Art | PRO MPA II | User`s guide | Art PRO MPA II User`s guide

Professional Two Channel Tube Microphone
Setting Up
AC Power Hookup
Audio Connections
Safety Precautions
Powering Up
Front Panel Controls and Indicators
Input Level Control
Output Level Control
+20dB Gain/Norm Switch
Phase Switch
Phantom Power Switch
HPF Control
10 Segment Tube Character Array
VU Meter
Rear Panel Connections
Warranty Information
Service Information
PRO MPA Specifications
On-line Information
Thank you for purchasing Applied Research and TechnologyÕs
PRO MPA. Offering a superb level of sound quality, the PRO
MPA has a unique design which will enhance the sonic textures
of your audio system for years to come.
If you havenÕt done so already, please take the time to fill out
the User Registration Card for your purchase. Having you in our
data base allows us to keep you informed of updates, application notes, and new product introductions. It only takes a
moment and will ensure you are constantly up to date with your
Fill in the following for your future reference:
Date of purchase: ___________________
Purchased From: ____________________
Serial Number: 210-________
The PRO MPA is one of the finest microphone preamplifiers
available. Developed in partnership with studio and live sound
engineers, the PRO MPA possesses a ÒsoundÓ that is not available from any other microphone preamp on the market - at any
price! A member of the A R T Reference Series, the PRO MPA
was designed and constructed with the absolute best components, assuring a lifetime of quiet, reliable performance. The
PRO MPA offers:
- The ÒSOUNDÓ! - (not available elsewhere)
- Two independent channels of operation
- VU metering
- Unique 10 segment Tube Character Array
- Variable high pass filter
- XLR balanced inputs and outputs
- 1/4Ó TS unbalanced inputs and outputs
- Hybrid- 12AX7/ Triple differential transistor gain stages
- +48V Phantom power
- Phase reversal
- Over 70dB of gain
- Independent input and output level controls
- >100dB dynamic range
- Internal power supply
- 5-year warranty
- Designed and manufactured in the USA
The PRO MPA is member of A R TÕs Reference Series of professional signal processing products.
The PRO MPA (Microphone Pre Amplifier) is a multi-purpose
tool for audio engineering and recording. Enclosed in a 2U (3.5Ó
high) rack-mountable chassis are two independent channels of
analog microphone preamplifiers designed to work seamlessly
with any recording, sound-reinforcement, or electronic instrument setup.
A R TÕs PRO MPA circuitry is a hybrid design utilizing the latest
and most advanced solid state and tube technology. Using a
transformerless design throughout, the PRO MPA maintains
exceptional signal integrity and extremely low noise. The Active
balanced input utilizes a hybrid, triple-differential transistor
design, providing extremely low noise and excellent CMRR. A
second stage 12AX7A tube running on a regulated DC voltage
provides an additional 40 dB of gain. The design causes the
tube to overload before the input or output stage. This allows
the user to manipulate the tube gain to meet their sonic requirements. The 1/4Ó input has a high impedance, which prevents
the loading of any device connected to it and makes the PRO
MPA perfect for DI or line level applications.
Your PRO MPA was packed with care at the factory. The shipping carton was designed to protect it during initial shipment.
Please retain this carton for use in transporting the PRO MPA
when it is not installed in a rack, or in the unlikely event that you
need to return your PRO MPA for servicing.
The shipping carton should contain:
- PRO MPA with the same serial number as shown on the shipping carton
- The ownerÕs manual
- User Registration Card
AC Power Hookup
The PRO MPA has an internal power supply designed to operate at 100 to 125VAC, 50 to 60Hz. Units manufactured for use
outside of the United States of America have been modified to
comply with the required electrical specifications. Under no cir-
cumstances should the power cable be altered. If the cable
becomes cut or damaged, discontinue its use and have it
replaced before operating the Pro MPA.
Audio Connections
Audio connections to and from the PRO MPA are balanced XLR
(Pin 2 Hot (+), Pin 3 Cold (-), Pin 1 Ground) and unbalanced
1/4Ó (Tip Hot (+), Sleeve Ground). We recommend using only
high-quality cables equipped with the appropriate connectors.
The PRO MPA may be employed in a number of setups including:
- Between a microphone and a mixer, digital multi-track
recorder, DAT machine, hard disk recorder, or analog recorder.
- In a mixerÕs channel insert points.
- Between a microphone and signal processors.
- Between electronic musical instruments (synthesizers, guitars,
bass, samplers, acoustic instruments with pickups) and down
line gear.
Note: the PRO MPA should be securely mounted in a standard
19Ó rack.
Warning: To avoid the risk of shock or fire, do not expose this
unit to moisture. Do not remove metal panels from chassis
parts. Removing the chassis from its cabinet parts exposes
dangerous high voltages. There are no user-serviceable parts
inside. Hazardous voltages are present inside the chassis.
Refer all servicing to qualified personnel.
Caution: If your power cord becomes damaged and must be
replaced, always replace it with the proper type (3 prong).
When the power switch is turned on, the VU meters will light.
LEDs will light if its associated switch is in its ÒonÓ position. It is
important to remember to turn the PRO MPA on before any
monitoring levels or power amps are turned on. The PRO MPA
has the ability to add over 60dB of gain to its input signal. This
can cause the PRO MPA to produce a ÒthumpÓ on power up
and power down.
PRO MPA with the +20dB gain switch in is needed. Use the setting that best fits your application.
If the PRO MPA fails to power up when the power switch is
turned on, check to see that its power cord is plugged into an
active outlet. If the unit still fails to operate properly, turn it off
and unplug it. Then consult your dealer or A R TÕs Customer
Service department.
Phase Switch
The Phase Switch is provided to reverse the phase of a signal.
This switch works on Pins 2 and 3 of the XLR Output jack of the
channel. The Phase switch also reverses the polarity of the 1/4Ó
output jack. In the Normal position, the signal is in-phase. In the
Reverse (or ÒinÓ) position, Pins 2 and 3 are reversed as the signal is changed to 180 degrees out of phase. The Phase LED
will illuminate when the Phase Switch is in its ÒreverseÓ position.
The Power switch supplies and removes power from the unit.
The PRO MPA should be powered ÒonÓ with all monitor levels
turned down, or off, to protect against any ÒthumpingÓ caused
by high gain settings. Likewise, the PRO MPA should be turned
ÒoffÓ after turning all monitor levels down.
Input Level Control
The Input Level Control sets the amount of input gain of the
PRO MPA. Turn the control clockwise to increase gain and
counterclockwise to decrease gain. You may control two ranges
of gain with this control, +26 to +60dB and +6 to +40dB.
Selection of the gain range is made with the +20dB gain switch.
When setting the Input Level Control, refer to the 10 segment
Tube Character Array for a visual reference to the PRO MPAÕs
internal signal levels (applied gain).
Output Level Control
The Output Level Control sets the output level of the PRO MPA.
When the control is fully counterclockwise, there is no output
Level. Turning the control clockwise increases the level of the
output to a maximum of +10dB of gain. This gain is in addition
to the existing input gain. When setting the Output Level
Control, refer to the Vu Meter for an accurate level leaving the
+20dB Gain/ Norm Switch
Use the +20dB Gain/ Norm switch to set the gain range of the
Input control. When the switch is in the out (Normal) position
the gain range is +6 to +40dB. Depressing the switch adds
20dB of gain. With the switch in, the gain range is +26 to
+60dB. With most microphone applications youÕll find using the
In multiple microphone applications, the placement of the microphones can affect the phase of a signal. If two microphones
pick up the same signal from different locations, the result can
be a hollow or frequency ÒshiftedÓ sound. In some cases it may
sound as if an instrument disappears if it happens to be 180
degrees out of phase. Depressing the Phase switch of one
channel can remedy this problem. Likewise, if a microphone
cable is wired incorrectly, when used with a properly wired
cable the signal will be out of phase.
**Note: for single microphone applications switching the phase
switch in and out will produce little to no change in the output
Phantom Power Switch
Each channel of the PRO MPA can power any microphone
needing +48 volts DC Phantom power. The Phantom power is
engaged and disengaged with this switch. The Phantom Power
LED will illuminate when Phantom Power is ÒonÓ. Phantom
power is supplied to pins 2 and 3 of the XLR input jack.
**Note: Be sure to turn down or mute the output of the PRO
MPA when engaging or disengaging Phantom power.
Additionally, when disengaging, allow 30 - 45 seconds for the
power to completely dissipate. Most microphones will make a
sound like air leaking from a tire when phantom power is disconnected, but some can make some very nasty low rumbles
and whines as well.
**Another Note: Dynamic microphones should not be affected
or damaged if they are plugged into a line where Phantom
power is present. However, if the mic doesnÕt need it, donÕt use
it. Some things are best left untested!
HPF (High Pass Filter) Control
The HPF is a low frequency roll-off intended for use to Òtune
outÓ unwanted rumbling or breath noises. A High Pass Filter
allows frequencies above its set point to pass unaffected while
gently rolling off frequencies below its set point. The range of
the PRO MPAÕs HPF is 7Hz to 150Hz with a slope of 6dB per
octave. This gentle slope allows unwanted low frequency information to be rolled off while not affecting the tonality of the input
signal. In its fully counter-clockwise position, the filter has a set
frequency of 7Hz which can be considered ÒbypassedÓ or off.
The filter is located after the Input Level Contol and before the
tube circuitry.
Tube Character 10 Segment LED Array
Ten LEDs are provided on each channel which display how the
tube gain is affecting the input signal. These LEDs are calibrated with the tube circuitry to give you an accurate visual of its
output signal (**Note: these LEDs are pre-output level control).
Use this meter as a visual for setting the Input level to the PRO
MPA. The first four LEDs are labeled Clean. The tube is producing a clean output when this LED is lit.
The next four LEDs are labeled ÒwarmÓ. This is the optimal
operating range for the PRO MPA. At this level, the tube is producing an output signal which most would term ÒwarmÓ.
Whatever you would like to call it is fine. YouÕll find the output
signal has an enhanced bottom to low mid quality with smooth
high frequency detail.
The last two LEDs are labeled ÒClipÓ. The first LED will light
approximately 6dB before audible distortion occurs. If this light
flickers, do not panic. The unique design of the PRO MPA
allows the tube to distort well before any other gain stage.
When a tube goes into distortion it is a gradual process and
tends to sound pleasing for a range before it turns into a distortion box. After some use youÕll find the Òsweet spotÓ of the PRO
MPA is with this light flashing fairly regularly. You may find a
ÒclippedÓ level is suitable for some applications.
**Note: Use the Tube Character Array to aid in setting the Input
Level Control.
VU Level Meter
Each channel of the PRO MPA has a backlit VU meter showing
its output level. The Ò0Ó level is calibrated to +4dBu. Use the VU
meter when adjusting the Output Level Control to aid in sending
the proper level to your next piece of equipment.
ItÕs easy to interface the PRO MPA with other equipment.
Balanced XLR and unbalanced 1/4Ó phone, input and output
connectors are located on the rear panel.
The PRO MPAÕs XLR connectors follow the AES standard of:
Pin 1 = Ground, Pin 2 = Hot (+), Pin 3 = Cold (-). The unbalanced 1/4Ó phone jacks are typical Tip - Hot (+), Sleeve Ground connections.
Ideally, one input jack per channel should be used at a time.
However, because of its design, the PRO MPA can be hardwired into a rack without having to disconnect the XLR inputs
when using the 1/4Ó jacks. If no load is placed on the XLR input
(no instrument or microphone connected) the 1/4Ó jack will function as if there was nothing connected to the XLR input. Both
PRO MPA inputs may be used simultaneously. However, the
two signals will sum and the signal present at the XLR jack will
tend to attenuate the signal of the 1/4Ó input.
Both balanced and unbalanced output connections may be
used simultaneously. This is particularly useful when using the
PRO MPA as a direct box for instruments or line level signals.
**Note: If you experience a grounding hum when using both
output connectors (one to the console, one to an instrument
amp) simultaneously, a ground loop may be the problem. To
remedy this problem, disconnect the ground wire (pin 1) from
the XLR cable plugged into the PRO MPAÕs output (or use a
ground-lifted cable). This interrupts the ground path and therefore breaks the loop.
Microphone Preamp
The main application of the PRO MPA is a microphone preamplifier. Plug any microphone directly into either input and set the
input and output controls to provide an appropriate level into the
next stage of your system.
Limited Warranty
Warranty service for this unit will be provided by Applied
Research and Technology, Inc. in accordance with the following
warranty statement.
DI (Direct Input)
The PRO MPA is ideal for use as a DI box. Plug the instrument
into either input and use the XLR or 1/4 (or both) outputs to
connect to your recorder, board or PA system. Experiment with
different Input Level settings for different textures.
Mastering (2-mix processing)
Because of its low noise and excellent tonal qualities, the PRO
MPA is ideal for running mixes through before recording to DAT
or cassette. Used as a mastering device, the PRO MPA is capable of adding warmth and, if set properly, gentle tube compression to the incoming signal.
Applied Research and Technology, Inc. (A R T) warrants to the
original purchaser that this product is free from defects in workmanship and materials for a period of five years from the date
of purchase. A R T will, without charge, repair or replace, at its
option, defective product or component parts upon prepaid
delivery to the factory service department or authorized service
center, accompanied by proof of purchase date in the form of a
valid sales receipt.
EXCLUSIONS: This warranty does not apply in the event of
misuse or abuse of the product or as a result of unauthorized
alterations or repairs. This warranty is void if the serial number
is altered, defaced or removed.
Low noise and variable Input and Output level controls make
the PRO MPA ideal for level matching material in post production situations.
A R T reserves the right to make changes in design and make
additions or improvements upon this product without any obligation to install the same on products previously manufactured.
Special Effects
For industrial, metal, or just ÒflavorÓ textures, experiment with
the PRO MPA. Cascading the channels can produce overdrive
and tube distortion that can add interesting textures when
blended with vocals and different instruments. Placing signals
purposely out of phase can yield interesting results. No harm
will come to the PRO MPA with this type of experimentation.
However, be sure to have output and monitoring levels turned
DOWN before ÒtestingÓ the sound. When running one channel
into another (cascading), you have the potential for upwards to
120 to 140dB of gain.
A R T should not be liable for any consequential damages,
including without limitation damages resulting from the loss of
use. Some states do not allow limitation of incidental or consequential damages, so the above limitation or exclusion may not
apply to you. This warranty gives you specific rights and you
may also have other rights which vary from state to state.
For units purchased outside the United States, service will be
provided by an authorized distributor of Applied Research and
Technology, Inc. products.
The following information is provided in the unlikely event that
your unit requires service. Use this procedure to return units in
the United States only. For service outside the United States,
please contact your authorized A R T distributor.
1) Be sure the unit is the cause of the problem. Check to make
sure the unit has power supplied, all cables are connected correctly, and the cables themselves are in working condition.
2) If you find the unit to be at fault, write down a description of
the problem, including how and when the problem occurs.
3) Call the factory for a Return Authorization (RA) number.
4) Pack the unit in its original carton or reasonable substitute.
The packing box is not recommended for a shipping carton. Put
the packaged unit in another box for shipping. Print the RA
number clearly under the address.
5) Include with your unit: a return shipping address (we cannot
ship to a P.O. Box), a copy of your purchase receipt, a daytime
phone number and the description of the problem.
6) Ship the unit to:
Applied Research and Technology, Inc.
215 Tremont Street
Rochester, NY 14608
Atten: Repair Department
R.A.# _______________
7) Contact our Customer Service department at 716/436-2720
for your Return Authorization number or questions regarding
your repair. Customer Service hours are Monday through Friday
8:30AM to 4:30PM Eastern time.
Input Connections:
Output Connections:
Input Impedance: XLR, 1/4Ó
Output Impedance: XLR, 1/4Ó
Maximum Input Level: XLR
Maximum Input Level: 1/4Ó
Maximum Output Level: XLR
Maximum Output Level: 1/4Ó
Frequency Response
Dynamic Range
Total Harmonic Distortion(THD)
Maximum Gain: XLR to XLR
Equivalent Input Noise (EIN)
XLR to XLR (shorted input)
3.50Ó H x 19Ó W x 6.5Ó D
XLR (balanced), 1/4Ó unbal.
XLR (balanced), 1/4Ó unbal.
1.67k ohms, 840K ohms
600 ohms, 300 ohms
>90dB (typical @ 1kHz)
20Hz to 40kHz (+0, -1dB)
>100dB (20Hz to 20kHz)
<0.1% (typical)
>-124dBu unweighted
>-133dBu (ÔAÕ weighted)
100-125VAC, 25W - (USA)
Internal fuse. Other power require
ments configured for country of desti
Power Requirements:
A R T retains a policy of constant product improvement. A R T reserves the right
to make changes in design or make additions to or improvements upon this
product without any obligation to install the same on products previously manufactured. Therefore, specifications are subject to change without notice.
Designed and manufactured in the United States of America.
Applied Research and Technology, Inc.
215 Tremont Street
Rochester, NY 14608 USA
(716) 436-2720 (Phone)
(716) 436-3942 (FAX)
For Product information, questions, applications, tips, answers and general discussion with A R T employees look for
A R T on the Internet..
Look for the A R T folder on America Online in Craig AndertonÕs Stage Studio
and Sound (keyword ÒSSSÓ) under the Manufacturer Supported Forums. Email
us at
Look for the A R T supported area in the MIDI Forum B area on CompuServe
(Go MIDI). CompuServe address: 76702,3700. Email us at
Check out our Web Page at:
©1996 Applied Research and Technology, Inc.
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