Avalon VT-737SP Class A Mic Processor

No longer available at zZounds
Dial in warmth and detail with this channel strip! Avalon's Class A tube mic pre boasts an opto compressor, sweepable EQ, VU meter, front-panel DI and more.

Ever since this "Class A Mic Processor" was introduced in the late 1990s, studios large and small have relied on its platinum-sounding tube preamplification, world-class optical compressor, and musical four-band equalization controls. A gleaming, glowing VT-737SP in your rack tells clients you've been in this game for more than little while, and that you're ready for anything they've got. Let's take a closer look at this modern classic:

One Classy Front End

Technically speaking, the VT-737SP's Class A preamplification section is arranged as two cascaded, dual vacuum tube triodes, configured with minimum negative feedback as single-ended, anode-coupled followers. What matters, however, is the sound that this circuit produces. The Avalon sound is one that's beautifully transparent and smooth. It takes whatever instrument, electronic audio, or human voice you feed into it, and gets it ready for international stardom, all without changing the central character of the signal. And the VT-737SP is ready for any input: it supplies 48 volts of phantom power for use with highly detailed vocal microphones, sports a high-gain switch for extended headroom (great for loud sources like amplified guitar), and a direct hi-z input for tracking warm, shimmering electric bass.

A Tube Compressor That's Opto-Smooth

From the preamp stage, your signal then travels to Avalon's opto-compressor. While it can be used on any signal, the VT-737SP's compression profile works best on instruments with read more a long decay. Optical compressors respond to changes in dynamics by presenting a photo-resistor with a light source that dims as the volume gets lower--this non-linear decay can't be matched by solid-state compression circuits, and makes sources like voice, guitar, bass, string ensembles, and piano really sing and breathe. Also handy: if you're tracking a stereo source like drum overheads or a choir and you've got two VT-737SPs, you can link their compression circuits together for perfectly synchronized dynamics processing.

EQ-Shaping That's Perfectly Matched to the Preamp

The equalizer section of the Avalon VT-737SP is a perfect complement to the unit's preamp stage. Each band's range and sweep is tuned with the preamp character in mind, and adjusting each quickly enhances or tames your input signal in a transparent way. Still, there's quite a bit of range you get on the VT-737SP's EQ controls; with shelving on the treble and bass bands, and two separate, sweep-able mid controls with variable Q-widths, you can really focus in on problematic frequencies, or bring out the shimmer. For added flexibility, the EQ can be moved ahead of the compression circuit with the flip of a switch.

Built to Outlast the Latest Musical Trend

You want your career to last longer than the current crop of radio-hit copycats, and so does Avalon -- the more professionals who see their gear in your studio, the better for everyone! With this common interest in mind, the VT-737SP has been built for the long haul. A beefy metal chassis, robust toroidal power transformer and other top-notch internal components, and rugged control pots and knobs make for a 2-RU processor that'll outlive the rack it's mounted on.

Having an Avalon VT-737SP in your studio makes an important statement about your commitment to the recording profession. Those in the know will know you're serious once they step into your control room and see that unmistakable VU meter. Those who haven't heard the VT-737SP before will walk away amazed by your engineering prowess. The Avalon VT-737SP Channel Strip is an investment you can't afford not to make.
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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
1/4" connector, output trim gain -45dB to20dB

Noise 20kHz unweighted

Noise microphone EIN
-116dB, 22Hz to 22kHz unweighted

Distortion THD, IMD

Frequency response -/2.5dB
10Hz to 120kHz input filter included

Frequency response -3dB
1Hz to 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 to 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 to 2k8Hz and 2kHz to 28kHz, +/- 16dB range, hi-lo Q Low mid - variable 30Hz to 450Hz and 300Hz to 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

19 x 12 x 3.5 in (482 x 305 x 89mm)

22 lbs (10 kg)

Dimensions - Shipping Carton
21 x 18 x 8 in. (533 x 457 x 203mm)

Weight - Packed
26 lbs (11.8 kg)

For support or warranty questions, please contact the manufacturer:
Phone: 949-492-2000

Avalon VT737SP Class A Mic Processor

The Avalon VT-737SP features a combination of tube preamplifiers, opto-compressor, sweep EQ, output level and VU metering. VT737SP's preamp provides a 48V phantom powered input, an Instrument DI and a balanced line input. The Opto-compressor features twin Class A tube triodes for gain matching. 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-compressor. The high and low EQ bands provide the smooth characteristics of an all passive design, while the dual mid bands include variable frequency and switched Q-width selection. Whether you're recording a solo vocalist or an acoustic instrument, mastering, or recording symphonies, let Avalon take you to the leading edge in analog and experience sonic reality like never before!

Black and Blue Version

To celebrate Avalon's 10th Anniversary, they have released a special Black and Blue faced model. Same great features as the regular finish VT737SP but in a finish sure to attract onlookers.


The VT-737SP has 3 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 2 cascaded, dual vacuum tube triodes configured with minimum negative feedback. A high gain switch boosts the overall gain of the preamplifier. The 4 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 3 inputs.


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.


- Vacuum tube triode signal path
- Transformer balanced microphone input
- High-voltage circuits for maximum headroom to +30dB
- Low noise floor -92 dB
- Internal discrete power supply with toroidal transformer
- Soft-start tube life extender
- Stereo link for compressors
- All-discrete Class A equalizer with musical passive filter design
- Sealed silver relays for signal routing
- Large control knobs with professional conductive plastic potentiometers
- VU meter for output level monitoring and compressor gain reduction

Reviewers gave this product an overall rating of 5 out of 5 stars. (82 ratings)
Submitted January 5, 2004 by a customer from aol.com
"The standard by which other preamps are judged."
Overall: 5 out of 5 stars
(see rating details)
Verified Customer zZounds has verified that this reviewer made a purchase from us.
This review has been selected by our experts as particularly helpful.
This preamp (plus a great mike) gives my customers and me no excuse for not recording great vocals. I also have a Joe Meek pre which is dirty and therefore complementary to the Avalon.
This is the standard to which all others are compared. Beautiful, clean, clear "glassy" tube sound, warm yet clear. The best.
Everything you need in a channel strip: preamp, equalizer, compressor.
Solid, heavy, metal everything. I worry my rack will break.
I paid $1400 new, so it was worth that to me. It is a bit pricey at the usual $2000 price tag. But worth it!
Manufacturer Support
Haven't had to find out (there's no N/A choice). Everyone I talked to and everything I read says Avalon gives great support.
The Wow Factor
It's a beautiful piece of gear that inspires great confidence. The Avalon name is well known to everyone in this business, like Neumann mikes or Vox amplifiers, it actually brings in customers.
Musical Style:
Pop, Funk
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