Paralleling Yamaha's introduction of this new class of PC receiver and spurred on by the rapid growth of the MP3 phenomenon, major players from the virtual 3D world, including Spatializer Inc., SRS Labs, and QSound, have joined the fray with "stereo-enhancing" plug-ins for popular MP3 software players. Spatializer and SRS now offer competing plug-ins for the popular Winamp media player, StreamFX and Wow-Thing, respectively. Spatializer also has a version of StreamFX for the Xing media player, and SRS claims their Wow-Thing will…
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Sidebar 3: the Yamaha @PET RP-U100 & other spatializers
Sidebar 4: Measurements
Most of the Yamaha's digital measurements were taken by driving one of its optical S/PDIF inputs from the Audio Precision System One's digital data output, with the DSP effects bypassed and the volume control set at "25." This is the unity-gain setting for analog sources; with a 1kHz tone at 0dBFS, it resulted in a maximum output at the speaker terminals of 2.506V, or 785mW into 8 ohms. Although the volume control will go up to a maximum setting of "64," a 0dBFS digital input clipped the amplifier's output stage at "41."
The digital input was noninverting…
The bottom traces in fig.4 are a similar spectral analysis taken of the receiver's output while it decoded data representing a 1LSB DC offset. Other than the presence of identical power-supply components, this noise floor is suspiciously lower than that in fig.3. Repeating the analysis with data representing a dithered 16-bit tone at -110dBFS resulted in the upper traces in fig.4. Now the noise floor correlates with that in fig.3. The difference between the two sets of traces in this graph indicates that the DAC actually turns off in the presence of a signal that its designers have…
The restricted dynamic range (in the presence of a signal) can also be seen in fig.7, which is a high-resolution spectral analysis of the Yamaha's output made with the Miller Audio Research Jitter Analyzer while the receiver decodes a signal consisting of a high-level tone at 11.025kHz and the data's 16th bit toggles on and off at 229Hz. (This analytical signal for jitter was developed by Julian Dunn, then with PrismSound.)
Fig.7 Yamaha RP-U100, high-resolution jitter spectrum of analog output signal (11.025kHz at -6dBFS with LSB toggled at 229Hz), driven by PS Audio Lambda…
Like the digital inputs, the analog inputs are noninverting. The analog input impedance was 33.6k ohms at 1kHz, the maximum voltage gain into 8 ohms was a high 40.6dB. Fig.10 shows the crosstalk via the analog inputs, which should be compared with that through the digital inputs (fig.2). The sharp drop-off above 20kHz is due to the aggressive anti-alias filtering, and the decrease in channel separation below 1kHz is, again, due to power-supply coupling. But note the peculiar scalloped shape of the crosstalk traces. I have no idea what this is due to. The presence of highish levels of…
The highish noise levels for analog sources mean that the percentage of distortion when plotted against output power (fig.14) is actually dominated by noise. But this little receiver more than meets its specified output power, even with both channels driven continuously. For our standard 1% THD+noise clipping point, I measured 30.1Wpc into 8 ohms (14.8dBW), 39Wpc into 4 ohms (12.9dBW), and, with one channel driven continuously, 60.5W into 2 ohms (11.8dBW). With a low-duty-cycle 1kHz toneburst (10 cycles on, 4000 cycles off)—which is more representative of how the amplifier will behave with a…
As strongly as I believe that the listening experience is the most reliable method of judging the quality of audio equipment, I've been biased against single-ended tube amplifiers because of their quirky measured performances. Without having heard single-ended under good conditions—much less living with an SE amplifier—I had concluded that many listeners must like them because they're euphonically colored by large amounts of low-order distortion and impedance interactions with the loudspeakers. SE amplifiers seem to be a departure from the goal of making the electronics transparent. Moreover…
All the components inside the 300SEI are connected with silver-conductor, Teflon-coated wire instead of printed circuit boards. Looking inside the 300SEI gave me the impression that building this amplifier is labor-intensive. Resistors are 1% metal-film types throughout, and the bypass caps are Kimber film and foil. The volume and balance controls are made by Noble. The output coupling caps are custom-made, oil-filled types specially designed for the 300SE and 300SEI.
The 300SEI's build quality, parts pedigree, finish, and overall look are exemplary.
System
In addition to…
The 300SEI's tonal balance wasn't perfect, however. The top octave lacked air and extension, making the presentation slightly closed-in. This characteristic tended to make the soundstage less expansive in both width and depth and imparted a smaller sound to the recorded acoustic. With small-scale music, the effect wasn't a drawback; but on full-scale orchestral or choral works, the presentation lacked the halo of bloom at the soundstage's outer edges I get from the VT150s. Rather than presenting a huge acoustic the way the VT150s do, the 300SEI's more intimate portrayal of space lent itself…
Sidebar 1: Specifications
Description: Single-ended integrated amplifier. Inputs: three line-level inputs on RCA jacks. Tube complement: 6SN7 input and driver (x3), 300B triode output (x2). Power output: 11Wpc into 8 or 4 ohms (10.4 and 7.4dBW, respectively). Frequency response: 23Hz-20kHz +0, -0.75dB (at 11W output). S/N ratio: 90dB ref. rated power output. Headphone output: 4-50 ohm-compatible (¼" stereo jack).
Dimensions: 14" W by 14" D by 8" H. Weight: 42 lbs.
Finish: chrome chassis with black front panel (24k-gold front panel and knobs, $500 additional).
Serial number of…