Axiom Home Page Forums General Discussion The Water Cooler Question for the iExperts

I think the headphone jack of the more recent iDevices has an impedance measuring circuit in it. When it detects headphone level impedance it enables the full drive of the amp, but when plugged into something that feels like a line device it cuts it back.

It used to be that plugging a headphone out into a line in, you'd have to cut the volume back almost all the way to keep the amp from overdriving the input. But with modern devices that can judge what they're plugged into it's the opposite. You have to turn the volume up almost all the way to get full line level.