Antigua wrote: ↑Wed Mar 14, 2018 7:56 am
A guitar string is not a significant factor in the magnetic circuit, because it is very small and very far away from the pickup. It's presence probably doesn't alter the inductance of the pickup more a fraction of a millihenry. That's something that could be determined with an LCR meter.
Sure, it is not a significant factor while at rest, pluck the string and we get output. It is at least as important as any other part of the circuit since if you remove it, we no longer have a working system.
Antigua wrote: ↑Wed Mar 14, 2018 7:56 am
Interesting, not a bad idea, but as you say, still somewhat unlike a guitar string, and it would a cumbersome test rig to create. I also have issues with electric motors producing noise. I'm not sure how they deal with that in a Hammond.
Unlike a guitar string, but more like a string then your air coil. Creating it is mostly an issue of the time required which is probably on par with the time it took you to create/calibrate your rig, or just an issue of cost and buying a tone wheel from an organ. The motor is not really an issue, there are plenty of quite motors out there, if there were not we would not have had tape recorders or record lathes and the world of music would be a very different place. Even if you were to use a noisy motor, that noise is easy enough to remove from the equation.. But as I said, if I do go down this path I plan on using a hand cranked grinder, which has no motor and I do not need to design/build a control circuit to get a frequency sweep.
Antigua wrote: ↑Wed Mar 14, 2018 7:56 am
I think it's best that the test coil have an air core, the keep the reluctance path as high as possible between the test equipment and the thing being tested.
But that is not accurate to reality, driving the pickup that way does not show what a pickup actually sees, you do not even need the magnetic circuit to drive the pickup this way, you just created an air coupled transformer were one coil has an magnetic core and one does not. A pickup and a string is a generator (transducer), not a transformer, your test is electrical to electrical and not mechanical to electrical. As to how accurate this is, I have found nothing concrete to address this and such studies as yours are fundamentally flawed without this information. After doing the tests it may indeed turn out that driving the pickup with a coil is close enough, or even accurate, as of now it is just an assumption.
In the end I think a combination of your test, testing without the magnetic circuit, the tone wheel and the string wound coil would provide a great deal of information. None of them are ideal, but the comparative results would be interesting, all four tests tell us different things about the whole and also tell us (hopefully) how reliable any of the other tests are.
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