Regarding our discussion of exchanging op amp in D10 I found a great article which covers this topic in detail and in, what I consider to be, a professional way: Here are some of the parts of the article that I found particularly interesting:
MYTH: MOST OP AMPS SOUND DIFFERENT - There’s a general perception that op amps sound different. Many gear manufactures tout op amp brands and part numbers in their marketing literature. The $3 OPA2134 is supposed to sound much better than the $1 NE5532 and the $10 AD8610 is supposed to sound better still. But do they? The chip companies don’t help the perception implying some of their op amps offer better sound. But used properly, in a typical audio application, I’ll challenge anyone to a listening test and bet they won’t be able to tell the above three op amps apart. The only catch is it would be a
blind test and the listener won’t know which op amp is which.
MYTH: MOST OP AMPS ARE COMPATIBLE - Op amps are complex devices. While many have the same pin configuration making it appear you can simply substitute one for another, that’s often not the case. They’re optimized for different input bias values, configurations, gains, feedback circuits, load impedances, quiescent currents, speeds/bandwidths, compensation values, operating voltages, noise trade-offs, etc. But some audiophiles can’t be bothered by, or don’t understand, all those details. So they simply swap them out without changing anything else in the circuit. Many have a favorite op amp or two they like to use in most everything without considering if it’s a good match. It’s like the old quote “when you have only a hammer everything looks like a nail”. But that just doesn’t work for op amps. And, not surprisingly, some op amps do better than others when you ignore their requirements. Again, this is a lot like the Second Grain Of Truth above. If you use a given op amp incorrectly, it may well sound different. But it’s not the op amp’s fault.
The person misusing it is creating the audible differences.
MYTH: OP AMP UPGRADES ARE USUALLY WORTHWHILE -The forums are full of posts from people who buy some perfectly nice piece of audio gear, open it up, discover the manufacture used a “cheap 5532” op amp, and they promptly pop in something much more expensive and exotic to “improve the sound”. These are usually people who lack the test equipment to have any idea if their op amp swaps help, hurt, or are just a waste of money. They simply use their ears, in
highly biased sighted listening, and draw all sorts of erroneous conclusions. I know of op amp swaps causing potentially harmful oscillation. Someone might hear ultrasonic artifacts from the oscillation as “newfound detail” when, in reality, they have unwittingly created a radio transmitter. And this isn’t as rare as you might think because of the “faster is better” mentality. (photo: photozou.jp)
TRANSPARENCY: If op amps really have a “sound”, as many audiophiles suggest, it would follow when you add op amps to the signal path the sound should change. Two guys named
Meyer and Moran conducted a very interesting rigorous study. They played high resolution SACDs on a high end system and sometimes inserted an extra A/D and and D/A into the signal path to “down convert” the high resolution audio to CD quality (16/44) audio. After 500+ trials lasting more than a year, using audiophiles, recording engineers, and students as listeners, they found
nobody could tell when the extra A/D and D/A was in the signal path. On top of demonstrating the supposed benefits of SACD are highly questionable they also managed to demonstrate that A/D and D/A converters can be audibly transparent as well. And, as you may have guessed, both the A/D and D/A add several op amps to the signal path. But nobody could tell they were even there. There have been many more blind tests that also demonstrate different op amps (and much more) indeed sound so much alike even audiophiles can’t hear the difference. See the
Matrix audio test for another example.
Complete article can be found here:
http://nwavguy.blogspot.hr/2011/08/op-amps-myths-facts.html
While I do believe pretty much everything stated here, it would still be interesting to see what will happen with the performance when that op amp is swapped with a "better" op amp.
Since Topping stated that those 2 op amps that cannot be replaced are doing I-V conversion I am assuming that 3rd op amp that can be replaced is acting as an output buffer. I asked Topping to confirm it and will post there reply here when I get it. I am of course very sure that if difference can be heard it could only be for much worse as slightly better THD and/or SNR we wouldn't be able to hear.