[theBigD]

i just purchased some akg 701 headphones. now i need an amp. i noticed many amps have a switch or dial to adjust the impedance. some dont. how important is this feature and can it negatively impact the sound?

 

[laxx]

Are you lookign for a portable or home amp. It's more important for portable amps as you might eventually move into the IEM world, where you'll have alot of hiss with high gain amps. But for a home amp, it's not important at all.

 

[Balisarda]

I couldn't care less about variable output impedance--I want that figure as low as possible!

As an amplifier's output impedance nears or surpasses the transducers' input impedance, the amplifier becomes less able to control the transducers tightly (damping factor) and the output signal is attenuated, with a disproportionate bias against treble, making the final product sound darker.

But I suppose if you enjoy a darker sound and don't mind slightly mushier bass, you may prefer a higher output impedance.

As an aside, I've experimented with both the high- and the low-impedance output jacks of my Corda using both my HD 650 (300 Ohms?) and my RS-1 (32 Ohms?). The RS-1 is effected MUCH MORE than the HD 650. This is in part because even the high-impedance jack's output impedance (120 Ohms) is much lower than the headphone's input impedance. Still, for what it's worth . . .

EDIT: Sorry, after reading laxx's post, I wonder: are you talking about variable output impedance or variable gain?

 

[mrarroyo]

I would say that one advantage to having a gain switch it that it allows more control by the volume control. For example if you have a "hot" source (high output say 2.2 Vrms) and you hook it up to an amp w/o a gain you probably could only bring the volume up to 9am before you say way to loud. However by having a gain switch to low you may be able to go all the way to noon. IMO this is the advantage it offers.