Fact is, the predominant digital source at audio shows is now a computer, and Stereophile has been covering…
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If an audiophile visiting an audio show in 1991 were to have been transported two decades into the future, at first he would not be aware of any difference: A two-channel system would be playing in a hotel room. But on closer inspection, he would notice that the CD player, the ubiquitous source 20 years ago, would be conspicuous by its absence. Yes, there might be a turntable—"Good to see that people are playing LPs in the future," he would think—but why is there a PC in the room?
Up to this point I'd been using a generic USB cable with the Off-Ramp. I now substituted the expensive AudioQuest Coffee cable ($295/1.5m). If I heard a difference, it was very small, but if I had to swear on J. Gordon Holt's unwritten autobiography, I'd say that the AQ continued in the same direction the improvement I'd heard with the battery supply.
I spent the rest of that day trying to measure the differences between these two USB cables. It proved as frustrating as a snipe hunt, though I did find a very slight difference in jitter between the AudioQuest and generic cables with the…
Sidebar 1: Specifications
Description: USB-AES/EBU, -S/PDIF, or -I2S data format converter for use with PCs and Macs (driver software included). Drivers available for Windows 7/Vista, Windows XP/2003, Mac OS X 10.6 (Snow Leopard), Mac OS X 10.5 (Leopard), Mac OS X 10.4 (Tiger). Input: USB 2.0–compliant. Operates in asynchronous isochronous mode. Output: S/PDIF electrical on RCA jack, AES/EBU on XLR jack, I2S on RJ-45 jack. Sample rates supported: 32, 44.1, 48, 88.2, 96, 176.4, 192kHz. Input/output bit depth: 16 or 24. Power supply: 12V DC wall wart. Options: Monolith lithium-ion battery…
Sidebar 2: Associated Equipment
Digital Sources: Ayre Acoustics DX5 universal player; G4 Mac mini running OS X 10.5.8, iTunes 10.4.1, Pure Music 1.82; Logitech Transporter, dCS Debussy, Bricasti M1 DAC D/A converters; Halide S/PDIF Bridge USB-S/PDIF converter.
Preamplifier: Ayre Acoustics K-5xeMP.
Power Amplifiers: Classé CTM-600 monoblocks.
Loudspeakers: Sonus Faber Amati Futura, TAD Compact Reference, Vivid B1, BBC LS3/5a.
Cables: Digital: Kimber Orchid AES/EBU. USB: AudioQuest Coffee. Interconnect (balanced): AudioQuest Wild. Speaker: AudioQuest Wild. AC: PS Audio Lab…
Sidebar 3: Measurements
I measured the behavior of the Empirical Audio Off-Ramp 4 using the Audio Precision SYS2722 system (see www.ap.com and "As We See It" in the January 2008 issue). I installed the correct version of the driver program for the Snow Leopard operating system, and played test tones at various sample rates and bit depths from BIAS Peak 7 on an Intel MacBook running OS X 10.6.8. The Macintosh USB Prober utility reported both the manufacturer and product strings as "Empirical Audio Async 192." The interface was identified as "vendor-specific," with no information offered…
In his "Manufacturer's Comment" in response to my review of the original Music Reference RM-200 power amplifier in the April 2002 issue, designer Roger Modjeski admitted that being a manufacturer was not his first choice. "Frankly, I'd rather consult than produce," he claimed. "I'd rather be making a living doing stand-up comedy," I said to myself after reading his comment.
But a decade later here I still am, and Modjeski is still producing his own Music Reference brand of electronics and marketing computer-matched tubes sold under the RAM Tube name—not that both of us aren't also doing…
JA's measurements of the various taps' total harmonic distortion plus noise vs frequency indicated that "When its output transformer is matched to or less than the load, the RM-200 offers superbly low distortion from the upper bass through the midrange to the mid-treble. With lower-impedance loads, the distortion rises significantly with the degree of mismatch between the output tap and the load."
So choosing the optimal tap should take into account your speakers' nominal impedance as well as the lowest impedance they dip to. My Wilson Audio MAXX 3s dip down to 3.4 ohms at around 20Hz…
Sidebar 1: Specifications
Description: Stereo power amplifier with solid-state input stage and tubed driver and output stages. Tube complement: two 6BQ7, four KT88. Output transformer taps: 8, 4, 2, 1 ohm. Output power: 100Wpc (20dBW) into 8 ohms. Frequency response: 6Hz–20kHz, ±0.5dB; 2Hz–60kHz, ±3dB. Bandwidths: 13Hz–65kHz (half power), 20Hz–35kHz (full power). Harmonic distortion: <0.5% at 1kHz/100W. Signal/noise: not specified. Input sensitivity: 1.1V (full output). Input impedance: 15k ohms (one leg driven), 30k ohms (balanced).
Dimensions: 17.25" (440mm) W by 7" (180mm) H by…
Sidebar 2: Associated Equipment
Analog Sources: Continuum Audio Labs Caliburn, Cobra, & Castellon turntable, tonearm, & stand; Graham Engineering Phantom II tonearm; Ortofon A90, Haniwa HCTR01, Miyajima Labs Kansui cartridges.
Digital Sources: Playback Designs MPS-5 SACD/CD player/DAC, BPT-modified Alesis Masterlink hard-disk recorder, Sooloos music server, Pure Music software.
Preamplification: Ypsilon VPS-100 phono preamplifier & PST-100 Mk.II line preamplifier.
Power Amplifiers: MBL 9011 monoblocks, Musical Fidelity Titan.
Loudspeakers: Wilson Audio…
Sidebar 3: Measurements
I used Stereophile's loan sample of the top-of-the-line Audio Precision SYS2722 system (see the January 2008 "As We See It" and www.ap.com) to measure the RM-200 Mk.II. Before performing any tests, I checked that the output tubes were all correctly biased. However, the left channel's bias couldn't be optimized and the distortion in that channel was 100 times higher than in the right. I performed a number of tests on the correctly operating right channel while awaiting word from Music Reference's Roger Modjeski. It turned out that each output tube is protected by a…