The integrated headphone amplifier has not changed since the Auzen Forte, so I did not measure it again under load. I did check it out aurally, though. This amplifier consists of a dual-channel opamp NJM4580 and eight transistors. It does not have coupling capacitors at the outputs and features very low distortions even at a load of 32 Ohms. In my previous review I could not fully examine its sound properties because of the bizarre sound of the line output the amplifier received the signal from. This time the situation is more favorable as the line output sounds perfect and cannot be a limitation. So what can the amplifier do?
So, when I installed the Auzen HomeTheater and replaced its default LME49720 with an LM6172, the integrated headphone amplifier was definitely inferior to the C.E.C. HD53R-80 in transparency and detailedness during the first month. But it improved suddenly in the course of my opamp tests and even surpassed the C.E.C. in many respects, proving to have a better resolution, a lower coloring of vocals, a more detailed treble and more realistic bass. However, all of this was often negated by one important factor – dynamics.
As long as there is a calm intro or a barely compressed live recording, everything is perfect. But as soon as there is some action like a tumult of guitar and drums, let alone an emotional outburst of a whole orchestra, the integrated amplifier finds itself lacking power and the C.E.C. leaves a much better impression. The reason is simple: the integrated amplifier doesn’t have that much electric power. The C.E.C. has an almost 50-watt transformer and many thousands of microfarads of smoothing capacitances whereas the Auzen amplifier has but a tiny coil, two 470µF capacitors and the slim conductors of the printed circuit board.
It is a shame that the potential of the amplifier designed by Auzentech is still not fully unlocked. It is only in high-sensitivity headphones that you will be able to enjoy it since such headphones do not require much power to develop a high sound pressure. On the other hand, the “free” amplifier of the Auzen HomeTheater card has a very clear sound even with low-impedance headphones and you don’t often have this clarity even with external amplifiers. It introduces very little distortions of its own, so those opamps that are best with the external amplifier are also best with the internal one, with a few exceptions due to an unlucky superimposition of the opamp’s peculiarities with the amplifier’s ones. For example, the integrated amplifier produced a less saturated bass in comparison with the C.E.C. and worked better with bass-oriented and detailed opamps such as the LME49860NA and LME49710HA.
The Auzen HomeTheater driver is incompatible with the Auzen Prelude one, so I had to compare the card’s line output with the front output of the ASUS Xonar D2 card, having replaced its default pair of NJM2114 opamps with AD8066 ones. This modification eliminated an unpleasant coloring of medium frequencies and increased resolution but did not push the card up to a new level of performance. Using the same opamps (LM4562), the Auzen HomeTheater HD had less mud in high frequencies and, in some cases, even in the medium frequency range. The Auzen also boasts an impressively detailed bass that takes your breath away with the 2004 year concert of Evanescence. As opposed to it, the Xonar D2 has an insufficiently sharp, rubber-like bass. The ASUS card is superior to the Auzen in dynamics and, somewhat, in detail and resolution, but the Auzen delivers an overall more consistent sound scenery, immersing you into the music and making you forget about everything else as you are listening to each sound and dancing to the rhythm.
Replacing the LM4562 with an LM6172 adds realism to the high frequencies and enlivens the medium ones but makes the low frequencies muddy. When replaced with an OPA2132P, the resulting sound is more analytic, making the bottom register lighter. The OPA637 could combine the resolution of the OPA2132 with the vigor of the LM6172 and the richness of the LM4562 but at what a price! Considering that the OPA637 works in this sound card without any problems, you may want to try another decompensated opamp from the same maker, OPA2228P, which can deliver even higher sound quality for much less money. It also won’t require you to solder anything as it comes in an appropriate case.
I must acknowledge that the CS4382A DAC employed on this sound card is not the best one in the Cirrus Logic product range but it can deliver a very high quality of sound. I guess this quality is going to satisfy 9 out of 10 potential buyers of the sound card. The remaining 1 buyer may want to consider external devices of a higher price category instead.