Thank you guys for all the replys.
With a single +5 V supply, even if you find an amplifier that can swing rail to rail, you have 5 V p-p, that means less than 1.8 V rms.
That results in 98 mW on 32 ohm load, 1 mW on 2500 ohm load.
That power level is absolutely inadequate in a noisy studio. even with efficient headphones.
With a bridge amplifier (if you can correctly wire the headphones with a 4 pin connector) you'll get 4 times that power, still inadequate (it's the same power you could get with a 10 V supply).
There is lots of truth to that, I guess.
There are several problems in a studio environment.
During recording the instruments are really loud. I'm not talking about roaring guitar amps or anything. I record mostly Jazz bands. Even acoustic instruments are really loud. This is especially a problem when I am tracking multiple musicians in the same room. I'm a musician myself (not actually a full time audio engineer) so I know the problem first hand.
Also, a piece of music that was recorded, mixed and mastered has had its dynamic range severely reduced by the various compressors involved. That makes it possible to get high RMS levels without clipping the peaks. In a monitoring scenario, the signals are mostly unprocessed. Therefore there is potentially high peaks and low RMS levels. So lots of headroom is needed, or some form of limiter to attenuate the peaks.
4Vpp is plenty to listen to music really loud. But I guess there is not enough headroom for producing good RMS levels when dynamic range is so high.
8Vpp only gives me 6dB more headroom. To get 12dB I already need 16Vpp. With the NE5532 I get an output swing of about Vcc-2x2V which means I need a Supply that can give me 20V, which means using a 24V wall wart.
That is kind of the classical approach.
My DAC runs on only 5V and draws at least 100mA ... that means I will lose lots of power here.
About headphone sensitivity:
I don't need to worry about completely high impedance and inefficient heaphones. If someone really comes to me and wants to use it, I just use a seperate powerful headphone amp.
But I might sometimes run into the situation where someone brings his beloved Beyerdynamic DT770 Pro and he has bought the 250 Ohm version which is actually meant for mixing, while there is an 80 Ohm version for recording.
So this is basically my "typical worst case" that I want to have covered. The DT770 Pro 250 Ohm has a sensitivity of 96dB(SPL)/mW@500Hz.
http://europe.beyerdynamic.com/shop/dt-770-pro.html?SID=13d123e7ed1c60159b44a60d3f9a62b8&___store=en&___from_store=deMaybe I can find a solution that uses an only slightly higher supply voltage (maybe 10V) but uses an amplifier with an integrated charge pump?
Maybe someone can point me to one of those ICs, becaus on ti.com I can not find one. I am in Germany, by the way.
EDIT: I just took some readings of a piano track in my audio software. rms level is about 20dB below the peak level. So 4Vpp output means about 0.4Vrms which is about 84dB(SPL) on a DT770Pro ... I guess it's back to the drawing board for me.