[MatthewK]

I ask because the manual for my PD XM5 portable amp says it supports headphones with an impedance rating of 24 to 600 ohms.

Do the opamps determine the headphone impedance it supports?

Thanks.

 

[FallenAngel]

Output impedance? The amp design itself determines that. It's basically what the output stage of that amp is and as far as I know, it should be as low as possible so that it doesn't oscillate or burn itself up when driving low impedance loads. I think solid state amps should technically support ALL output impedances, whether they have the power to drive them properly is another matter altogether. I know my PPAv2 doesn't like anything too low, but after fixing it as much as I could, it drives my MylarOne X3 (12Ohm) without overheating.

 

[MatthewK]

Hmm, thanks for the info FallenAngel. What about a 20hz to 20kHz frequency response rating? Would that also be defined by the output stage, or does the opamp determine that? You're talking to a total newbie here, sorry.

 

[FallenAngel]

Again, the amp as a whole (just an opamp, opamp + buffer chip, opamp + discrete buffer or full discrete amp) would determine the frequency response. As far as I know, all modern opamps should have a flat response throughout the audible range.

 

[error401]

Quote:

Originally Posted by FallenAngel /img/forum/go_quote.gif Again, the amp as a whole (just an opamp, opamp + buffer chip, opamp + discrete buffer or full discrete amp) would determine the frequency response. As far as I know, all modern opamps should have a flat response throughout the audible range.

True, and most far beyond it. However, most commercial products will have some filtering to reject non-audio signals. Where these filter starts to rolloff usually has nothing to do with the 20Hz-20KHz that's almost always quoted, but you can at the very least expect a high-pass on the input (to reject DC) and a low-pass either at the input or in the feedback loop of a gain stage (to reject non-audio signals and ensure stability). For this one you really have to crack the amp open. Without any filters most amps are good for at least 100KHz, but many designs will oscillate if no filters are in place.

A properly designed amp shouldn't break no matter what you connect to the outputs (I DO NOT suggest you try it with audiophile gear, however).