This talk about Q meters got me thinking. What's the most useful test equipment?

[David Schwab]

boy, and I thought that having a mac is about having less problems running stuff...

It is, and Macs have less problems when running Mac software. I know from being everyone's computer tech (in-laws, friends, etc.) how often the PC users I know have issues just getting printers and scanners to work! Good thing I know more Mac users, including my father-in-law after my wife got tired of him complaining about his Dell! He has two Macs now.

A properly written Java application will run anywhere equally well. LimeWire is a good example. Runs fine on a Mac. If this program isn't working right, it's because of the way it was coded.

OS X even runs Linix and BSD Unix apps because it's based on BSD Unix and has X 11 (the windowing system) installed.

If I had one of the newer Intel based Macs, I would also be able to boot into Windows. I can try running the Windows version in VirtualPC, but I think that will have sound issues because it has to go through a hardware abstraction layer (HAL).

[Possum]

bummer....

I dug around their forums at Home Theater, it looks like REW just plain doesnt work on a Mac, how stupid is that? Others get the buzz saw signal generator and the weird alert when booting up, there is no support for it on Mac that I can see there either. It looks like it may work on Windows on an Intel Mac though...

[Possum]

trying a PC with REW...

Bela, your frequency response chart looks suspisciously like the sound card calibration test I did, What pickup did you use? Are you using a laptop? My wife was going to give away a laptop PC that got dropped once and sometimes shuts itself off so messing with that. Haven't tried a pickup yet but the sound card measure test looks real close to your pickup chart? This is a cool program too bad they don't know how to do Mac programming, it sure doesn't work on one...

[Béla]

The measurement was taken from a damaged humbucker that's in a guitar that has an onboard buffer (I don't know the input impedance of the circuit - Vref is on one end of the pickup and the other end is going into the non-inverting input of the TL082, and there are no tone or volume pots directly on the pickup).

A sound card calibration should not look like that at all. It should be mostly flat (within 0.5 dB), with a roll-off at the extremes, at around 5Hz on the bass side and 18kHz-20k on the treble. I'm using the built-in AC'97 sound card output on my desktop PC, and it's going into the input of a Boss GT-8 (going back into the computer via SPDIF).

[Possum]

...

the sound card test on my laptop looks alot like your chart :-) if you look at the help files in the program they have an example thats pretty close to what I got. You have to save that as a calc file then it compensates for the cards' flaws.
How did you hoook up the driver coil? It has to be set vertically between the two coils, not flat over one of the coils, that Lemme article shows how to do that....I"ve never measured humbuckers before, just single coils with a driver coil. will be interesting to do this with buckers if I have time to mess with this.....

[Béla]

Check the scales on the charts. On the response that I've posted the resonance is at 4kHz, and it's 6dB high. That's a lot compared to the examples in the help file. Those are flat within a decibel, and even the first example with the passband ripple, the response is within 1dB in the range most important for pickups.


Btw, I was using the integrating .cal file for that test. Otherwise the result is a big peak with no flat parts. I've also tried this with a cassette tape reading head that I removed from a 5$ Chinese cassette player, and that gave the same results without the integrator.

I'll post a couple of charts with other guitars that are laying around the house, gimme a few minutes...


edit: I'm getting problems with consistency. I can't seem to be able to properly repeat the measurements, but this is most likely due to the unfit equipment I'm using.
I think you guys got the idea. It's not about REW, you can use any frequency analysis program. REW was a free alternative that I came across a while ago that I could use for transfer function measurements of stuff. You could use another program on a MAC.

[Possum]

driver coil

you should really wind a humbucker bobbin driver coil, very low impedance, using a cheap earphone probably isn't the way to go and your resulting chart is including the response of the headphone. I made a driver coil after alot of discussion with Joe Gwinn, I used 36 gauge wire to about 50 ohms if I remember right. for a bucker you flip that up on its side and place between the two humbucker coils, to drive both coils simultaneously. If I find time to do this and get it working on the laptop I'll post a chart and see how it works out.

Also I got an email from the programmer and some suggestions for setting up a Mac but on the forums, those trying his suggestions didn't have any luck. It does run on the Mac Intel mini's he says so there's that......

[R.G.]

no this is different method, AC resistance, AC voltage, the other method is to use a spectrum analyzer, charting software, I don't think it operates the same way. Joe Gwinn had a similar method of hooking the frequency generator directly to a pickup and a resistor and reading voltage across the resistor to find peak resonance, trouble is it didn't work very well with hand wound pickups that can have very smooth peaks so you kinda got lost trying to find it. I kinda like SK's method because it deal in numbers not lines on paper. Simple. Yes there's no standard way to measure any of this, if it works for your needs that all that I care about...

Then either I didn't do a good job of describing or it was otherwise hard to read. Same process.

I've had good luck with it on the "fence post guitar" from the little time I've been able to put into it.

Enjoy.

[Possum]

....

I'll be real curious to see what kind of charts this REW program does, the one Bela did looks weird compared to my experience with two other programs. By his chart I would say that is one screechy bright pickup, so I think something is amiss there. Probably won't be til the weekend til I can try this and I'm not sure how great the sound card in this laptop is, worth a try I guess.....

[Joe Gwinn]

You should really wind a humbucker bobbin driver coil, very low impedance. ... I made a driver coil after alot of discussion with Joe Gwinn. I used 36 gauge wire to about 50 ohms if I remember right.

That sounds right. The 50 ohms was to match certain kinds of instrument input or output, but isn't otherwise important. Specifically, my signal generator has a 50-ohm output impedance, and my scope has 50-ohm inputs as well. Fifty ohms is an industry standard.

The key is to use a coil whose impedance is dominated by the DC resistance of the wire, not inductive reactance or resonance, so the coil will not add too much to the measured response. If I recall, I ended up putting a resistor in parallel with the coil, to damp resonances. It will take some research into my lab notebooks to reconstruct the analysis of the day.

What are the output specifications of the sound card in question? It may be designed to drive a low-impedance speaker.

[Béla]

I'll be real curious to see what kind of charts this REW program does, the one Bela did looks weird compared to my experience with two other programs. By his chart I would say that is one screechy bright pickup, so I think something is amiss there. Probably won't be til the weekend til I can try this and I'm not sure how great the sound card in this laptop is, worth a try I guess.....

Actually, you are right. It is a bright pickup, combined with the preamp.
That was my "experiment guitar's" bridge pickup, and it has a built in buffer with a very high input impedance (I don't know how high it is actually).
Also, that pickup probably has a few shorted windings... It's a bit noisy for a humbucker, though it is shielded with aluminium foil (told you, experiment guitar)

Here's another chart from a different guitar. It is a neck-through sandwich body type from an unknown manufacturer, and it has two humbuckers.



Green plot is the bridge humbucker, blue is the neck, red is the bridge humbucker with the tone pot at 0.
The bass is probably rolled off because of the coil's response

[Possum]

my graphs....

OK, here's the result of dinking around on this stupid PC, jeez these things are archaic compare to Macs. Anyway this is a sweep of 3 different pickups or is it 4? I can't see the jpeg here, oh wait there it is. OK, I'm getting the same kinds of results that Fuzz Measure gives me. I'm basically outputting the sweep signal into a computer powered set of speakers made by Yamaha and using that to power the 55 ohm drive coil, the pickup is corrected direclty back into the PC. Stupid simple. The only difference is I'm getting a weird peak around 7 hz, I have no idea what that is about.

The pickups are a strat pickup of mine, and you can see the peak at about 5.8Khz. NOw here is why I find this stuff kind of useless, the other 3 pickups are a Kleenex box pickup by Kay, my Pig-90 early prototype bridge, and my Little Charley blade pickup. The blade you can see has a drop in the bass response around 20hz. Other than that look how closely those 3 charts are, they all follow a similar trace, but I can guarantee you they have very distinct tonal characteristics. So how useful are these charts really? I'm going to try swapping out an alnico 3 for a 2 in a bucker and see what that does but I'm betting you wont even see the change :-) OK, I think I'm done wasting alot of time making this dang thing work, it was fun but gotta get back to work....

[Possum]

........

I guess it would make sense to not have the sweep start from zero, is there really a peak at 7 hertz? who could hear that any way ?

[Possum]

oh shit....

some hookup problems some of those graphs were of noise. here's one done right, this makes more sense. hmmmm, could be useful in some ways, will have to experiment more, not sure how volume level of drive coil affects the outcome yet.....

[Béla]

I don't understand something.
Shouldn't the pickup be a lowpass filter of some sorts? How this can be?