The amplifier/DAC combo, in fact, make up for certain weaknesses in the audio source thanks to a specific construction. Such devices can prove to be ideal allies when you want to fully exploit the capabilities of your headphones but you need to take into account the characteristics of your headphones, so as not to be mistaken in choosing the best DAC/AMP combo.
It is not uncommon to see the headphone amplifier and the DAC coexist in the same device. 
We are talking about a headphone amplifier with DAC allowing you to fully exploit the audiophile capacities of your headphones and this with any type of audio source. They can be presented in a sedentary configuration with a substantial housing or adopt a minimalist format integrating a battery for more portability (in this case, it is a portable audio DAC).
What the role of the amplifier?
The source device can limit the performance of your headphones. To compensate for a limited audio device such as a smartphone, a Hi-fi system, or an entry-level audio player; you should, therefore, use a headphone amplifier. The latter provides the best possible support for your headphones which due to its hi-fi pretensions can be brought to have a high impedance. And having a high impedance requires a substantial power supply so that the headphones can deliver the best sound possible. It thus compensates for the weaknesses of the source audio device so that your hi-fi headphones operate at full speed.
What the role of DAC?
With the digital era, there is a device that has made its place in the audiophile landscape, this is the DAC also called DAC converter. The latter is in a way a bridge connecting your audio sources such as a computer, network player with your headphones.
Thanks to its internal architecture, it is able to manage Hi-Res audio files with a high sampling rate (24Bits / 192kHz, etc.) as well as DSD. With suitable connectors, this “small” box is a precious ally.
It is not uncommon to see the headphone amplifier and the DAC coexist in the same device. We are talking about a headphone amplifier with DAC allowing you to fully exploit the audiophile capacities of your headphones and this with any type of audio source. They can be presented in a sedentary configuration with a substantial housing or adopt a minimalist format integrating a battery for more portability (in this case, it is a portable audio DAC).
