excellent initial post with great explanations. Now my simple question is if it makes sense using a DAC AMP Stack for the laptop when listening to CD-rips in 16bit? or is it enough to just plug in the headphone to the audio port of the laptop?
Electricity is very simple.
V = R * I
That means if the resistence is the same and the voltage is the same, the volume is the same. So in theory, if you have the same voltage, you should have the same sound.
But, and here comes the but, the output resistence of nothing is linear. Resistence is generally measured at 1kHz but grately varies and especially with digital amps, the output resistance of the capacitors play a big role.
The better the capacitor, the more linear is its output resistance, but no matter what you do, its never flat.
That means you need a lot of capacitors and good capacitors if you want an as flat as possible output resistance. That is why the second generation Walkman for example uses 21 wound capacitors that were developed over years.
There is an explanation from Panasonic in details how temperature and capacitor design effects its output resistance and so the sound
Here an small screenshot
You see, the type and design of the capacitor and especially how many you use and how you implement them does heavily influence the output resistance of the capacitor and so the sound of the overall amp. Capacitors are not(!) linear, even when they are marketed as such.
And you also see the mark "25°", that is because this value changes with temperatur. That is why some amps start to sound different when they get warm. Also this value changes with the amount of power you draw from them. So the higher your volume, the more does it change the frequency response.
More informations are here:
https://industrial.panasonic.com/ww/ss/technical/b2 but this is just scratching the surface.
As capacitors are also used in LC-Filters, the size and implementation of LC Filters further change the sound.
As a rule of thumb (important, this is getting less relevant over the years as technology advances), if you want good sound, you need big components. You want big wound capacitors and a lot of them and large LCs. But as they will never fit into your Notebook, your Notebook will sound different.
That is why Digital Amps like the Walkman have so many big capacitors and large LCs, even in an portable player
But in theory, there is more space in an Notebook to implement these things than in an DAP, so an Notebook could sound better than an DAP, if the Amp section is shielded good enough, just for the sake of more space for good components.
The Mid-Level DAPs (ZX-Series) from Sony uses different capacitors for 3.5mm and 4.4mm (to cut cost) which is the reason why 3.5mm sounds different than 4.4mm on Sony Walkmans. Most people mix that up and think this is due to the advantage of an balanced connection while the WM1 Series, who uses the same capacitors on 3.5mm and 4.4mm, sounds pretty much identical. So its the choice of capacitors that causes the change from 3.5mm to 4.4mm in the ZX-Series which shows, how big the influence of the capacitors actually are.
A lot of people think that Desktop Amps sound better, because they have more power and the more power you have, the better you can drive an headphone. As you seen in the formula above, that is nonsense. Desktop Amps driver Headphones better because they have better components and more space to properly implement them and only for that reason.
And 3000mW Desktop Amp wouldn't sound any different if you would limit its power to 250mW. So the choice and implementation of the Amp and its capacitors defines how good the amp can drive an Headphone.