Originally Posted by tr8rjohnk
I think he's referring to the windows sound slider, not the knob on the e9.
Is it really ok to use the high gain option on the e9 with low impedance/high sensitivity headphones like the 598's? I wanted to try the high gain setting with my ATH-A900 but was worried about damaging the drivers.
It would be difficult to do. Audio-Technica rates the A900 at a maximum input power of 2000 mW, nominal 40 ohms impedance. FiiO E9 can only output about 7V before clipping (20V peak-to-peak, if you prefer). A full-scale sine wave at 7V would only deliver 7^2 / 40 = 1.225 W = 1225 mW to the headphones. It would also be deafeningly loud and undoubtedly way distorted. So even if you crank volume up to maximum on high gain, you're probably not going to fry them.
High gain is just a larger gain factor--a multiplication more or less--of the input so really, higher gain and lower volume setting does almost pretty much the same thing as low gain and higher volume setting.
Many other full-size headphones are rated closer to 200 mW max input though. Maybe this is because of the relatively large drivers on the AD / A Audio-Technica line?