ART DIGITAL-MPAII User manual
DIGITAL MPA II™
ART DIGITAL MPA II™ Microphone Preamplifier
USER’S GUIDE
IMPORTANT SAFETY INSTRUCTIONS – READ FIRST
alerts you to the presence of uninsulated you to important operating and maintenance
dangerous voltage inside the enclosure. Voltage instructions in the accompanying literature.
that may be sufficient to constitute a risk of shock. 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 the 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 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 guide.
This symbol, wherever it appears, This symbol, wherever it appears, alerts
II
IMPORTANT SAFETY INSTRUCTIONS – READ FIRST ......................................................... II
DIGITAL MPA II OVERVIEW – FEATURES AND GENERAL INFORMATION: ...................... 1
FRONT PANEL CONNECTIONS AND CONTROLS ................................................................ 3
Input Gain control ..................................................................................................................................... 3
Input Impedance control ........................................................................................................................... 4
Low Cut Filter control................................................................................................................................4
Gain switch ............................................................................................................................................... 4
Phantom switch ........................................................................................................................................ 5
Phase switch............................................................................................................................................. 5
Plate Voltage switch ................................................................................................................................. 5
Mid/Side switch.........................................................................................................................................6
Analog Output control ...............................................................................................................................6
STEREO/Dual switch................................................................................................................................ 6
+4/-10 switch (rear panel).........................................................................................................................7
Meter Trim ................................................................................................................................................ 7
Digital section front panel controls........................................................................................ 7
Digital Level control .................................................................................................................................. 7
Sample Rate control ................................................................................................................................. 8
Dither settings...........................................................................................................................................9
Optical switch............................................................................................................................................9
Front Panel connections ....................................................................................................... 10
Instrument Inputs .................................................................................................................................... 10
Rear Panel connections ........................................................................................................ 11
Balanced Inputs ...................................................................................................................................... 11
Balanced Outputs ................................................................................................................................... 11
Insert jacks.............................................................................................................................................. 12
Wordclock jacks......................................................................................................................................12
ADAT Input ............................................................................................................................................. 12
Optical output.......................................................................................................................................... 12
S/PDIF output ......................................................................................................................................... 13
AES/EBU output ..................................................................................................................................... 13
DIGITAL MPA II OPERATING INSTRUCTIONS..................................................................... 14
Obtaining the best noise performance with the DIGITAL MPA II............................................................ 14
Adjusting the Input Impedance ............................................................................................................... 14
Obtaining the perfect digital level setting ................................................................................................ 15
Setting the Tube Plate Voltage ............................................................................................................... 16
Using the Mid/Side mode........................................................................................................................ 17
WARRANTY INFORMATION.................................................................................................. 18
SERVICE ................................................................................................................................. 19
DIGITAL MPA II SPECIFICATIONS........................................................................................ 20
Analog Section:....................................................................................................................................... 20
Digital Section:........................................................................................................................................20
List of Figures
Figure 1 – Block Diagram .......................................................................................................... 2
Figure 2 – Front controls............................................................................................................ 3
Figure 4 – Rear connections .................................................................................................... 11
Figure 4 – Mid/Side Mic alignment........................................................................................... 17
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DIGITAL MPA II OVERVIEW – FEATURES AND
GENERAL INFORMATION
:
The ART DIGITAL 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. The DIGITAL 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 DIGITAL MPA II a world-class microphone pream-
plifier. Its 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
• Selectable between output level and tube warmth
• Improved discrete class A input microphone preamplifier
• Lower noise at low gains
• Lower THD
• Wider frequency response
• Front accessible Instrument Input Jack
• Very high input impedance
• Mid/Side micing support
• +4dBm/-10dBV output level selection
• Automatically switches to the instrument input when you plug in
The DIGITAL MPA II also features digital connectivity for use with various digital processors and
digital recording devices. The Digital interface supports the following features and functions:
• 24-204KHz External sample rate
• 44.1K, 48K, 88.2K, 96K, 176.4K, 192K Internal sample rates
• 24/16 bit switchable dithering
• Wide dynamic range A/D
• Rotary Encoder for quick selection of sample rate
• Separate analog and digital output level controls
• Digital Level LED meters display both Average and Peak level.
• ADAT optical I/O
• Sync to incoming ADAT data rate
• Switch selectable optical output (S/PDIF or ADAT)
• AES/EBU and S/PDIF outputs
• Two wordclock jacks allowing loop through
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The signal path of the DIGITAL 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. At this point the signal passes to both the analog output and the Insert jacks. The insert jacks
allow processing of the signal before its’ level is adjusted by the Digital Level control and passed to
the A/D. You can use the A/D converters of the DIGITAL MPA II independent of the analog functions
by simply inserting a signal into this insert point!
The DIGITAL MPA II is an attractively styled processor, with a black anodized front panel and match-
ing knobs. The switches on the DIGITAL MPA II are backlit and illuminate when depressed.
Figure 1 – Block Diagram
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FRONT PANEL CONNECTIONS AND CONTROLS
Input Gain control
Figure 2 – Front controls
This control optimizes the input signal level before the tube gain is applied. Both Microphone and
Instrument input gains remain the same and are affected by this adjustment. Input gain can be ad-
justed from 0dB (for line level signals) to 40dB of gain.
The analog meters are used to see the effects of the input gain setting.
Additional gain is available via the Gain switch (+20dB) and the Analog Output control (+10dB) for a
maximum of 70dB total.
The combination of these controls allows the user to adjust the signal level through the tube section,
providing more or less “tube” sound as needed. To obtain more “tube’ sound, increase input gain, use
the +20dB Gain switch, “normal” plate voltage, and less Analog output gain.
Both the microphone and instrument inputs are optimized for their respective sources as far as signal
levels and noise performance. Running most of the gain on the input generally provides the best
performance of the DIGITAL MPA II. Refer to the section titled “Obtaining the best noise performance
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with the DIGITAL MPA II for more detailed instructions on setting the Input Gain control for the best
results.
Input Impedance control
This knob controls the Mic/line input amplifier impedance. This function allows variable voicing of any
microphone.
Refer to the application section titled “Adjusting the Input Impedance” for more information on making
the most of this function.
The ¼” instrument input is NOT affected by this control, and remains high (>1M Ohm) impedance.
Low Cut Filter control
The Low Cut Filter is a single tuned High Pass Filter that is frequency tunable. The input signal can
be filtered to remove “pops” or other extraneous low frequency information. This control moves the
rolloff frequency from 10 Hz (fully CCW) to 200 Hz (fully CW). Since it is single tuned, it preserves
some low frequency content so its use is less obtrusive. It is especially useful in close mic’d applica-
tions.
Gain switch
The Gain switch is used in conjunction with the input gain control to adjust signal levels through the
DIGITAL MPA II. When depressed, the tube circuit provides 20dB more gain in the signal path. This
also has the effect of driving the tube harder and making the tube the dominant source of gain and
overload character.
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Phantom switch
Phantom power on the microphone input is turned on and off with this switch. Depressing the switch
will power condenser microphones and other 48volt phantom powered devices. Phantom power is
supplied to pins 2 and 3 of the input jack.
NOTE:
1) Dynamic microphones are NOT affected by Phantom power, although it should be turned off when
using dynamic microphones or line level inputs.
2) Although the 48volt phantom power ramps up and down slowly it may still create a pop. Mute the
output of the DIGITAL MPA II when engaging or disengaging phantom power to prevent damage to
equipment following the DIGITAL MPA II.
Phase switch
The Phase switch can invert the phase of the audio signal path in either channel. The Phase switch
is located after the tube circuit in the signal path, so you can hear slight differences between different
phase selections in the “normal” plate voltage mode near saturation. There are a number of reasons
why adjusting the phase is needed these include, wiring errors and inversions in some audio equip-
ment. Some microphones sound different depending on the phase chosen.
If two microphones are out of phase, they may cancel at various frequencies (depending on the
distance between them). If this happens, try changing the phase of one of the microphones and see if
there is an improvement.
Plate Voltage switch
This switch sets both the tube bias point and the plate voltage level the balanced differential tube
circuit runs at. The amount of headroom is adjusted by using the Gain switch and the input Gain
control. The DIGITAL MPA II takes about 10-30 seconds to smoothly transition from one mode to the
other. There is a slight increase in gain in the “High” plate voltage mode.
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