how do you measure pickup impedance?

Discussion in 'Just Pickups' started by jivetrain, Jan 20, 2008.

1. jivetrainTele-Holic

Jun 1, 2006
iowa
i'm selling some pickups and have the ohmmeter out but am not really sure how to test. i am 100% incompetent with electronics. i'm assuming i put the negative needle of the ohmmeter to the black wire of the pickup and the positive needle to the colored wire, then just read the display right?

2. aznrambo481Friend of Leo's

Mar 9, 2006
La Jolla, California
yes. In fact, you could switch up the wires and still get the same reading.

3. BogoTele-Meister

Dec 25, 2006
NY
Just watch out not to hold both bare leads while measuring. Your body impedance in parallel with the pickup could have some effect in lowering the reading a bit.

5. RonkirnPoster ExtraordinaireVendor Member

Age:
70
May 1, 2003
Jacksonville, FL
Put your VOM on about the 20K range and touch a test probe to each lead, you should see something like 7.95 which would be 7 point 95 Kilo ohms or 8K rounded up.

Some VOM will have a 10 K range, maybe a 15K range or a 30 or 50 K range.... whatever is closest to the impedance but a bit higher is fine.

Ron Kirn

6. tdownsFriend of Leo's

Nov 8, 2003
Texas
Just to clarify...when you measure a pickup with an ohmmeter, you are measuring the DC resistance, not the impedance. The impedance can be measured with an impedance bridge, which would be at a single frequency. The ohmmeter just measures the resistance of the thousands of windings of copper wire. It is pretty much a meaningless measurement.

If were to use the same gauge wire, and wind it around the exact same pickup physical structure and magnets, the relative difference between two resistances could then represent a realtive difference in output.

It is the inductance of the pickup that matters the most. This varies with many factors, including the strength of the magnets.

Last edited: Jan 20, 2008
7. Nick JDDoctor of Teleocity

May 12, 2007
Queensland, Australia
How does one measure inductance, Terry?

8. KokoTele<img src="http://www.tdpri.com/gifs/vendor.png" />Vendor Member

Age:
41
Mar 17, 2003
albany, ny [not chicago]
With a meter that measures inductance Most multimeters don't have the capability.

I'm afraid that this is one of the few times that I disagree with Terry. It's misleading to say that the measurement is meaningless. It is true that you can't necessarily tell what a pickup will sound like just from its DC resistance, but it does give you some clues. For a given pickup design, increasing the number of winds simultaneously increases both the resistance and inductance.

Part of the reason why DC resistance is useful is that all traditional pickups are made of similar materials. Even though they do use slightly different gauge wire for the coils, it's all pretty close. So it's safe to say that in general, a pickup with a higher DC resistance will sound hotter. You can't say that every pickup that's 8.5k-ohms will sound a lot hotter than every on that's 7.9k-ohm, but it is true more often than its not.

There was a time at Fender where they were using a winding machine that was out of calibration. Someone doing some research asked someone in the shop something like "Your winding machine is off by about a hundred turns, isn't it?" and they said "Yeah, how did you know?" Well... he knew because he'd been measuring DC resistance of a lot of pickups and found that ones from certain time frame had a higher DC resistance and tended to sound a little hotter.

DC resistance is also useful to tell if you have a short or a break in your pickup.

I don't think inductance alone is sufficient to guess what a pickup will sound like either. I think you'd need to measure the impedance at different frequencies, and the graph will tell you more about the sound than any single measurement.

9. TwangbangerTele-Holic

Mar 16, 2003
Marble Falls, TX
Where I used to work we had an inductance/capacitance meter, but I did work for a Transformer company.
To my understanding ya'll are both correct. But the principle of a magnetic pickup works off of the inductance. When the string vibrates it changes the inductance of the pickup and induces current in the windings from the resistance of the windings. The more resistance the hotter the voltage output.
I would love to sit down and design a few pickups and modify current vintage specs and just experiment to see the changes in frequency response vs wire gauge and turns or wire. I just couldn't stand sitting there and hand winding ever again. That is some of the most boring work I've ever done.......the transformer company. I made a transformer there that had 20K turns on the secondary once. The normal ones had layers of 34gauge wire, 200 turns a layer X15 layers.

10. jivetrainTele-Holic

Jun 1, 2006
iowa
i got the test done well, thanks for the info. i suppose i did mean resistance rather than impedance. and i may have inadvertently started a long argument

11. tdownsFriend of Leo's

Nov 8, 2003
Texas
eryque, I don't think we disagree. Let's not disagree. Please allow me to correct my post. I shouldn't have said it was meaningless. The reasons you state are true.

What I should have said is that variation in wire gauge, the winding structure, and the permeability of the magnets will make it very difficult to make the DC resistance of a pickup a completely relevant number. As you state, if the resistance is higher, it is likely to have a higher output, in probably more cases than not.

Regarding the number of turns on a pickup production line, this is definitely relevant!! Miles of wires = a finite DC resistance.

Thanks for your post, and accept my apologies for the snap response of pickup resistance measurements.

Nick JD,
How does one measure inductance of a pickup? You can't do it with an inductance meter, that's for sure. Inductance meters only work when the DC resistance of the inductor is very low. A geetar pickup has so much resistance, it messes up the measurement. I have a way to measure it with a fairly good degree of accuracy using a signal generator, voltmeter, and applying some math to the results. I basically put the pickup under test in series with a resistor, and read the output voltage across the resistor. I then use math to back out the effects of the large pickup resistance. I have confirmed the measurements with PSPICE simulations and it is quite accurate. It doesn't work for any high resistance inductor (like a wire wound resistor), but the load resistor and test frequency is optimized for guitar pickups. It will take some time, but I will document it. I'm not sure if anyone really cares.

Some high dollar impedance bridges can measure it. I believe you dial in the the DC resistance into the bridge to match the device under test.

More later.

12. KokoTele<img src="http://www.tdpri.com/gifs/vendor.png" />Vendor Member

Age:
41
Mar 17, 2003
albany, ny [not chicago]
Terry, I just saw your last post (a week later), but wanted to say thanks for clarifying your statements, and even more importantly, thanks for explaining more about measuring inductance! I actually have (or had, can't remember) a meter that measures inductance, but I never used it on anything bigger than what came in a Radio Shack grab bag.

13. dobrodocTele-Holic

Age:
61
Jan 15, 2004
Ware Shoals, S.C.
An electric guitar pickup's impedance can't be measured, as impedance in frequency-dependent (AC in an inductive load).

14. Nick JDDoctor of Teleocity

May 12, 2007
Queensland, Australia
After reading about inductance I am more confused than ever. I think I held a pickup too close to my brain and the iron molecules in my blood have, through magnetic flux, aligned - and now I have an overwhelming desire to head south for winter.

If one put a large DC current through a pickup, would the magnets become stronger relative to the pickup's inductance?

15. Westerly SunnPoster Extraordinaire

Jul 28, 2006
S.E. North Carolina
16. RonkirnPoster ExtraordinaireVendor Member

Age:
70
May 1, 2003
Jacksonville, FL
Often there is a tendency to go a bit overboard with answers to questions zooming way over the heads of those posing the query.

Some of us are graced with 1st phone tickets, and others are dazzled by the selection of batteries available at Radio Shack. Even basic electronics can overwhelm those who have never explored the field.

All Jive wanted to know was how to measure a pup with a VOM… a discussion of inductance vs. resistance vs. impedance could easily dissuade a novice from even pursuing a basic knowledge of electronics. Remember haw baffling that 1st crystal set was? Certainly assigning the correct nomenclature is a good idea, but let’s not scare away the un-initiated.

I encourage all to keep it simple, if a questioner wants additional info, perhaps they will ask.

Ron Kirn

17. BDSDreamsNEW MEMBER!

Aug 28, 2008
Ringgold, Georgia
Pickup Testing

I would like to see if someone could assist me in learning an accurate means of testing some pickups I have wired up. I followed the wiring diagram at this site http://www.guitarelectronics.com/product/WDUHH5L1102.

I have been told tapping on the poles is not the best means to test if the switch is correct. As it stands, it sounds as if the wiring is off. I'm wanting to know a definitive way to test this. Preferrable using a DMM. Any suggestions or recommendations?

18. banjovi800TDPRI Member

Age:
41
Jan 29, 2009
Davenport Ia
ohming out vintage p-bass pickups

Do you know what early 70's p-bass pickups should read out?

19. musicmattyFormer Member

Aug 18, 2008
Maryland
Amen to what is stated above. I've done fine so far replacing pups by paying close attention to where each wire was to be connected.. by replacing one pup at a time..so I don't lose myself. Ignorance is no excuse..and Im a little slow with electronics..and somewhat confused with what has been discussed above.

20. tdownsFriend of Leo's

Nov 8, 2003
Texas
Well thanks guys for reprimanding me on how to post.

Someone asked how to measure impedance and admitted they didn't know much about electronics. I "thought" it would be helpful for them to know there is a distinct difference between impedance and resistance. They indicated they were selling the pickups. Imagine a person looking at buying a pickup with an impedance value vs. a resistance value. It would automatically be suspect.

I was then asked DIRECTLY by another person in the thread to explain how inductance is measured. Perhaps I should have said no...sorry. Someone may be offended by the explaination.

21. musicmattyFormer Member

Aug 18, 2008
Maryland

Mr.Downs, I Appologize if my post sounded like a slam against your insightful and helpful post, this was not my intention. I think what I was trying to say, is that it doesn't take much to get over my head when talking about impedance and resistance, the differ between the two and how to measure for this. Maybe we should have a basic class on this subject ..here on this forum explaining this and the tools that are needed to assist. I admit..Im still a little confused about how this is done.

Thanks Mr.Downs

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