So what exactly is needed to make this graph?

[Possum]

...

One question I have is in the Lemme article he says this method is terrible for looking at humbucker frequency responses and mention there are notched frequencies even on each string because of the cancelling coils, I wonder what method would show these notches, I've known about this for years but have never actually seen it plotted on a graph. And how would you see harmonics of any pickup as well? I'm just full of questions aren't I

[Yves]

BTW, my driver coil is being driven by an amplified speaker for computers , not straight out of the Mac as I said before

Still not driving a constant current though.

Actually, I've come accross this:
http://www.analog.com/static/importe...7846AN_843.pdf

I believe this could be a starting point for someone willing to set up something less "crude"

This article BTW describes the HOWLAND CURRENT SOURCE (p5): apart from the actual analog device chip this current source set up allow to drive an impedance with a fixed current independent on the frequency.

Finally, an evalluation board for the Anolog device chip is availlable (I think at arround 170$ or so), with a built in usb interface and a PC software that is ready to use the board.

Now this setup allows an impedance measure accross the frequency range, but I guess it could be used to drive a coil with a fixed current accross the frequency range (the device has a built in sweep tone generator)

FWIW

crude but it works fine enough for my purposes

That's what count anyway

[Possum]

....

I'm finding Fuzzmeasure has its flaws, I tried substituting different slugs I know sound very different and getting the same graph. Plus if I lower the input volume the graph doesn't drop it stays the same. I looked for a couple hours to try to find some other audio software for the mac that will do similar graphs, and no luck. The only other software I know will do it is Mac The Scope for $500, too expensive for simple testing. That device someone posted for $200 looks interesting but that company doesn't answer email, I asked them if I couldn't navigate their very complex Mac installation instructions, written by someone else no less, could I get a refund. No reply. At this point I'm thinking of getting an LCR meter that will do 10khz test signal but that frequency is really up there past most pickups peaks, especially humbuckers, so wonder ho useful it would be not really getting a good reading on where the action is happening.

[Possum]

....

Is there such a thing as an AC resistance meter? It seems to me that would be the most useful instrument for pickups, if there was one I could use my own frequency generator and measure at pickup relevant frequencies....

[David Schwab]

Is there such a thing as an AC resistance meter?

Doesn't the Extech measure AC resistance?

[Possum]

...

Yes but only at 120hz, and 1khz. It would be useful to have something that would measure at 20-20KHz

[belwar]

Correct me if im wrong, but the AC resistance shoudnt change depending on frequency should it? You should get the same reading regardless of frequency.. i.e. if you use an extech in SER mode, your readings at 120 and 1000 should be the same. See page three in the lane poor mm thread for an example set of measurements and you'll see the measurements are the same (or within the margin of error of the device).

[belwar]

... another thought, probably incorrect but a thought none the less! I dont know if this would work in AC as it would in DC.

You could hook up an oscillator to your pickup, as well as a good DMM. Select any frequency on the oscillator, and measure the Voltage and Current using a DMM.. Use the forumula R = V/I to calculate the resistance at that frequency. I'll try it tommorow.. I've set the oscillator @ 120 and then do the calculation. I'll compare that to the Extech reading.

[David Schwab]

Correct me if im wrong, but the AC resistance shoudnt change depending on frequency should it?

AC resistance increases with frequency. It's akin to impedance.

[Possum]

Yes AC resistance readings change with frequency, I use it all the time and its usually the first thing I look at,inductance is second, Q last.

Yeah I wonder.....use a driver coil with a frequency generator and measure output voltage from the pickup, might work, worth a try....

[Possum]

...

Hmmmmm, interesting. I hooked up my frequency generator to my driver coil set over a humbucker at right angles ala Lemme style. Plugged my DMM set on AC voltage and got a definite peak voltage at 8khz. Maybe I can try one of the cheapie free osciloscope programs to look for the signal to peak or just do it this way. At least I can see a peak at a certain frequency and use that as a baseline for comparative measurements. I used Joe's method before and never could find definite peaks in alot of pickups, maybe I was doing something wrong. ....

[Possum]

...

Tried Signalscope, interesting stuff but have no clue what I'm doing and can't discern peaks of any kind, looks like it won't do a frequency response chart....

[belwar]

** What im writing might not be factually accurate.. Im still learning at 100mph and I may be getting things wrong **

I just bought a USB scope (as seen in another thread) and i've already learned quite a bit from the device. It's purpose is to show Voltage (or current if set up correctly) over time.. Voltage on the vertical, time on the horizontal..

So bar I believe these Frequency response charts are done on Signal Analysers which might also be called Network Analysers. These devices show Voltage on the vertical, FREQUENCY (not time) on the horizontal. There is one built into the USB scope software I just got, but I havent got to mess with it yet.

I learned the very basics about scopes from a very cool set of you tube vids. I put them below. Dont worry they are short.



Part 1
[ame="http://www.youtube.com/watch?v=qIfo_-d82Co"]YouTube - Oscilloscope Tutorial Part 1[/ame]

Part 2
[ame="http://www.youtube.com/watch?v=hUIgAu3QQWQ"]YouTube - Oscilloscope Tutorial Part 2[/ame]

Part 3
[ame="http://www.youtube.com/watch?v=g_KuGEh0PyA"]YouTube - Oscilloscope Tutorial Part 3[/ame]

[belwar]

Hmmmmm, interesting. I hooked up my frequency generator to my driver coil set over a humbucker at right angles ala Lemme style. Plugged my DMM set on AC voltage and got a definite peak voltage at 8khz. Maybe I can try one of the cheapie free osciloscope programs to look for the signal to peak or just do it this way. At least I can see a peak at a certain frequency and use that as a baseline for comparative measurements. I used Joe's method before and never could find definite peaks in alot of pickups, maybe I was doing something wrong. ....

Joes method hasnt let me down yet. Works like a charge. .. That was until I tried to measure a low impedance Lane poor.. I thought it was broken, just turns out the resonance peak was about the 20k my oscillator could go to...

Im thinking of building a oscillator as a learning electronics project.

[Possum]

....

Can you show me how your Joe test setup is done? In non-engineer terms with pictures done with crayons, third grade style :-)