MJ Acoustics PRO 50Mk2 User manual

Brand: MJ Acoustics

Model: PRO 50Mk2

Category: Musical Equipment

Type: User manual

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.

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;

B. Objects have fallen, or liquid has been spilled onto the

appliance;

C. The appliance has been exposed to rain;

D. The appliance does not appear to operate normally or

exhibits a marked change in performance;

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)

MJ Acoustics PRO 50Mk2 User manual

Brand: MJ Acoustics

Model: PRO 50Mk2

Category: Musical Equipment

Type: User manual

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