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previous: moocow Sorry for being absent, but I've be... -- 7/17/2004 12:41 AM View Thread

Re: Measuring Pickup Resonant Frequency

7/23/2004 7:54 AM
Dave StephensRe: Measuring Pickup Resonant Frequency
Moocow: damn I wish I had your email address, you have got me started on this quest and I mean to make this thing work somehow with what I have. So here goes again:  
Well......the method for finding resonant frequency according to your method (or my stupidity) just plain doesn't work in real life. I got a nice audio signal generator on Ebay that goes from 1hz-1mhz, nice deal for $50. Anyway, so I take my strat pickup, connected a 1megohm resistor across the leads. Then I connected the frequency generator to either side of the resistor, and also across the resistor connected my digital DVM (Wavetek Meterman, which also measure frequency and inductance, very cool...). I put the meter on volts AC and start sweeping the generator through the various ranges. Problem is the lower the frequency the lower the voltage, the higher the frequency the higher the voltage, there is no peak and no drop anywhere. Am I doing something wrong? Needless to say I was VERY disappointed.  
So ok, I thought about it a bit and got a bit pissed off. So I start thinking ok, a resonant peak (in my warped theoretical brain) should be putting out the most voltage from the pickup right? So (ok don't wretch here....) I hooked up a cheap pair of headphones to the signal generator and taped my pickup to the ear piece. Hook the DVM to the pickup and started sweeping the frequencies again. OK, this time there IS a definite high voltage peak. Samples I got are: a Fender strat coil (one that really sucks FYI) peaked at 8,2KHZ, one of my Twister neck strat pickups at 6.7KHZ, and one of my P90 style pickups in a humbucker casing at 6KHZ.  
Now of course I realize that the headphone piece has a magnet in it and that the headphone itself has its own peak resonance and maybe these readings are kinda OFF. But this goes back to windng a coil just to drive the pickup in such a test. I have gotten various opinions on how that coil should be wound and what gauge wire etc. but this should be a cleaner method of driving a signal into the pickup. But, is it true that the resonant peak will produce the most voltage coming from the pickup in such a test?  
Sorry for being obsess here but thats how I am......OK, so what if you want to put a signal into the pickup and want to use a cheap oscilloscope (they are cheap on Ebay for old ones), would this or some other method make the peak more readily apparent than all this math or whatever? I have thought that (I think I read this somewhere) that if you put white or pink noise into a pickup and put it on an oscilloscope you will see where the peak is visually since supposedly white or pink noise is a combination of all frequencies, is this right?  
Another subject covered awhile back was the effect of capacitance in a pickup, but it seems that the capacitance is so awfully low that its probably not really something that you can use to design a coil right? We also discussed whether a normal DVM can actually read the capacitance of a coil, a very confused thread if I remember right....  
OK, Moocow you got me into this now get me out of it and thanks for your input too......Dave

Dave Stephens Well I had to revisit this site fro... -- 7/23/2004 8:03 AM