Sidebar 3: Measurements
Because of the Von Schweikert Ultra 55's bulk and weight, I drove my measurement gear to Michael Fremer's place in deepest, darkest New Jersey to perform the measurements. I chose a day that was forecast to be sunny with minimal wind, because I was going to measure the speaker in his driveway, so that the only source of reflections would be the ground. (Even so, the proximity of the ground necessarily led to aggressive windowing of the time-domain data, which reduced the measurements' midrange resolution.)
I first measured the speaker's spatially…
Jazz collecting has an archaeological aspect to it; it's one of my favorite aspects of the hobby. Far more than most other genres, jazz evolved over its first several decades, and it did so on record. Every musician was distinctive, changed from session to session, and interacted with other musicians in ways specific to the ensemble, the time, the place, and the mood. Every record, live or from a studio, is a snapshot of where jazz was precisely then and there. You can get to know musicians' styles, and with practice, you can really hear what's going on.
I called it "archaeological," but…
Canadian audio manufacturer Classé Audio was founded in 1980 by engineer Dave Reich and entrepreneur/audiophile Mike Viglas. The name "Classé" was a pun on the fact that Reich was a firm believer in an amplifier's output stage operating in class-A, where the output devices never turn off (see sidebar). Though the brand was established with the 25Wpc DR-2, the first review of a Classé amplifier to appear in Stereophile, by Larry Greenhill, was of the later DR-3, in December 1985. No fewer than 22 reviews of Classé products are available in our free online archive. These include the CAM-350…
The first surprise using the Delta Monos was that the meters showed that I almost never used an average level greater than 6W to drive the Vimberg Mino loudspeakers that I reviewed in April. (The meters actually maxed out at "3W," but as they are calibrated in 8 ohm watts and the Mino is a 4 ohm speaker, the indicated power needed to be doubled.) A power of 6W into 4 ohms is equivalent to a voltage of 4.9V RMS. If the music I typically listen to has a high crest factor of 10dB, that means the instantaneous peak voltage would be 15.5V. This is just below the amplifier's maximum voltage…
Sidebar 1: A Class-A Icy Tunnel
Up to their continuous-current limit, a class-A amplifier's output transistors are fully turned on all the time. As well as the devices thus being in thermal equilibrium and therefore relatively immune from having their transfer function thermally modulated by the signal current, the nonlinearities that result from switching the devices on and off during every cycle of the signal—generally referred to as crossover distortion—are sidestepped. Electronically, this is an elegant solution; practically, it is the opposite, in that two-thirds of the power drawn…
Sidebar 2: Specifications
Description: Solid-state monoblock power amplifier. Inputs: 1 single-ended (RCA), 1 balanced (XLR). Outputs: 2 pairs Furutech Torque Guard binding posts. Power output: 300W into 8 ohms (24.8dBW), 600W into 4 ohms (24.8dBW), 1kW into 2 ohms (24.0dBW), with AC line held constant. Class-A output power: 35W (15.44dBW). Maximum output voltage: 113V p–p, 40V RMS, into 8 ohms. Frequency response: 1Hz–650kHz, –3dB. Voltage gain: 29dB at 1kHz, balanced and single-ended. Input impedance: 82k ohms, single-ended and balanced. Input sensitivity (for nominal output): 1.74V.…
Sidebar 3: Associated Equipment
Analog source: Linn Sondek LP12 turntable with Lingo power supply, Linn Ekos tonearm, Linn Arkiv B cartridge, Channel D Seta L phono preamplifier.
Digital sources: Roon Nucleus+ music server; Ayre Acoustics C-5xeMP universal player; PS Audio PerfectWave DirectStream and Weiss DAC502 D/A processors, Ayre Acoustics QA-9 A/D converter.
Power amplifiers: Parasound Halo JC 1+ and Lamm Industries M1.2 Reference (both monoblocks).
Loudspeakers: Vimberg Mino.
Cables: Digital: AudioQuest Vodka (Ethernet), AudioQuest Coffee (USB), DH Labs (1m, AES/…
Sidebar 4: Measurements
I tested the Classé Delta Mono with my Audio Precision SYS2722 system (see the January 2008 "As We See It"). I preconditioned the amplifier by operating it at one-third the specified power into 8 ohms for an hour. At the end of that time, the chassis was cool, at 76.9°F (24.9°C), though the grille over the rear-mounted fan vent was warmer, at 105.0°F (40.6°C).
The Classé's voltage gain into 8 ohms measured 28.7dB from both the balanced and unbalanced inputs and the amplifier preserved absolute polarity (ie, was noninverting) with both input signals. At 86k…
I've been wrestling with my elders about new ways to measure loudspeakers, lobbying for methods that might correlate more directly with a listener's experience. And wouldn't you know? Right in the middle of this Socratic dialogue, I put the fresh-from-UPS, $1000/pair, Tannoy Revolution XT 6s into my reference system, plunking them down on my 24" Sound Anchor Reference stands in the same spot my Harbeth P3ESRs had been sitting. And I freaked! I was using the Rogue RP-7 preamp and the Rogue Stereo 100 (100Wpc) amplifier, and I could never adequately describe how bad the shiny white Tannoys…
During my second cup of coffee, while listening to Ito Ema play Bach's Goldberg Variations (CD, MA recordings MO24A), I heard a dip around 120Hz and some boosted energy just above the 1.8kHz crossover point. The 120Hz dip made the left side of Ito's piano seem less corporeal than I prefer. The 2kHz boost made the upper registers sound lively and direct.
With both the Rogue Stereo 100 and now the Schiit Aegir, I would have to describe the Revolution XT 6's sound as pure and focused but slightly soft. Orchestral soundstages were accurately mapped. There were multitudes of fine detail, but…
