Misadventures and other anecdotes gathered along the way

• Before I bought the Bryston, I had been living with an elderly Dynaco Stereo 400, which is a fairly simple big solid-state amp from the early 70s. Over the years it has never given me cause for complaint. However, one of our cats loves to sleep on it, and so last winter, the protection relays began to hang up due to cat hairs and general grunge and it finally refused to operate at all. I took it in to be repaired and borrowed the Bryston as a loaner from Parsons Audio. When I fired the Bryston up, the monitor system sounded newly terrific, with a brilliance and transparency that was a little startling to me. “Voila,” I said. “I’ve stumbled into a major upgrade. The dated performance of the Dynaco has been limiting the transparency of the monitor system.” So inspired, I plunged for the Bryston. Parsons was happy because he sold a loaner, the repair shop was happy because they could take their sweet time repairing the Dynaco (they still have it), and I was happy that I’d improved my system.
  
  But wait a minute! I just found out I can’t tell the Bryston from the Crown D75, which I’ve also owned for years and never liked as much as the Dynaco, yet didn’t I prefer the Bryston to the Dynaco? So it looks like I’ve got one of these rock-scissors-paper Escher loops. Bryston beats Dynaco beats Crown ties Bryston. Hmmmm. Time to reboot. I’d hoped to get the repaired Dynaco into these tests, but naturally, it isn’t fixed yet. Back when I reported on the microphone tests (Recording, June, 1994), I related the story of a studio owner who found himself in a similar situation: he found a new amp was a major improvement over the old one, but when faced with an ABX test, he couldn’t tell them apart. Will I find myself in the same boat? Could be. When the Dynaco comes back, I’ve got to see if I can hear a difference. Stay tuned.



• During these tests, I decided that whenever I did hear a difference, I’d stop and make measurements with the TEF, to see if I could objectively measure a difference that I could correlate with the perceived difference. Well, the first time I got a subjective difference, I’d just brought the levels up to about 92 dB SPL, and fully expected that the D75 would run out of steam. But I wasn’t prepared for just how badly it came apart. Differences were instantly obvious. The Crown sounded distant and tilted oddly toward the right, while the Bryston sound fat, clear and glorious. “Voila, “ I said (it’s a favorite phrase). Then I looked. Our new kitten Max had jumped onto the console and bumped down the fader for the Left channel of the D75. Turned out he’d moved it about 2.5 dB. Once I got the levels reset, I could hear that the Crown was clipping slightly on peaks, but hanging right in there otherwise. The interesting thing about this was that I didn’t hear Max’s headroom change as a loudness change so much as a clarity and image change. And even though the Crown was slightly over its power limit, once I got the levels the same again, differences went back to being negligible, except on overloaded peaks.



• This kind of loudness difference really showed up with a vengeance later on. I started these trials with just the Bryston and the Crown, and spent a lot of time getting their levels matched, a channel at a time, using the RTA software in the TEF analyzer to accumulate acoustic energy over a minute and adjusting so that both amps yielded the same accumulation to within about 0.2 dB. Picky, picky. Well, when I added the Yamaha and the Hafler, I simply ran a 400 Hz. tone through everything and used my Ivie RTA with bar-graph meter to confirm that levels were the same everywhere. When I got to the Yamaha, its levels could only be trimmed in 1 dB steps, so I set it to the correct indicated level on both channels, checked the Ivie meter, and went ahead with testing. As soon as we included the Yamaha in a trial, we all immediately noticed that it sounded enough different (louder) that we halted the trial. When I measured with the TEF, we found that one channel of the Yamaha was about .5 dB louder than the other. Now this is supposed to be less than the threshold of audibility, but none of us had any trouble hearing it, grooved in as we were at that point. So, I retrimmed levels for all the amps, using the Yamaha as the reference. Soon as I did, they all sounded the same.
  
  What I learned from this was that a quick level match using a single sine tone read by a bar graph meter wasn’t nearly good enough for these tests, and that level differences of less than a dB were easily audible as a change in sound quality, even if such differences aren’t generally audible in a stereo pair and are viewed as being less than the Just Noticeable Difference (JND) of loudness for humans.
< 1 2 3 4 5 >
SIMILAR ARTICLES
About Buying A Console
Whadda Ya Mean, It’s Indistinguishable From Chance?
Whaddya Mean The Sound Is Fluffy?
Power Amps Revisited: The Joys Of An “Audiophile” Amplifier
Some Reminiscing About My Experiences With Subjective Testing
NuVerb: Why, It’s Virtually a Reverb!
Eight Vocal Microphones Tested and Compared
Members
Login | Register

More Info
Mailing List