Originally Posted by Hamilcar Barca
Originally Posted by Hifisound
How much should one worry about the output impedance of the headphone amp , esp for headphones like Grado (32 ohm) ? Does the amp need to be ideally below 10 ohm ?
I was also looking at Behringer Mini Mon 800 - http://www.behringer.com/EN/Products/MON800.aspx
but looks like its suitable only for HD600 as it says impedance of 100 ohm
The headphone's impedance should be at least 8 times the amp's output impedance or damping may suffer. I don't know how 32-Ohm Grados react to excessive output impedance.
At 100 Ohms, the MiniMon 800's impedance is probably too high for the best sound.
BTW I believe that the source impedance of headphone jack on Behringer's UCA 202 USB DAC is more like 50 ohms.
Damping is generally not an issue with headphones because they are generally inherently well-damped. With speakers damping is pretty much just another name for source impedance as they can be defined in terms of each other. And while I's at it, all of this talk about counter-emf can be simplified into something that is far less mysterious, being the device's impedance curve.
I think your basic idea is good, but there are other considerations. For example, the uniformity of headphone impedance curves vary from flat to mountainous. If the headphones have a flat or relatively flat impedance curve, then source impedance matters far less. Headphone impedance curves get some publication, so you can often look before you leap.
I would never use a pair of headphones comfortably in a situation where I didn't not have an equalizer in the signal chain. What a high source impedance plus headphones with a bumpy impedance curve do is alter the frequency response of the headphones. If the listener can use an equalizer to push back and restore his desired frequency response, then the ill effects of the high source impedance and bumpy impedance curve are reduced or eliminated.
If your headphone amp has more than adequate output voltage, putting a 16 or 32 ohm resistor in parallel with your headphones can lower the source impedance.