Page 1
Benchmark MPA1
Instruction Manual
2-Channel Microphone Preamplifier
Page 2
Safety Information
Voltage Selection
CAUTION: THE FUSE DRAWER INCLUDES
A VOLTAGE SELECTION SWITCH WITH
TWO SETTINGS: “110” AND “220”.
CHECK TO SEE THAT IT IS PROPERLY
CONFIGURED FOR YOUR LOCATION
BEFORE CONNECTING AC POWER.
Incorrect configuration may blow fuses or
cause erratic operation.
Repairs
CAUTION: DO NOT SERVICE OR REPAIR
THIS PRODUCT UNLESS PROPERLY
QUALIFIED. ONLY A QUALIFIED
TECHNICIAN SHOULD PERFORM
REPAIRS.
Fuses
CAUTION: FOR CONTINUED FIRE
HAZARD PROTECTION ALWAYS REPLACE
THE FUSES WITH THE CORRECT SIZE
AND TYPE (0.5A 250 V SLO-BLO
MM – LITTELFUSE® HXP218.500 OR
EQUIVALENT).
®
5 X 20
Modifications
CAUTION: DO NOT SUBSTITUTE PARTS
OR MAKE ANY MODIFICATIONS
WITHOUT THE WRITTEN APPROVAL OF
BENCHMARK MEDIA SYSTEMS, INC.
MODIFICATION MAY CREATE SAFETY
HAZARDS AND VOID THE WARRANTY.
NOTICE: CHANGES OR MODIFICATIONS
NOT EXPRESSLY APPROVED BY
BENCHMARK MEDIA SYSTEMS COULD
VOID THE USER'S AUTHORITY TO
OPERATE THE EQUIPMENT UNDER FCC
REGULATIONS.
Page 3
Contents
Safety Information 2
Voltage Selection 2
Repairs 2
Fuses 2
Modifications 2
Contents 3
Overview 4
Features 5
Connections 6
Microphone Inputs (L and R) 6
Balanced XLR Outputs 6
Output Signal Levels 7
Driving Unbalanced Loads 7
AC Power Entry Connector 7
Fuse Holder 7
Preamp Section 8
Preamp Overview 8
Microphone Gain Controls 8
Input Topology 8
Two-Stage RF Filter and CMRR 8
Phantom Power Switches 9
Input Protection 9
Polarity Switch 9
40 Hz High-Pass Filters 9
LED Output Level Meters 10
THD Spectrum at 10 KHz 21
Specifications 22
Microphone Preamps 22
Direct Outputs 23
HPA2™ Headphone Amplifier 23
LED Output Meters and Gain Indicators 24
AC Power Requirements 24
Dimensions 25
Weight 25
Regulatory Compliance 26
FCC Notice (U.S. Only) 26
RoHS Compliant Information 26
CE Certificate of Conformity 27
Warranty Information 28
Benchmark Extended Warranty 29
Calibration 30
+48V Adjustment 30
HPA2™ Headphone Output 11
“0-Ohm” Output Impedance 11
Headphone Performance 11
Rack Mounting 12
System1™ Universal Rack Adapter 12
Blank Rack Panel 12
Mounting Near Other Equipment 12
Performance Graphs 13
Frequency Response 13
High-Pass Filter - Frequency Response 14
Inter-Channel Phase Response 15
THD+N vs. Frequency 16
Wideband THD+N vs. Frequency 17
Equivalent Input Noise vs. Gain 18
Noise Spectrum 19
THD Spectrum at 1 KHz 20
Page 4
Overview
The MPA1 is a 2-channel microphone
preamplifier that is designed to achieve the
highest performance available in a
microphone preamplifier. The MPA1 is
designed for maximum transparency, wide
bandwidth, low-noise, low-distortion, and
superior EMI immunity. It is well suited for
the most demanding applications in studios
and live venues.
The MPA1 is the next evolution of
Benchmark’s legendary microphone
preamplifier systems. In all respects, the
MPA1 meets or exceeds the performance of
Benchmark’s current and legacy mic preamps.
The MPA1 achieves outstanding performance
over a wide range of input levels. Gain is
controlled by precision matched switched
resistor networks and is adjustable over a
range of 0 dB to 74 dB without using a pad.
Each channel of the MPA1 has an XLR direct
output. These outputs feature low-distortion,
high-current drivers that easily handle long
cables and other less-than-ideal loads.
Each of the MPA1's two channels includes a
switch for +48V Phantom power, polarity
inversion, and a 40Hz high-pass filter.
The entire MPA1 has a 500 kHz bandwidth.
Wide bandwidth demands exceptional RF
filtering and shielding: The multi-layer printed
circuit board uses a special construction
technique that creates a 3-dimensional shield
surrounding all signal traces. Each
microphone input features Benchmark’s
exclusive precision-tuned, two-stage RF input
filter. This circuit removes RF interference
without affecting the microphone input signal.
RF filters have always been a key component
in Benchmark preamps, and has resulted in a
proven track record for exceptional
performance in difficult high-RF venues.
Microphone pre-amplifier circuits usually
suffer from non-linear performance at ultrasonic frequencies. This non-linearity causes
inter-modulation distortion (IMD) components
that fold down to audible frequencies. Unlike
harmonic distortion (THD), IMD produces
distortion tones that are very un-natural and
non-musical. IMD also masks and alters the
subtle details of delicate high-frequency
transients such as those produced by bells.
Benchmark preamps have always had
outstanding high-frequency performance as
well as freedom from IMD. The MPA1 takes
the Benchmark design one step further, and
achieves the lowest IMD that we have ever
measured in a microphone preamplifier.
The MPA1 includes the HPA2™ - Benchmark's
signature high-current, 0-Ohm headphone
amplifier. The HPA2™ is capable of delivering
the full performance of the MPA1 into the
difficult load presented by most headphones.
A rugged half-rack (½ RU) enclosure includes
an internal power supply that supports all
international voltages and has generous
margins for over-voltage and under-voltage
conditions. It features a core-banded toroidal
transformer in a shielded enclosure.
We believe that you will enjoy the
performance and features of the MPA1.
MPA1 Instruction Manual Page 4
Page 5
Features
• Two Transformerless Microphone Inputs
• Two Balanced Direct Outputs (XLR)
• Monolithic Low-Noise Transistor Quads on Each Microphone Input
• Precision-Tuned, Two-Stage RF Filter on Each Microphone Input
• Precision-Matched Resistor Gain Control Switches on Every Microphone Input
• 2-dB per Switch Step; Maximum Gain - 74 dB; Maximum Gain - 0 dB (Unity)
• ‘Virtual’ 38-position Gain Control Switch for Continuous Gain Control
• Four Segment Gain Range Indicator
• +27.5 dBu Maximum Input Level
• +27.5 dBu Maximum Output Level on Balanced Outputs
• Actively Balanced Transformerless Outputs
• High-Current High-Speed Low-Capacitance Phantom Protection Circuits
• Fully Protected Against Phantom Hot-Plug and Cable-Shorting Scenarios
• Phantom-Disable Feature for Dedicated Ribbon Microphone Application
• +48v Phantom Power Switch on Every Microphone Input
• 40 Hz High-Pass Filter Switch on Every Microphone Input (12 dB/octave)
• Polarity Switch on Every Microphone Input
• Four-Segment LED Output Level Meter (-20 dBu, +4 dBu, +24 dBu, +29 dBu)
• HPA2™ “0-Ohm” 1/4” TRS Headphone Output
• +23.5 dBu Maximum Headphone Output Level
• 41-Detent Headphone Level Control
• Ultra-Quiet Linear Power Supply with Rear-Panel Input Voltage Selector
• Complies with FCC and CE Regulations
• RoHS Compliant
MPA1 Instruction Manual Page 5
Page 6
Connections
Microphone Inputs (L and R)
power several seconds before connecting or
disconnecting a microphone.
The balanced transformerless microphone
inputs use locking Neutrik™ gold-pin female
XLR jacks with both pin 1 (Ground) and the
XLR shell directly bonded to the chassis. This
direct bonding is important for maximum RF
shielding and for immunity to hum due to
shield currents. Each input includes
Benchmark’s precision-tuned, two-stage RF
filter for outstanding RF immunity.
• XLR pin 2 = + Audio In
• XLR pin 3 = - Audio In
• XLR pin 1 = Cable Shield – bonded to
chassis
• XLR shell – bonded to chassis
The microphone inputs have a wide operating
range. The maximum input level before
clipping is +29 dBu.
Each channel is equipped with a switch for
+48V phantom power. Under certain
circumstances, phantom power can cause
large voltage transients. The MPA1 is
equipped with high-current input protection
circuits that protect the sensitive low-noise
input transistors from the worst-case
phantom-induced transients. Large transients
are produced when a microphone is
connected or disconnected while phantom
power is on. The worst possible transients
occur when a microphone cable has an
intermittent short to ground from either pin 2
or pin 3. The MPA1 is very well protected
against both of the above. For the protection
of your equipment (and your ears), we
strongly recommend shutting off phantom
The MPA1 is designed to work with balanced
microphones, balanced line-level inputs, and
unbalanced sources as well. The MPA1
maintains rock-solid performance even in
difficult RF environments.
Common-mode signals in the audio band are
removed with a precisely trimmed differential
amplifier. The MPA1 even includes a subsonic
common-mode trim adjustment on each
microphone input that eliminates sensitivity
to +48V ripple caused by power supply noise
and/or the loading of microphone electronics.
Balanced XLR Outputs
The MPA1 has two balanced direct outputs.
These outputs use gold-pin Neutrik™ male
XLR connectors with direct chassis bonding of
both pin 1 and the connector shell. This
direct bonding is important for maximum RF
shielding and for immunity to hum due to
shield currents.
All outputs are transformerless and have an
impedance of 60 Ohms balanced or 30 Ohms
unbalanced. All outputs are equipped with
high-performance drivers that can drive high
signal levels into load impedances as low as
300 Ohms without an increase in distortion.
These outputs are well suited for driving long
lines.
XLR pin 2 = + Audio Out
XLR pin 3 = - Audio Out
XLR pin 1 = Cable Shield – bonded to chassis
XLR shell – bonded to chassis
MPA1 Instruction Manual Page 6
Page 7
Output Signal Levels
AC Power Entry Connector
The maximum output level on the balanced
outputs is +27.5 dBu. Each channel’s output
can be monitored with the four-segment LED
output level meter.
Driving Unbalanced Loads
CAUTION: ALWAYS LEAVE XLR PIN 3
FLOATING WHEN DRIVING UNBALANCED
LOADS.
XLR to RCA Wiring:
1. Connect XLR pin 2 (+) to RCA center pin.
2. Connect XLR pin 1 (GND) to RCA shield.
3. Make no connection to XLR pin 3 (-).
XLR to ¼” TS Wiring:
1. Connect XLR pin 2 (+) to Tip.
2. Connect XLR pin 1 (GND) to Sleeve.
3. Make no connection to XLR pin 3 (-).
The AC power input uses a standard IEC type
connector and includes a power switch.
Factory-configured 110V units ship with a
power cord. 220V units ship without a power
cord. Location-specific IEC style power cords
may be purchased from a local source
(including any local Benchmark dealer).
Fuse Holder
The fuse holder is built into a drawer next to
the IEC power connector. The drawer requires
two 5 x 20 mm 250 V Slo-Blo
The drawer includes a voltage selection switch
with two settings: “110” and “220”. Both
settings use a 0.5 Amp fuse.
The AC input has a very wide input voltage
range and can operate over a frequency
range of 50 to 60 Hz. At the “110” setting,
the MPA1 will operate normally over a range
of 105 to 140 VAC. At the “220” setting, the
MPA1 will operate normally over a range of
200 to 285 VAC.
®
Type fuses.
CAUTION: FOR CONTINUED FIRE
HAZARD PROTECTION ALWAYS REPLACE
THE FUSES WITH THE CORRECT SIZE
AND TYPE (0.5A 250 V SLO-BLO
MM – LITTELFUSE® HXP218.500 OR
EQUIVALENT).
®
5 X 20
MPA1 Instruction Manual Page 7
Page 8
Preamp Section
Preamp Overview
Each preamp channel includes switches for
phantom power, polarity, and 40 Hz highpass filter. Each channel also has a 38position gain control switch and a 4-segment
output level meter. Inputs are fully protected
against overloads and phantom power
transients.
Microphone Gain Controls
The gain controls are a unique approach to
the popular switched-resistor network
topology. Each gain switch of the MPA1 can
sweep the entire 74 dB gain range with
continuous rotation. This is achieved with a
‘virtual 38-position’ switch – a 13-position
switch that triggers automatic adjustment of
the gain-range.
These resistor networks are precisionmatched for inter-channel gain matching
within +/- 0.03 dB. This precision provides
precise control of stereo microphone pairs.
Input Topology
The first gain stage on each microphone input
is built around precision-matched, monolithic,
low-noise transistor quads. Bandwidth is 500
kHz, IMD and THD are virtually non-existent.
The MPA1 is designed to achieve faithful and
transparent microphone amplification.
Two-Stage RF Filter and CMRR
Each microphone input is precision-trimmed
at 3 frequencies for common-mode rejection.
High-frequency RF interference is blocked by
Benchmark’s two-stage RF filter. This filter
maintains the MPA1’s outstanding
performance in very difficult RF
environments.
Maximum gain is calibrated for exactly 74 dB.
Minimum gain is 0 dB (unity). The MPA1 does
not attenuate the signal with pads or
otherwise. When the gain is set at 0 dB, the
MPA1 can accept a signal at +27.5 dBu
without clipping.
MPA1 Instruction Manual Page 8
Page 9
Phantom Power Switches
Input Protection
Up = Phantom On
Down = Phantom Off
CAUTION: ALWAYS TURN OFF PHANTOM
POWER AND WAIT SEVERAL SECONDS
BEFORE CONNECTING OR
DISCONNECTING MICROPHONES.
The MPA1 has an internal ‘Phantom Defeat’
jumper. When this jumper is removed,
phantom power cannot be applied to the
respective microphone input. This feature
should be used when the MPA1 is dedicated
to ribbon microphone. The purpose is to
protect the ribbon element in case the +48V
switch is thrown. The internal ‘Phantom
Defeat’ jumper is located behind the left
channel’s +48V switch (bottom-left in the
following picture).
Under certain circumstances, phantom power
can cause large voltage transients. The MPA1
is equipped with high-speed, high-current,
low-capacitance protection circuits that
protect the sensitive input-transistors from
the worst-case phantom-induced transients.
Large transients are produced when a
microphone is connected or disconnected
while phantom power is on. The worst
possible transients occur when a microphone
cable has an intermittent short to ground
from either pin 2 or pin 3. The MPA1 is very
well protected against both of the above. For
the protection of your microphones (and your
ears), we strongly recommend shutting off
phantom power several seconds before
connecting or disconnecting a microphone.
Polarity Switch
Up = Polarity is Inverted
Down = Polarity is Normal
The polarity switch allows the polarity of the
input signal as to be easily reversed. Typical
applications that require polarity inversion
include using the back-side of a figure-8
microphone (such as a ribbon), having two
microphones on one instrument but facing
opposite directions, or when a microphone or
cable is constructed with inverted polarity.
CAUTION: ALWAYS DISCONNECT POWER
FROM THE MPA1 FOR FIVE MINUTES
BEFORE ADJUSTING THE PHANTOM
DEFEAT JUMPER.
MPA1 Instruction Manual Page 9
40 Hz High-Pass Filters
Up = Filter Enabled
Down = Filter Off
The 40 Hz high-pass filter is a second-order
filter with a slope of 12 dB per octave. This
filter is intended to remove unwanted
subsonic noise and rumble caused by sources
such as HVAC, air currents, and vibration.
Page 10
LED Output Level Meters
Each preamp channel is equipped with a foursegment LED output level meter.
The LED’s are driven by a peak detection and
stretching circuit so that very short transients
can be observed.
The first green LED (-20 dBu) illuminates
when the output signal has an amplitude of at
least -20 dBu.
The second green LED (+4 dBu) illuminates at
an output level of at least +4 dBu.
The yellow LED (+24 dBu) illuminates at an
output level of at least +24 dBu.
The red LED (+28 dBu) illuminates at an
output level of at least +27.5 dBu. The red
LED indicates a clip has occurred.
MPA1 Instruction Manual Page 10
Page 11
HPA2™ Headphone
Output
The output of each channel’s preamp is
directed to the headphone amplifier,
Benchmark’s signature HPA2™ headphone
amplifier. This high-current, high-output
amplifier has an output impedance of 0Ohms. It is designed to drive loads as low as
30-Ohms without any increase in distortion.
It also has sufficient amplitude to drive lowsensitivity 600-Ohm headphones.
The HPA2™ includes current-limiting circuits
that fully protect against damage from short
circuits. This is important because the right
channel of a headphone amplifier will
experience a short whenever a mono phone
plug is inserted into the stereo headphone
jack. Shorts may also occur when a plug is
partially inserted.
Headphone Performance
In our tests we have measured substantial
distortion across resistors that are wired in
series with headphones. We conducted
measurements with a variety of headphones.
In general, distortion increases as headphone
impedance decreases. This distortion can be
eliminated with a properly designed 0-Ohm
headphone amplifier.
The performance of the HPA2™ does not
change when headphones are driven. THD+N
measurements for no-load, 30-Ohm resistive
load, and 30-Ohm headphone load, and 600Ohm headphone load are virtually identical.
The HPA2™ will substantially improve the
sound of 30 and 60-Ohm headphones. It will
make very noticeable improvements with
600-Ohm headphones.
“0-Ohm” Output Impedance
Most headphone amplifiers use series
resistors to maintain stability and protect
against short-circuit conditions. These
resistors are usually at least 30-Ohms, and
have a negative impact on performance. A
headphone amplifier with series resistors may
measure very well when driving resistive
loads. However, the same amplifier will
measure very poorly when driving a
headphone load. Unfortunately most
manufacturers do not specify headphone
amplifier performance with anything other
than ideal resistive loads. Our measurements
show that headphones do not behave like
resistive loads.
MPA1 Instruction Manual Page 11
Page 12
Rack Mounting
Mounting Near Other
There are multiple solutions for rackmounting the MPA1. An optional Rack-
Mount Coupler allows the mounting of any
two Benchmark System1™ products in a
single rack space. A Blank Rack Panel can
be added when only one unit is being racked.
The System1™ Universal Rack Adapter is
a tray solution.
These rack-mount solutions are available
from Benchmark. Call us, visit our website
http://www.BenchmarkMedia.com), or
(
contact your dealer to purchase these
accessories.
System1™ Universal Rack
Adapter
The Universal Rack Mount Adapter is a
tray that mounts up to two System1™
products in a single race space. The tray
accepts any combination of System1™
products (with or without rack-mount type
faceplates).
Blank Rack Panel
Equipment
CAUTION: STRAY MAGNETIC FIELDS
FROM ADJACENT EQUIPMENT MAY
CAUSE MAGNETICALLY INDUCED HUM IN
THE SENSITIVE HIGH-GAIN PREAMP
CIRCUITS.
The MPA1 is shielded in 3-dimensions with
mu-metal panels, which drastically reduces
susceptibility to stray magnetic fields. The
MPA1 may be mounted directly above or
below any other equipment, but we cannot
guarantee that the MPA1 will be impervious to
interference from all equipment mounted too
close to the MPA1. It is recommended that
the user apply caution by using the following
procedure when mounting near other
equipment:
TIP: TO CHECK FOR MAGNETIC
INTERFERENCE FROM ADJACENT
EQUIPMENT:
1. Disconnect all microphones
2. Back-terminate microphone inputs
3. Set all preamp gain controls at maximum
4. Listen to headphone output
5. Unplug adjacent equipment to determine
if there is any magnetic interference
TIP: IN MANY CASES, POWER SWITCHES
DO NOT TURN OFF ALL OF THE
MAGNETIC COMPONENTS IN AN
ELECTRONIC DEVICE. THEREFORE, WHEN
PERFORMING MAGNETIC INTERFERENCE
TESTS, IT IS IMPORTANT TO UNPLUG
The Blank Rack Panel is a ½-wide 1-RU
black-anodized aluminum panel for covering
an unused slot in a System1™ Universal
Rack Adapter.
MPA1 Instruction Manual Page 12
THE ADJACENT EQUIPMENT TO INSURE
THAT THESE DEVICES ARE TRULY OFF.
Page 13
Performance Graphs
Audio Precision
Frequency Response
+3
+2.8
+2.6
+2.4
+2.2
+2
+1.8
+1.6
+1.4
+1.2
+1
+0.8
+0.6
+0.4
d
+0.2
B
+0
r
-0.2
A
-0.4
-0.6
-0.8
-1
-1.2
-1.4
-1.6
-1.8
-2
-2.2
-2.4
-2.6
-2.8
-3
10 200k20 50 100 200 500 1k 2k 5k 10k 20k 50k 100k
02/19/07 11:33:00PRE420 - Frequency Response
Hz
ColorSweep Trace Line Style Thick Data Axis Com ment
1 1 Red Solid 4 Anlr.Level A Le ft HP Filter Off
The above graph shows the frequency response of the MPA1 with the 40 Hz high-pass filter off. The
amplitude response measures -0.020 dB at 10 Hz and -0.165 dB at 200 kHz. The bass response
extends well below the 10-Hz limitation of the test equipment, and the high-frequency response
extends well above the 200 kHz limit of the test equipment.
MPA1 Instruction Manual Page 13
Page 14
Audio Precision
High-Pass Filter - Frequency Response
+3
+2.8
+2.6
+2.4
+2.2
+2
+1.8
+1.6
+1.4
+1.2
+1
+0.8
+0.6
+0.4
d
+0.2
B
+0
r
-0.2
A
-0.4
-0.6
-0.8
-1
-1.2
-1.4
-1.6
-1.8
-2
-2.2
-2.4
-2.6
-2.8
-3
10 200k20 50 100 200 500 1k 2k 5k 10k 20k 50k 100k
Hz
02/19/07 11:33:00PRE420 - Frequency Response
ColorSweep Trace Line Style Thick Data Axis Com ment
2 1 Red Solid 4 Anlr.Level A Le ft HP Filter On
The above graph shows the response of the 40 Hz high-pass filter. Response is -3 dB at 40 Hz with
a slope of 12 dB/octave.
MPA1 Instruction Manual Page 14
Page 15
Inter-Channel Phase Response
Audio Precision
+1
+0.9
+0.8
+0.7
+0.6
+0.5
+0.4
+0.3
+0.2
+0.1
d
+0
e
g
-0.1
02/19/07 11:35:37PRE420 - Inter-Channel Phase Response
-0.2
-0.3
-0.4
-0.5
-0.6
-0.7
-0.8
-0.9
-1
10 100k20 50 100 200 500 1k 2k 5k 10k 20k 50k
Hz
This graph shows that the differential phase is significantly better than ± 0.05 degrees from 10 Hz
to 20 kHz.
MPA1 Instruction Manual Page 15
Page 16
THD+N vs. Frequency
Audio Precision
Measurement Bandwidth = 10Hz to 80 kHz, Gain = 30 to 60 dB, Output Level = +4 dBu
02/21/07 09:56:41PRE420 - THD+N vs Frequency at 60 dB Gain, BW=80 kHz
-80
-82
-84
-86
-88
-90
-92
-94
-96
-98
d
-100
B
-102
-104
-106
-108
0.01
0.005
0.002
0.001
0.0005
%
-110
-112
-114
-116
-118
-120
20 80k50 100 200 500 1k 2k 5k 10k 20k 50k
Hz
ColorSweep Trace Li ne Style Thick Data Axis Com me nt
1 1 Red Solid 4 Anlr.THD+N Ra tio Left 60 dB Gain (top trace)
2 1 Magenta Soli d 4 Anlr.THD+N Ra tio Left 5 0 dB Gain
3 1 Blue Soli d 4 Anlr.THD+N Ra tio Left 40 dB Gain
4 1 Green Solid 4 Anlr.THD+N Ratio Left 30 dB Gain (bottom trace)
This graph shows that THD+N does not rise with frequency – even at maximum gain.
0.0002
0.0001
MPA1 Instruction Manual Page 16
Page 17
Wideband THD+N vs. Frequency
Audio Precision
Measurement Bandwidth = 10 Hz to 500 kHz, Gain = 30 to 60 dB, Output Level = +4 dBu
02/19/07 16:16:11PRE420 - Wideband THD+N vs Frequency, BW=500 kHz
-60
-62
-64
-66
-68
-70
-72
-74
-76
-78
d
-80
B
-82
-84
-86
-88
0.1
0.05
0.02
0.01
0.005
%
-90
-92
-94
-96
-98
-100
20 200k50 100 200 500 1k 2k 5k 10k 20k 50k 100k
Hz
ColorSweep Trace Li ne Style Thick Data Axis Com me nt
1 1 Red Solid 4 Anlr.THD+N Ra tio Left 60 dB Gain (top trace)
2 1 Magenta Soli d 4 Anlr.THD+N Ra tio Left 5 0 dB Gain
3 1 Blue Soli d 4 Anlr.THD+N Ra tio Left 40 dB Gain
4 1 Green Solid 4 Anlr.THD+N Ratio Left 30 dB Gain (bottom trace)
0.002
0.001
This graph shows that THD+N does not rise above noise – even at very high frequencies. The 500
kHz measurement bandwidth elevates the noise by 28 dB relative to a 20 kHz measurement
bandwidth.
MPA1 Instruction Manual Page 17
Page 18
Equivalent Input Noise vs. Gain
The above plot shows the Equivalent Input Noise (EIN) of the MPA1 as a function of gain.
Measurement bandwidth is 20 Hz to 20 kHz. Input termination is 150 Ohms.
MPA1 Instruction Manual Page 18
Page 19
Noise Spectrum
Audio Precision
dx=120.996 Hz
dy=-3.948 dB
32k B-H FFT, Gain = 60 dB, 0 dBr = 0 dBu at input
+0
-10
-20
-30
-40
-50
-60
-70
-80
-90
d
B
-100
r
A
-110
02/19/07 11:27:19Noise Spectrum, Gain = 60 dB, 0 dBr = 0 dBu at Input
-120
-130
-140
-145.066
-150
-149.014
-160
-170
-180
-190
-200
10 30k20 50 100 200 500 1k 2k 5k 10k 20k
ColorSweep Trace Line Style Thick Data Axis Com ment Curs or1 Curs or2
1 1 Red Solid 4 Fft.Ch.1 Ampl Left *-145 .066 dBr A *-149.014 dBr A
59.6606 180.657
Hz
The above graph demonstrates that the MPA1 is free of hum and noise. The highest tone is 60-Hz
line-related hum and is at a level equivalent to an input level of -145 dBu. 180-Hz hum is at an
equivalent input level of -149 dBu.
MPA1 Instruction Manual Page 19
Page 20
THD Spectrum at 1 KHz
Audio Precision
dx=1.00024 kHz
dy=-11.343 dB
02/21/07 09:43:491 kHz FFT at 60 dB Gain, Output Level = +24 dBu, 0 dBr = +24 dBu
-111.404
-122.747
d
B
r
A
-100
-102
-104
-106
-108
-110
-112
-114
-116
-118
-120
-122
-124
-126
-128
-130
-132
-134
-100
-102
-104
-106
-108
-110
-112
-114
-116
-118
-120
-122
-124
-126
-128
-130
-132
-134
d
B
r
A
-136
-138
-140
-142
-144
-146
-148
-150
2.00513k3.00537k
2k 20k4k 6k 8k 10k 12k 14k 16k 18k
Hz
ColorSweep Trace Line Style Thick Data Axis Com ment Curs or1 Curs or2
1 1 Red Solid 4 Fft.Ch.2 Ampl Left *-111 .404 dBr A *-122.747 dBr A
-136
-138
-140
-142
-144
-146
-148
-150
The above FFT plot shows that the MPA1 has very little harmonic distortion. The 1 kHz test tone is
notched out with a THD analyzer to improve the resolution of the test. Distortion is exceptionally
low. 2
nd
-harmonic distortion measures better than -111 dB. 3rd-harmonic distortion measures
better than -122 dB. Note the absence of higher-order harmonics.
MPA1 Instruction Manual Page 20
Page 21
THD Spectrum at 10 KHz
Audio Precision
dx=10.0073 kHz
dy=-9.515 dB
-100
-102
-104
-106
-108
-109.271
-110
-112
-114
-116
-118
-118.787
-120
-122
d
-124
B
r
-126
A
-128
-130
-132
-134
02/19/07 11:09:3010 kHz FFT at 60 dB Gain, Output Level = +24 dBu, 0 dBr = +24 dBu
-136
-138
-140
-142
-144
-146
-148
-150
2k 32k4k 6k 8k 10k 12k 14k 16k 18k 20k 22k 24k 26k 28k 30k
Hz
ColorSweep Trace Line Style Thick Data Axis Com ment Curs or1 Curs or2
1 1 Red Solid 4 Fft.Ch.2 Ampl Left *-109 .271 dBr A *-118.787 dBr A
20.022k 30.0293k
The above FFT plot shows that the MPA1 has very little harmonic distortion at high frequencies. The
10 kHz test tone is notched out with a THD analyzer to improve the resolution of the test. The 20-
nd
kHz 2
-harmonic distortion measures better than -109 dB. The 30-kHz 3rd-harmonic distortion
measures better than -118 dB.
MPA1 Instruction Manual Page 21
Page 22
Specifications
Microphone Preamps
Number of Preamps 2
Connectors Gold-Pin Neutrik™ female XLR with
direct ground feature
Grounding Direct bonding of pin 1 to chassis
Input Impedance 8.1k Ohms
Gain Range 0 dB to 74 dB
Maximum Input Level @ Rated THD+N +27.5 dBu (+25.3dBV, 18.4 Vrms)
Phantom Power +48V w/individual switches
High-Pass (rumble filter) 40 Hz second-order 12-dB/octave
RF Protection Dual-stage
Preamp Bandwidth -0.02 dB at 10 Hz
-0.17 dB at 200 kHz
- 3 dB at 500 kHz
EIN at 60 dB Gain (20 Hz to 20 kHz) – to any output -128 dBu at 150 Ohms
-131 dBu at 40 Ohms
-133 dBu at 0 Ohms
THD+N (1 kHz, BW=20 kHz, to any output at +27 dBu) -112 dB, 0.00024% at 22 dB Gain
-110 dB, 0.0003% at 35 dB Gain
-108 dB, 0.00038% at 40 dB Gain
-101 dB, 0.00085% at 55 dB Gain
IMD (50Hz and 7 kHz, to any output at +24 dBu) -104 dB, 0.0006% at 35 dB Gain
-104 dB, 0.0006% at 40 dB Gain
MPA1 Instruction Manual Page 22
Page 23
Direct Outputs
Number of Outputs 2
Connectors Gold-Pin Neutrik™ male XLR with
direct ground feature
Output Impedance 60 Ohms Balanced
30 Ohms Unbalanced (pin 3 floating)
Maximum Output Level at Rated Spec +27.5 dBu
Drive capability at rated THD+N 300 Ohms
Output Type Transformerless
Voltage and Impedance Balanced
HPA2™ Headphone Amplifier
Number of Outputs 1
Connector ¼” TRS with switch contacts
Output Impedance < 0.11 Ohms, 10 Hz to 200 kHz
Maximum Output Level at 0.001% THD+N +23.5 dBu into 600 Ohms (0.24 W)
+19.5 dBu into 30 Ohms (1.78 W)
Maximum Output Current 250 mA
Drive capability at rated THD+N 30 Ohms
Overload Protection (independent per channel) Current limited at 300 mA
Thermal Shutdown
Bandwidth > 500 kHz
-0.014 dB at 10 Hz
-0.013 dB at 200 kHz
THD+N -106 dB, 0.0005% into 30 Ohms at
+18 dBu (1.26 W)
MPA1 Instruction Manual Page 23
Page 24
LED Output Meters and Gain Indicators
Output Meters 4-LED Meter (per channel)
Output Level Indicators +28 dBu (red)
+24 dBu (orange)
+4 dBu (green)
-20 dBu (green)
Gain Indicators “Max 74 dB” RED LED: Total Gain =
+74 dB (Maximum preamp gain)
“+48 dB” GREEN LED: Total Gain =
Dial + 48 dB
“+24 dB” GREEN LED: Total Gain =
Dial + 24 dB
NO LED: Total Gain = Dial + 0 dB
“Min 0dB” RED LED: Total Gain =
Unity Gain (Minimum preamp gain)
AC Power Requirements
Input Operating Voltage Range (VAC RMS) 120 V setting: 105 V min, 140 V max
220 V setting : 200 V min, 285 V max
Frequency 50-60 Hz
Power 27 Watts Idle
27 Watts Typical Program
35 Watts Maximum
Fuses 5 x 20 mm (2 required)
0.5 A 250 V Slo-Blo®
Littelfuse® HXP218.500 or Equivalent
MPA1 Instruction Manual Page 24
Page 25
Dimensions
Form Factor ½ Rack Wide, 1 RU High
Depth behind front panel 8.5” (216 mm)
Overall depth including knobs and connectors but without
power cord
Width excluding 19” rack ears 9.5” (249 mm)
Height excluding removable feet 1.725” (44.5 mm)
9.33” (237 mm)
Weight
MPA1 only 3.5 lb.
MPA1 with power cord, extra fuses, and manual 4.5 lb.
Shipping weight 7 lb.
MPA1 Instruction Manual Page 25
Page 26
Regulatory Compliance
FCC Notice (U.S. Only)
NOTICE: This equipment has been tested and found to comply with the limits for a Class B
digital device, pursuant to Part 15 of the FCC Rules. These limits are designed to provide
reasonable protection against harmful interference in a residential installation. This equipment
generates, uses, and can radiate radio frequency energy and, if not installed and used in
accordance with the instructions, may cause harmful interference to radio communications.
However, there is no guarantee that interference will not occur in a particular installation. If
this equipment does cause harmful interference to radio or television reception, which can be
determined by turning the equipment off and on, the user is encouraged to try to correct the
interference by one or more of the following measures:
Reorient or relocate receiving antenna.
Increase the separation between the equipment and receiver.
Connect the equipment into an outlet on a circuit different from that to which the receiver is
connected.
Consult the dealer or an experienced radio/TV technician for help.
This device complies with Part 15 of the FCC rules. Operation is subject to the following two
conditions:
1. This device may not cause harmful interference.
2. This device must accept any interference received including interference that may cause
undesired operation.
Instructions to Users: This equipment complies with the requirements of FCC (Federal
Communication Commission) equipment provided that following conditions are met:
1. XLR Digital Input: Shielded 110-Ohm AES/EBU digital audio cable with connector shell
bonded to shield must be used.
2. BNC Digital Connections: Shielded 75-Ohm coaxial cable must be used.
NOTICE: Changes or modifications not expressly approved by the party responsible for
compliance could void the user's authority to operate the equipment.
RoHS Compliant Information
This statement clarifies Benchmark Media Systems, Inc. product compliance with the EU’s
(European Union) directive 2002/95/EC, or, RoHS (Restrictions of Hazardous Substances).
As of July 01, 2006, All Benchmark Media Systems, Inc. products placed on the European Union
market are compliant (containing quantity limit weight less than or equal to 0.1% (1000 ppm)
of any homogeneous Lead (Pb), Mercury (Hg), Hexavalent Chromium (Cr VI), and flame
retardant Polybrominated Biphenyls (PBB) or Polybrominated Diphenyl Ethers (PBDE)).
MPA1 Instruction Manual Page 26
Page 27
CE Certificate of Conformity
MPA1 Instruction Manual Page 27
Page 28
Warranty Information
The Benchmark 1 Year Warranty
Benchmark Media Systems, Inc. warrants its products to be free from defects in material and
workmanship under normal use and service for a period of one (1) year from the date of
delivery.
This warranty extends only to the original purchaser. This warranty does not apply to fuses,
lamps, batteries, or any products or parts that have been subjected to misuse, neglect,
accident, modification, or abnormal operating conditions.
In the event of failure of a product under this warranty, Benchmark Media Systems, Inc. will
repair, at no charge, the product returned to its factory. Benchmark Media Systems, Inc. may,
at its option, replace the product in lieu of repair. If the failure has been caused by misuse,
neglect, accident, or, abnormal operating conditions, repairs will be billed at the normal shop
rate. In such cases, an estimate will be submitting before work is started, if requested by the
customer.
Attempts to deliberately deface, mutilate, or remove the product's label will render this
warranty void. Any MPA1 returned from the European Union for warranty repair must have the
required RoHS logo on the product label; otherwise, repairs will be billed at the normal shop
rate. Benchmark will not honor warranties for any products disingenuously purchased on the
US or Canadian markets for sale outside the US or Canada.
The foregoing warranty is in lieu of all other warranties, expressed or implied, including but not
limited to any implied warranty of merchantability, fitness or adequacy for any particular
purpose or use. Benchmark Media Systems, Inc. shall not be liable for any special, incidental,
or consequential damages, and reserves the right to charge this information without notice.
This limited warranty gives the consumer-owner specific legal rights, and there may also be
other rights that vary form state to state.
Notes on Warranty Repairs
An RMA (return merchandise authorization) number, issued by our Customer Service
Department, is required when sending products for repair.
They must be shipped to Benchmark Media Systems prepaid and preferably in their original
shipping carton with the RMA number clearly visible on the exterior of the packaging. A letter
should be included giving full details of the difficulty.
MPA1 Instruction Manual Page 28
Page 29
Benchmark Extended Warranty
The Benchmark Extended 5* Year Warranty
Benchmark Media Systems, Inc. optionally extends the standard one (1) year warranty to a
period of five (5)* years from the date of delivery.
*For the extended warranty to become effective, the original purchaser must register the
product at the time of purchase either by way of the prepaid registration card or through the
product registration section of the Benchmark Media Systems, Inc. website. This optional
warranty applies only to products purchased within the US and Canada and is extended only to
the original purchaser.
Attempts to deliberately deface, mutilate, or remove the product's label will render this
warranty void. Benchmark will not honor warranties for any products disingenuously purchased
on the US or Canadian markets for export. The terms of the extended warranty are subject to
change without notice. For products purchased outside the US and Canada, please refer to the
Extended Two (2)** Year International Warranty.
The Benchmark’s Extended 2** Year International Warranty
Benchmark Media Systems, Inc. optionally extends the standard one (1) year warranty to a
period of two (2)** years from the date of delivery.
**For the extended warranty to become effective, the original purchaser must register the
product at the time of purchase either by way of the prepaid registration card or through the
product registration section of the Benchmark Media Systems, Inc. website. This optional
warranty applies only to products purchased outside the US and Canada and is extended only
to the original purchaser.
Attempts to deliberately deface, mutilate, or remove the product's label will render this
warranty void. Benchmark will not honor warranties for any products disingenuously purchased
on the US or Canadian markets for export. The terms of the extended warranty are subject to
change without notice. For products purchased in within the US and Canada, please refer to the
Extended Five (5)* Year Warranty.
MPA1 Instruction Manual Page 29
Page 30
Calibration
CAUTION: ROUTINE CALIBRATION
SHOULD NOT BE REQUIRED. THE
FOLLOWING PROCEDURE SHOULD ONLY
BE USED BY A QUALIFIED TECHNICIAN.
This procedure will restore the MPA1 to
factory calibration if controls have been
moved from factory settings.
+48V Adjustment
1. Using a DC voltmeter, measure the
voltage across D23 and adjust “+48V
Adjust” (R107) until the meter reads
48V.
Copyright © 2008 Benchmark Media
Systems, Inc.
All rights reserved.
Benchmark Media Systems, Inc.
203 Hampton Place, Ste. 2
Syracuse, NY 13206
USA
+1-315-437-6300, FAX +1-315-437-8119
www.benchmarkmedia.com
MPA1 Instruction Manual Page 30
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