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Power Resistor Inductance Measurements
Power Resistor Inductance Measurements
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Old 16th September 2019, 05:47 PM   #21
phase is offline phase  United States
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Any particular model of Allen Bradley resistor?

Am sorting out a fet output amp and am looking at options.
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Old 16th September 2019, 06:04 PM   #22
edbarx is offline edbarx  Malta
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If this inductance component of wirewound resistors manifests itself in real circuits, a frequency source can be used to obtain a table of readings as follows:
Column: Frequency/Hz, Voltage/V, Current/mA, Current Phase with respect to input voltage.
Several reading (not less than 5) should be taken.

Using an equivalent circuit for the resistor plus parasitic inductance and parasitic capacitance, the values of both can be calculated, and then tested to predict current and phase values out of the measurement range (extrapolation).

The parasitic inductance is in Series with the resistance and the capacitance in Parallel with the series RL arm.

The derivation of the formulae can be done using BOTH phasor diagrams (2D vectors), and complex numbers.

Since these are measurable qualities of wirewound resistors, the quickest way to ascertain oneself of their behaviour is to measure them and simulate them.
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Old 17th September 2019, 02:32 AM   #23
johnego is offline johnego  Indonesia
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Quote:
Originally Posted by phase View Post
Any particular model of Allen Bradley resistor?

It's the regular carbon composition one. I have stocks of 0.47 Ohm. I think it must be good ones that the resistance value is accurate. Must be hard to find such values?
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Old 20th September 2019, 12:28 AM   #24
phase is offline phase  United States
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Thanks, those are certainly getting harder to find it looks like.
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Old 20th September 2019, 02:02 AM   #25
AllenB is offline AllenB  Australia
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Quote:
Originally Posted by johnego View Post
It is not to be used in feedback and almost anywhere else in an amp.
Can be used as a plate load, carrying DC so that it has a chance to enhance even harmonics.
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Old 20th September 2019, 05:09 AM   #26
johnego is offline johnego  Indonesia
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Quote:
Originally Posted by AllenB View Post
Can be used as a plate load, carrying DC so that it has a chance to enhance even harmonics.

For tube amps, we have many better low noise carbon options than the Allen-Bradley, tho probably expensive.
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Old 20th September 2019, 05:34 AM   #27
kecapmanis021 is offline kecapmanis021  Indonesia
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Quote:
Originally Posted by AllenB View Post
Resistor types have different Voltage coefficients. The resistance changes slightly depending on the Voltage across the resistor. This may create odd-order harmonic distortion in a crossover, and sometimes even orders in an amp.
I agree with AllenB, I believe V coefficient has something to do with the way certain resistor material respond to transient in music.
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Old 20th September 2019, 06:49 AM   #28
johnego is offline johnego  Indonesia
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Quote:
Originally Posted by kecapmanis021 View Post
I agree with AllenB, I believe V coefficient has something to do with the way certain resistor material respond to transient in music.

AllenB talked about its effect on harmonic types when used in crossover. I didn't perceive any change in harmonics type by ears. It may also be undetectable when measured. In amps, V/T coefficients are probably the most important parameters, but not all. I don't even know what the most critical parameter that makes my favorite resistor (secret! ) sounds the way it does.
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Old 20th September 2019, 11:32 AM   #29
AllenB is offline AllenB  Australia
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Some components in a crossover are either too small/large or in the wrong position to make any noticeable difference this way.

What else could there be to make a difference, carbon composition are non-inductive?
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Old 20th September 2019, 02:58 PM   #30
johnego is offline johnego  Indonesia
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I didn't find resistor type crucial in passive crossover. Sound different doesn't mean better or worse. In amps it is different. I think it is inductance.
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