ART PRO MPA II

Important Safety Instructions – Read First

[Caution Symbol] 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.

[Information Symbol] 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 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 II™ 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.

Front Panel Connections and Controls

Figure 1 – Block Diagram

The signal flow diagram illustrates the path of audio through the PRO MPA II, from input stages including gain and impedance selection, through the low cut filter, tube circuit with plate voltage and phase controls, the Mid/Side matrix, and finally to the output level and meter stages.

Figure 2 – Front controls

The front panel features two identical channels, each with controls for Input Gain, Input Impedance, Low Cut Filter, Gain switch (+20dB), Phantom switch (+48V), Phase switch, Plate Voltage switch, Mid/Side Matrix switch (on Channel 2), Tube Warmth meter, VU meter, and Output Level. There is also a Master Output Level control and a Stereo/Dual switch.

Front Panel Connections

Instrument Inputs

The 1/4-inch jacks on the front panel serve as instrument inputs with high impedance (>1M Ohm). Gain is adjustable via the Input Gain control. Plugging into this jack disables the rear balanced input, allowing the unit to function as a DI device.

Rear Panel Connections

Figure 3 – Rear connections

The rear panel features balanced XLR inputs and outputs, balanced 1/4-inch inputs and outputs, and an AES/EBU output. The +4/-10 switch is also located on the rear panel.

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

Available on both 1/4-inch and XLR connectors. They offer low impedance for long cable runs. 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.

PRO MPA II Operating Instructions

Obtaining the best noise performance

To optimize gain elements for the widest dynamic range: Turn down Input Gain and center Analog Output. Set the +20dB switch to the out position. Increase Input Level until the meter reads above -10dB. If the level is still below -10dB with Input Gain fully clockwise, center Input Gain, depress the Gain switch, and increase Input Gain until sufficient level is achieved.

Adjusting the Input Impedance

The input impedance control allows for variable microphone voicing by changing the load presented to the microphone. Start by centering the Input Impedance knob for a 600-Ohm load. Lower impedance loads reject noise and dampen resonance, while higher impedance settings provide a more "open" sound. This control affects XLR inputs only; the 1/4-inch instrument input remains at >1M Ohm.

Setting the Tube Plate Voltage

The PRO MPA II offers two tube bias and power supply levels: "Normal" and "High". The "Normal" setting provides a smooth transition to a "round" saturated clipping, suitable for instruments. The "High" setting offers increased bandwidth, headroom, and very clean operation, ideal for vocals. Transition between modes takes 15-30 seconds.

Using the Mid/Side mode

For stereo recording, use the Mid/Side switch with two microphones, one of which must have a figure-8 pickup pattern. Align two mics 90 degrees apart. Connect the primary mic (omni or cardioid) to CH1 and the figure-8 mic (facing left) to CH2. Engage the Mid/Side Matrix switch and center the Output Gain controls. Adjust Input Gain so both meters show the same level. CH1 becomes the "Left" channel, and CH2 becomes the "Right" channel.

Figure 4 – Mid/Side Mic alignment

This diagram shows the positioning of a figure-8 microphone turned sideways and an omni-directional or cardioid microphone for Mid/Side stereo recording.

Warranty Information

Limited Warranty

Applied Research and Technology (ART) warrants the PRO MPA II to the original purchaser against defects in workmanship and materials for 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, with 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. Some states may have different rights regarding limitations of incidental or consequential damages.

Service

If your unit requires service, follow these steps:

1. Verify the unit is the cause of the problem. Check power, cables, and connections. Consult your dealer for 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 securely, preferably in its original carton or a suitable substitute, in a separate shipping box if necessary. Clearly print the RA number and your return shipping address on the outside of the box.
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. Attach this note to the unit and include a copy of your purchase receipt.

For your reference:

Date of purchase: ___________________

Purchased from: ___________________

Serial number: ___________________

Specifications