[eyal1983]

When I turn the volume knob on the O2, to the volume level which is normal for me, then more mW is released into the headphone, in comparison to an amp which gives less mW at a specific ohm amount?
 
if 2 amps are at the same volume- still- the "stronger" produces more mW, or is it the same ?

 

[xnor]

If you have two completely different amps and match their volume with the same headphone the power into the headphone will be identical.

 

[eyal1983]

Then, if someone has an amp which gives 3,500mW into 32ohm,
This means that even the minimal volume will be too much for a 32ohm IEM (for ex.) ?

 

[xnor]

3.5 W into 32 ohms is a lot so without more information I would guess that the amp has pretty high gain (~15 dB).
 
High gain and highly sensitive in-ears are certainly not the best combination. You may have problems with the volume control (imbalance at low setting but turning up the volume would blow your in-ears up) and you might also hear the noise floor of the amp (hiss during quiet passages).
 
 
Even if the amp could output 100 W into 32 ohms you'd still need only a fraction of 1 mW with highly sensitive in-ears.

 

[eyal1983]

How do i know how much power is best for a certain headphone?
 
for example-
an AKG K701/2 really don't need much to get to a full volume.. but DOES need more power (mW? Voltage?) than a normal headphone.
same goes for Sennheiser HD600.
and with Orthodynamic headphones it's even worse.. I can get them to a loud volume.. but they will not sound as good as they can..

 

[xnor]

You can calculate the required voltage and power based on specs or measurements, or just take a look at my table: http://www.head-fi.org/t/668238/headphones-sensitivity-impedance-required-v-i-p-amplifier-gain
 
Even if you add a couple of dB of excess gain you would be fine if the amp output only 400 mW into 32 ohms or 200 mW into 62 ohms for the K701.
 
I calculated it this way: K701 need 1.778 V from the table. Added 6 dB (doubling the voltage) excess gain => about 3.5 V.
P = V * V / R = 3.5 * 3.5 / 32 = 0.383 W = roughly 400 mW into 32 ohms
 
Without the 6 dB excess gain you need only 1/4th of that power. The requirements of my table are calculated so that a full-scale tone would be played at 110 dB SPL if there is no excess gain and of course you have to turn up the volume of the amp to 100%.

 

[ScarTonKpilS]

I have question too please,

I have the Meze 109 Pro and it has maximum power input 100mw but my Hiby FC 4 has 280 mW
1. question ,can I hear maximum volume with Hiby fc4 on the Meze 109 Pro or will it destroy the Meze 109 Pro ?
2. question when a amp has 280mW means that is the power on maximum volume Level ?
3.question, more volume means more mW to the headphone ?

I know no one will hear on max volume I just want to know
or better buy amp with less power than the Headphone max input power ?
Like Hiby FC 3 it have 70mW and Meze 109 Pro max input is 100mW everything should be fine on maximum volume ,right ?