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Amplifier Dummy Load for THD measurements / non-inductive?
Amplifier Dummy Load for THD measurements / non-inductive?
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Old 15th October 2017, 01:26 PM   #31
Zymorg is offline Zymorg  Germany
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Just ordered a tpa6120 headphone amp module from china as well. It's so unbelivable cheap and has even the power supply on board (except for traffo).
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Old 15th October 2017, 01:31 PM   #32
Zymorg is offline Zymorg  Germany
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@Burnedfingers: Are they really non-inductive? What size of amps are you testing?
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Old 15th October 2017, 02:06 PM   #33
Mark Johnson is offline Mark Johnson  United States
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Amplifier Dummy Load for THD measurements / non-inductive?
Among many other applications, I use dummy loads for amplifier slew rate testing. So I prefer them to remain noninductive all the way up into the dozens of megahertz when possible.
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Old 15th October 2017, 03:21 PM   #34
1audio is offline 1audio  United States
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Amplifier Dummy Load for THD measurements / non-inductive?
Once you add cables all bets are off. If you have the right instrumentation you can characterize to whatever you need but its not cheap. Above a few KHz you really are best served with a vector network analyzer. Connecting with a cable then adds to the problem since the cable will be 50 Ohms or higher.
I'm away from my shop for another 2 weeks but I can plot the resistors to 3 GHz when I return if its of interest.
Slew rate into a resistive load is interesting. Do you sweep to 3% HD to find where the output departs from feedback control? How does capacitive loading affect the slew rate? Lots to explore.
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Old 15th October 2017, 04:47 PM   #35
Mark Johnson is offline Mark Johnson  United States
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Amplifier Dummy Load for THD measurements / non-inductive?
Nah, I just remove the input LPF and apply a fast risetime square wave whose amplitude is chosen to swing the output almost to clipping. Slew Rate =approx= deltaV/deltaT .

In the picture below, 35V / 320nsec = 109 Volts/usec

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File Type: png slew.png (30.3 KB, 42 views)
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