Sound
The MB 175s replaced a pair of Cary 805s I'd been auditioning for the previous few months. When Luke Manley told me "bass punch" with large woofered speakers was not the 175's strong suit, I was concerned about losing the Cary's luxurious, single-ended, triode midrange purity and getting nothing compensatory from the VTLs. So I was more than pleasantly surprised by the 175's low-frequency performance; to my ears, it bettered what I got from the larger 300 in every respect save that of sheer power. In fact, the MB 175 proved to be an ideal match for the Audio Physic Virgos,…
While the 175s imaged superbly through the Virgos, they didn't offer the ultimate in soundstage depth. Both the VTL 300s and the Carys push the rear of the sonically visible stage somewhat farther back and out to the corners. The 175's stage picture is more ovoid than square, probably due to the amp's faster, more prominent top end. Brighter balance equals more forward picture—not that the VTLs sound bright. I've come to find the 175s more neutral and pleasingly "analytical," if not as seductive as the Carys or as "massive"-sounding as the 300s. Despite its outstanding high-frequency…
You can have that by shifting to triode operation at a flick of the front-panel switch (after turning the amps off!). I tried it but didn't end up liking it very much. Ninety watts sounded anemic to me, with sloppier bass and compressed dynamics. Rock music got stuck in the mud, solo violin sounded a bit more rich but too syrupy for my taste. Perhaps the amps would work better in triode mode with other, easier-to-drive loudspeakers. I preferred the taut bottom-end control, the outstanding high-frequency extension, and the overall dynamic thrust tetrode operation offered. I did all of my…
Sidebar 1: Specifications Description: Vacuum-tube monoblock amplifier. Output power (20Hz-20kHz into 4 ohms): 175W (19.4dBW) (tetrode), 90W (16.5dBW) (triode). THD (20Hz-20kHz at maximum power): 3%, tetrode or triode mode. S/N ratio: 106dB (tetrode, 120Hz); 108dB (triode, 120Hz). Input sensitivity (for full output): 1V. Input impedance: 130k ohms. Load impedance: 3-8 ohms. Power consumption: 160W idle, 380W full power.
Dimensions: 19" W by 8.5" H by 10" D. Weight: 50 lbs.
Serial numbers of units reviewed: 501262 & 3.
Price: $4990/pair. Approximate number of dealers: 35.
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Sidebar 2: Associated Equipment Analog Front-End: Transfiguration Temper, Lyra Parnassus and Clavis D.C., AudioQuest Fe-5, Dynavector XX-1L, Crown Jewel cartridges. Rockport Series 6000, Graham 1.5t/C, JMW Memorial, Immedia RPM 2, Wheaton Triplanar IV Ultimate tonearms. VPI TNT Mk.IV turntable.
Digital Front-End: Audio Alchemy DDS•Pro transport, DTI•Pro 32 enhancer/jitter reducer, Enlightened Audio DSP 9000 III HDCD processor.
Preamplification: Audible Illusion Modulus 3A preamp, Millennium line-stage, Audio Research PH-3, FM Acoustics 122, Plinius 14 phono sections.
Power…
Sidebar 3: Measurements The VTL MB 175 amplifier developed a glitch about halfway through my first attempt at measuring it, the S/N and THD+noise deteriorating markedly. I suspected a bad tube, but Luke Manley of VTL elected to fly to Santa Fe to repair the amp on the spot. In the process he also made some minor upgrades to the power supply and tweaked the bias. The measurements presented here reflect those changes. I suspect that the initial defect I discovered happened either in transit or on the bench. Had MF experienced the noise level the unit exhibited for me at its worst (it was -…
The distortion curves in figs.3 and 4 show a rising distortion at higher frequencies but a reasonable performance, particularly up to 10kHz. The triode distortion in fig.4 is actually slightly higher than that for tetrode operation, though the differences are not huge. The THD+noise waveform is shown in fig.5. The triode result (shown here) is marginally worse than the tetrode. As MF conjectured, it is heavily low-order, but it is mainly third- rather than second-order. There are also unmistakable higher harmonics present. The 2 ohm result (not shown) transitions to a dominant third harmonic…
A plot showing the output spectrum resulting from a 50Hz input is shown in fig.6 (the power level was 99.4W into 4 ohms). The artifacts are relatively high (-47.4dB or about 0.4% at 100Hz, and -36.7dB or about 1.5% at 150Hz). A similar spectral plot in fig.7 shows the IM at the output resulting from a 19+20kHz input at 70.3W into 4 ohms (the highest output possible with this signal prior to visible clipping). The 1kHz IM distortion here is relatively high (46.2dB or 0.5% at 1kHz, and -36dB or about 1.5% at 18kHz). The corresponding spectral responses in the triode mode, and also into our…
Okay, what does a turntable look like? Take your time—I'll wait. Dum de dum de dum dum dum... Oh, you're tired of this game already?
I never thought much about what a turntable looked like until I got Immedia's RPM2 in for review. After all, there are a lot of high-end turntables out there, from the venerable Linn Sondek LP12 to VPI's TNT, and few of them look like one another. Right?
Well, maybe they do, at that. Because I took one look at the Immedia and thought, Where's the rest of it? And simultaneously, This is a high-end turntable? Then I tried to pick it up. I thought it…
In fact, the two parts of the bearing proper, as well as the spindle and the platter, must all be machined at the same time. Most bearings are simple devices, consisting of a spindle and a cup—or some variation on that theme. The RPM's bearing has two cups, one of which is attached to the platter and fits down over the bearing well, rotating around it. This outer cup contains a downthrust spindle that fits into the bearing well inside the inner cup. The bearing well has a wedge-shaped bottom, into which is fitted a steel ball. A sapphire disc sits atop the ball, acting as the bearing. The…
