Phil Jones Bass BG-75 User manual

PJB DOUBLE FOUR
BG-75
OWNER’S MANUAL
Thank you for purchasing the PJB Double 4 BG-75. A great deal of dedication and passion went into
designing and building this no-compromise, high performance combo amplifier. It was conceived to
be a dedicated amplifier for the “connoisseur” bassist. Reading and following this manual will
enable you to get the best performance from the amp and ensure its longevity.
READ THIS FIRST
 Before using the Double 4, please read ALL the instructions.

 On receipt of product, check for any signs of physical damage arising from shipping. If any
damage is visible, contact your retailer.
 Do not install this equipment in a confined or building-in space such as a bookcase or similar
unit. The amp should remain in well ventilation conditions at an open site. The ventilation
should not be impeded by covering the ventilation openings with items such as newspaper,
table-cloths, curtains, etc.
 WARNING: Only use attachments/accessories specified or provided by the manufacturer.
 WARNING: To reduce the risk of fire or electric shock, do not expose the amp to rain or
moisture. The amp shall not be exposed to dripping or splashing. Objects filled with liquids
such as a coffee cup shall not be placed on top of the amp.
 When not in use and during movement, please take care of the power cord, e.g. tie up the
power cord with cable tie. It shall be free from sharp edges which can cause abrasion of the
power cord. When put into use again, please make sure the power cord being not damaged.
If any damages found, please replace it with one specified by the manufacturer or with the
same specifications as the original one.
 Correct Disposal of this product. This marking indicates that this product should not be
disposed with other household wastes throughout the EU. To prevent possible harm to the
environment or human health from uncontrolled waste disposal, recycle it responsibly to
promote the sustainable reuse of material resources. To return your used device, please use
the return and collection systems or contact the retailer where the product was purchased.
They can take this product for environmental safe recycling.
OVERVIEW OF THE DOUBLE FOUR
With the great success of the PJB Bass Cub, we had many requests to make a truly affordable bass practice amp.
The chellange: it had to be incredibly small and yet still deliver the great PJB bass sound. We realized we could not
achieve this goal by using existing parts. So, our jorney started again with the combination of new driver design,
cabinet acoustic loading and the latest digital amplifier technology.
The DOUBLE FOUR is a single channel bass amplifier that has an auxiliary input for ipad/ipod, mp3 or drum
machine. It features 3 band EQ that is perfectly tailored for bass guitar, headphone out jack and a line out for
recording. It is ideal for all kinds of basses, and can handle the open B string on a 5 string bass with ease.
The Enclosure
It is well known that big speakers are capable of reproducing true bass fundamental frequencies but as you
decrease the physical size of a speaker, the bass response will fade away. This is the reason Violins are small and
Double Basses are big!
So how do you get big bass sound from a small speaker cabinet? With our know how of using smaller drivers to
get the ultimate bass sound, we applied our vast experience to an even smaller driver just 4 inches across. It is
built with Swiss watch precision; it has to cope with the extreme signals coming in from an amplified bass guitar.
Using our extensive R&D facility which includes the largest anechoic chamber in the bass guitar amplifier industry
and the KLIPPEL transducer measurement system (it uses lasers!), we were able to develop the perfect 4 inch
loudspeaker. We analyzed the neodymium magnetic system, the cone behavior at all frequencies in 3D
representation, cone suspension and frame, etc., until we had achieved a transducer beyond what anyone would
have ever thought possible. Then we looked at the acoustic loading using the acoustic simulation software and
calculated exactly the full power cone displacement at every frequency.
We designed a custom Rectangular Auxiliary Low Frequency Radiator (RALFR®). That is a pneumatically coupled
radiator loaded to the rear of the two 4 inch speakers that operates at the lowest bass frequencies only. It

augments the output of the loudspeakers at frequencies from 30 to 150 Hz. It also reduces the cone excursion of
the speakers, allowing greater power handling.
The proprietary PJB NeoPower 4-inch speakers have full frequency range to the highest audio frequencies. Not
only does this give greater clarity and transparency to your instrument, but also a high fidelity sound to any
backing track fed into the auxiliary input.
Each speaker is fed with its own Pulse Width Modulation PWM amplifier. PWM amplifiers are extremely efficient
compared to more traditional analog solid state amplifiers converting more electrical energy to power the
speakers instead of getting hot. Heat in electrical circuits is the enemy to reliability and since the amp is running at
lower working temperature, the DOUBLE FOUR will give years of service long after other amps have faded away.
By using dual amplifiers one to each speaker, the bass control is greatly improved since the damping factor is
doubled. Damping factor is the amplifiers ability to put on the “brakes”, stopping the speaker cone from overshoot
and tightening up the bass sound, so the sound is punchy, tight but never muddy or bloomy out of control bass.
The cabinet may be as small as a shoe box, but it is built to the same standards of all PJB cabinets, heavily braced
internally and damped with acoustic damping materials to prevent cabinet coloration that can kill the true sound
of your instrument. What you hear from the DOUBLE FOUR is the closest you can get to how your instrument
actually sounds.
The DOUBLE FOUR may just be a practice amp but it does not mean that it has to sound like a practice amp. The
sound is huge for its size and you may find it hard to believe that all the sound from your bass is just coming out of
such a tiny jewel.
AMPLIFIER FEATURES
 Switchable high gain input OR low gain stage with mute function.
 One stereo input for Drum machine or I-pod/MP3 player.
 3 Band EQ.
 Line Output for recording or driving another amplifier.
 Sophisticated protection circuitry.
 70watt RMS Amplifier.
 Can use on any AC voltage worldwide. (90~240V)
PANEL OVERVIEW
PANEL DESCRIPTION
1. Input Jack
This is a high impedance input and is designed for all passive and active instruments.
2. Clip Light
When the amplifier output is clipping, the LED will light up with red. When the amplifier muted, the
LED will light up with green.
3. Input Switch
High: higher sensitivity, high impedance input. for passive guitars.

Low: lower sensitivity input setting for guitars with onboard electronics.
Mute: mute the input stage, when switch on, the clip LED will light up with green.
4. Input Level Control
Different instruments and also different playing styles and even players will affect the signal level so
adjust this control so that the signal overload Clip light does not light up. This optimizes the best
signal to noise ratio between amp and instrument and will give you the full extent of the amplifiers
tone and power.
5. Bass Control
This is centered on the fundamental frequencies of 4 and 5 string basses. Boosting or cutting this
will have significant effect on the weight of the tone.
6. Mid Range Control
This gives the "voice" of your instrument. Generally you will find that cutting this control instead of
boosting will have more of a truer bass sound. Boosting may be useful for soloing or special effects.
7. Treble Control
This gives the instrument the definition to the sound. Boosting it for "slap" bass or cutting back for
"Reggae" bass sound.
If you boost excessively you may get more noise as hiss and that could be due to the noise coming
from the pre amp in your bass or a poorly shielded instrument cable. PJB has a dedicated bass
instrument cable (Model BI-12) that is totally noise free and actually will improve the tone of your
instrument.
8. Master Volume
This controls the volume of both instrument and auxiliary input.
9. Auxiliary Input Jack
This is a stereo mini jack and can accept any signal from iPod, iPad, computer or drum machine.
10. Auxiliary Input Level
Adjust this to balance you backing track to your bass level.
11. Line output jack
The pre amp in the DOUBLE FOUR is recording studio quality so the line out is a very pure signal for
recording or driving another amplifier.
12. Headphone Jack
You can use any kind of stereo headphones on this jack but remember you will only sound good in
your headphones if they are high quality. Don't try using those cheap ones you get with a phone,
you will be disappointed. We recommend the best you can afford and PJB have designed a high
quality headphone (model HD850) that can handle bass guitar (many can not!) and they sound
great on music too.
13. Power Switch
This switches off the amplifier from the DC supply but AC signal will still be in the external supply.
We advise that you disconnect the power supply from AC source if you do not intend to use the
DOUBLE FOUR for long periods of time.
14. Power Indicator
Will light up when you have DC supply connected and amp switched on.
NOTE: When power is on, the indicator will light up, if no signal come in the standby mode will
active after 30 minutes, power indicator will turn off. When signal come in from INPUT or AUX
socket, the amplifier will restart in about 2 seconds.
15. AC INPUT SOCKET
We recommend that you use the supplied cable or a heavier gauge one.

OPERATION & POSITIONING
TURN THE VOLUME DOWN on the DOUBLE FOUR before plugging in your instrument. You may
notice the clip light blinks once on turn on. This is normal and the amplifier is functioning correctly.
It is just a characteristic of the circuit.
Positioning the DOUBLE FOUR for Best Sound
Often, playing in different venues will cause your bass to sound different. This is partially due to the
acoustics of the hall influencing the low frequency waves that are coming from your speaker. Bass
waves are large and room dimensions heavily influence them when the walls reflect the sound
waves, causing them to collide by adding together or canceling each other out. This causes some
fundamental notes (the ones you feel more than hear) to ring out louder than others and some
notes not to be heard at all.
Here is an indication of where fundamental bass frequencies are, showing open string’s
approximate frequencies and acoustic wavelength:
B string 31Hz 36 feet
E string 41Hz 27 feet
A string 55Hz 20 feet
D string 73Hz 15 feet
G string 98Hz 11 feet
C string 130Hz 9 feet
This may give you some indication of the offending notes (frequencies) that may be booming or
resonating louder or quieter than others. For example if your speakers are five feet from a wall, the
open A string may sound weak. That could be because the path length of the reflected sound off the
wall from your speaker is exactly corresponding to half a wavelength on the open A string causing at
that particular note to cancel out.
Where you position the DOUBLE FOUR will ultimately affect your low frequency limit. For best
results keep the DOUBLE FOUR on the floor. Placing it on objects off the floor will cause it to sound
thin and lack bass punch. Placing the DOUBLE FOUR with the back close to a wall will help reinforce
the lower notes. Placing it in a room corner will further enhance the low notes.
Room size makes a large difference in how deep the bass will sound. The further the distance to the
listener the less the bass will be. This is due to the physics of acoustics not the unit itself.
Unfortunately for bass players, low frequencies are always very difficult to control with room
acoustics. The reproduced wavelengths of the notes you are playing often correspond to the room
dimensions, in which case the reflected sound off the walls interferes with the sound from the
speaker as you get further away from it.
Getting the most from your DOUBLE FOUR
It is important to understand that this is a very different amplifier from conventional analog amp.
The controls send information to two internal micro computers: one for the pre amp and the
second for the power amp. This information is processed as EQ changes or level changes so it takes
a very small amount of time for the computers to act on changes to EQ and volume controls. This is
known as latency and if you change a control while playing simultaneously, you will notice a very
slight delay as the changes are processed. It is simply the characteristic of the processers and not a
fault on the unit.

All amplifiers will be affected by the room they are in and in fact it can make a huge difference to
the sound where you place your amplifier. If you place the amp on a table far from any wall, this will
give you the least bass (low frequency) output. Walls, Floor and Ceiling act like a mirror to the
amplifier because the sound wave is reflected back and it will magnify the sound. So placing the
unit on a floor and close to a room corner will give you the most bass output. You should
experiment to see the best placement for your sound.
Speakers are a bit like shoes, new ones are never as comfortable as worn in older ones and in time
speakers will "soften" up. The sound will be warmer and fuller in time and a break-in period of
playing is required to get the amp to perform its best. This can also be done just by playing music
through the aux input instead of playing.
TRANSPORTING AND STORING THE DOUBLE FOUR
When transporting in a vehicle, it is recommended that you use an external case or heavy-duty
cover to prevent it being damaged by falling over or other objects falling on it.
When Storing:
 Keep in a dry location preferably at room temperature.
 Do not store in temperatures below -20 Degrees C or above 40 Degrees C.
 Do not allow it to get wet. If this occurs, never turn it on in this condition.
 Do not leave the DOUBLE FOUR permanently connected to a power source.
SPECIFICATIONS
Speaker
Rectangular Auxiliary Low Frequency Radiator (RALFR) Enclosure
Speaker Frequency Response: 60 Hz-15 KHz
Speaker Compliment: 2 x 4 inch proprietary, extended-range drivers
Internal Speaker Impedance: 4 Ohms
Weight: 9.3 lbs / 4.2 kg
Dimensions(WxDxH): 8.2 x 8 x 6.8 inch (208 x 203 x 172 mm)
Amplifier
70watt, digital amplifier with DSP. (Digital signal processing)
Signal to Noise Ratio
≥82dB(A) (EQ off, Volume on Full.)
Impedance
High Input: >500 KΩ / 22 pF
Low Input: >30 KΩ / 22 pF
Pre Amp Line Out: < 2 KΩ
Levels
High Input: 30 mV-1 V
Low Input: 50 mV-2.4 V
Pre Amp Out: 1.2 V
Included Parts
6 ft AC Power Cord
SERVICE/WARRANTY INFORMATION
The DOUBLE FOUR carries a 2-year limited warranty on parts and labor.
Products must be purchased from an authorized PJB dealer.
Buyer must complete and return the enclosed warranty card within 15 days of purchase, or register

online by www.pjbworld.com
This warranty covers defect in materials or workmanship that occurs in normal use. Within warranty
period PJB or its local distributor will repair or replace the defect unit free of labor and parts charge.
It is the buyer’s responsibility to use the unit strictly according to instructions written in the owner’s
manual.
This warranty is not transferable; it is provided to original owner only.
Damage/defects caused by the following conditions are not covered by this warranty:
3. Improper handling, neglect or failure to operate the unit in compliance with the instructions
given in user manual;
4. Connection or operation in any way that does not comply with the technical or safely regulations
applicable in the country where the product is used;
5. Repairs or modifications by anyone other than authorized PJB service agent;
6. Damages/defects caused by force majeure or any other condition that is beyond the control of
PJB.
IMPORTANT:
7. In all warranty issues your first line of communication should be to the retailer you purchased
from, even if you have purchased product from an online source.
8. When a local distributor is available, customer who prefers to purchase across country online
maybe required to pay shipping charges to retailer in order to obtain service.
Warranty policies differ in countries outside of USA. Please check with local distributors for warranty
information in your region. Register first with your local distributor if available will give you better and quicker
service when needed.
Further questions, please contact your local distributors, or PJB by email
[e-mail].
PHIL JONES BASS
American Acoustic Development LLC
8509 Mid County Industrial Dr
St Louis, MO 63114
USA
Tel: [phone] (855-BASS-510)
www.pjbworld.com
[e-mail]
For servicing outside USA please contact our distributor in your country.
Information can be found on our website.

PHIL JONES BASS
American Acoustic Development LLC
8509 Mid County Industrial Dr, St Louis,
MO 63114 USA
WWW.PJBWORLD.COM
Printed in China