Viola Audio Laboratories Crescendo Preamplifier and Concerto Power Amplifier

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Equipment report
Categories:
Solid-state power amplifiers,
Solid-state preamplifiers
|
Products:
Viola Audio Laboratories Concerto,
Viola Audio Laboratories Crescendo
Viola Audio Laboratories Crescendo Preamplifier and Concerto Power Amplifier

Overview
The Crescendo and Concerto look and operate unlike any other electronics I’ve seen. The identical chassis have no apparent front- panel knobs or controls, just a small truncated-pyramid-shaped display with nothing more than a few symbols illuminating it. The minimalist look is possible because the system is controlled via an included iTouch and dedicated Wi-Fi network. Power-on and -off, source selection, volume, muting, and other functions are all made through the iTouch. The units are supplied with a pre-configured Wi-Fi router that can be plugged into any AC socket within Wi-Fi range. The Crescendo and Concerto are connected by an Ethernet cable, but get their instructions from the iTouch wirelessly via the router.

Via the iTouch interface you can change the display color (globally or by selecting a different color for each input), apply 10dB of attenuation on select inputs, name the inputs, monitor the heatsink temperature, and access other functions beyond those found on traditional remote controls. In practice, I appreciated that the iTouch liberated me from requiring a line- of-sight between the remote and the equipment rack. Of course, Viola’s remote app will run on any iDevice. As much as I like the feel of a heavy machined remote, the iTouch proved a welcome change in daily use. If the iTouch is out of power, the Crescendo and Concerto can be operated by the rudimentary front-panel display. The Crescendo’s display has power and volume up/down controls, and the Concerto a power on/off. These displays are contained within the small “V” shape cut into the front panel, which extends to the top plate and the back of the unit.

The chassis are machined from solid blocks of aluminum and have a monolithic look. Ridges are cut into the top plates that suggest heat sinks, but without the fins and sharp edges.

The power amplifier, housed in an identical chassis, has within this top-plate groove an unusual heat sink integrated into a slot running down the middle of the chassis. The metal work is gorgeous—as good as it gets. Moreover, the aluminum is anodized with a slightly grayish patina that gives the Crescendo and Concerto an elegant, yet businesslike vibe. The visual effect of the whole package is stunning.

The Crescendo is the second model up in Viola’s four- preamplifier line, and the only one to incorporate a digital- to-analog converter. In addition to digital inputs on USB and SPDIF, the Crescendo offers analog connectivity via three balanced and three unbalanced analog pairs. The output choices include balanced or unbalanced connection. The DAC can accept datastreams up to 192kHz/24-bit, with the sampling frequency and word length displayed on the iTouch.

The circuit is based on Viola’s discrete operational-amplifier module. Op-amps needn’t be integrated circuits; they can be built from discrete components into a module that functions as an op- amp but without the sonic compromises of an integrated-circuit op-amp. Viola’s discrete op-amp is built from a low-noise FET input stage, a differential voltage-gain stage, and a low-output- impedance voltage follower. Volume control is realized with a discrete thin-film-resistor network controlled by switches (in 1dB steps—2dB steps below -50dB). The integral DAC section is built around an XMOS processor running on Viola’s own clock circuit and a BurrBrown PCM1794A DAC. The DAC section had no trouble locking to any sampling frequency and word length I fed it. Finally, the power supply is housed in a separate subsection within the monolithic chassis.

The Concerto is the entry point in the Viola power-amplifier line, with four models above it. The amplifier delivers 100Wpc into 8 ohms, and commendably, can double that output power into 4 ohms. The dual-mono design extends to the power supply, which employs a choke just after the transformer. This technique, developed many years ago for Cello products, is deployed throughout the Viola line. According to designer Paul Jayson, the choke smoothes the current spikes that charge the reservoir capacitors, keeping them more fully charged at all times. It’s intuitive to think of a power supply as drawing current from the wall on a consistent basis, but in fact current is pulled from the wall in spurts during the peaks of the 60Hz AC power waveform. The choke, with its inherent energy storage, spreads this energy out over a longer time and keeps the capacitors fully charged between the peaks in the 60Hz AC waveform. Incidentally, the power supply for both the Concerto and Crescendo automatically configures the transformer for the correct line voltage.

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