I was able to quickly put together a unity gain audio amp using an extra filter kit board. For a fair comparison, I will step this up to a gain similar to the LM386 audio outputs we are familiar with and post those results. However, the results for this test were very promising.
As shown above, the noise floor came in at about -138 dBFS. In practical terms, that’s zero hiss in a pair of sensitive ear buds.
When applying the 1 kHz signal at a level 0f -10 dBFS, the THD+N came out to 0.0058%, which is excellent. This corresponds to a fairly high level input with a low amplification factor of 1.0. In other words, this is a pleasant volume level in earbuds and the noise contribution was minimal.