Questions for those with LCR Meters

[soundmasterg]

well am getting back late in this thread. Why measure anything except the lowest frequency? Because seeing only one part of the elephant tells you nothing about the whole elephant. It really doesn't matter if the meter is "accurate" at either test frequency, what matters is that you use the same meter in all your measurements that you do with your pickups. You establish a baseline based on one measuring instrument. Measuring only at the lowest frequency doesn't tell you what is happening at 1khz, the two aren't related to eachother, in some meausrements they may be real close to eachother in others, far apart. I have a suspiscion that the meters that go to 10khz even though they are not accurate in pickups up there it still might be useful in relative measurements. the biggest disappointment of the Extech is that you have no clue what is happening in the higher frequencies, the meter can give you nearly identical readings on two different pickups yet one pickup may be doing something completely different in the high frequencies that you can hear but the meter can't. Doing a frequency analysis chart I found interesting but not very useful either, maybe I didn't go far enough with it, I probably should have "pegged" certain higher frequencies to get actual digital read numbers at those spots for side by side comparisons against other variants in pickup design. there is a point though where all this geek stuff becomes useless. A Charlie Christian pickup isn't going to sound like a strat or a humbucker and numbers on a chart will never tell you what a pickups character will be like. Numbers are good when comparing doing changes in pickup design, its a tool and is helpful but ears and playing tests always should be the final test and this should be a studio recording test, a home bedroom scenario and playing loud at a live gig, which is probably the most important. Owning alot of expensive test gear isn't going to make your pickups sound better :-)

Owning a lot of expensive gear would imply that I have a lot of money, and therefore, I could afford to hire a really good player to play my pickups, and then they would of course sound better.

Greg

[Mike Sulzer]

Owning a lot of expensive gear would imply that I have a lot of money, and therefore, I could afford to hire a really good player to play my pickups, and then they would of course sound better.

Greg

Ah, did I notice a glimmer in my snark detector? But it is better than you say. You can save your money to pay for that good player, because if you are on this forum regularly, then you already have the expensive part of the equipment you need to do pretty sophisticated analysis: you computer. You do need a sound card, some software, and a preamp that can be made from a $1 op amp, a few resistors, and a couple of batteries.

[David Schwab]

Or better yet, become a great player.

[Joe Gwinn]

well am getting back late in this thread. Why measure anything except the lowest frequency? Because seeing only one part of the elephant tells you nothing about the whole elephant. It really doesn't matter if the meter is "accurate" at either test frequency, what matters is that you use the same meter in all your measurements that you do with your pickups. You establish a baseline based on one measuring instrument. Measuring only at the lowest frequency doesn't tell you what is happening at 1khz, the two aren't related to each other, in some measurements they may be real close to each other in others, far apart. I have a suspicion that the meters that go to 10khz even though they are not accurate in pickups up there it still might be useful in relative measurements. The biggest disappointment of the Extech is that you have no clue what is happening in the higher frequencies, the meter can give you nearly identical readings on two different pickups yet one pickup may be doing something completely different in the high frequencies that you can hear but the meter can't. Doing a frequency analysis chart I found interesting but not very useful either, maybe I didn't go far enough with it, I probably should have "pegged" certain higher frequencies to get actual digital read numbers at those spots for side by side comparisons against other variants in pickup design. There is a point though where all this geek stuff becomes useless.

The poor man's approach would be to use the Maxwell-Wein bridge (http://home.comcast.net/~joegwinn/) to measure at various frequencies (not just 10 KHz), allowing you to follow the response right up to and past resonance. Use your sound card to generate the test signal. It will be a significant amount of work, but it will answer the question.

[Possum]

...

Is there some comparable commercial instrument that would make it simple? Lately I've been doing way too many experiments, and even using the Extech becomes a pain....

[Joe Gwinn]

Is there some comparable commercial instrument that would make it simple? Lately I've been doing way too many experiments, and even using the Extech becomes a pain....

Such instruments do exist, but even used ones are $5,000 and up.

There are also fancy LCR meters that will take data at far more than three frequencies:

Agilent 4263B does 100 Hz, 120 Hz, 1 KHz, 10 KHz, and 100 KHz, costs $4000 new, but has too few test frequencies to answer the question.

Agilent E4980A does 200 points at frequencies in the range 20 Hz to 2 MHz, and is $15,200 new. There are a number of similar instruments available, at a like price.

A HP 4274A might suffice, although it doesn't really have enough frequencies in the relevant range. No longer made, but available used for a few thousand dollars.

To get data, go to http://www.agilent.com and enter the instrument number in the search box.


I would do a series on one pickup manually using the maxwell bridge first, so see if there is any real advantage to it.

[Mike Sulzer]

Inductance as a function of frequency?

Looking at the impedance of a pickup as a function of frequency is useful. But inductance as a function of frequency? The measurement I presented a few posts above convinces me that a pickup has a single value of inductance, period. But I will listen, if you can show some evidence that inductance really does vary as a function of frequency.

[Possum]

Well I don't know the tech explanations but the Extech at 120hz and 1khz for sure doesn't get the same readings. 120hz will always read lower in most pickups because bass gets lost the more winds you put on, and 1khz doesn't get so clogged up so fast. Treble can't be read unfortunately but the 1khz readings show whats going on in the mids somewhat. when the two readings are real close you know you got a real clear sounding pickup like a heavy formvar low wind strat....

[Possum]

....

How would these really expensive LCR meters read better at high test frequencies than the current LCR meter's you see on ebay in the $200 range? they do have some that have 10khz which would be real useful to me, these won't work at all?

[Mike Sulzer]

Well I don't know the tech explanations but the Extech at 120hz and 1khz for sure doesn't get the same readings. 120hz will always read lower in most pickups because bass gets lost the more winds you put on, and 1khz doesn't get so clogged up so fast. Treble can't be read unfortunately but the 1khz readings show whats going on in the mids somewhat. when the two readings are real close you know you got a real clear sounding pickup like a heavy formvar low wind strat....

When I wind more turns on a pickup, the inductance goes up, the capacitance goes up, and so the resonant frequency goes down. This generally gives a pickup with less treble. I think the reason the meter does not give the same reading at the two frequencies is because of eddy currents in the cores, as Joe said. But I do not think the inductance is really different, but rather the increased losses in the coil at the higher frequency alter the reading. The Extech manual has equations for computing the accuracy based on the inductance and the losses. It might be a good idea to check this.

[Joe Gwinn]

Looking at the impedance of a pickup as a function of frequency is useful. But inductance as a function of frequency? The measurement I presented a few posts above convinces me that a pickup has a single value of inductance, period. But I will listen, if you can show some evidence that inductance really does vary as a function of frequency.

Inductance does vary with frequency in practical coils. (It also varies with DC bias, but that's not an issue here.) In iron-cored low-frequency (ie, not RF) inductors, the dominant effect is due to eddy currents in the iron. There are entire chapters on this in books on inductor and transformer design. It isn't simple.

There is a very good discussion in "The Theory and Design of Inductance Coils", V.G. Welsby, Macdonald & Co., 1950, 180 pages. Welsby worked for the British Post Office, which built and operated the British telephone system.

[Joe Gwinn]

How would these really expensive LCR meters read better at high test frequencies than the current LCR meters you see on ebay in the $200 range?

The expensive LCR meters are more accurate (0.01% or 0.1% versus 1%), and measure at more frequencies. They do the same basic thing as the $200 LCR meters, only better. For pickups, 1% is plenty, so the issue is frequencies.

They do have some that have 10khz which would be real useful to me, these won't work at all?

The problem with 10 KHz is not with the LCR meter, so even a $10,000 LCR meter won't work any better if you are too close to resonance. With more frequencies, you can see where you are. With one frequency, you have no idea what is going on.

[Mike Sulzer]

Inductance does vary with frequency in practical coils. (It also varies with DC bias, but that's not an issue here.) In iron-cored low-frequency (ie, not RF) inductors, the dominant effect is due to eddy currents in the iron. There are entire chapters on this in books on inductor and transformer design. It isn't simple.

There is a very good discussion in "The Theory and Design of Inductance Coils", V.G. Welsby, Macdonald & Co., 1950, 180 pages. Welsby worked for the British Post Office, which built and operated the British telephone system.

Thanks, Joe. That looks like an interesting book. A casual search turned up two copies for sale in Britain, and one in Australia, but none in the US. I will try again later.

Most things involving ferromagnetism are not simple. But it ought to be possible to determine how big the effect is. A possible improvement on the measurement above would be to wind a second coil, air core, with the same "inductance" as the one with the slugs. "Same" would be defined as the two curves of relative impedance magnitude vs. frequency lying as close as possible. Deviations from a single value of inductance (coil with slugs) would show up as systematic deviations from zero of the difference between the two measurements over some range of frequencies.

[Joe Gwinn]

Thanks, Joe. That looks like an interesting book. A casual search turned up two copies for sale in Britain, and one in Australia, but none in the US. I will try again later.

I've bought books from UK booksellers. It works just fine. The book just arrives in the mail.

Most things involving ferromagnetism are not simple. But it ought to be possible to determine how big the effect is. A possible improvement on the measurement above would be to wind a second coil, air core, with the same "inductance" as the one with the slugs. "Same" would be defined as the two curves of relative impedance magnitude vs. frequency lying as close as possible. Deviations from a single value of inductance (coil with slugs) would show up as systematic deviations from zero of the difference between the two measurements over some range of frequencies.

Yep. I'd wind a coil on a plastic tube so I could slide various slugs in and out.

In a solid round slug, eddy current effects vary as the square of the rod diameter.

[David Schwab]

In a solid round slug, eddy current effects vary as the square of the rod diameter.

Is there anything different about a round slug v. a square slug as far as eddy currents?

I notice Bartolini used square poles in his original designs. He talks about it in the patent, but it's mainly about the shape of the magnetic field v. round poles.