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How do you read amplifier power output specifications?

post #1 of 2
Thread Starter 
Sometimes an amp has a single number reported for its power output at a certain load.
e.g. FiiO X3 2nd gen outputs >200 mW (32 Ω/THD+N<1%)
http://www.fiio.net/en/products/39/parameters

Sometimes an amp has two numbers reported for its power output at a certain load.
e.g. Sony PHA-1 outputs Approx 175mW+175mW (8Ω, 10% distortion)
http://www.sony-asia.com/product/pha-1

Usually multiple numbers indicates output channels. The PHA-1 has a single 3.5 mm stereo TRS output. Does the reported power output mean 175 mW for the left channel and 175 mW for the right channel?


A headphone is often reported with just a single impedance value.
e.g. AKG K 701 has a 67 ohm impedance rating
http://www.innerfidelity.com/images/AKGK701SampleB.pdf

Does this mean the headphone has a total resistance rating of 67 ohms, or does that mean each channel (left or right) has a resistance of 67 ohms each?
post #2 of 2
Quote:
Originally Posted by miceblue View Post

Sometimes an amp has a single number reported for its power output at a certain load.
e.g. FiiO X3 2nd gen outputs >200 mW (32 Ω/THD+N<1%)
http://www.fiio.net/en/products/39/parameters

Sometimes an amp has two numbers reported for its power output at a certain load.
e.g. Sony PHA-1 outputs Approx 175mW+175mW (8Ω, 10% distortion)
http://www.sony-asia.com/product/pha-1

Usually multiple numbers indicates output channels. The PHA-1 has a single 3.5 mm stereo TRS output. Does the reported power output mean 175 mW for the left channel and 175 mW for the right channel?
 

 

Yes.

 

Also, FiiO X3 2ndG has 200mW on the left, as well as on the right channel. If it were to be written in the Sony way, it will be '200mW + 200mW'. That's kind of a waste of time to write so, given both channels have to be equal or else it must be faulty. Of course sometime manufacturer also list the rather misleading 'combined power', which adding power from both channels together.

 

Quote:
Originally Posted by miceblue View Post

A headphone is often reported with just a single impedance value.
e.g. AKG K 701 has a 67 ohm impedance rating
http://www.innerfidelity.com/images/AKGK701SampleB.pdf

Does this mean the headphone has a total resistance rating of 67 ohms, or does that mean each channel (left or right) has a resistance of 67 ohms each?

 

It usually means the headphone has a 67ohm impedance @ 1kHz on the right and left channel. Not combined. Remember, the transducers ain't driven in serial, but in parallel.

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