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Finding the Optimal OPAMP

With sound cards of this level and sound quality, even small trifles are important.

The Auzen X-Fi Bravura 7.1 didn’t do well in terms of its line output quality. Even after it had warmed up, it would be often inferior to the Creative card based on the same controller and costing only half its price. The high-quality components help the Bravura outperform the more expensive cards in some situations, yet there’s something wrong with it anyway. The Auzen HomeTheater HD with the same analog section components was free from the downsides I observed with the Bravura. Besides, its LM4562 opamp didn’t suit it well. While drawing a good sound scene and delivering very detailed medium frequencies, it was not just vivid but aggressive.

I combined my search for the optimal opamp with tests of the Bravura’s integrated headphone amplifier by comparing the latter’s sound quality with that of the external amplifier C.E.C. HD53R-80 connected to the card’s line output. For the comparison to be fair, I installed identical opamps into both of the card’s channels by using all opamps I could find in two samples. I mostly used Evanescence’s Origin as the music material. The comparison took a long time and coincided with the card’s warming up and improving the quality of its line output but I didn’t re-listen to all the opamps, limiting myself to but a few models.

LME49720NA

The headphone output provides a darker sound with somewhat more clarity and dynamics. These small improvements combine to make the listening to music via the card’s own amplifier far more exciting but Judas Priest was more fierce and detailed when listened to via the line output with external amplifier even though the integrated amplifier had more powerful and detailed low frequencies, good bass being so important for rock music.

To find out if it was the problem with the integrated amplifier I had noticed during my tests of the Auzen X-Fi HomeTheater HD, I connected the external amplifier to the headphone output but didn’t find any more details in the sound. It must be due to the output filter because the AK4396 played rock most vigorously on the Auzen X-Fi Forte.

Thus, the line output has a lower resolution with calm music, yet it doesn’t lower more with heavy music. The line output was also tiresomely clamorous with this opamp.

The chips surprised me with their large variations in sound quality. I had no complaints about only one of the three I tested whereas the other two delivered muddy trebles and a flat scene, even though to a different degree. This explains my negative impressions from the LME49720 in the reviews of the Auzen Forte and Auzen HomeTheater. The good sample proved to produce a clear and consistent sound.

LM6172IN

This one delivers a viscous bass and smoothed-out dynamics on both outputs. Evanescence was reproduced downright sloppy, with a lack of energy and an unstable sound scene. The line output seems to produce more details but this may be due to a higher level of harmonics because the headphone output plays the music in a more natural way with better bass. The piano was listless when listened to through the line output whereas the drums were clearer through the headphone output and the subsequent low-frequency hum was more saturated. The two outputs of the sound card were equal in terms of vocals. High frequencies differed but I couldn’t determine the better output for reproducing them: the line output was perhaps more natural in some recordings.

Overall, the headphone output produced a more voluminous and freer sound with a saturated bottom range.

NJM5532

The line output seemed to be somewhat more comfortable to listen to at first, but also simpler and far less exciting than the headphone output. But after the card’s warming up for a few months my preferences shifted towards the line output even though its sound was still far from ideal.

This opamp wasn’t very expressive in the headphone output, lacking a sharp bass even though its macrodynamics was okay. It was merrier in the line output: although there might be less bass overall, the low frequencies were very detailed.

One sample of this opamp distorted high frequencies, made the sound scene flat, cut off low frequencies and reduced the level of detail. It produced a distorted sound of the piano, an annoying sax and uncomely high vocals. The sound of rain would be something like hail with it. Another sample was more voluminous, brighter and prettier to listen to except that its high frequencies were not very detailed.

NJM2114D

This opamp is most energetic but somewhat flat. There is no punch, the high frequencies are smoothed out, the level of detail is far from impressive, and the vocals do not excite, either. On the other hand, the sound is not irritating, contrary to the Creative X-Fi Elite Pro that has this opamp in its front channel. So, the NJM2114 turns to be able to sound comfortably under some conditions, yet it is still inferior even to the NJM5532.

The two samples of this opamp I had differed in nearly everything: dynamics, the depth of low frequencies and the quality of high ones, the spaciousness and detailedness of the sound scene. One sample was obviously better than another and produced a rather good sound in the headphone amplifier.

OPA2132P

This opamp produced a condensed and saturated sound in the headphone output but high frequencies were fuzzy (without a clearly defined attack) and lusterless. The sound was not very detailed and the bass was just barely noticeable.

When installed into the card’s line output, this opamp delivered a lively and voluminous sound with beautiful vocals, but the piano didn't sound pretty. The bass was soft but there was enough of it; the high frequencies were more sonorous but not very detailed.

It’s hard to prefer one output here: the headphone output was clearer and more detailed but the line output had more spaciousness. The sound quality wasn’t very high in both cases, though. It’s similar to the NJM5532 but somewhat more comfortable to listen to.

OPA2228P

This opamp isn’t very good in terms of bass but delivered detailed high frequencies and a characteristic sound scene. Its sound doesn’t resemble the other opamps. It may be unpleasant in some places but fascinating in others. The more I was listening to it, the more I liked it. I wonder if opamps take some time to warm up, too.

The two samples of this opamp were different, too. One was somewhat inferior in terms of dynamics and low frequencies, producing a flat and irritating sound. The other produced a full, comfortable and vigorous sound; the drums and thunder had the necessary sharpness.

When used with the OPA2228P, the headphone output produced a smoothed-out sound, like with the NJM2114, yet with clearly defined details.

The line output, on the contrary, was voluminous and dynamic, and the two samples of this opamp differed less dramatically in it. This seems to be the first opamp worthy of the line output.

LT1364?N8

When in the line output, it produces a sound scene which is deep but not broad. It also gives you a detailed bass, good medium frequencies and rather odd trebles which are clear and detailed at low sound volume (like the sound of rain, for example) but loud sounds (sibilants or cymbals) become more like a hiss.

When in the headphone amplifier, this opamp, to my surprise, was not so good. While delivering somewhat more details than I could hear via the external amplifier connected to the card’s line output, its sound was not so rich in timbres, the sound scene lacked depth and the bass lacked energy.

The LT1364 adds transparency and “darkness” to the line output. When playing various genres of rock, the line output with the LT1364 was often superior to the headphone output with the LME49720.

Unfortunately, the two samples of this opamp that I tested differed greatly in terms of sound quality. The worse one emphasized medium frequencies too much, also producing hissing trebles and lowering the level of detail. While I couldn’t decide which of my two LM6172IN opamps was better, this choice was simple with the LT1364 pair: listening to music was a pleasure with one sample and an annoying experience with the other. However, the annoying one had better dynamics and reproduced the sound of rain in a more realistic way whereas the other one muffled trebles somewhat.

LT1361CN8

The two samples of this opamp didn’t differ much. One was clearer, deeper and had more bass whereas the other was more aggressive and had muddy high frequencies.

At first I liked them more in the headphone amplifier as they played many compositions (e.g. Roger Waters) with more spaciousness, neatness and purity compared to the line output where their sound was less transparent. The situation changed dramatically after the card had warmed up: they then delivered a very energetic and comfortable sound via the line output, with a responsive bass, detailed trebles and attractive vocals. When used in the headphone amplifier, they seemed to lack dynamics and accuracy.

Overall, I liked the OPA2228P and the LT1361CN8 the most on the line output whereas the LME series opamps seemed to be the best choice for the sound card’s headphone amplifier. The series includes the LME49710 you can order from Auzentech. The LME49710UA produces a spacious and accurate sound scene with a good bass and nice trebles whereas the LME49710HA is less energetic but had the best results according my measurements.

I also liked the AD826 in the headphone amplifier. It produced a very dynamic and spacious sound but it was the metallic OPA637SM that, like with the Auzen X-Fi HomeTheater, had the biggest effect on me. I could not hear so many details, so much air and liveliness with any other opamp, including the similar OPA637AU which was somewhat more clamorous. Alas, the pleasure of using this opamp is going to cost twice the price of the sound card itself!

As a matter of fact, I wonder if purchasing replacement opamps is really worth the trouble because the difference in subjective sound quality between different opamp models is not much larger than between different samples of the same model. This may be the reason why expensive opamps that have passed a stricter quality assurance check are so valued among audiophiles. Anyway, if you are not satisfied with the sound of your Auzen Bravura half a year after purchasing it, try swapping round its default opamps. If you do notice some positive changes then, you may want to purchase other opamps to improve the sound even more.

As for the quality of the integrated headphone amplifier, I could not find any fault with it. Even at a load of 32 Ohms it was as good as the expensive external amplifier C.E.C. HD53R-80 in purity, dynamics and power which was more than enough for my Grado SR 325i headphones. The only problem was the incessant hiss when the card was working at a sampling rate of 44.1 kHz. For the background noise to get inaudible, less sensitive headphones are necessary.

Winding up my subjective tests of sound quality, I checked out the different operation modes of the sound card’s outputs. Pressing the onboard switch changes the sound volume of both outputs. A smooth decline of high frequencies is enabled for the headphone amplifier in three out of the four modes. I personally think that the integrated amplifier is more comfortable and natural in modes 2, 3 and 4. For more details about that see the Measurements section.

 
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