ecmalmo
Apprentice Shielder
Posts: 46
Likes: 7
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Post by ecmalmo on Apr 4, 2022 10:45:21 GMT -5
What does the DCR to inductance ratio say about how a pickup will sound or behave, if anything? For example, I can wind a humbucker with 9K DCR and 5.6H inductance using 42 AWG wire. But I can also wind a humbucker with 8.4K DCR and 5.6H inductance by increasing the tension while keeping the wind count similar. I generally try to keep the tension as high as possible without snapping or deforming, seems like a waste of wire otherwise. I can't really say anything definite about sonic differences.
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Post by ms on Apr 4, 2022 12:53:56 GMT -5
When you decrease the resistance while keeping the inductance the same you make the Q of the circuit higher: that is, the resonant peak becomes a bit narrower and higher. Your pickup is a humbucker, presumably with steel cores. In this case most of the loss (that is, current in resistances) in the pickup electrical circuit might be from eddy currents in the steel. Then a slight change in the DCR of the coil might not make enough difference to hear because its contribution to the total loss is relatively small.
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Post by stratotarts on Apr 4, 2022 13:31:36 GMT -5
Also, the bare unloaded Q of the pickup is never heard in practice, when you listen, you are hearing it in the guitar circuit which loads it. The resistive load of the controls has approximately 10 times the influence on the Q, as does the wire resistance. Potentiometers are usually specificied with very wide tolerances compared with most fixed resistors, so it doesn't make sense to agonize over a small difference in the coil resistance, even if you are worried about Q generally.
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Post by JohnH on Apr 4, 2022 17:31:21 GMT -5
When you use an analysis tool such as a Spice program to model a pickup in circuit and then adjust only its resistance, it generally shows negligible difference. Inductance is far more significant.
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Post by aquin43 on Apr 5, 2022 4:14:31 GMT -5
The following is roughly true and neglects shifts in the resonant frequency due to loading among other things.
For a resistance R in series with the coil, the Q is ω0 * C * R where ω0 is 2*pi*(resonant frequency) and C is the load capacitance.
For a lossless coil with a resistive load r across the capacitor, the Q is ω0 * r/L.
From these results, for the same Q in both cases, you could say that a load resistance r across the output is roughly equivalent to
R = L /(C * r) in series with the coil.
So, assuming our standard load of 470p and 200k with inductance 5.6h
r = 200k C = 470p L = 5.6
R = 59k57
So the standard load swamps the coil resistance in this case.
Very large coil resistance will have an effect when the tone control is turned right down. The typical peak around 400 Hz will not appear.
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Post by ms on Apr 5, 2022 10:33:36 GMT -5
Yes, my mistake. With the guitar cable in the circuit, the resonance is low enough in frequency so that the most important loss is from the parallel combination of the volume and tone pots. (With the tone pot on 10, the capacitor can be modeled as a short circuit near the resonant frequency.) Eddy current losses increase with about the square root of frequency, so there is a frequency where they become dominant, but that frequency is higher than we are concerned with.
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Post by antigua on Apr 6, 2022 12:24:17 GMT -5
What does the DCR to inductance ratio say about how a pickup will sound or behave, if anything? For example, I can wind a humbucker with 9K DCR and 5.6H inductance using 42 AWG wire. But I can also wind a humbucker with 8.4K DCR and 5.6H inductance by increasing the tension while keeping the wind count similar. I generally try to keep the tension as high as possible without snapping or deforming, seems like a waste of wire otherwise. I can't really say anything definite about sonic differences. There wouldn't be an audible difference, because with tone and volume pots modeled in LTSpice with that small of a series R difference, the change in Q factor is way below 1dB, which is the practical floor of human hearing. So I know that customers use DC resistance as a proxy for inductance, but if you make two pickups with identical inductance and varying DC resistance, the pickups are much more identical in terms of sound than if you can altered the inductance for the sake of having a the DC resistances match. Hopefully quality LCR meters will come down in price some day, and more people will judge pickups in terms of inductance instead of resistance.
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