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Re: damping factor

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You got the idea, but measuring the source impedance is not as easy as that. You do it by applying a signal to the amp with no load, driving the amp to the rated output voltage (based on it's power rating), and then loading the amp with a resistor and measuring the output voltage again. From the change in voltage you can calculate the internal impedance of the amp, and from that you can calculate DF.

I do it at three frequencies (50, 1000, and 10,000 Hz)as the impedance can change with frequency. Since most DMM's are not accurate at higher frequencies (my Fluke is good to 1 kHz, and my Wavetek to 2 kHz), I use a broad band AC voltmeter above 1 kHz, but it's an analog meter ands resolution suffers. Some of the True RMS DMM's do go to over 20 kHz, and that would be the best.

If it's a tube amp, you need to make the measurement for each tap as they are different. Also, on a tube amp, or a SS amp with an output transformer (like the Macs)you calculate DF by dividing the source impedance measurement by the tap impedance. For direct or capacitvely coupled SS amps you just use 8 as the divisor.

Jerry


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Topic - damping factor - KLHman 14:42:39 06/28/05 ( 15)