Listening impressions
Click on the picture to see a larger view of the pcb.
How does it sound really?
First impression is really, really, really good. The second impressions are even better. This amp is crystal clear with extremely well controlled behaviour. "s"-sounds sounds excellent, tight bass, warmth in the mids. This headphone amp may be the best in the world? And the best of all: The parts aren't particulary expensive!
I have made a simple distortion measurment with the excellent russian freeware Rightmark Audio Analyzer. What we can see is that the amp is better than the sound card I have used.
Read what Suzy thinks about the QRV07 (similar to the QRV09):
The beginnings of a new amp to drive my Sennheiser HD595 headphones. I was greatly impressed by the TI TPA6120 current mode feedback headphone amp chip, with incredibly low distortion levels. I began designing a board to try one out, but found almost exactly what I was designing had already been done by a Swedish designer, Per-Anders Sjostrom. So I bought a bare board off him. Here's the board mostly assembled, being test-fit in a Hammond extruded aluminium box, with Alps volume pot. I'm extremely impressed by Per-Anders work. This is a beautiful design, with great attention to detail. I couldn't have done better myself.
In use the amp is wonderful. Totally transparent, with no audible noise at all. I haven't wound it up all the way, as I value my hearing too much for that.
I've finished the amp and have been using it for a few months, and am still totally impressed with it. I really don't think you can make a better headphone amp, no matter what you do.