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previous: Joe Gwinn On 5/7/2006 7:04 AM, moocow said: -- 1147010959 View Thread

Re: Insulation tonal differences?

5/7/2006 12:41 PM
moocowRe: Insulation tonal differences?
The error is caused by the loading of the pickup by the meter. Winding capacitance can't be measured directly, it has to be calculated based upon the pickup resonant frequency. At the resonant frequency, the pickup impedance becomes very, very high. The meter itself has an input impedance that is also high but it can only give accurate readings when used to measure voltages across components with an impedance much lower than the meter impedance. The pickup impedance at resonance is so high, and the meter's impedance affects the response of the pickup.  
 
In my experience, I can measure a resonant frequency of 12kHz or so for a Stratocaster pickup. Here is the setup I use:  
 
http://home.comcast.net/~bcbarrera/files/pickup/Resonant_Frequency_Measurement.gif  
 
Voltage is measured across the 1M resistor and the frequency is adjusted for minimum voltage across this resistor. But I put the meter across the pickup itself and measure voltage directly, I measure a resonant frequency around 8kHz. The pickup and test conditions are the same, only the placement of the meter is different. I challenge anyone to try this and get the same readings with the meter in both positions.  
 
Most of the other resonant frequency mesurements I've seen are les than 10kHz which tells me people are doing it wrong. Seymour Duncan is able to measure resonant frequencies above 10kHz, which tells me his people know the correct method of measuring resonant frequency.  
 
The driving coil gives the wrong result because the meter is loading down the pickup and throwing off the reading. Fortunately, the driving coil does give good results when measuring the in-circuit resonant frequency of the pickup. The pickup is already loaded down by at most 200K of resistance. The meter impedance is much higher than this value so it will not throw off the performance of the circuit.

 
Replies:
Joe Gwinn On 5/7/2006 6:41 PM, moocow said: <... -- 5/7/2006 1:06 PM