[stv014]

Quote:

Any amp worth its salt will have a fuse or circuit that prevents run-away current and shuts down the unit.

That is true, but why test it if not necessary (especially if fuse(s) may need to be replaced as a result) ?
 

 

[Mauricio]

Wouldn't it be swell if the amp faced just a narrow, known range of impedances, and therefore it could be designed specifically to compensate for them?

 

[wuwhere]

Quote:

It can, for example if its output is capacitor coupled. This is common with low end sources that have a single power supply. For example, a 100 uF capacitor would have an impedance of 32 Ohm at 49.7 Hz, and with a 32 Ohm resistive load and insignificant output resistance, it would attenuate the signal by 3 dB. The same capacitor at 1 kHz has (in theory) only about 1.6 Ohm impedance, and the attenuation is insignificant at that frequency.
 

Described in here?  http://www.allaboutcircuits.com/vol_3/chpt_4/11.html

 

[JefferyK]

This is how it was explained to me years ago:
 
- The impedance of your headphones should be higher than the output impedance of your amp.
 
- The wider the difference between the two, the better.
 
So, for example: I use Sennheiser HD-800s plugged into a HeadRoom desktop balanced amp. The impedance of the headphones is 300 ohms. The output impedance of the amp (supposedly -- I did not get this number from HeadRoom) is 2 ohms, and that number is halved by running balanced, to 1 ohm. The sound is heavenly -- I am very, very pleased.
 
Here's another example: years back, I used Sennheiser HD-650s plugged into a Rotel integrated amplifier. Headphone impedance: 300 ohms. Amplifier output impedance: 180 ohms (or close, can't remember the exact number; I got the number by e-mailing Rotel). The HD-650s sounded pretty good. However, my Grado SR-225s (50 ohms, I believe) plugged into the same amp sounded bad -- overexaggerated on the low end.
 
So, that's my understanding, perhaps oversimplified.

 

[JefferyK]

Quote:

Wouldn't it be swell if the amp faced just a narrow, known range of impedances, and therefore it could be designed specifically to compensate for them?

Well, an output impedance of 0 ohms would mean an amp would match perfectly with all headphones, I think.