chillysalsa
Headphoneus Supremus
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- Sep 26, 2002
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I had the chance to gather up a selection of opamps from my parts bin, including BB OPA2604, OPA637, AD823, LME49860, JR4556, Muses8820 and 8920, and compare them against each other along with a Burson V6 Classic (thanks to them for sending me an evaluation). Two cases were evalutated – in a Breeze Audio AK4495 based DAC, driving a ATHA5000 amp (listening via Beyer T1’s), and then driving a Grado RA1 clone (basically a CMOY circuit) to hear the amp character more closely through a set of Senn HD800. This made it a pretty minimalistic set-up to get a close view of the opamp differences. The amp was running from two 6-cell AAA cell packs wired to produce +/- 9V to give a supply close to the middle of all their ideal supply voltages. Here are my general impressions in terms of strengths/weaknesses of each:
OPA2604
This has become a good choice for an all around opamp. It is very smooth and has a low noise background, almost inky dark. It has one of the politest and non-fatiguing presentations of the group, and allows one to listen for hours without strain. The overall sound balance is quite neutral, and detail is very good but not extreme. It is more of a subtle detail that is not in your face, but there when you are paying attention.
OPA627/37
I tried both OPA627 and OPA637 in this circuit, and both were pretty much the same because of the low gain setting of the feedback resistor. This presented itself as a more refined and detailed version of the OPA2604. It has a more forward presentation, with a much wider soundstage. The noise was marginally higher, but still very low and not noticeable. This is pretty much one of the best all around opamps of the group. Bass is very detailed an textured while also going deep - there is no ‘one note’ bass problem here.
AD823
This was one of the most analog and organic sounding opamps of the group. It was one of my favourites to use in the old phono preamp I made, such good synergy with vinyl. It has a very natural timbre, presenting the midrange organic sounds involving acoustics and voices with such effortless accuracy. Really quite enjoyable for those genres. Over the long term, I think the only drawback is that the sound stage was not anything spectacular, and the noise was a little bit more noticeable, perhaps the most audible his of the group. Of course, with the HD800 or T1s, the high impedance means you will never have audible his even with this opamp, unless you have it cranked full – but that would not be a volume you’d listen at. Overall it is also a ‘keeper’ candidate if I was mainly listening to acoustic music.
LME49860
This is a very sophisticated and smooth sounding opamp. It was overall falling something in between the OPA2604 and the AD823 in character, more refined and detailed, with better soundstage than either of the two, but combining many of the attributes of each. Midrange sounds very natural, but the bass is still not reaching as far or extracting as much detail as the OPA627. Overall the character of this one is very clean and neutral, with a very snappy drive. This also made it a rather non-fatiguing opamp, with rather low distortion and no overtly emphasized upper range, while still being very detailed and dynamic. This is also a keeper for the all around category, along with OPA627 for the headphone application. In the case of the DAC output circuit, it was also a good choice for this application for the transparent signature it provides.
JR4556
This is the selection for the Grado RA-1 design, and has been used in numerous guitar pedals. I can see why, the midrange tone is very textured and organic, with a rich energy that makes it amazing for rock. It would be a great match with Grados, and I see why there was a great synergy with those when I had them used with this amp. The sound stage is fairly up close, and not terribly wide, but that still lends itself to more intimate and acoustic music like jazz. One possible drawback was this one had the highest level of hiss and background noise, though it was not intrusive at normal listening levels. Having a trace of it there was a bit comforting in fact like the background floor in tape or vinyl sources.
Muses8820
Wow, this is really refined opamp, with the least ‘opamp sounding’ signature of the bunch, also known as the ‘budget Muses02’. It was perhaps the closest to sounding like a tube amp of the bunch so far, with a bipolar transistor input design. The signature was not particularly in your face, but still very detailed, ranking almost as good the OPA627. The one area it excelled was the sound stage width compared to the other opamps, and it was really easy to let go and just enjoy the music with this one. Made it seem like this brought out the spirit of the music more than the other opamps. Though one area was that it did not have the attack and dynamics that you can find in others, but the bass had pretty good slam and detail.
Muses8920
This is a JFET input version of the 8820 as I understand, the ‘budget’ version of the Muses01. Overall this had much of the same characteristics, very tube-like, with great soundstage. However, a few things stood out much more, than the 8820: the upper range detail is superior, and attack is far more aggressive. The surprising thing was that it still never got fatiguing or overbaked. This is a fantastic choice for taming the ‘digital harshness’ of the output of a DAC.
Burson V6 Classic
The first noticeable characteristic about this was the dynamics of this opamp. It has a discrete circuit, so that could be part of it. Instruments really jump out at you, and the ability to maintain the subtle detail of quitter instruments while hitting with the bass slam of louder instruments was unmatched here. The second notable characteristic was the strong hold on the bass, the most detailed and textured bass of the group. Overall the midrange and soundstage width were in the top 3 as well here, and quite natural. This made acoustic music come across in a very believable tone, with a generally neutral and true feeling. Soundstage was able to scale to the actual music much better than the other opamps, it was not over done when the music was small-scale and intimate, nor constricted when larger ensembles played. For me, it is a keeper for the headphone application, a toss-up with the OPA627 depending on the music and what is the source or headphones.
I guess that was the biggest demonstration in all of this, there is no ‘best all around’, just strengthens that vary with each (it would be hard to say any of them do anything wrong or are missing something). As for the measurements, there were some challenges in finding differences, but some useful comparisons can be at least made. My approach was to use square wave test signals to see how each respond to the signal. First of all, from the DAC, I could not detect any measurable difference between them my MSO-19 computer-based oscilloscope, and generating a 1kHz tone from the computer to the USB connected DAC, see below just with the Muses8920, LME49860 and Burson V6 for comparison:
DAC Outputs
Notice the pre and post ringing artifacts, these are normal with DACs trying to reproduce an ideal square wave, and caused by the roll-off filtering applied after conversion.
So, next was to see how they responded to a square wave on the amp, driving a 35 ohm load resistor, and it was basically showing very little difference either when 800 Hz is used. Still, for comparison:
Amp output, 800 Hz square:
So, moving to 20kHz square wave, there was finally some characteristics revealed in the ramp-up and slope-down behaviour of each. However, this did also emphasize a problem with my signal generator – notice all the noise ripple on the plateaus. Actually, one glitchy noise with some ringing came at a pretty regular cycle in synch with the square, but intermittently, so I know it is the signal gen (an old BK Precision from the 1980’s?). However, ignoring the ripples at the flat periods, we can still compare the ramp-up shape, and see the varying degree of overshoot / undershoot. The oscilloscope was probed after the opamp output, and before the big Solen output capacitors (even though they don’t affect the transient that much), see below.
Setup / probe location:
Amp outputs, 20kHz square wave:
OPA2604
This has become a good choice for an all around opamp. It is very smooth and has a low noise background, almost inky dark. It has one of the politest and non-fatiguing presentations of the group, and allows one to listen for hours without strain. The overall sound balance is quite neutral, and detail is very good but not extreme. It is more of a subtle detail that is not in your face, but there when you are paying attention.
OPA627/37
I tried both OPA627 and OPA637 in this circuit, and both were pretty much the same because of the low gain setting of the feedback resistor. This presented itself as a more refined and detailed version of the OPA2604. It has a more forward presentation, with a much wider soundstage. The noise was marginally higher, but still very low and not noticeable. This is pretty much one of the best all around opamps of the group. Bass is very detailed an textured while also going deep - there is no ‘one note’ bass problem here.
AD823
This was one of the most analog and organic sounding opamps of the group. It was one of my favourites to use in the old phono preamp I made, such good synergy with vinyl. It has a very natural timbre, presenting the midrange organic sounds involving acoustics and voices with such effortless accuracy. Really quite enjoyable for those genres. Over the long term, I think the only drawback is that the sound stage was not anything spectacular, and the noise was a little bit more noticeable, perhaps the most audible his of the group. Of course, with the HD800 or T1s, the high impedance means you will never have audible his even with this opamp, unless you have it cranked full – but that would not be a volume you’d listen at. Overall it is also a ‘keeper’ candidate if I was mainly listening to acoustic music.
LME49860
This is a very sophisticated and smooth sounding opamp. It was overall falling something in between the OPA2604 and the AD823 in character, more refined and detailed, with better soundstage than either of the two, but combining many of the attributes of each. Midrange sounds very natural, but the bass is still not reaching as far or extracting as much detail as the OPA627. Overall the character of this one is very clean and neutral, with a very snappy drive. This also made it a rather non-fatiguing opamp, with rather low distortion and no overtly emphasized upper range, while still being very detailed and dynamic. This is also a keeper for the all around category, along with OPA627 for the headphone application. In the case of the DAC output circuit, it was also a good choice for this application for the transparent signature it provides.
JR4556
This is the selection for the Grado RA-1 design, and has been used in numerous guitar pedals. I can see why, the midrange tone is very textured and organic, with a rich energy that makes it amazing for rock. It would be a great match with Grados, and I see why there was a great synergy with those when I had them used with this amp. The sound stage is fairly up close, and not terribly wide, but that still lends itself to more intimate and acoustic music like jazz. One possible drawback was this one had the highest level of hiss and background noise, though it was not intrusive at normal listening levels. Having a trace of it there was a bit comforting in fact like the background floor in tape or vinyl sources.
Muses8820
Wow, this is really refined opamp, with the least ‘opamp sounding’ signature of the bunch, also known as the ‘budget Muses02’. It was perhaps the closest to sounding like a tube amp of the bunch so far, with a bipolar transistor input design. The signature was not particularly in your face, but still very detailed, ranking almost as good the OPA627. The one area it excelled was the sound stage width compared to the other opamps, and it was really easy to let go and just enjoy the music with this one. Made it seem like this brought out the spirit of the music more than the other opamps. Though one area was that it did not have the attack and dynamics that you can find in others, but the bass had pretty good slam and detail.
Muses8920
This is a JFET input version of the 8820 as I understand, the ‘budget’ version of the Muses01. Overall this had much of the same characteristics, very tube-like, with great soundstage. However, a few things stood out much more, than the 8820: the upper range detail is superior, and attack is far more aggressive. The surprising thing was that it still never got fatiguing or overbaked. This is a fantastic choice for taming the ‘digital harshness’ of the output of a DAC.
Burson V6 Classic
The first noticeable characteristic about this was the dynamics of this opamp. It has a discrete circuit, so that could be part of it. Instruments really jump out at you, and the ability to maintain the subtle detail of quitter instruments while hitting with the bass slam of louder instruments was unmatched here. The second notable characteristic was the strong hold on the bass, the most detailed and textured bass of the group. Overall the midrange and soundstage width were in the top 3 as well here, and quite natural. This made acoustic music come across in a very believable tone, with a generally neutral and true feeling. Soundstage was able to scale to the actual music much better than the other opamps, it was not over done when the music was small-scale and intimate, nor constricted when larger ensembles played. For me, it is a keeper for the headphone application, a toss-up with the OPA627 depending on the music and what is the source or headphones.
I guess that was the biggest demonstration in all of this, there is no ‘best all around’, just strengthens that vary with each (it would be hard to say any of them do anything wrong or are missing something). As for the measurements, there were some challenges in finding differences, but some useful comparisons can be at least made. My approach was to use square wave test signals to see how each respond to the signal. First of all, from the DAC, I could not detect any measurable difference between them my MSO-19 computer-based oscilloscope, and generating a 1kHz tone from the computer to the USB connected DAC, see below just with the Muses8920, LME49860 and Burson V6 for comparison:
DAC Outputs
Notice the pre and post ringing artifacts, these are normal with DACs trying to reproduce an ideal square wave, and caused by the roll-off filtering applied after conversion.
So, next was to see how they responded to a square wave on the amp, driving a 35 ohm load resistor, and it was basically showing very little difference either when 800 Hz is used. Still, for comparison:
Amp output, 800 Hz square:
So, moving to 20kHz square wave, there was finally some characteristics revealed in the ramp-up and slope-down behaviour of each. However, this did also emphasize a problem with my signal generator – notice all the noise ripple on the plateaus. Actually, one glitchy noise with some ringing came at a pretty regular cycle in synch with the square, but intermittently, so I know it is the signal gen (an old BK Precision from the 1980’s?). However, ignoring the ripples at the flat periods, we can still compare the ramp-up shape, and see the varying degree of overshoot / undershoot. The oscilloscope was probed after the opamp output, and before the big Solen output capacitors (even though they don’t affect the transient that much), see below.
Setup / probe location:
Amp outputs, 20kHz square wave:
