As I mentioned, I'm now using the BB OPA2107 biased into class A with a cheap mod - see
http://tangentsoft.net/audio/opamp-bias.html. (The OPA2107 has a reputation of responding well to being biased into class A.) Basically, I soldered 4.7k ohm resistors from the top of the pins 4 to 1 and then 4 to 7
Now this setup sounds much different from the stock setup. IMO it pushes the amp to another level and the results are rather jaw dropping. The retrieval of low level information, rendering of harmonics, and clarity is now quite astounding. It's hard to describe. I'm not talking about hearing stuff I've never heard before. But it's more like I'm hearing certain new specific qualities to stuff that I've heard before. This is particularly noticeable from the midrange to the highest treble registers. For example, whereas before, percussion such as high-hats and cymbals tended to have a homogeneous quality (even with the OPA2107 not pushed into class A), I can now hear very very different qualities, of how and where the sticks hit the surface, the quality of the metal and how the ringing perpetuates. The same holds true for guitar, how the strings are plucked, the individual vibrations of each string, the feedback and distortion settings on the guitar amp, etc. This of course also applies to noise in the recording, but you hear not only hiss, but the quality of it - the individual grains that make up the hiss.
On the track
Daughter from
Pearl Jam's Rearview Mirror CD, I used to be able to make out someone saying
something before the band began the song. With the OPA2107 biased into class A, it now becomes very obvious. You can very
clearly hear someone say "Are you guys ready" in the background - just above the individuals grains of hiss.
BTW, I tried the class A mod with the stock OPA2132. It does improve it, but not nearly as much as the OPA2107. The above setup really reveals how much the stock OPA2132's bass sounds "tubby". Tubby in the sense of a plastic food container tub. The downside to the above change is that the amp becomes less warm.
I'll be taking a closer look at the OPA2111 next since I upon an initial listen, I didn't find it offensive, and it doesn't cost a ton of money (like the OPA627s, not to even mention the Bursons).
