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Vintage threads from the first ten years

Re: Insulation tonal differences?

5/6/2006 10:14 PM
SK	Re: Insulation tonal differences? I'll need to go back a bit, but I have capacitance measurements, as well as inductance and peak voltage/freq measurements for many pickups. I can tell you inductance (due to #turns or additional metal) capacitance (due to tension/scatter)seem to be the big factors. I have measured capacitance for pickups wound very similar (hey, I hand wind...they're never identical) but using different insulation materials and thicknesses and they fall within "error tolerance" of each other. I could easily change the capacitance that much by a bit less scatter or winding a bit tighter.

5/6/2006 10:14 PM

Re: Insulation tonal differences?

I'll need to go back a bit, but I have capacitance measurements, as well as inductance and peak voltage/freq measurements for many pickups. I can tell you inductance (due to #turns or additional metal) capacitance (due to tension/scatter)seem to be the big factors. I have measured capacitance for pickups wound very similar (hey, I hand wind...they're never identical) but using different insulation materials and thicknesses and they fall within "error tolerance" of each other. I could easily change the capacitance that much by a bit less scatter or winding a bit tighter.

5/7/2006 1:04 AM
moocow	I agree that inductance is a part of how a pickup sounds. But if you are changing inductance as well as capacitance and hear a change in sound, you don't know for sure which is responsible for the change. I claim that even significant changes in winding capacitance alone will be inaudible. If you are changing inductance as well, then of course your pickups will sound different. But the discussion so far addresses winding capacitance only, and this is not a contributor to the sound of the pickup. I should add that I do not claim to know why scatter winding, potting, insulation thickness, etc. changes the sound of the pickup. I have some ideas but I don't have enough conficence (repeatable evidence) in my ideas to discuss them. At this point, all I feel comfortable with saying is that it has to do with how the signal is physically generated within the pickup, not how the impedance of the pickup affects the frequency response of this signal after it has been generated within the pickup. Give me some capacitance numbers and I can prove it to you. Hopefully, you didn't arrive at the peak voltage frequency by using the driving coil method. This gives a reading that is at least 25% low, indicating more pickup capacitance than is actually there. I'd still be interested in the variation in resonant frequency you see for a change in capacitance only. Inductance and # turns must be the same or else the change in sound could be due to those factors, not the capacitance alone.

5/7/2006 1:04 AM

moocow

I agree that inductance is a part of how a pickup sounds. But if you are changing inductance as well as capacitance and hear a change in sound, you don't know for sure which is responsible for the change. I claim that even significant changes in winding capacitance alone will be inaudible. If you are changing inductance as well, then of course your pickups will sound different. But the discussion so far addresses winding capacitance only, and this is not a contributor to the sound of the pickup.

I should add that I do not claim to know why scatter winding, potting, insulation thickness, etc. changes the sound of the pickup. I have some ideas but I don't have enough conficence (repeatable evidence) in my ideas to discuss them. At this point, all I feel comfortable with saying is that it has to do with how the signal is physically generated within the pickup, not how the impedance of the pickup affects the frequency response of this signal after it has been generated within the pickup.

Give me some capacitance numbers and I can prove it to you. Hopefully, you didn't arrive at the peak voltage frequency by using the driving coil method. This gives a reading that is at least 25% low, indicating more pickup capacitance than is actually there. I'd still be interested in the variation in resonant frequency you see for a change in capacitance only. Inductance and # turns must be the same or else the change in sound could be due to those factors, not the capacitance alone.

5/7/2006 2:22 AM
Mick	What does a capacitor do? and also does a capacitor change affect the sound? Mick

5/7/2006 8:09 AM

Joe Gwinn

On 5/7/2006 7:04 AM, moocow said:

quote:
"... Hopefully, you didn't arrive at the peak voltage frequency by using the driving coil method. This gives a [frequency] reading that is at least 25% low, indicating more pickup capacitance than is actually there."

How should one measure capacitance? Why would the driving-coil method be off by 25%?

5/7/2006 12:41 PM
moocow	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.

5/7/2006 12:41 PM

moocow

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.

5/7/2006 1:06 PM

Joe Gwinn

On 5/7/2006 6:41 PM, moocow said:

quote:
"The error is caused by the loading of the pickup by the meter. "

Right. My DMM has 100 pF input capacitance in parallel with 20 Mohms. That would certainly lower the resonant frequency significantly if connected directly across a pickup.

However, a 10:1 scope probe is only a few picofarads, so a scope will cause far less trouble.

quote:
"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."

Agree.

[QUOTE]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.[/QUOTE]It strikes me that because the generator impedance is low, probably 50 ohms or less, the 100-pF capacitance of the meter may still be able to lower the resonant frequency of the pickup. Does frequency at which the peak occurs change if the meter has a 100K or 1M resistor in series?

[QUOTE]Most of the other resonant frequency mesurements I've seen are less 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. [/QUOTE]Again, I'd be tempted to use a 100K or 1 Mohm resistor in series with the meter, to isolate the meter's input capacitance.

5/7/2006 4:45 PM
SK	You may be correct in that capacitance isn't a big factor in the signal, BUT capacitance does change notably with scatter/wind tension and those DO affect the tone...I attribute it to capacitance. I've never worried that my testing methods are "scientificly accurate", just that they are repeatable and consistent...I use the data as "comparative". I use a GenRad RLC Digibridge and a signal generator/driving coil/ac voltmeter. I also have a dual channel scope, but not much knowledge on how to use it.

5/7/2006 4:45 PM

You may be correct in that capacitance isn't a big factor in the signal, BUT capacitance does change notably with scatter/wind tension and those DO affect the tone...I attribute it to capacitance.
I've never worried that my testing methods are "scientificly accurate", just that they are repeatable and consistent...I use the data as "comparative". I use a GenRad RLC Digibridge and a signal generator/driving coil/ac voltmeter. I also have a dual channel scope, but not much knowledge on how to use it.

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