Choosing Your Opamp
I’ve got a long list of opamps today. Besides the popular models I used in earlier reviews, I’ve got seven opamps from Auzentech. Unfortunately, they did not send me a module with highly promising AD797 opamps but instead I received LME49710 opamps which were not even mentioned at the manufacturer’s website.
As usual, I listened to all music material in Grado SR 325i headphones using a C.E.C. HD53R-80 amplifier. The recordings (in FLAC, APE and WAV formats) were reproduced with the foobar2000 0.9.6.9 player using the foo_out_asio 1.2.7 plugin. Audio CDs were reproduced with the PlexTools 2.36 disc player. I used diverse musical material, from special audiophile recordings to engaging albums of such performers as Robert Plant (Manic Nirvana), Manfred Mann’s Earth Band (Nightingales and Bombers), Rainbow (Bent Out Of Shape), Queensryche (American Soldier), Evanescence (Anywhere But Home), Pinetop Perkins (Born In The Delta). I also used a piece of classical music (Rimsky-Korsakov’s Scheherazade performed by Chicago Symphony Orchestra).
For you to understand my subjective evaluations, here are the definitions of the terms I will use in the description.
Resolution is the ability of the sound card to reproduce clearly all the sound sources in a sound scene. A high-resolution card can “draw” the sounding objects against a dark background so that the objects do not get fuzzy or intermingle. The resolution is lacking if you don’t feel the distance to the sounding objects.
Lack of depth versus flat scene. In the former case, all the objects are too close to the listener but the resolution is not poor since you can tell that the objects are at a different distance from you. In the latter case, the objects all merge into a solid wall of sounds and there is no resolution at all.
Transparency is one more constituent of high resolution. Sounds and echoes do not merge together. There is always a perceivable layer of air between sound sources.
Coloring, particularly of vocals, is the addition of unnatural or irritating intonations to the timbre. Coloring often provokes a desire to switch the sound off but never to make it louder.
Tonal balance is the perception of the total volume of all the objects sounding at different frequencies. Comparing the tonal balance by quickly switching sound sources allows to easily discover a coloring as it makes a certain range of frequencies stand out above the rest.
Micro-dynamics is the sound card’s ability to reproduce the quietest sounds and reverberations in all detail. For example, a struck string is going to get quieter and quieter, but its timbre must remain the same until its sound goes out completely.
Detailedness, as opposed to micro-dynamics, does not tell anything about how natural the quiet sounds are. Some sounds can be heard but you won’t know their origin.
I will be mentioning Queensryche quite a lot throughout the description of the opamps because the music of this band, combining hard guitar riffs with stereo effects, proved to be unexpectedly difficult to reproduce. Many opamps that cope well with other genres of music fail at this task and produce annoying artifacts. I might have disregarded this as a poor quality of the recording itself, but there are some chips that play it perfectly: elegantly, bravely, pensively, depending on the context.
The number in the brackets is my subjective evaluation of the capabilities of the opamp to reproduce music beautifully. The grades go from 1 (worst) to 5 (best). To get the best grade the opamp has to show something exceptional in one genre of music or be an all-purpose device that is good at playing any genre. The plus and minus signs added to the grade are meant to add more gradations to differentiate between good and very good opamps since even the worst opamp in this test session is actually no worse than 4. None of them is without downsides, but none has fatal problems, either.
NJM4580 (4) introduces minor distortions at medium and high frequencies which worsen the sound of violins. Its bass is rather thin but trenchant and it has excellent dynamics and depth*, but the resolution is rather poor. However, this opamp was good at playing Queensryche.
LME49720NA (4+) produces a more detailed sound with a clear middle, shallow bass and blurred treble. Its sound scene is flat, lacking reverberations. With the integrated amplifier the scene is deeper, the sound is more energetic, the vocals are colored less, and the bass is more realistic, but the CEC yields a richer sound, especially when reproducing a piano. Queensryche sounds good on this opamp.
LME49710MA (4+) is rich, precise and epic. It is clearer, with higher resolution and more dynamics than the previous chip. It has sharper but somewhat synthetic high frequencies and scrambled echoes. The integrated amplifier is inferior to the external one in bass saturation as well as scene depth and transparency. Queensryche would be very good if it were not for the unpleasantly ringing high frequencies.
LME49710HA (5-) is good with echoes and sounds softer but less spacious. It has a coloring of the top middle. Being very detailed at medium frequencies, it becomes no better than the 49720NA in this respect at high ones. It delivers a strong bass with the integrated amplifier which is even superior to the external one in micro-dynamics. Queensryche is rather good.
LME49860 (5) is exceptionally detailed, particularly at high frequencies. It produces splendid vocals and features a rich and nonaggressive sound. The only downside is its bass which lacks hardness. Queensryche is good, the integrated amplifier is near perfect.
LM4562NA (4+) features a deep and rather sharp bottom register of drums, but bass guitars are muddy. This opamp features a high resolution, a clear middle and too accented high frequencies. The integrated amplifier sounds more vigorous and emphasizes the high frequencies in a different way, being more transparent and realistic in terms of vocals, but inferior to the external amplifier in terms of bass and scene depth. Queensryche is good.
LM6172IN (5-) has a wonderfully transparent sound, clear high frequencies and excellent vocals. Its bass is soft and not excessive**. It lacks depth and detail with the integrated amplifier. With the external amplifier it lacks dynamics and Queensryche sounds less energetic. This opamp suits best for jazz and other live recordings.
AD826 (5-) has a vigorous but not aggressive sound with a good resolution. Its bass is lead-heavy but detailed and its top frequencies are rather clear. However, its vocals are not realistic and there are minor distortions at medium and top frequencies. There are more of them with the integrated amplifier but its sound is more detailed and sharp. Queensryche is good with this opamp.
AD823 (5-) is energetic, collected and transparent. It has everything in just the necessary measure, except that it often lacks a depth of the sound scene. The medium frequencies are clear but the high ones are grainy. The sound of the integrated amplifier is hollow and unnatural. Queensryche is good.
AD8620 (4) is high-resolution and detailed throughout the entire frequency range but produces a shallow and narrow scene. This opamp has a good total balance, realistic vocals, and very clear medium frequencies. With the external amplifier the treble is hissy. The sound is more realistic with the integrated amplifier but there are more distortions as well. It is also occasionally too aggressive.
OPA627AU (4+) is rich in overtones and drive, but also booming sound, reduced resolution and cut reverberations . The highs are moved to the background, the mids are obscured at low volume and aggressive at high volume, but Queensryche is good. This opamp is almost the same as the 4580 tonally.
OPA627SM (4+) offers a good resolution at medium frequencies, but has fuzzy highs, rather booming bass and a flat scene. It loses dynamics, resolution and timbre clarity with the integrated amplifier but may be good for low-quality recordings.
OPA637AU (5-) has soft and detailed high frequencies with a specific “frost”. There is a slight accent on the top middle as if adding transparency. The sound scene is specific, as if shifted away from the listener. This opamp features a high resolution and good drive, but is somewhat lazy at reproducing Queensryche, perhaps due to the undersaturated bottom register.
OPA637SM (5) is exceptionally detailed and features a very high resolution and clear high frequencies. Its sound is soft, even somewhat too soft. The top-medium frequencies have a slight coloring with the external amplifier. The integrated amplifier produces a dull bass. Queensryche is very good.
OPA2132P (5-) is highly detailed and dynamic. It features a clear middle, a well-defined, “wooden” bass. There is a specific accent on high frequencies and a certain lack of depth, but the spaciousness can be felt fully. The integrated amplifier worsens the resolution and adds coloring to medium frequencies. It is very good for classics but not quite pleasant at rock recordings.
NE5532P (4+) produces a voluminous and brave sound with good transparency but without smallest details. It has a heavy, low-detail bass, realistic vocals, a characteristic oversaturation of high frequencies and dirt in the most intensive sections of a phonogram. It sounds surprisingly good with the integrated amplifier: the somewhat suppressed middle is comfortable but, occasionally, not as emphatic as with the other opamps.
*The rear and side outputs differed slightly in the depth of scene and the reproduction of high frequencies.
**Two samples purchased together differed in tonal balance and resolution.
The results are rather interesting, as you can see. The exclusive OPA637SM in metal armor did not win easily. It could only make it to the top when I listened to the Perkins disc. It is also at the end of my tests that I had to lower the mark of the LM4562. It had contended for a top place (a little lower than the maximum due to the accented high frequencies) and had done well at concert recordings and classics and some rock recordings, but proved to be less good at reproducing pop music. By the way, it was the old LM4562NA with a light-gray marking. I also have to note that its performance was affected by the interconnect cable and this opamp shines when united with Moster Standard Interlink 200. Interestingly, the LME49860 is superior to all other chips of the same series although formally differs from them only with the maximum voltage. It turns out that the most expensive versions of chips in a series indeed have better sound properties.
The popular NJM4580, which is recommended by its maker for audio applications, is surprisingly similar to such famous devices as the OPA627 and only differs from the highly expensive OPA637SM with a lower resolution, higher distortions and a shallower bass, but not in tonality or imaging. The old NE5532 also did well, proving to be suitable for all music genres and delivering rather high sound quality at low volume. With the integrated headphones amplifier it was one of the best in the tests.
By the way, the replaceable opamp panel on my HomeTheater passed through a number of replacements whereas the similar panel on a Forte card had lost its tight contact after I had installed a module from Auzen with cylindrical pins of a rather large diameter into it. After that adapter, I had to bend the legs of ordinary DIP-packaged chips a little so that they could hold firmly in the socket.