PRO VLA II

Important Safety Instructions

CAUTION: RISK OF ELECTRIC SHOCK - DO NOT OPEN
[Symbol: Warning triangle with lightning bolt] This symbol, wherever it appears, alerts you to the presence of uninsulated dangerous voltage inside the enclosure. Voltage that may be sufficient to constitute a risk of shock.

ATTENTION: RISQUE DE CHOC ELECTRIQUE - NE PAS OUVRIR

[Symbol: Exclamation mark in a circle] This symbol, wherever it appears, alerts you to important operating and maintenance instructions in the accompanying literature. Please read manual.

• Read Instructions: Retain these safety and operating instructions for future reference. Heed all warnings printed here and on the equipment. Follow the operating instructions printed in this user guide.
• Do Not Open: Aside from two vacuum tubes, there are no user serviceable parts inside. Refer any service work to qualified technical personnel only.
• Power Sources: Only connect the unit to mains power of the type marked on the rear panel. The power source must provide a good ground connection.
• Power Cord: Use the power cord with sealed mains plug appropriate for your local mains supply as provided with the equipment. If the provided plug does not fit into your outlet consult your service agent. Route the power cord so that it is not likely to be walked on, stretched or pinched by items placed upon or against.
• Grounding: Do not defeat the grounding and polarization means of the power cord plug. Do not remove or tamper with the ground connection on the power cord.
• Ventilation: Do not obstruct the ventilation slots or position the unit where the air required for ventilation is impeded. If the unit is to be operated in a rack, case or other furniture, ensure that it is constructed to allow adequate ventilation.
• Moisture: To reduce the risk of fire or electrical shock do not expose the unit to rain, moisture or use in damp or wet conditions. Do not place a container of liquid on it, which may spill into any openings.
• Heat: Do not locate the unit in a place close to excessive heat or direct sunlight, as this could be a fire hazard. Locate the unit away from any equipment, which produces heat such as: power supplies, power amplifiers and heaters.
• Environment: Protect from excessive dirt, dust, heat, and vibration when operating and storing. Avoid tobacco ash, drink spillage and smoke, especially that associated with smoke machines.
• Handling: To prevent damage to the controls and cosmetics avoid rough handling and excessive vibration. Protect the controls from damage during transit. Use adequate padding if you need to ship the unit. To avoid injury to yourself or damage to the equipment take care when lifting, moving or carrying the unit.
• Servicing: Switch off the equipment and unplug the power cord immediately if it is exposed to moisture, spilled liquid, objects fallen into opening, or the power cord or plug becomes damaged during a lightning storm or if smoke odor or noise is noted. Refer servicing to qualified technical personnel only.
• Installation: Install the unit in accordance with the instructions printed in the user manual.

Introduction

Thank you for purchasing Applied Research and Technology's Pro VLA II. This two-channel opto-isolator/tube-based leveling amplifier offers superb sound quality and a unique design to enhance audio system sonic textures. Developed with studio and live-sound engineers, the Pro VLA II provides a distinct musical sound, adjusting to signal level changes much like the human eye adjusts to light. It is designed and constructed with high-quality components for quiet, reliable performance.

Key Features of the Pro VLA II:

• Two-channel opto-isolator/tube-based leveling amplifier
• Stereo linking of channels
• Master Volume and Balance control in Link Mode
• Hand-selected 12AT7 Tubes
• OPTO - Analog Optical Isolators (AOI)
• Non-VCA design for transparent, classic sound
• VU metering of input and output levels
• LED metering of output level with peak-hold function
• XLR balanced inputs and outputs
• 1/4" TRS active balanced inputs and outputs
• Variable Threshold & Ratio controls
• Variable Attack and Release controls
• Variable Output Level rotary controls
• 10-segment Gain Reduction LED array
• 10Hz to 100KHz Frequency Response (+/-0.5dB)
• >100dB Dynamic Range
• Low noise (-99dBm 'A' weighted EIN)
• Internal power supply
• 3-year parts and labor warranty

Installation

The ART Pro VLA II is designed for continuous professional use in a rack-mountable, all-steel enclosure. While mounting location is not critical, avoid placing the unit on top of power amps or near strong magnetic fields for optimal performance. The tube circuitry requires approximately one minute to warm up and stabilize.

Unpacking

Your Pro VLA II was carefully packed. Retain the shipping carton for future transport or servicing needs. The carton should contain:

• The Pro VLA II unit
• The owner's manual
• IEC Power Cord

AC Power Hookup

The Pro VLA II operates on 100-125VAC, 50-60Hz. Units for use outside the USA are modified for local specifications. Never alter the power cable. If damaged, discontinue use and replace it. Ensure the power source provides a good ground connection; the ground pin on the mains plug must never be defeated.

Audio Connections

Audio connections use standard XLR and 1/4" TRS connectors.

Balanced Inputs:

• XLR: Pin 2 = Hot (+), Pin 3 = Cold (-), Pin 1 = Ground
• 1/4" TRS: Tip = Hot (+), Ring = Cold (-), Sleeve = Ground

Unbalanced 1/4-inch cables can be used without damage. High-quality cables are recommended.

Balanced Outputs:

• XLR: Pin 2 = Hot (+), Pin 3 = Cold (-), Pin 1 = Ground
• 1/4" TRS: Tip = Hot (+), Ring = Cold (-), Sleeve = Ground

The output is active pseudo-balanced with a 100 Ohm impedance.

Front Panel Controls and Indicators

The front panel features controls for comprehensive audio processing and monitoring.

POWER

Turns the unit on and off. Power on the Pro VLA II before monitor levels or power amps. Power off after monitor levels are down to prevent thumping. The VU meters light when power is on. Associated LEDs light when their respective switches are engaged.

The 12AT7 tubes require 1-3 minutes to warm up. Sound variations during warm-up are normal as tube bias stabilizes.

INPUT THRESHOLD Control

Sets the signal level at which compression begins. Turning counter-clockwise lowers the threshold (increasing compression). Turning clockwise raises the threshold. Set by slowly turning counter-clockwise until the yellow '0' LED on the Gain Reduction meter lights, then adjust for desired compression amount.

RATIO Control

Determines the amount of gain reduction applied once the signal exceeds the threshold. Expressed as a ratio (e.g., 4:1 means for every 4dB above threshold, output increases by 1dB). Ratios of 10:1 and higher are considered limiting. The range is 2:1 to 20:1. Suitable for multi-track recording, mixer inserts, between preamps and processors, or with instruments.

OUTPUT LEVEL Control

CH1 knob controls CH1 output level, or acts as MASTER output level in Link Mode. Fully counter-clockwise mutes the output. CH2 OUTPUT LEVEL control acts as CH2 level or BALANCE control in Link Mode. In Link Mode, fully counter-clockwise mutes CH2 and maximizes CH1; centered balances both; fully clockwise mutes CH1 and maximizes CH2.

ATTACK Control

Sets the time for the compressor/limiter to respond to signal level increases (gain reduction). Shapes the "front end" of the dynamics envelope. A shorter attack can make transients sound "thin," while a longer attack emphasizes "thump." Fast attack times can cause "pumping" artifacts.

RELEASE Control

Sets the time for the compressor/limiter to increase gain after the input level drops. Longer settings preserve dynamics; shorter settings reduce dynamics and can increase apparent reverberation or cause "breathing" artifacts at extreme settings.

GAIN REDUCTION LED Meter

Displays the amount of attenuation. The yellow '0' LED illuminates when the input signal reaches or exceeds the threshold.

BYPASS Switch

Provides a hardwire bypass, connecting the input jack directly to the output jack. The switch lights when engaged. The bypass is passive and functions even when the unit is powered off.

VU Meter

Monitors input or output levels. The VU METER SOURCE switch selects the meter source. VU meter ballistics provide average signal level indication. For peak levels, use the central stereo LED bar graph OUTPUT LEVEL meter.

VU METER SOURCE Switch

Selects either the input or output signal for the analog VU meter. Illuminates when the input signal is selected, allowing comparison of input vs. output levels. This switch does not affect the LED meter source.

Meter Trim

Adjusts the VU meter's "0" point, especially if the unit is not mounted perfectly perpendicular to the floor. Use a small flat-blade screwdriver to fine-tune the meter indicator position when the unit is off.

LED OUTPUT LEVEL Meter

Displays average and peak output signal levels. LEDs indicate deviation from maximum output in dB. A single LED stays lit for over one second to show peak levels, which may cause clipping in subsequent equipment. Average levels are shown in a histogram style, similar to the VU meter when monitoring output.

In +4dBu mode, "0" on the meter is +16dBu output. In -10dBV mode, "0" is +6dBu output.

LINK Switch

Enables stereo operation by linking both channels. In Link Mode, CH1 OUTPUT LEVEL knob controls attenuation for both channels, and CH1 Attack/Release controls affect both. CH2 OUTPUT LEVEL becomes a balance control. This ensures identical processing for stereo signals, preventing image shifts or distortion. Bypass and meter-source functions remain unchanged.

Rear Panel I/O

The Pro VLA II features balanced XLR and 1/4" TRS connections.

Connections Standard:

• XLR: AES standard (Pin 1=Ground, Pin 2=Hot (+), Pin 3=Cold (-))
• 1/4" TRS: Tip=Hot (+), Ring=Cold (-), Sleeve=Ground

Balanced Inputs

Provides both XLR and 1/4" balanced input jacks. The 1/4" jack accepts unbalanced signals with an unbalanced cable. Inputs are designed for line-level signals (-30dBm to +20dBm). For instruments, using a preamp before the Pro VLA II is recommended for a stronger signal and reduced noise. Microphones require a preamplifier (e.g., ART PROMPA) before connecting. Input impedance is 10K Ohms. The bypass is passive (hardwire) and works even when the unit is powered off.

Balanced Outputs

Available on both 1/4" TRS balanced jack and XLR jack. Outputs are active pseudo-balanced with a 100 Ohm impedance. The LED and VU meters monitor output levels. "0" VU on the analog meter corresponds to +4dBu, and "0" on the LED meter corresponds to +16dBu (in +4dBu mode).

I/O LEVEL Switch

Optimizes the unit for "professional" (+4dBu) or "consumer" (-10dBV) I/O levels. When depressed, the unit is in "professional" mode, setting "0" VU to +4dBu. In "-10" mode, "0" VU is approximately -10dBV. (+4dBu = +4dBm into a 600 Ohm balanced load).

Applications

• Compressor/Limiter: Control dynamic range of audio signals by setting threshold and output controls.
• Stereo Mix and Mastering: Ideal for processing mixes for DAT, hard disk, or analog recording. Adds warmth and impact to overall signal level. Suitable for live use.
• Vocal and Instrument Leveling: Musical nature makes it suitable for various instruments and vocals. Use in channel inserts, after preamplifiers, or in-line with mixer outputs.

Warranty Information

Limited Warranty

Applied Research and Technology (ART) warrants the Pro VLA II and its components to be free from defects in workmanship and materials for a period of three years from the date of purchase. ART will repair or replace, at its option, defective products upon prepaid delivery to the factory service department or an authorized service center, accompanied by proof of purchase.

Exclusions

This warranty does not cover misuse, abuse, unauthorized alterations, or repairs. It is void if the serial number is altered or removed. ART reserves the right to make design changes without obligation to apply them to previously manufactured products. ART is not liable for consequential damages, including loss of use. Specific rights may vary by state.

For units purchased outside the United States, service is provided by an authorized distributor.

Service

If your unit requires service:

1. Verify the unit is the cause of the problem. Check power, connections, and cables. Consult your dealer for troubleshooting assistance.
2. If the ART unit is at fault, visit www.artproaudio.com.
3. Select "Support," then "Return Authorization Request" to obtain an RA number.
4. Pack the unit in its original carton or a suitable substitute. Print the RA number clearly on the outside of the shipping box and include your return shipping address.
5. Include a note with your RA number, contact information (including return shipping address, no P.O. boxes), a daytime phone number, and a description of the problem. Include a copy of your purchase receipt.

For Your Reference:

Date of purchase: _________________________ Purchased from: __________________________ Serial Number: ___________________________