Audio Power Amplifier Output Impedance

A power amplifier may have a rated impedance of 8 ohms but the actual output impedance will vary depending on circuit conditions.

Audio power amplifier output impedance. For the final stage where a last amplifier supplies a transducer lets say a loudspeaker the output impedance of the amplifier must be lower than the internal loudspeaker resistance. That is high enough to be driven comfortably by any audio source output. Generally the input impedance to an audio amplifier is high. Again for the same reasons the power is transferred more efficiently to the transducer if the amplifier has a low output impedance.

Preamps usually have an output impedance of less than 1k ohm and power amps will have an input impedance of at least 10k ohms but more commonly 22k or 47k. The power output will be increased with lower impedance speakers but the maximum power output will not be doubled when the impedance is halved. That means the output impedance of your power amplifier should be at least 0 3 ohms and probably better at 0 03 ohms to really have very little affect. 10k to 100k is the usual sort of range we find though some can be less.

We have no impedance matching power matching we use impedance bridging voltage bridging whereby the power amplifier often has an output impedance of only one hundredth of the speaker s input impedance. Input impedance z in or input resistance as it is often called is an important parameter in the design of a transistor amplifier and as such allows amplifiers to be characterized according to their effective input and output impedances as well as their power and current ratings. The actual output impedance for most devices is not the same as the rated output impedance. As an example of a real world amplifier let s look at the specifications of a popular pa amplifier purchased at amazon through this site the crown xls1000.

Generally it is desirable that the output impedance is low and the destination impedance high and this is the case with the majority of modern equipment. The rated output impedance is the impedance into which the amplifier can deliver its maximum amount of power without failing. Tubes generally have higher output impedance than solid state products. On the output side a loudspeaker may still have a nominal impedance of something like 8 ohms which formerly would have required having an amplifier output stage carefully matched to 8 ohms.

One piece of evidence you see in most tube power amplifiers is the output transformer of the tube amp. An amplifiers impedance value is particularly important for analysis especially when cascading individual. But of course without a proper specification you are taking something of a gamble. But now with the active output circuitry of audio amplifiers the effective output impedance may be very low.

4 ohms to 8 ohms to tell the user that a 4 ohm speaker or.