The OP Amps thread!
First of all, keep in mind that this thread is for advanced users only, I mean that if you don't give a shit about optimizing your audio setup, you should completely ignore it
Now before going further, I will answer two questions:
Q: Why this thread?
A: Because manufacturers uses cheaper components to sell their products, this way they can pretend it's a quality product while keeping it in a decent range of price. If you're looking to optimize your audio setup in order to reach the best sound quality possible, you must get aware of the difference between those components that we call OP Amps (operational amplifiers).
Q: So what is an OP Amp?
A: Well it exists many different types of OP Amps, i'm not gonna enter in all the complicated details so to make it simplier: it is used in audio devices to amplify the signals, you would've understood.
Operational amplifers in audio devices
Most of the time, the OP amps are welded to the printed circuit board, so if you want to change those you will need to equip yourself of special tools (elsewise if you try to practice any modification with non adequate materials you might damage your device).
However, certain manufacturers allows you to change those very easly like on the Asus Essence sound cards. All you have to do is to pull it off.
In those little devices such a PCI sound card they use 3 OP amps (double): 2 in I/V (DAC) and one Buffer (RCA output). It's generally recommended to use the same amps for I/V, however the third one (Buffer) can differ from the others.
note that the anti EMI shield has been removed
Why it is important to consider replacing the stock amps by better ones
The OP amps can affect the global stereo image: like I said in those little devices, they are using double op amps instead of one for the left channel and one for the right. That means it can ruin the diaphony (channel separation). So you will need double OP amps having a proper isolation between the two chanels, also providing less distortion.
I won't post here all the measures taken from the tests but I know by having done a lot of research what it is recommended to use by most of the audiophile people, so i'm gonna list several products below:
As I am using an Asus Xonar Essence sound card, i'm gonna take it as example: old Asus Essence devices used crappy OP amps, so in order to improve the sound you will have to replace all of these.
Their latest product brings two Muses 8920 and one Muses 8820. In the package they include 3 exchangable op amps: x2 LME 49720 and x1 Muses 8820. All you have to do is to take off the Muses 8820 from the Buffer and place a LME 49720 instead.
Muses 8820: The dark beast! Commercially speaking it sounds great because there's the name Muses on it, and they're well known for their Muses 01 which are certainly the most renowned op amps actually on the market. However, they are very crappy and you must take these off and use better ones!
Muses 8920: The best one, why? because it's specs are very close from the Muses 01 and it costs only 17€ instead of 75! It's pratically the same as the LME 49720 but the sound rendering is more like what tube amplifiers provides (J-FET technology) so that makes it a bit better than the LME 49720.
LME 49720: Well as I explained above, it's more like the same as the Muses 8920, slightly less good since it uses bi-polar technology. But it remains a sure value.
Muses 02: Don't get fooled! Its name would make you believe it's right behind the Muses 01, but that's not the case! That thing is not worth better than the crappy Muses 8820. And it's 50€ one!
Muses 01: The reference, the legend. Renowned by every audiophile, those amps belongs to the best actually comercialized on the market. It's 75+€ one.
Beware! Yes, some Chinese manufacturers are selling false copies! So watch out if you see, on ebay especially, resellers selling those for 15 bucks only.
There are a lot more models but I don't know them all. Those I listed above belongs to the biggest references and are probably the most used on all "audiophile" devices and materials. There are also some that costs a lot more money, but remember that in the audiophile world, the price doesn't always justify the quality!