless. If you search the Forum, you will find many threads on this.

One can also use a Maxwell-Wein Impedance Bridge as a cross-check. Go to Joe Gwinn's website homepage.

I realize it's not necessarily accurate on low-Q coils but was hoping someone might have a reliable figure.

Well, it's pretty difficult for us to measure a unit that is not in our hands, but 2 H is certainly plausible.

[dincz]

I think I need to word my question differently. Has anyone measured the inductance of a Seymour Duncan SMB-4A pickup? If so, would you mind sharing your results? TIA

[David King]

I've had these pickups in my hands but don't own said Extech LCR meter. If they are anything like the originals then they aren't wound very hot. Is there anyway we can guess at the inductance knowing the mag materials, dimensions and turns count??

[big_teee]

The Seymour chart shows each coil to measure 4.18k
That would be 8.4k in series, or 2.1k in parallel
The magnet type is Alnico 5.
Don't see how they could be too hot with those specs.
4-String Alnico Replacement for Music Man | Seymour Duncan Tone Details
T

[dincz]

OK, it's getting clearer. I just measured a small unloaded mains transformer primary. The measured inductance gets higher with added series resistance - with 50K series R, the L reading is 7% high. With series R equivalent to that of the pickup, it reads the same as with no added series R. So the meter appears to be usable although not dead accurate for low Q inductors. I conclude that cheap LCR meters are not necessarily as dire as they are often made out to be.

I also managed to get some numbers from another forum and they match mine fairly closely. 7.6Kohms and 4H (series) but again not measured with the holy grail of LCR meters

Thanks for the responses.

EDIT: As much as I like the taste of Wein, Wien makes a much better bridge.