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Thread: Measuring resonant peak

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    Measuring resonant peak

    Hey there fellas, anyone here attempt to measure resonant peak of pickups. Either with dual trace or one of them fancy syscomp design boxes? And if so, what was your method/chain?

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    There are many threads already regarding measurement of resonance peak and using the Syscomp goodies.

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    Supporting Member mozz's Avatar
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    A signal generator and a scope to show the Lissajous pattern works great. You need a good LCR meter also to measure the inductance. I have that and a Syscomp setup. The scope probes included with the Syscomp load down the circuit and give false readings due to the high capacitance, especially on 1x. You need decent probes with the lowest picofarads you can afford. I should draw my circuit out but it was pieced together from the web.

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    With a search I found a couple things to answer the questions I had. I was more curious of the different methods people use. I personally just started running the Syscomp Mini since its the easiest. But part of me really wants to grab a scope and generator.

    Also, thanks to the guys that sent me PMs on how they do it. Good reading!

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    Supporting Member StarryNight's Avatar
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    Quote Originally Posted by mozz View Post
    The scope probes included with the Syscomp load down the circuit and give false readings due to the high capacitance, especially on 1x. You need decent probes with the lowest picofarads you can afford. I should draw my circuit out but it was pieced together from the web.
    that's too bad. I have the CGR-101 and they even have a whitepaper on how to measure RP on a pickup using that unit. Why would they include probes that give a false reading for a device that they sell to many pickup makers with the intention of measuring RP? How false of a reading are we talking about?

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    Quote Originally Posted by StarryNight View Post
    Why would they include probes that give a false reading for a device that they sell to many pickup makers with the intention of measuring RP?
    Because super-low capacitance scope probes are way expensive?

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    Supporting Member mozz's Avatar
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    Quote Originally Posted by StarryNight View Post
    that's too bad. I have the CGR-101 and they even have a whitepaper on how to measure RP on a pickup using that unit. Why would they include probes that give a false reading for a device that they sell to many pickup makers with the intention of measuring RP? How false of a reading are we talking about?
    They don't give a false reading, they give a wrong reading. Add 30pf in your formula and you will see about 1000hz drop in the resonant frequency. That was with a single coil 120 pf and 2.2h. If you are just using it to compare pickups, it really doesn't matter. If you have a capacitance meter, measure the probe and you will see how much capacitance it has. A better probe and more expensive will have about 8pf.

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    Senior Member salvarsan's Avatar
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    Quote Originally Posted by mozz View Post
    You need decent probes with the lowest picofarads you can afford. I should draw my circuit out but it was pieced together from the web.
    Yeah, a drawing would help because without it, you come off as confrontational. Unless you're comfy with some schematic capture software, scrawl one on a legal pad with a Sharpie and upload the photo.

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    On the subject of resonant peaks and capacitance, there's not really a benefit to finding the true resonant peak of a pickup, for it's own sake, unless your goal is to calculate the capacitance of the coil from the resonance and the inductance. The capacitance of a given single coil will vary by about +/- 50pF, but that will combine with the guitar cable to tack on another few hundred more pF. For data gathering purposes, I measure a "raw" resonant peak as well as a resonant peak with a 470pF load in order to get a value that is more "real world". For a Strat pickup of around 2 henries, it's common to see a raw resonant peak of 10kHz, but with a 500pF guitar cable, it falls down to around 4kHz.

    The scope probe will add about 10 to 20pF, and the CGR-101 will add another 20pF according to the spec sheet CGR-101, so you can get pretty close to calculating the true resonant peak by taking the inductance and the calculated capacitance, then subtract, say 25pF from that calculation, and then recalculate for resonance with that lowered capacitance estimate.

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    Supporting Member mozz's Avatar
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    Yes that's all true. I like to experiment with different winding techniques and see the variations of capacitance. They will affect the sound. When I often wind a set of 3 single coils, the first wound usually has higher capacitance due to me paying more attention how i am laying down the wire, after that i get sloppy and impatient and they get more scatter wound.

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    Quote Originally Posted by mozz View Post
    Yes that's all true. I like to experiment with different winding techniques and see the variations of capacitance. They will affect the sound. When I often wind a set of 3 single coils, the first wound usually has higher capacitance due to me paying more attention how i am laying down the wire, after that i get sloppy and impatient and they get more scatter wound.
    How do you regulate the winding tension?

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    Senior Member LtKojak's Avatar
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    Quote Originally Posted by Antigua View Post
    How do you regulate the winding tension?
    Mojotone Hand Guided Tensioner | stewmac.com

    A little overpriced, but definitely a helpful tool, specially for the beginner.

    HTH,

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    Pepe aka Lt. Kojak
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    ToneOholic! big_teee's Avatar
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    I still tension with my fingers!
    T

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    Supporting Member mozz's Avatar
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    I have the spool about 1 ft off the floor, goes through 2 pieces of felt sandwiched between 2 pieces of metal, then i use my fingers to hold the wire and guide it.

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    Quote Originally Posted by mozz View Post
    I have the spool about 1 ft off the floor, goes through 2 pieces of felt sandwiched between 2 pieces of metal, then i use my fingers to hold the wire and guide it.
    Same here!

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