Heya,
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Hey I've been playing with those headphones for a couple of days and noticed a weird phenomenon:
When I plug them directly into my HP 4411s (a business notebook). It sounds OK and the volume's set at about 70-75%.
But when I use E17, I use 12 gain and the volume is about 30 (out of 60).
Did my notebooks gain some super power secretly or Fiio sucks?
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Ok my question is, if the laptop alone is enough to drive my headphones,(in terms of loudness?), then an additional amp is unnecessary?
Also how is it possible that my business laptop being able to drive high impedance headphones (DT990) fine, but back when I had Denon AHD5000, I had to crank the volume to MAX?
Amplification occurs in two steps, voltage and then current. Each device you're using has different builds, so they are designed differently. You laptop can't raise voltage fast enough, so you have to turn the volume up high. Your E17 hits voltage faster, so it doesn't have to be turned up as high (or you've set a base gain increase, which is the same as just increasing the volume by that much automatically).
Your laptop can drive them enough to listen to them, but that doesn't mean they're fully dyanmic. I would play back some low bass tones, usually underpowered headphones reveal right there, play back a 30hz or 40hz tone and listen. If it's muddy, loose, and clipping, then you need power. If it's tight, controlled, and a very solid hum with no breaks, then you're power is sufficient probably.
The Denons were low impedance, but they still really benefit from current. It just shows that your laptop has high impedance output, so it basically drives some voltage, but has next to no current output in the second step, so a low impedance headphone like the Denon needs everything it's got to make volume. The higher impedance headphone that just needs voltage, but little amounts of current, will operate better on your laptop's output, because your laptop is clearly ok for voltage gain, but terrible at current gain.
It's not that your laptop is good or bad, it's simply using a different kind of amplification method.
The E17 is superior in every way and handle both headphone types without being maxed out the way your laptop is.
Very best,