About a year ago I purchased the Sennheiser HD 598 headphones. I have been listening to music with them through my Onkyo TX-SR604. The quality seems decent and I love the sound on the HD 598 (great for vocals and that hi range). However, the potential for a better listening experience has convinced me to try hardware devoted to headphone amplification versus the standard headphone output on the Onkyo. Rather than selling the Onkyo, I will take advantage of its DAC abilities to convert digital signals to analog. Thus, my loss-less FLAC audio collection and the HD audio on YouTube should sound pretty good with an amplifier.

First, the Qinpu and Woo Audio WA3 are both tube amplifiers. Since I didn’t know much about amplifiers I thought tubes were cool. However, upon further investigation I found that they may not be the best way to go. Apparently they “add color” to the sounds they reproduce. The WA3 is a little pricey ($495 at the date of writing) while the Qinpu is a little better in pricing (around $280). After reading some reviews (head-fi WA3 review) of the WA3 on the Internet and finding a like-new one for sale on Ebay for $350 I was intent on buying it. As my luck died, the WA3 was sold before I made up my mind. Looking at the Qinpu on the Internet I found various reviews. The Amazon reviewers seemed very impressed and happy with there purchase. However, it was at this point that I discovered the Matrix M-Stage.

The Matrix M-Stage Amplifier has some great reviews (check Amazon and head-fi).  I was sold on this amplifier.  Up until today I was going to buy the M-Stage. But when I looked once more for headphone amplifiers I came across the O2.

The O2 was recommended for the HD 598 headphone on head-fi in one of the forums. After reading that, I looked for more information on the O2. Here is the webpage of NwAvGuy (the creator of the O2). His webpage also contains a great many other reviews and links for audiophiles. So, I then made my decision to buy this amplifier. The best site I found was Mayflower Electronics, which had a holiday special for the standard version of the O2. I bought the O2 for $115.