I misunderstood that you want basically a combined preamp/headphone amp
Hello again ! Exactly ! the idea is to optimize the audio chain up to the HPs and then "adjust" the HPamp output reducing is Vout in order to drive properly a power amp or a pair of powered speakers, adding a pair of RCAs on the back of the HPamp.
The DIY approach sounds very good to me.
Of course the selected HP amp must be quite good in itself and usable for this purpose.
A good pair of HPs can be extremely revealing and therefore an excellent tool to evaluate what there is upstream, sources and headphone amps.
And it is also extremely convenient. I do not need to set up different speakers in a listening room.
Swapping sources and HPamps is much easier that to swap speakers of course.
Moreover most of my listening is actually through HPs during evening and night hours. But i like also the opportunity to listen through speakers when possible.
You may not even need resistors for this. One consideration is the impedance of the cans. Low impedance, like grados at 32 ohms, need more current to drive them.
High impedance, like senns at maybe 300 ohms, need higher voltages to drive them. And then planars are harder to drive in general.
My planars are lowish impedance, around 50 ohms. But my amp has taps for low, med and high impedance cans. Preamps usually don't need much current or voltage since they just need to drive the amp's input.
If i understand right
should i aim at high sensitivity HPs and usually these are also low impedance ? i would like to use normal HPs and not earspeakers. I do not bear them.
as you say current is not an issue with power amps but V out is. Clearly the HP amp out must be reduced a lot ... at least 5 times i guess.
I don't even use a traditional preamp, I usually go direct from my dac to my amp, although I am looking at adding a buffer in the path. Buffer would have no gain, just for driving the signal.
then how do you set the volume ? your dac has a variable output maybe ?
As an aside i really do not understand why they make the power amps so sentitive.
I was looking at some lab reports of line preamps, both tube and SS, on the Stereophile site.
A preamp has no problem at all to output even 10V with very low THD+noise.
Then why to place so much voltage gain in power amps ? Why not design them to have 10V of sensitivity ? in this way it would be possible to use just one high gain preamp for HPs and power amps. Less gain implies also simpler circuits i think.
However i will start to look at high sensitivity HPs of decent quality. Not an easy task i guess.
If you have any recommendation of specific HPs of good quality and high sensitivity i would be grateful.
Thanks again and kind regards. gino
P.S. it seems that
in ear speakers are indeed the best options to do what i have in mind
Reading here
https://www.innerfidelity.com/images/SonyMDREX1000.pdf they
require very little Voltage to produce good dB levels.
I do not like the idea of use in ear speakers ... but if it is the only way ....