Page 8
MJ Acoustics Pro 50Mk2 User’s Manual
SPECIFICATIONS
120watt rms, DC-coupled MOSFET Amplifier * Speaker and line level inputs
with Gain Control Range 80dB * Neutrik Speakon connectors (Gas Tight)
(High level 100k ohm) * Unbalanced RCA (phono) connector (Gold Plated)
(Low level 10k ohm) * Twin Sophisticated crossover circuits - variable
increments between 20Hz and 120Hz with LFE By-pass @ 200Hz * Phase
Control infinitely adjustable between 0º and 180º * Frequency response 13hz
to 200hz * I.S.P. (Intelligent Speaker Protection) * Specially designed cabinet
structure, volume, and configuration made from inert 18mm MDF * Power
LED and switched fused IEC mains input socket * 250mm (10”) Ultra Long-
throw Driver with heavy duty chassis and double magnet * 1 year
manufacturers return to base warranty * Dimensions (WxHxD) 278mm X
332mm X 278mm * Weight 11.50kg (25.3 lbs) * Black Satin finish as
standard.
Specifications subject to change without notice. All rights reserved. E & O E.
Owner’s Name:…………………………………………...……………………………
Address:………………………………………………………………………………..
………………………………………………………………………………………….
………………………………………………………………………………………….
Date of purchase:…………………………….Serial number:…………………………
MJ ACOUSTICS warrants to the original purchaser only, that this product is free from defects in material and
workmanship under normal use within one year from date of purchase, in the United Kingdom only, extended to 2 years
provided registration is submitted to M J Acoustics within 28 days from date of purchase. All parts, except the external
cabinet finish are warranted as stated from date of purchase. Under this warranty M J Acoustics agrees to repair any
defect or at the company’s discretion, replace the faulty component(s) without charge for parts and labour provided the
unit is returned carriage paid both ways. Defective parts will be replaced if in the sole judgement of MJ ACOUSTICS
they be deemed defective over and above that considered to be normal wear and tear.
This warranty does not apply to equipment showing abuse, misuse, neglect or damage or to parts that in the judgement of
MJ ACOUSTICS are not defective or have been used for purposes outside the scope of its design , nor does it extend to
any equipment which may have been tampered with, altered or repaired outside an authorised MJ ACOUSTICS service
station, and on which the serial number has been defaced, modified or removed. This warranty is in lieu of any other
warranty expressed or implied and there is no other warranty or warranties valid for your purchase. No one is authorised
to assume any liability on behalf of MJ ACOUSTICS or impose any obligation on it in connection with the sale of any
equipment other than as stated in this warranty and outlined above.
MJ ACOUSTICS’s liability, for any defective product, is limited to repair or replacement of the product, at our sole
option. MJ ACOUSTICS shall not be liable or responsible, under any circumstances, for such indirect or consequential
damages as from interrupted operations or other causes howsoever related. Additionally the Pro 50 is not intended for
use in a commercial environment and the warranty applies for domestic use only.
If your unit requires service it should be sent to MJ ACOUSTICS service department, any shipping charges are the
responsibility of the owner, this includes return shipping charges. SERVICE DEPARTMENT:- MJ Acoustics, Service
Department, 9 Venture Court, Boleness Road, WISBECH, Cambridgeshire. PE13 2XQ
WARRANTY
10/10/2006 (Pro – 50Mk2)
Page 1
User’s Manual
Model
PRO 50Mk2
Table of Contents
Safety Instructions ………………….. page 2
Precautions ………………….. page 3
Introduction ………………….. page 3 & 4
Controls ………………….. page 4 & 5
Features ………………….. page 5 & 6
Connectivity ………………….. page 6
Panel Layout ………………….. page 7
Set-up Hints & Tips ………………….. page 7
Specifications ……………..…… page 8
Warranty ………………….. page 8
Natural Bass Impact Unparalleled in the Entertainment Environment
10/10/2006 (Pro – 50Mk2)
Sub
Professional
Woofer
for Home Cinema, Audiophile Specialists & Studios
Page 2
"WARNING"
“TO REDUCE THE RISK OF FIRE OR ELECTRIC
SHOCK, DO NOT EXPOSE THIS APPLIANCE TO RAIN
OR MOISTURE.”
SAFETY INSTRUCTIONS
1. Read Instructions - All the safety and operating instructions
should be read before the appliance is operated.
2. Retain Instructions - The safety and operating instructions
should be retained for future reference.
3. Heed Warnings - All warnings on the appliance and in the
operating instructions should be adhered to.
4. Follow Instructions - All operating and use instructions
should be followed.
5. Water and Moisture - The appliance should not be used
near water - for example, near a wet basement, or near a
swimming pool, and the like.
6. Carts and Stands - The appliance should be used only with
a flight case or stand that is recommended by the
manufacturer.
7. Wall or Ceiling Mounting - The appliance should be
mounted to a wall or ceiling only as recommended by the
manufacturer.
8. Ventilation - The appliance should be situated so that its
location or position does not interfere with its proper
ventilation. For example, the appliance should not be
situated such that may block the ventilation openings: or,
placed in a built-in installation, such as a bookcase or
cabinet that may impede the flow of air over the amplifier
panel.
CAUTION:
TO PREVENT ELECTRIC SHOCK, MATCH WIDE BLADE
OF PLUG TO WIDE SLOT. FULLY INSERT.
ATTENTION:
POUR EVITER LES CHOCS ELECTRIQUES,
INTRODUIRE LA LAME LA PLUS LARGE DE LA FICHE
DANS LA BORNE CORRESPONDANTE DE LA PRISE ET
POUSSER JUSQU AU FOND.
9. Heat - The appliance should be situated away from heat
sources such as radiators, heat registers, or other
appliances that produce heat.
10. Power Sources - The appliance should be connected to a
power supply only of the type described in the operating
instructions or as marked on the appliance.
11. Grounding or polarization - Precautions should be taken
so that the grounding or polarization means of an
appliance is not defeated.
12. Power Cord Protection - Power supply cords should be
routed so that they are not likely to be walked on or
pinched by items placed upon or against them, paying
particular attention to cords and plugs, convenience .
receptacles, and the point where they exit from the
appliance.
13. Cleaning - The appliance should be cleaned only as
recommended by the manufacturer.
14. Nonuse Periods - The power cord of the appliance should
be unplugged from the outlet when left unused for a long
period of time.
15. Object and Liquid Entry - Care should be taken so that
objects do not fall and liquids are not spilled onto the
enclosure paying particular attention to the amplifier
panel.
16. Damage Requiring Service - The appliance should be
serviced by qualified service personnel when:
A. The power supply cord or the plug has been damaged;
or
B. Objects have fallen, or liquid has been spilled onto the
appliance;
or
C. The appliance has been exposed to rain;
or
D. The appliance does not appear to operate normally or
exhibits a marked change in performance;
or
E. The appliance has been dropped, or the enclosure
damaged.
17. Servicing - The user should not attempt to service the
appliance. All servicing should be referred to qualified
service personnel.
CAUTION
RISK OF ELECTRIC SHOCK
DO NOT OPEN
Caution: To Reduce Risk of Electric Shock,
Do Not Remove Amplifier.
No User Serviceable Parts Inside.
Refer Servicing to Qualified Personnel.
The lightning flash with arrowhead symbol within an
equilateral triangle is intended to alert the user to the presence
of uninsulated “dangerous voltage” within the product’s
enclosure that may be of sufficient magnitude to constitute a
risk of electric shock to persons.
The exclamation point within an equilateral triangle is
intended to alert the user to the presence of important
operating and maintenance (servicing) instructions in the
literature accompanying the appliance.
MJ Acoustics Pro 50Mk2 User’s Manual
10/10/2006 (Pro – 50Mk2)
Page 7
MJ Acoustics Pro 50Mk2 User’s Manual
I.S.P. (Intelligent Speaker Protection)
This circuit monitors the output and the
input of the amplifier. As the output
reaches close to the limit of the power
supply rails the input is instantly reduced
to prevent the amplifier from clipping.
The dynamic range of the amplifier is not
compromised as the circuit has been set to
activate at a point beyond the full
dynamic range before protection is
activated.
Connect your subwoofer to your audio system using the low level phono interconnect supplied or
the optional high level lead. Please refer to the instructions that came with the high level lead for
this connection. Please ensure:
All controls are set to minimum gain, 0° phase, and 20hz frequency contour
on first power-up.
For downward firing subwoofer speakers the phase control should be set to 0°. Remember that
these are just starting points and it is suggested that you experiment with this setting over a
period of time to determine the best position of the phase control relative to your subwoofer
placement and the natural acoustics of the room.
After powering up the sub, audition a piece of music you are familiar with and set the main audio
system volume to your normal listening level. Slowly increase the gain control on your Pro 50Mk2
to approx one quarter to half its travel (12 o’clock position). You should now be experiencing
sub-bass in your overall mix. How much bass output is determined by the position of the gain
control.
Now adjust the frequency contour until you hear the subwoofer output the bandwidth of bass
frequencies your main speakers lack. For example, most main speakers roll off the bass output
at around 40hz – 80hz so this is where the subwoofer should take over. For AV/LFE signals set
the Rolloff to 90Hz as the LFE channel is already filtered within the AV processor to output
frequencies from 80Hz and below.
SET-UP HINTS & TIPS
10/10/2006 (Pro – 50Mk2)
Page 6
Features
Using a die-pressed steel chassis of significant proportions creates the rigidity that is so
important in sub-bass speaker designs. Any distortion of the chassis under extreme load will
detract from the goal of pure sound wave formation. As we all know the creation of sound waves
comes directly from the movement of the cone surface through the air. The longer the movement
of the cone, termed as its excursion, the more air it moves and up goes the sound pressure level.
We like to think of our 10” driver as the best of all worlds. It has agility, rigidity and decelerative
damping to enable the cone to move with lightning speed back and forth through the air. The
heavy duty cone surround together with the semi-rigid lower damping apron serve to bring the
cone to an almost instantaneous return to its resting place between transients. The weight of this
unit says it all when referring to construction rigidity. It weighs 7Kg representing over half the
total of 11.5Kg. Truly, the muscle of the system and the working end of this bass producer.
Speaker
MJ Acoustics Pro 50Mk2 User’s Manual
Connectivity
You can connect an unbalanced RCA input direct from a mixing desk
or line level pre-amplifier with or without a sub output . Either mono or
stereo input detail may be used. When connecting from an A/V
amplifier use the subwoofer LFE output.
For connection directly to the parallel output from the speakers of the
main audio system in order for the filter circuit to extract the
information required to output the required bass frequencies. The
maximum amplifier that can be connected is 250watts and only when
connected in parallel with speakers designed to handle this power.
Do not connect direct to an amplifier unless in parallel with a speaker.
Damage may well occur if you do, to the input circuit of the filter stage.
The LED on the rear panel shows that the unit is powered and the
amplifier is ready for use. Please note that the LED will remain lit for a
short while following switch-off whilst the power is dissipated from the
internal power supply. It is always good practice to remember to turn all
input gain controls down when powering down The unit’s fuse is located
below the mains input connector. The fuse should only be replaced,
when required, with one of the same type and rating as installed. (2
amps).
10/10/2006 (Pro – 50Mk2)
NOTE. An Optional interface box is required if you connect to a Digital or BTL (Bridge Tied
Load) power amplifier stage at the same time as using the RCA input for LFE. The High level
input will not work correctly and may cause your Digital or BTL Power Amplifier to enter
protection mode if this interface box is not used
Page 3
Location
Avoid using the “Pro 50Mk2” in the following locations:
* Locations of extreme low or high temperatures, or extreme changes in temperature.
* Sources of heat such as near commercial heaters, fires or other sources of heat.
* Unstable locations or where the unit can fall due to vibration.
* Locations with excessive moisture or dust.
* Locations where electrical voltage varies.
Power Supply
* When unplugging the AC adaptor from the outlet, be sure to grasp the adaptor. Attempting to unplug it by pulling on
the AC cable may damage the wiring or the mains socket on the amplifier.
* Always power-down amplifier and switch off before making any connections.
* It is dangerous to use any power cable that is cut or frayed. If the power cable is damaged, stop using it
immediately, and have it repaired.
* Do not plug in or unplug the AC adaptor with wet hands. Doing so may result in dangerous electric shock.
* Do not remove the amplifier or touch any parts inside. Doing so may result in a dangerous electric shock, and could
damage the delicate electronic circuits. The voltages inside the amplifier are very dangerous.
* Do not let water or other liquids, flammable materials, or metal objects such as pins get inside any of the input
sockets. These things can cause an electrical shock or short circuit the amplifier, and damage it. If the amplifier
should become wet, unplug the AC adaptor from the AC outlet at the wall first, and contact the manufacturers
directly. There are NO user serviceable parts inside.
Precautions
Thank you very much and congratulations on choosing the MJ Acoustics Pro-50Mk2 Active Sub-
Bass System - a compact active lower octave loudspeaker, designed for stereo and multi-
channel use to provide you with outstanding performance. The use of a Subwoofer is essential
to provide a proper balanced spectrum of sound .
Please take a few moments to read this manual. The advice offered will enable you to get
the very best performance from your Pro 50Mk2 subwoofer.
The Pro 50Mk2 features a critically shaped paper pulp cone bass driver providing transparent
and dynamic bass registers. The Pro 50Mk2 has been specifically designed for use with stereo
and in multi-channel (AV) systems but can also be used on main front, rear and centre channels.
Using our specially designed enclosure, dedicated amplifier and active crossover filter system
you have purchased a musically accurate Active Sub-Bass System. By adding the Pro 50Mk2
powered sub-bass system to your audio equipment you will have the benefits of a transparent
and fully dynamic sound stage.
Introduction
MJ Acoustics Pro 50Mk2 User’s Manual
10/10/2006 (Pro – 50Mk2)
Page 4
The Low Level Gain Control enables you to adjust the amount of gain and thus
output, the unit produces in relation to the input from the Gold plated RCA (phono)
connectors.
NOTE. The amplifier has an available gain level of 80dB and it is therefore quite easy to over drive the
speaker. An over driven speaker will emit a loud cracking noise. This occurs when the voice cone of the driver
is forced hard against the top plate of the magnet. The ability of the system to exhibit this is a design feature and
a by-product of catering for lower input levels which require additional gain. When cracking occurs the gain
should be reduced. Constantly overdriving the system will result in a damaged driver and will invalidate your
warranty.
The High Level Gain Control enables you to adjust the amount of gain and thus
output, the unit produces in relation to the input from the Neutrik Speakon connector.
NOTE. An Optional interface box is required if you connect to a Digital or BTL (Bridge Tied Load) power
amplifier stage. The High level input will not work correctly and may cause your Digital or BTL Power Amplifier to
enter protection mode if this interface box is not used.
Controls
MJ Acoustics Pro 50Mk2 User’s Manual
The “Pro-50Mk2” has Twin sophisticated crossover circuits, setting the upper
response limit in musically accurate variable increments between 20hz to 120hz and
20Hz to 200Hz. A "straight-through" LFE bypass facility is activated at one end of the
LFE input controls travel which allows the input signal to bypass the filter circuit with
a roll off limit set to 200Hz. The LFE bypass is used where an already filtered signal
is offered to the low level input sockets. An example of this would be a sub output
from a dedicated control pre-amplifier such as found in a Home Cinema system.
These twin crossovers can be used at the same time and enable connection of AV
and audiophile equipment for the best possible integration
Connect the Sub to the amplifier
Either using the Low Level Input (Phono)
or the High Level Input (Neutrik Speakon) available as
an optional extra.
Please Note:
The Neutrik Speakon lead (used for High Level
Input) referred to is NOT included The connection
of the High Level input is detailed in the separate
Instructions with the lead. Please read carefully and
make sure all Connections are correct
SEE NOTE BELOW!
CAUTION!
When using the Neutrik Speakon cable, connect the Red wire to the
positive terminal of the Left Main Speaker and the Yellow
wire to the positive terminal of the Right Main Speaker.
The Black wire is connected to either one of the negative
Terminals of the Left or Right Main Speakers.
DO NOT CONNECT BLACK WIRE TO BOTH TERMINALS!
10/10/2006 (Pro – 50Mk2)
Page 5
Controls
MJ Acoustics Pro 50Mk2 User’s Manual
Features
Resulting from years of development, the 120W DC-coupled MOSFET amplifier provides the
engine to power a perfectly matched 10” ultra long-throw woofer. The power supply has been
designed to provide the required headroom for developing the sub-bass registers. A Double
Insulated Toroidal transformer is fitted which has been designed specifically for this audio
application. The rectifier used is a bridge configuration utilising high quality fast recovery diodes;
an example of how over engineered this amplifier is, and substantiates why, when deep
transients are required, the amplifier has enormous reserves of power to accommodate with
consummate ease even the deepest of explosions. To aid this the capacitors used are the large
bucket type with a high ripple current and selected because of their high temperature and
minimal loss characteristics. The transistors used are the Metal Oxide Semiconductor Field Effect
Transistor (MOSFET) type lateral and specifically designed for audio applications.
Amplifier
The “Pro-50Mk2” has Twin sophisticated crossover circuits, setting the upper response limit in
musically accurate variable increments between 20hz to 120hz and 20Hz to 200Hz.
There are separate gain controls for high and low level inputs, a "straight-through" LFE bypass
and an audibly transparent, "Intelligent Speaker Protection" (I.S.P.) circuit which monitors the
output stages for clipping and limits the cone movement if the amplifier is being over-driven.
Professional Neutrik Speakon connector is standard for the “Pro-50Mk2’s” stereo high level
input. An approved touch proof design to cater for potentially high voltages that can be connected
to it complete the high level input socketry. The “Pro-50Mk2” also offers an un-balanced low-level
RCA input for use with professional mixing desks and suitably equipped domestic systems.
Additionally this connector is gold plated for longevity and minimal resistance between
interconnect and socket. The amplifier panel is constructed from high grade 3mm thick
aluminium sheet which acts as a Heat-sink. The MOSFET transistors are bolted to the 3mm
aluminium face plate. This combination enables the amplifier, even under continuous high loads
to run amazingly cool during operation for its power output.
Crossover
The “Pro-50Mk2” has a sophisticated network of filter circuits which
includes an adjustable phase control. Setting the phase in musically
accurate variable increments between 0º and 180º. This control is used to
enable the accurate and musical integration of the unit when placed in a
system. By adjusting this control almost infinite placement combinations
can become possible. Most people will not experience phasing. The
effects of which are only apparent to the ear if your main speakers produce the same frequency
note at the same volume level as the subwoofer. For example, if your main speakers produce a
note of 40hz at an equivalent volume level to the subwoofer, also producing 40hz, and the phase
of each is out by 180° then they cancel each other out resulting in a reduction of bass at this
frequency. To remedy this you adjust the phase control on the subwoofer to bring them both into
phase. As a rule of thumb downward, firing subwoofers have a natural 90° out of phase angle
when compared to forward firing main speakers and forward firing subwoofers do not.
10/10/2006 (Pro – 50Mk2)
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