The HELM Audio DB12 AAAMP portable amp is a well-built and compact solution for Hi-Fi headphones. The portable THX-certified amp increases the volume and clarity of audio, resulting in a noticeable improvement in quality. However, at US$200, the prohibitive cost will price out all but the most dedicated audiophiles.
https://www.notebookcheck.net/HELM-Audio-DB12-AAAMP-portable-headphone-amplifier-hands-on.527584.0.html
And what is good here? You get low distortion only at a tiny 5mW power (for which you don't need an external amplifier, any smartphone or laptop could provide even more), whilst on full volume you get 100mW and 0.1% THD.
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