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JBL 16th September 2001 04:48 PM

Is it possible to mesure power output of an amplifier with a DMM. Also wath factor influence the slew rate of audio amp, and how do you mesure/predict slew rate for a given amp.

Hoffmeyer 16th September 2001 07:01 PM

No, since you'll have to observe when the clipping of the sinewave occures. What you'll need is a sinewave-generator, an osciloscope and a loadresistor, preferably on a heatsink.

Slewrate expresses the ability to respont to an input, and is limited by any capacitance, such as Miller- and straycapacitance, and any kind of frequency compensation. Please correct me if I've missed something.
To meassure slew-rate, you'll need all of the above mentioned. Slew-rate is meassured at full output, and you can start at say 1kHz, and then raise the frequency till the sinewave at the output is distorted. Then the slew-rate is calculated using the equation : SR = 2*PI*U(peak)*f, where f is the frequency where the distortion occured, and U(peak) is the maximum voltageswing. The latter is NOT always equal to Max voltageswing at 1kHz, due to possible bandwidth-limitation.
I hope this will answer your question.

P.Lacombe 16th September 2001 10:51 PM


Slewrate is also limited :

In vacuum tube amplifiers, by the leakage inductance between the primary and the secondary of the transformer(s)

In jonction transistor amplifiers, by the accumulation of charge carriers in the jonctions, specially of output devices.

Regards, P.Lacombe

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