Hi!

What is typical output impedance for audio amplifier and for which frequency this impedance is valid ?

Thanks for replays


Sniper

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There are two major products that came out of Berkeley: LSD and BSD. We don't believe this to be a coincidence. —Jeremy S. Anderson

 

Well for standard class A/B DC coupled output the output impedance is inversely proportional to it's power output. Well under a tenth of an ohm for the higher power amps.

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Measurement changes behavior

 

An audio amplifier has a specification called "damping factor" which is its damping effect on the resonances of speakers due to its extremly low output impedance. Most modern audio amplifiers have a damping factor of 200 (its output impedance is 8/200= 0.04 ohms but some have a damping factor of 1000 (0.008 ohms). The open-loop voltage gain of an audio amplifier is high at low frequencies so a lot of negative feedback is used to reduce the gain to a useable amount which also decreases the output impedance. The gain drops at higher frequencies and the output impedance increases.

Many old vacuum tube amplifiers had an output impedance the same as the speaker's impedance. They provided very poor damping so their speakers had damping built-in to reduce resonances.

Attached Images

damping factor.PNG (8.0 KB, 14 views)

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Uncle $crooge

 

Tnx alot

Sniper

__________________
There are two major products that came out of Berkeley: LSD and BSD. We don't believe this to be a coincidence. —Jeremy S. Anderson