ART PRO MPA II

Important Safety Instructions – Read First

⚠️ WARNING: This symbol indicates the presence of uninsulated dangerous voltage inside the enclosure, which may be sufficient to constitute a risk of electric shock.

? NOTE: This symbol indicates important operating and maintenance instructions in the accompanying literature. Please read the manual.

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 a 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 it.

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 that 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 an opening, or if 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 MPA II. Offering a superb level of sound quality, the PRO MPA II has a unique design that will enhance the sonic textures of your audio system for years to come. The ART PRO MPA II microphone preamplifier features a new low noise, high performance preamplification circuitry, designed for superior audio fidelity. Building upon the quality and success of great sounding products like the Pro MPA and MPA GOLD, ART engineers set out to develop the next generation of professional microphone preamplifier. PRO MPA II is the culmination of years of research and development, and sets a new standard for quality and value. Professional features and spectacular tone are what make the PRO MPA IITM a world-class microphone preamplifier.

The PRO MPA II's impressive feature set includes:

• Variable input impedance for flexible microphone voicing (150 Ohms to 2400 Ohms).
• Selectable plate voltage.
• Large VU meters.
• Front accessible meter trim.
• Discrete class A input microphone preamplifier.
• Low noise at low gains.
• Low THD.
• Wide frequency response.
• Front accessible Instrument Input Jack.
• Very high input impedance.
• Mid/Side micing support.
• +4dBm/-10dBV output level selection.
• Switch selectable Stereo/Dual operation of the output controls.
• Automatically switches to the instrument input when you plug in.

The signal path of PRO MPA II consists of a discrete class A microphone pre-amp followed by a Low Cut Filter, a balanced differential tube circuit with a 20dB Gain switch and then the phase switch. The Mid/Side Matrix switch sums the adjacent channel to decode left and right information following the gain switch function and before the output level control. The Tube Warmth display monitors the signal level before the output level control as well. The analog meter monitors the output level of the PRO MPA II before the +4/-10 switch but after the output level control. The PRO MPA II is an attractively styled processor, with a black anodized front panel and matching knobs. The switches on the PRO MPA II are backlit and illuminate when depressed.

Signal Flow Overview

The PRO MPA II's signal path begins with either the microphone or instrument input. The signal then passes through an Input Gain control, which optimizes the input signal level before the tube gain is applied. This is followed by the Input Impedance control, which allows for variable voicing of microphones. A Low Cut Filter is present to remove extraneous low-frequency information. The signal then goes through a balanced differential tube circuit, which includes a 20dB Gain switch and a Phase switch. The Mid/Side Matrix switch allows for stereo recording techniques by decoding Left/Right information. A Tube Warmth display indicates the signal level before the output level control, and analog VU meters monitor the output level after the output level control but before the +4/-10 switch. Finally, the output level is adjusted, and the +4/-10 switch selects the appropriate system output level.

Front Panel Connections and Controls

The front panel of the PRO MPA II features comprehensive controls for each channel and master output.

Channel Controls (Left and Right):

• GAIN: Input Gain control adjusts signal level from 0dB to 40dB. A +20dB Gain switch provides additional gain.
• IMPEDANCE: Variable input impedance control (150 Ohms to 3K Ohms) for microphone inputs.
• LOW CUT FILTER: Tunable High Pass Filter with a rolloff frequency adjustable from 10 Hz to 200 Hz.
• PHANTOM: 48V phantom power switch for condenser microphones.
• PHASE: Phase invert switch.
• PLATE VOLTAGE: Switch to select between "Normal" (tube crunch) and "High" (clean, extended headroom) plate voltage settings.
• MID/SIDE MATRIX: Switch for decoding Mid/Side stereo recordings.
• OUTPUT LEVEL: Adjusts the output signal level from muted to +10dB gain.
• TUBE WARMTH: Display indicating signal level before the output level control.
• METER TRIM: Allows adjustment of the VU meter's "0" point.

Master Controls:

• MASTER OUTPUT LEVEL: Controls the overall output signal level.
• STEREO/DUAL: Switch to select Stereo mode (CH1 controls both channels, CH2 acts as balance) or Dual mode (controls affect respective channels independently).
• +4/-10 SWITCH (Rear Panel): Sets the output level to match system requirements (+4dBu or -10dBV).

Front Panel Connections:

Instrument Inputs:

Two 1/4-inch jacks serve as instrument inputs with impedance always greater than 1M Ohm. Plugging into these jacks disables the rear balanced inputs, allowing the PRO MPA II to function as a DI device.

Rear Panel Connections:

The rear panel features balanced XLR and 1/4-inch connectors for inputs and outputs, along with an AES/EBU output.

Balanced Inputs: XLR connectors follow the AES standard (Pin 1=Ground, Pin 2=Hot, Pin 3=Cold). Input impedance is variable from 150 to 3K Ohms via the front panel control. Maximum input level is +19dBu balanced and +17dBu unbalanced.

Balanced Outputs: Active balanced outputs are available on both 1/4-inch and XLR connectors. They offer low impedance for long cable runs and maintain consistent output levels. XLR connectors follow the AES standard. Balanced 1/4-inch phone jacks are Tip=Hot, Ring=Cold, Sleeve=Ground. Maximum output level is +27dBu balanced and +20dBu unbalanced.

Operating Instructions

Obtaining the best noise performance with the PRO MPA II

To achieve optimal noise performance, start by turning down the Input Gain knob and centering the Analog Output knob. Set the +20dB switch to the out position. Increase the Input Level knob until the meter reads above -10dB. If the level is still below -10dB with the input knob fully clockwise, center the input knob, depress the Gain switch, and increase Input Gain until sufficient level is achieved. This procedure optimizes gain elements for the widest dynamic range.

Adjusting the Input Impedance

The Input Impedance control allows for variable voicing of microphones by changing the load presented to the input. This control affects only the XLR (cannon) connector inputs; the 1/4-inch instrument input always maintains a high impedance (>1M Ohm). Lower impedance loads can reject more noise and dampen microphone resonance, while higher impedance settings provide a more "open" sound. Start by centering the Input Impedance knob, which provides a 600-Ohm load.

Setting the Tube Plate Voltage

The PRO MPA II offers two plate voltage settings: "Normal" and "High". The "Normal" setting provides a smooth transition from clean levels to a "round" saturated clipping, reminiscent of vintage tube gear, ideal for tracking instruments. The "High" setting offers increased bandwidth, headroom, and very low distortion, running extremely clean until saturated clipping, making it excellent for vocals. Transition between modes takes 15-30 seconds.

Using the Mid/Side mode

For stereo operation using the Mid/Side switch, two microphones are required, one with a figure-8 pickup pattern. Align two mics 90 degrees apart. Connect the front-facing mic (omni or cardioid) to CH1 and the figure-8 mic (turned sideways) to CH2. Depress the Mid/Side Matrix switch and center both Output Gain controls. Adjust Input Gain controls so both meters show the same level with a sound source at least two feet in front of the forward mic. CH1 then represents the "Left" channel and CH2 the "Right" channel. Adjust output gain controls as needed.

Mid/Side Mic Alignment Description: The diagram illustrates the positioning of two microphones for Mid/Side recording. An omnidirectional or cardioid microphone is positioned directly facing the sound source, while a figure-8 microphone is positioned perpendicular to the first, capturing the side information.

Warranty Information

Limited Warranty

Applied Research and Technology (ART) warrants the PRO MPA II to the original purchaser for a period of three years from the date of purchase, ensuring it is free from defects in workmanship and materials. ART will repair or replace, at its option, defective products or component parts 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, defaced, 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. Some states may have different regulations regarding these limitations.

For units purchased outside the United States, service will be provided by an authorized distributor of Applied Research and Technology.

Service

In the unlikely event that your unit requires service:

1. Verify that the unit is the cause of the problem. Check power, cable connections, and cable condition. Consult your dealer for assistance if needed.
2. If the ART unit is suspected to be at fault, visit www.artproaudio.com.
3. Select "Support", then "Return Authorization Request" to obtain a return authorization number (RA number).
4. Pack the unit in its original carton or a suitable substitute. Consider using an additional box for shipping. Print the RA number clearly on the outside of the shipping box and include your return shipping address.
5. Include a note with the RA number, your contact information (including return shipping address and daytime phone number), and a description of the problem, preferably attached to the unit. Include a copy of your purchase receipt.

For your reference:

Date of purchase: ___________________

Purchased from: ___________________

Serial number: ___________________

Specifications