Well, since last Wednesday, I let the Clairixa burn in for two and a half days and spent at least five hours on Friday listening to the system without any A-B-ing. The sound was fantastic, though different from what I've become accustomed to. Late Saturday, after again spending several hours listening, it seemed that i'd never heard the various drum solo's on the Bassface Swing Trio's Gerschwin album sound so real and energized. However female vocals (Eva Cassidy, Claire Martin, Alanis Morrissette-accoustic Jagged Little Pill, Ana Caram) didn't sound quite as natural and textured: the timbre seemed a bit too energized, tending toward a less nuanced or textured or less analogue sound. I adjusted settings and found that with Peter's recommended NOS1a settings, 16x oversampling ( I usually only do 8x) and the device driver buffer set to 8ms the sound became more like the sound I get from my YFS V4 data only cable. However it wasn't until yesterday when I finally put the YFS cable back into the system that it became clear that the active 5v power leg of the Clairixa adds a level of noise that on the one hand "energizes" the sound, but on the other hand colors the sound in a way that leaves vocals less satisfying because they sound less natural. With the YFS V4 cable the magic of a live vocal performance returned.
So this was my impression on March 30th, but, it turns out, that impression was with an NOS1a-75B that wasn't right. Apparently, the local guy who removed/installed the 75 ohm output resistors, when I converted to 75B, screwed it up: when removing one of the original resistors, he also removed the the contact attached to the pcb that the resistor is soldered too. So, by my estimation, I was only ever hearing about 80% of the NOS1a upgrade. Encountering problems, I had to package up and ship my DAC to Peter, where this problem was diagnosed and repaired. For the last ten days, I have been completely blown away by the full and correct sound of the NOS1a-75B upgrade. There now seems to be endless high end resolution. Using an SPL meter has become essential to the preservation of my hearing; otherwise, without realizing it, I could spend hours listening at levels that would certainly damage my hearing!
So how does the Clarixa sound now? Tone and timbre of vocals are every bit as textured and natural as my data only cable. All brightness or glare has disappeared. Every time I put the Clarixa in the system it feels totally correct and my first thought is that I don't see any reason to ever change this cable. However, when I put the data only cable back in, and I have gone through this exercise several times, I am even more surprised. It is now the V4, data only, that has a bit more sparkle and energy. The Clairixa has a darker, less translucent, and more "solid" sound. Now, I've never heard of "translucent sound" but I think it describes what I'm hearing: a kind of airiness that allows for pinpoint focus but, at the same time, is like a live performance where all individual sounds are merged into kind of "wall of sound." Very hard to describe but very, very pleasing.
Regarding my problems with the NOS1a-75B, I would be remiss if I didn't mention what incredible customer service I received from Peter and Ciska. The email support and turn around time were amazing! IT JUST DOESN'T GET ANY BETTER ANYWHERE ON THE PLANET!
Brian