HEADPHONE AMP

I'm no longer working in the home office so my headphone stereo is not getting used. I decided to move the headphone amp to our upstairs system for watching movies. This worked great, as it has deeper bass, smoother mids, and more extended highs compared to the Onkyo receiver's headphone jack we were using. Also, the amp's spatial processor is great for movies.

CD PLAYERS

I also did an A/B/X test of the headphone system CD player with my main system CD player. I had listened to and tested these players before, but never directly back-to-back with each other in the same system. I did this test with Emma (who recently turned 7). I put the same CD in each player (one a bit perfect error checked copy), played them both in sync, and one of us would listen while the other flipped the switch. The listener didn't know which one he was listening to.

Emma noticed that one was slightly louder than the other, though the difference is only 0.2 dB. I congratulated her on good concentration & attention especially for a kid her age. I noticed the same, plus three other very subtle differences, each on my threshold of hearing. One had more "presence" in the mids, a very slight ring or resonance at a particular frequency, which gave it a "harder" sound. It was much like the coloration that is audible in the overlap range of speaker crossovers. This worked well with some vocals but impaired most acoustic instruments. The same one also had very slightly rolled off highs. And the other one seemed to have more finely detailed gradations of micro-dynamics. I should note that all of these differences were subtle and required careful listening to detect. But they showed up consistently across multiple recordings of various types of acoustic music.

It turns out the player that

This was a bit surprising to me, as the Onkyo has a higher output impedance - 450 vs. 10 ohms of the Rotel RCD-1070. Due to its higher output impedance, I had some concern whether it could drive my 10k passive attenuator. I guess it should be no surprise that it did, as 10k / 450 is greater than 20:1, which should be a safe ratio for impedance matching. Also, the Onkyo has lower measured distortion (both harmonic and intermodulation) - though both are very low, theoretically either one is (or at least should be) below audible thresholds.

The Rotel has higher quality internals - a toroidal power supply, better opamps in the output stage, and higher quality / lower tolerance parts throughout. It also has a lower measured noise floor, mainly due to suppressing 60 Hz about 6 dB lower. But the Onkyo is low enough, lower than -90 dB. So it appears the Onkyo's internals are "good enough", and its superior A-D chip makes all the difference.

The Rotel is a beautiful unit but I'll have no use for it, so I may put it up on eBay soon.

SPEAKER POSITIONING

I also messed around with speaker positioning a bit and made a little discovery. Putting the speakers a bit closer together and further from the walls improved imaging, as one might expect. But it did more - it also eliminated a bit of midrange hardness that had been bothering me for years. Now the listening distance is 1 1/3 the distance between the speakers. I don't know why this sounds better - is it being further from the walls, or is it being closer together? I don't know, but the result is unquestionably better. My best recordings sound smoother, and it is more forgiving of the mediocre ones.