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DOUBLE FOUR PLUS (BG-80)
COMBO AMPLIFIER
OWNER'S MANUAL
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Thank you for purchasing the PJB DOUBLE FOUR PLUS BG-80. 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 FOUR PLUS please read ALL the instructions carefully.
Upon receiving the product, inspect it for any signs of physical damage that may have
occurred during shipping. If you notice any damage, please contact your retailer
immediately.
Ensure that the amplifier is not installed in a confined or built-in space, such as a bookcase.
The amplifier should be kept in an open area with good ventilation, and the ventilation
openings should never be obstructed by items such as newspapers, tablecloths, or
curtains.
Warning: To avoid any potential hazards, use only attachments and accessories specified
or provided by the manufacturer.
Warning: To prevent the risk of fire or electric shock, keep the amplifier away from rain or
moisture. The amplifier should not be exposed to dripping or splashing liquids, and no
objects filled with liquids should be placed on top of it.
When the amplifier is not in use or during transportation, take care of the power cord by
tying it up with a cable tie. The power cord should be free from sharp edges that may
cause abrasion. Before using it again, check that the power cord is not damaged. If any
damage is found, replace it with a cord specified by the manufacturer or with the same
specifications as the original one.
The marking "Correct Disposal of this product" indicates that this product should not
be disposed of with other household waste throughout the EU. To prevent possible
harm to the environment or human health from uncontrolled waste disposal, it should be
recycled 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 environmentally safe
recycling.
Warning: The apparatus with CLASS I construction shall be connected to a MAINS
socket outlet with a protective earthing connection.
OVERVIEW OF THE DOUBLE FOUR PLUS
The DOUBLE FOUR PLUS is a single channel bass amplifier that has an auxiliary input for
iPad/iPod, smart phone or drum machine. It features 3 band EQ that is perfectly tailored for
bass guitar, a stereo headphone out jack and a line out for recording, it can also play music
with the Bluetooth(V5.1 with Qualcomm® aptX™ HD) function. It is ideal for all kinds of basses,
and can handle the open B string on a 5-string bass with ease.
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The Enclosure
It is well known that big speakers are capable of reproducing true fundamental bass
frequencies. But as you decrease the physical size of a speaker, the bass response will fade
away. This is the reason why Violins are small and Double Basses are big!
So how do you get a 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 which is just 4 inches across. Built with Swiss watch precision, it can cope with
the extreme signals from an amplified bass guitar. Using our extensive R&D facilities which
include 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 cone behavior at all frequencies in 3D representation, cone
suspension and frame, etc. until we 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 the total 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 frequency 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 “long-throw” 4-inch speakers have a 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.
The cabinet may be as small as a shoe box, but it is built to the same high quality as all PJB
cabinets, What you hear from the DOUBLE FOUR PLUS is the closest to the original sound of
the instrument.
The sound is huge for its size and it is unbelievable that all the sound from your bass is just
coming out of such a tiny jewel.
AMPLIFIER FEATURES
Digital Amplifier with 90Watts (2x45W) 1% THD
Switchable high gain input OR low gain stage with mute function
Independent level control and mute function to both Aux and Bluetooth input
One stereo input for Drum machines or iPod/Smartphone players
3-Band EQ
Line Output for recording or driving another amplifier
Bluetooth 5.1 with Qualcomm® aptX™ HD codec
Use under any AC voltage worldwide. (90~240V)
DC input (USB Type-C port) connection supports Portable charger of USB PD (Power
Delivery) Protocol.
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PANEL OVERVIEW
1. Auxiliary Input Jack (3.5mm stereo)
This is a stereo mini jack that can receive any signal from iPod, iPad, smart phones or drum
machines.
2. Auxiliary Input Level
Rotate: increase or decrease the AUX input level.
Press: mute/unmute AUX input.
3. Auxiliary Mode Indicator
Orange light steady lit: AUX input is mute.
Light off: normal playing state.
4. Bluetooth Input Level
Rotate: increase or decrease the Bluetooth input level.
Press: mute/unmute Bluetooth input.
Press and hold: disconnect Bluetooth
5. Bluetooth Mode Indicator
Blue light flashes: wait for pairing.
Blue light steady lit: connected.
Orange light steady lit: Bluetooth input is mute.
6. Instrument Input Jack
This is a high-impedance input and is designed for all passive and active instruments.
7. Mute/ Active/ Passive selector switch
Mute: mute the input stage; when switched on, the clip LED will light up in green.
Low: lower sensitivity input setting for guitars with onboard electronics.
High: higher sensitivity and high impedance input for passive guitars.
8. Clip Light
When the power amplifier is overloaded and causes distortion, the clip light will light up in
red. When the amplifier is muted, the LED will light up in yellow.
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9. Level Input Control
The signal size of the input level will be affected by different instruments, players and
playing styles. And the input level can be adjusted to avoid the overload indicator from
lighting up during the vigorous playing. 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.
10. Bass EQ Control
Boosting or cutting this will have a significant effect on the tone.
11. Mid EQ Control
Boosting or cutting mid-range.
12. High EQ Control
Boosting or cutting treble.
13. Master Volume Control
This controls the volume of Speakers and Headphone output.
14. Headphone Jack
You can use all kinds of stereo headphones through this jack but you will only hear good
sound if your headphones are high-quality.
15. Line Out Control
Adjust the output signal for Line Out.
16. Line Out
It can be used for driving a second amplifier or loudspeaker.
17. Power Switch
Blue light steady lit: power on.
Note: 1. For Safety, we advise you to unplug the power supply from the AC power if you do
not intend to use the DOUBLE FOUR PLUS for long periods.
2. Before switching on the product, set the VOLUME, LEVEL, LINE OUT VOL. to the
minimum.
18. Power Indicator
Blue light flashes: although it is connected successfully to a PD protocol, the power is not
turned on.
Blue light steady lit: it is successfully connected to an AC power and power is turned on.
NOTE: When power is on, the indicator will light up. With no incoming signal, the standby
mode will activate after 30 minutes, the power indicator LED will light up red. With a signal
coming in from the INPUT, over BT or from the AUX connection, or with long pressing the
AUX LEVEL/BT LEVEL button, the amplifier will restart in about 2 seconds.
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19. Type-C Port
DC input (USB Type-C port) connection supports Portable charger of USB PD (Power
Delivery) Protocol.
1. This port is only used for power input but not for power supply.
2. Supports USB PD Protocol (20V/3A and above).
3. After it is successfully connected to a PD Portable charger, the power indicator will flash
during the shutdown. The product is ready for use.
4. When the power of the Portable charger is lower than 10%, it may cause the sound to cut
off or be intermitted.
5. The maximum power output of the power source and speakers:
DC 20V/3A/Speaker: 2x25W Max.
DC 20V/5A/Speaker: 2x40W Max.
6. The discharge time when using the power bank via Type-C (for reference):
About 8 hours continue working with a 20000mAh power bank output 20V/3A.
About 5 hours continue working with a 20000mAh power bank output 20V/5A.
20. AC Input Socket
Connect to your AC power. (90~240V)
Connect to a grounded outlet in accordance with the input power voltage and frequency
specified below the power inlet.
OPERATION & POSITIONING
TURN THE VOLUME DOWN on the DOUBLE FOUR PLUS before plugging in your instrument.
You may notice the clip light blinks once on turn on. This is normal and the amplifier is
operating correctly. It is just a character of the circuit.
Positioning the DOUBLE FOUR PLUS for best Sound
Generally, playing in different venues will cause your bass to sound differently. 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.
Below is an indication of what 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 away
from the wall, the open A string may sound weak.
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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 that particular note to
cancel out.
The position where the DOUBLE FOUR PLUS is placed will ultimately affect your low- frequency
limit. For best results, place the DOUBLE FOUR PLUS on the floor. Placing it on objects off the
floor will cause it to sound thin and lack bass punch.
Placing the DOUBLE FOUR PLUS next to a wall will reinforce the lower notes. Placing it in a
room corner will further enhance the low notes.
Room size makes a big difference in how deep the bass will sound. The further the distance to
the listener the weaker 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 PLUS
It is important to understand this is a quite different amplifier from the conventional analog
amp. The controls transmit information to two internal microcomputers: one for the pre-amp
and the other for the power amp.
This information is processed as EQ changes or level changes, so it takes a short time for the
computers to act on changes to EQ and volume controls. This is known as latency and if you
change control while playing simultaneously, you will notice a low delay as the changes are
processed. It is simply the character of the processor and not the fault of the unit.
All amplifiers will be affected by the room they are in and 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, Floors and Ceilings work like a mirror
to the amplifier because the sound wave is reflected 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 choose the best placement for the optimal sound.
Speakers are a bit like shoes, new ones are never as comfortable as old ones and in time
speakers will "soften" up. The sound will become warmer and fuller in time and it’s required to
play for a break-in period to get the amp to perform its best. This can also be done just by
playing music through the AUX input instead of playing.
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TRANSPORTING AND STORING THE DOUBLE FOUR PLUS
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.
Storing:
Keep in a dry location preferably at room temperature in the gig bag.
Do not store in temperatures below -4 F (-20 C) or above 104 F (40 C).
Do not allow it to get wet. If this occurs, never turn it on in this condition.
Do not leave the DOUBLE FOUR PLUS permanently connected to a power source.
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SPECIFICATIONS
Amplifier
Amplifier Type: Full Digital with DSP
Power Output: 90 Watts(2x45W) 1% THD
Signal to Noise Ratio: ≥85dB(A) (EQ off, Volume on Full)
Impedance
Input: ≥270KΩ / 22pF
Speaker
2xPJB 4-inch Full Range Speaker
1x Rectangular Auxiliary Low Frequency Radiator.
Usable Frequency Response: 40Hz to 17KHz
Levels
High Input: 120mV-2 V
Low Input: 400mV-3V
Aux Input: 200mV (MAX)
Bluetooth Input: 300mFFS
EQ Center Frequencies
Bass Shelf 100Hz, +/- 15dB
Mid 1KHz Bandwidth 120Hz-10KHz, +/- 15dB
Treble Shelf 10KHz, +/- 15dB
Included Parts
6 ft AC Power Cord, 5.5 ft Audio Cord.
Dimensions (W×H×D): 13×8×8.5 inch (329×203×215 mm)
Weight: 11.3 lbs / 5.1kg
PHIL JONES BASS
American Acoustic Development LLC
8509 Mid County Industrial Dr.
St Louis, MO 63114 USA
WWW.PJBWORLD.COM
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