Avalon Design VT-737SP Class A Mono Tube Channel Strip

The Avalon VT-737SP features a combination of TUBE preamplifiers, opto-compressor, sweep equalizer, output level and VU metering in a 2U space.

PREAMPLIFIER

The VT-737SP has three input selections:

1. The VT-737SP features a higher-performance microphone input transformer with +48v phantom selection.
2. Instrument DI high source input with jack located on front panel.
3. Balanced line input, discrete high-level Class A. The Class A preamplifier utilizes two cascaded, dual vacuum tube triodes configured with minimum negative feedback.

A high gain switch boosts the overall gain of the preamplifier. The four high quality tubes are configured as singled ended anode coupled followers. A passive-variable high pass filter and hard-wire relay bypass completes the input signal conditioning. The phase reverse relay is available on all three inputs.

OPTO-COMPRESSOR

The opto-compressor features a minimum signal path design with twin Class A vacuum tube triodes for gain matching. The optical attenuator acts as a simple passive level controller. Full dynamic control from soft compression to hard- knee limiting can be achieved with threshold, ratio-compression, attack and release controls plus gain reduction selection on the large VU meter. Special spectral control including de-ess is available with the dual sweep mid EQ to side-chain switch. The EQ section can be flipped pre or post the opto-compressor via a front panel switch for alternate effects and tone shaping. Two VT-737SPs can be linked via a rear panel link cable for stereo tracking. The compressor bypass is a sealed silver relay for the most direct signal path.

SWEEP-EQUALIZER AND OUTPUT LEVEL

The VT-737SP equalizer utilizes 100% discrete, Class A-high-voltage transistors for optimum sonic performance. The high and low frequency bands provide the smooth characteristics of an all passive design, while the dual mid bands include variable frequency and switched Q-width selection. The enhanced range of the mid bands is extended into the high and low bands by the use of X10 frequency multipliers. The bypass switch incorporates a sealed silver relay for the most direct signal path. When the EQ to sidechain is engaged, the high-low EQ remains in the audio path for "tone enhancement". The output level control provides a variable control of the overall signal path. The output amplifier utilizes another dual triode vacuum tube driving a 100% discrete, Class A, high-current, balanced and DC coupled low noise output amplifier.

Key Features

• Tube preamp
• Opto-compressor
• Sweep equalizer
• Output level control
• VU metering
• Balanced mic input, front-panel instrument DI, and balanced line inputs
• High-gain switch
• High-pass filter

Technical Specifications

Circuit topology
4 dual triode vacuum tubes (Sovtek 6922), high-voltage discrete Class A
Gain Range Microphone
Transformer balanced 850/2500 ohm, 0dB to +58dB Instrument: Unbalanced 1 meg ohm, 0dB to +30dB
Line
Balanced Class A 20k ohms, -27dB to 28dB
Maximum input level and connector types
Microphone26dB@25Hz, +30dB@1kHz balanced XLR Instrument+30dB unbalanced front panel jack socket
Line +36dB balanced XLR
Maximum output level
+30dB balanced 600 ohms, DC coupled, discrete Class A
Output type and gain
XLR connector, output trim gain -45dB to20dB
Noise 20kHz unweighted
-92dB
Noise microphone EIN
-116dB, 22Hz-22kHz unweighted
Distortion THD, IMD
0.5%
Frequency response -2.5dB
10Hz-120kHz input filter included
Frequency response -3dB
1Hz-200kHz line in-out
VU meter and gain reduction
High quality illuminated OVU =+4dB and gain reduction to -20dB
High cut filter
Variable 6dB per octave 30Hz-140Hz
Compressor type
Optical passive attenuator incorporating twin vacuum tubes and stereo link
Threshold - Ratio
Threshold variable -30dB to +20dB, ratio-compression variable 1:1 to 20:1
Attack - Release
Attack variable 2mS to 200mS, release variable 100mS to 5 seconds
Equalizer type
Discrete Class A, variable active and switched passive design
Frequency bands (4)
Treble - switched 10kHz, 15kHz, 20kHz, 32kHz, ±20dB range, shelf High mid - variable 200Hz-28kHz and 2kHz -28kHz, ±6dB range, hi-lo Q Low mid - variable 30Hz-450Hz and 300Hz-4k5Hz, ±16dB range, hi-lo Q Bass - switched 15Hz, 30Hz, 60Hz, 150Hz, ±24dB range, shelf
AC power
Internal toroidal 100v to 240v, 50-60Hz selectable, 75 watts maximum
Dimensions
19 x 12 x 3.5 in (482 x 305 x 89mm)
Weight
22 lbs (10 kg)
Dimensions - shipping carton
21 in x 18 in x 8 in (533 mm x 457 mm x 203 mm)
Weight-packed
26 lbs (11.8 kg)

Installation / Use Cases

• Recording vocals with a tube channel strip that combines microphone preamplification, compression, and equalization in one unit
• Tracking instruments through the front-panel instrument DI input for direct recording workflows
• Using the opto-compressor for dynamic control during tracking, from soft compression to limiting
• Shaping tone with the sweep equalizer in studio recording and mixing setups
• Integrating into professional racks as a 2U mono Class A channel strip for vocals, bass, guitar, and line-level sources
• Linking two units with the rear-panel stereo link for stereo tracking applications

Package Contents

• Avalon Design VT-737SP Class A Mono Tube Channel Strip