You're not going to believe this response. WARNING: long post!!!
I've been in correspondence recently with a guy from Audiogon who bought my Shanling T100, and he's in the process of doing some op amp rolling with that player. Something I didn't even know could be done.
Yet, he seems to be quite excited about it. When he mentioned trying the 627's, I asked him if he meant BP or AP. So here we go:
"No, the 627's I'm using aren't the BP's, they're the AP's.
The BP's do have a similar sound, but the output is considerably less, so you have to turn the gain up a bit more before you hit the "sweet spot" volume wise. I had a set of AP's and had gotten another set of BP's when a good audio buddy of mine told he he'd read on some forum that some people thought the BP flavor was more "analog like" and "smoother" for some reason. I'm always one for hearing for myself, so while he wondered, I ordered up a pair.
When I put them in, I noticed the sound was virtually identical to the OPA627AP's, but I had to turn the preamp up about 20 steps higher to get the same volume out of the speakers. Other than that, I couldn't tell any difference in any other aspect of the sound. But of course, with the output being lower with the OPA727BP's, you never got the dynamics, the vibrancy, the degree of resonance and so on that you noticed immediately with the higher gain from the AP's. When I relayed this to my buddy he said what I had relayed to him made sense and seemed to be in line with what others had reported. They liked the BP's because they were "softer". Personally, I found them frustrating as to get the same sound levels. So, I've got both the BP's and AP's, but it's the AP's that I use.
The volume of the OPA627AP's is the exact same volume level as the OPA2604's that come in the T-100, by the way, so they're really exact drop in replacements. Only the 627 BP's seem to have diminished output, which scanning the data sheets doesn't provide any insight into. In any case, it's the OPA627AP's that I use. After I put in the 627's I was so pleased with the improvements in all aspects of the sound, I didn't feel a need to even pursue any other flavors of op amps."
Then about a week later, there was more! I've cleaned it up a bit, added paragraph breaks, etc. It might be worth skimming if you're interested in a mini review:
"I think I mentioned that the 627BP's really didn't do it for me at first, and after leaving them in with the unit playing for a solid week now, they don't do it for me now, either, and they're surely burned in at this point having over 200 hours on them now.
So, what am I hearing from the OPA627BP's now that they've got about 200 hours on them? Well, how do I put this? The two words that come to mind is they sound "harsh" and "harder" than the AP's. I just had put the AP's back in when I got home after work tonight, and let me tell you, it was a relief. It was like "Ahhhhhh, there's the sound!"
In the acoustic piece I always use for my initial evaluation of any changes in my system ("Song for Juli" - Jesse Colin Young), it starts with solo finger-picked steel-string guitar for a verse as the drums come in with light brushwork, then it moves to a piano solo as the guitar moves to a light accompaniment role, then the piano and guitar provide accompaniment to a light accompaniment to a solo flute which plays for a verse, then all the instruments provide the background accompaniment for a male and female vocalist who sing the songs verse together in unison.
Well, with the BP's in, the opening guitar sounds harsh and hard, and to be honest, it doesn't sound convincing at all. I mean, normally, I'm used to having a sense that there's really someone standing just to the side of my right speaker to the left a bit, finger picking a Martin D-45, complete with left-hand finger taps and string squeaks and hearing exactly what strings the right hand fingers are picking and pulling throughout the opening section, with the body resonance of the guitar coming through with just the proper nuance and reverb from the instruments body with every note. But that wasn't the case with the BP's in the unit.
The one phrase that kept coming to mind to describe what I was hearing, was that it just sounded more "hi-fi" with the BP's in it. Certain frequencies and dynamics seemed inaccurate and exaggerated, and it just didn't' sound "real" as the piano came in it also sounded hard and bright, and when the flute came in it also sounded "harder" in the mids, and wasn't convincing as a flute at all. This is a track I've listened to at least a hundred times, and normally when that flute comes in, it's just like the flute is in the room in front of me. The tone is just superb, the sense of "air" is just right, and you swear there's a flautist standing in front of a microphone with pursed lips, fingers working the keys as it takes over the melody for it's short turn before the instrumental prelude is finished and the vocals finally arrive to tell their tale. When the vocals do come in, with the BP's in place, there's more raspiness in both the male and the female voices, which some might perceive as more "presence", but to me it's really just an exaggeration of that part of the frequency range and an unnaturalness that wasn't present when the recording was originally made.
Swapping the AP's back in once again, in contrast it seemed like something was now "missing", and I realized my ears had become a bit fatigued from listening critically and had become a bit accustomed to the exaggerated mids, as human hearing tends to do. So, I took a little break and watched some TV for a half hour or so, then went back and listened once again. Immediately, with the AP's in the system the guitar again took on it's familiar "realness", I could hear every nuance the left and right hands were producing, and the balance of tone, of timbre, of body resonance and of every string sound was conveyed convincingly and with accuracy. The piano has never had the "weight" to the notes I've believed it should have, but it no longer sounded "harsh" or "bright", in any case, and when the flute came in I found myself taking a big sigh of relief to once again hear a convincing rendition being performed before me in my listening room once again.
So, sure, there's something to be said about "synergy", and I might agree with some folks who believe that the 627 in either form is "light" in the bass, and due to this also call it "polite", but the BP is simply not nearly as refined and accurate as the AP is, the BP giving more of a "hi-fi" sound, while the AP provides quite a noticeable step up in the "audiophile" direction. And, oh yeah, they both have identical output levels. The only difference being in the sound itself, with the BP's being considerably less accurate than the AP's. And I'll also tell you this: in doing some research, I did come across some posts saying the BP's had better specs than the AP's and because of this they should have better sound. Well, I've been reading those op amp datasheets as of recently, and I don't know what specs these people are looking at, but the specs for these chips are actually identical for most items, and one thing I've discovered during the past week of investigation is that it is impossible to judge the sound of any op amp based on specs alone. Whoever put those posts up was terribly misinformed. The only way to tell how a chip sounds is by listening to it... and the AP is definitely a better sounding chip than the BP when compared side by side, judging from my recent tests with sets of chips that are now known to both be very well burned in."
Oh, there was more! I've cut out at least half of it!
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Now I'm getting off topic (as if I wasn't already!), but he also mentioned the THS4032 op amps, which seem interesting:
"As far as the THS's go, I must say that I'm also going on the reports that the fellow gave of the impressions of numerous people who did listen to the chip over two days at the HES show in two different units. According to the reports of those many listening tests the THS4032 is a superior audiophile quality chip unanimously chosen by virtually everyone who heard it regardless of the unit it was in. So, I think that chip holds great promise.
Also, amongst my reading so far, the one specification which does stand out is the "settling time", which is the time it takes for a chip to refresh it's signal and allow the signal to "settle" down once again. The 2604 has a settling time of 1,000 nanoseconds, the 2134 has a settling time of half that, 550 nanoseconds, while the THS (HS=High Speed) has a settling time of 40 nanoseconds! With a refresh rate that fast, there should be more accuracy of reverbs, more detail in timbre, more subtle nuances coming through, and so on. Providing the sound of the chip is tonally pleasing, it should be a superior op amp as far as details go. The 2604 is also a 22khz chip, I believe (although it may be 44khz) whereas the THS4032 is a 100Khz chip. What this translates to is greater transparency, more depth to the soundstage and more 3-dimensionality. So, the ear is, of course, the ultimate judge, but all things considered, I'm expecting to hear some good things from this chip in particular in the T-100."
