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Need help understanding output impedance...

post #1 of 3
Thread Starter 

Hey guys,

So, even after reading this: http://www.head-fi.org/a/headphone-impedance , I'm still having a hard time understanding what headphone out level is supposed to mean. I have this old DAT player that has a maximum output level of 30 mW for each channel, and it says 32 ohms output. Here is the link for the specs: http://www.datrecorders.co.uk/sv3800.php
But the link says that matching impedance should be 8-600 ohms. I thought that the 1/8 rule means that since there is a 32 ohm output, the lowest ohm headphone I can use is 256 (32 x 8=256) Am I wrong? Does the maximum output level mean that it always runs 30 mW, or it runs differently with different headphones? Sorry for the noobish questions, I'm just really confused.

post #2 of 3
No...the output power of 30mW is AT 32ohm load (headphone impedance). The output impedance is not 32ohm!

A lower load (headphone) impedance requires more current, and a higher value requires more voltage. But sources are generally limited in voltage (power), so maximum power is often rated at the lowest impedance, 32ohms being the lowest "common" headphone impedance

Power = (voltage)^2 / impedance

So your unit will put about 1mW into a 600ohm headphone

Damping factor is based on the actual output impedance of the unit, which is not listed in those specs for the headphone out (the analog XLR are listed at 50ohm)
Edited by ferday - 3/27/14 at 11:17pm
post #3 of 3
Thread Starter 
Quote:
Originally Posted by ferday View Post

No...the output power of 30mW is AT 32ohm load (headphone impedance). The output impedance is not 32ohm!

A lower load (headphone) impedance requires more current, and a higher value requires more voltage. But sources are generally limited in voltage (power), so maximum power is often rated at the lowest impedance, 32ohms being the lowest "common" headphone impedance

Power = (voltage)^2 / impedance

So your unit will put about 1mW into a 600ohm headphone

Damping factor is based on the actual output impedance of the unit, which is not listed in those specs for the headphone out (the analog XLR are listed at 50ohm)

Oh! Now I get it, so the maximum it will put out is 30mW for a 32 ohm headphone. Thanks for clarifying!

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