REVIEWS: From AUDIO MEDIA March, 1998
Avalon Design has turned their efforts toward the vacuum tube
pre-amplifier market. JAYSON CHASE reviews the VT-737.
For those of you who may still be unfamiliar with Avalon products, the best way to describe them is 'pure genius'. Avalon is renowned for its discrete class-A circuit designs and components, and phenomenal sound quality. Their VT-737 pre-amplifier is a tool for people who enjoy their work.
Once 'Round The Chassis
Everything about the VT-737 is solid, from the chunky cross-head rotary controls on the front panel to the rather large heat sink on the rear. At 22 pounds it's no lightweight. Looking through the unit's top vents reveals a nifty little LCD which displays the length of time that the tubes have been operating. Avalon recommends that the vacuum tubes be replaced after 5000 hours of use. Space is limited within the confines of the chassis, but it's clear to see the precision that was involved in developing the circuit layout. The solid aluminum front panel is equally well laid out. The cross head design of the large purple knobs does actually make them easy to use without your fingers moving the surrounding knobs.
The VT-737 has three input connectors: a front panel unbalanced quarter-inch mono TRS jack and rear mounted XLRs for the transformer balanced microphone input, and discrete high-level class-A Line input amplifiers. A phase reverse relay can be placed into any path. A high gain switch allows insertion of an additional 8dB for line level and an additional l8dB for the TRS jack and mic inputs. The variable range of pre-amplifier gain itself should be sufficient for most applications; Line inputs are -20dB to 30dB, quarter-inch TRS -30dB to 30dB and for microphones it's 0dB to +40dB. Phantom power (+48v) and a passive 6dB per octave high-pass filter with a range that can be varied from 30Hz to 140Hz is also supplied.
Alongside the pre-amplifier is the opto-compressor which features twin class-A triodes for gain matching. The amount of control for the dynamics is enough to put most compression boxes to shame. Ratios are variable from flat to hard knee limiting at 20:1, release times can be adjusted from 100ms to 5s, variable attack times range from 2ms to 200ms and threshold is adjustable. The large VU meter in the middle of the unit shows the amount of gain reduction or the overall output of the VT-737. The option to switch the equalizer into the side chain for de-essing and the ability to move the compressor pre or post EQ are the simple, useful, features so often missed by manufacturers.
The four-band EQ isn't parametric, nor is it the standard sweep variety, it's more of a cross between the two. The labels 'Bass' and 'Treble' look very out of place, but don't let this fool you into thinking there may be a dip in standards between the equalizer and the rest of the components in the VT-737. Bass control is in the form of a shelving EQ that has a center frequency selector with four positions ranging from an impressive 15Hz to 150Hz and a mighty boost-cut control which can add s24dB. The same type EQ is also employed for the high frequencies. The 'Treble' knob has four pre-selected positions from 10kHz to 32kHz. The boost-cut range is slightly lower at +20dB. The high and low shelving EQs cannot be totally removed from the signal path if you decide not to use them, although setting the boost-cut knob to 0dB is sufficient for signals to pass through untreated.
The two mid-range EQs are probably the most dynamic equalizers you will find on a pre-amplifier. Both are supplied with two settings for Q; with the high Q push button switch in, they form a narrow bell shape, and with the button out they form a wide bell shape. The low-mid can swing the center frequency from 35Hz to 450Hz; push the freq. x10 button and the range will switch to 350Hz to 4.5kHz. The same goes for the high-mid EQ. It will provide a range from 220Hz to 2.8kHz or 2.2kHz to 28kHz.
Many equalizers will sound good when they are processing signals, but fail the test when they are set to flat by coloring the signal that passes through them. Not so with the VT-737.
The VT-737 is simple to use with controls that are familiar and well laid out. The processor is not for the heavy handed; the precision of the equalizer coupled with the control that can be achieved using the Opto-Compressor, is the most agile de-essing combination that I have had the pleasure of using. The range of the equalizer section would hold its own against units built specifically for equalization and the compressor is just awesome. After all is said and done, there is a catch. To have only one Avalon VT-737 in the rack is not enough. The diversity of the system far exceeds the limitations of most mono applications; after the introductory period, it won't be long before the idea of stereo processing becomes almost impossible to resist.
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