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fosi audio box x3


Product Specifications

  • Fosi Audio BOX X3 is a mini stereo Bluetooth 5.0 Hi-Fi tube phono preamplifier for MM turntable that features Volume control and Bass/Treble control with DC 12V power supply.
  • The BOX X3 supports MM turntable input, 3.5mm AUX input or Bluetooth input and RCA line output for powered speakers or amplifiers for your home audio system.
  • Compact ultra-low noise phono turntable preamp that converts phono signals to line level signals.
  • The BOX X3 equipping with vacuum tubes stands up to the test and will provide you with serious sound performance.
Input InterfaceMM turntable input, 3.5MM AUX input,
Bluetooth input, 12V DC input
Output InterfaceRCA output
OutputActive(powered) speakers, Amplifier
Product Adapter Input /Voltage RangeAC 100V – 240V
DC Input Voltage12V
Output Voltage Level1kHz and 650mV
Frequency ResponseStandard RIAA
Product Weight0.34kg
Product Dimensions3.97×4.72×1.37 inch (10.09*12*3.5 cm)

Product Overview & Control Functions

Package Contents

Fosi Audio BOX X3 *1

Bluetooth Antenna *1

Vacuum Tube *2

DC 12V Power Adapter *1

User Manual *1

Quick Setup

Step 1: Install the vacuum tubes to the BOX X3.
Step 2: Install the Bluetooth antenna to the BOX X3.
Step 3: • Use RCA cable to connect the RCA line output of BOX X3 to your active(powered) speakers.
            • Or use RCA cable to connect the RCA line output of BOX X3 to your amplifier, then use speaker’s wire                to connect the amplifier with your passive speakers.
Step 4: Connect the power adapter to BOX X3 and the socket. Turn the Multi-function Knob(Volume                 Control/Power Switch) clockwise to power on the BOX X3. The the input mode indicator light (also the power indicator light) of BOX X3 stays red after power is on.
Note 1: The power adapter does not have a power indicator light, so connecting to the socket means power is on.
Note 2: Before connecting the power supply, please make sure that the BOX X3 is in “OFF” position when connecting to the power adapter. Otherwise there is a “POP” click sound from your speakers.
Note 3: Before connecting the power supply, please turn down the volume control, the bass and treble control to 0 (always to the left) to avoid your hearing from damage.
Step 5: Connect the audio source (MM turntable input, 3.5MM AUX input, Bluetooth input ) to the BOX X3.
(1): MM turntable input: Use RCA Cable to connect your MM turntable to the RCA inputs of BOX X3, then connect the ground wire of your MM turntable to the grounding post of BOX X3.

Note: MM Turntable Input can only be connected to the turntable, and cannot be used as a normal preamplifier connected to other audio sources, such as mobile phones, MP3, etc.
(2): 3.5mm Input: Use a 3.5mm Audio cable to connect the BOX X3 and your device.
Note: Once 3.5mm AUX plug in ,the MM input will automatically interrupted, so the input mode will turn to 3.5mm AUX input.
(3): Bluetooth Input: Turn on the Bluetooth on your device, then select “BOX X3” for pairing, the input mode indicator light will stays blue after a successful connection.
Note 1: Once Bluetooth is connected, the MM turntable input and 3.5MM AUX input will be interrupted. If you want to use the RCA input again, just disconnect the Bluetooth.
Input priority: Bluetooth Input > 3.5MM AUX input > MM turntable input.
Note 2: Input Indicator Light : After BOX X3 is powered on, the input indicator light on the front panel stays red either 3.5MM AUX input or MM turntable input is successfully connected, and the input indicator light on the front panel of BOX X3 stays blue when Bluetooth input is successfully connected.
Note : Please keep the BOX X3 away from other electric device. The BOX X3 can’t use with a radio simultaneously.

When the connection is completed, Please turn on the BOX X3 first, then turn on the amplifier(or powered speakers), at last turn on your turntable or other audio source, then enjoy.
Note: If you turn on the amplifier(or powered speakers) first, then turn on the BOX X3, there is a “POP”click sound from your speakers, it is normal that all the phono preamp have the same issues, please don’t worry about it, the “POP”click sound will not damage your amplifiers or speakers.


1: Get noise/humming when turn the BOX X3 on?

• Please know that when no inputs connected to BOX X3, the default input way is MM input mode, in this mode, the gain of the amplify is much large then other input modes, so it’s normal that will have some humming sound when no sound pass through.
• Please unplug all the inputs from the BOX X3, then turn it on to check if the noise still or not.
• If the noise disappear, the noise may from the the audio source or audio cable, please exchange the audio source and the audio cable to try again.
• If the noise still, the noise may from BOX X3 or amplifier/speakers:
• Please exchange the audio cables and amplifier(powered speakers) to have a try and make sure that the noise is from which devices.
• Please volume down the “Treble” volume on the BOX X3 to check if the noise volume follows or not.
• Please make sure all the cables completely pushed into the device, incompletely connection will cause this issue.
• Please make sure that your turntable is MM output and also make sure that it is phono output, some turntables built-in phono preamplifier, so it should connect the 3.5mm AUX input on the BOX X3 not the phono input. Also make sure the grounding wire is connnected well with the BOX X3, please reconnect it to have a try.
• Please keep this device away from other electronic devices, like the FM radio or WIFI router.
• Please make sure the tubes is completely pushed into the socket, incompletely connection will cause this issue.
• Please reconnect the power adapter to the BOX X3 to try again.
Note: • If the noise still, please contact us via email at
• BOX X3 is a preamplifier, not a power amplifier, can not be connected with passive speakers directly.

2. All cables are connected, but there is no audio output?

• Please check if your audio source, BOX X3, amplifier or powered speakers all are turned on and in working mode.
• Please check if the music in your audio source is paused.
• Please make sure that you are chose the correct input mode of the BOX X3, if the 3.5mm AUX input plug in, the MM input mode will be interrupted, and if the Bluetooth paired, the 3.5mm AUX input and the MM input will be interrupted, at this time if you want to use the line input, you need to disconnect the Bluetooth connection first. (if the LED light stay on RED,means the BOX X3 is in line in mode, if it stay on BLUE, means the BOX X3 is in Bluetooth mode)
– If the indicator light on the BOX X3 does not stay on, try another power supply(Any DC12V power adapter can work with BOX X3, you can use the power adapter of WIFI router or camera) that is suitable for the BOX X3. If the indicator light on the BOX X3 is on after replacing the appropriate power adapter, it means that the power adapter is probably broken, please contact us to replace the power adapter; if the indicator light on the BOX X3 is still not on after replacing the appropriate power adapter, it means that the BOX X3 is probably broken, please contact us to replace the BOX X3.
Note: Make sure that all the cables are completely pushed into the device.

3. My Bluetooth device cannot pair with BOX X3?

• Make sure that BOX X3 is powered on.
• Make sure that BOX X3 is not paired with other devices.
• Make sure that the distance between your device and BOX X3 is not too long, close your device to BOX X3 to have a try.
• Make sure there are no obstacles between your device and BOX X3, obstacles will affect the Bluetooth operation distance.
• Please try to change another Bluetooth audio source to test.
• Please reconnect the power supply to the BOX X3, and move the BOX X3 to your another room to have a try.
• Restart the BOX X3 and then try to connect again, try to use another brand of mobile phone.

4. Why Bluetooth is intermittent?

• Use another Bluetooth device to have a try.
• Ensure that there is no interference from other electronic equipment between the BOX X3 and the audio source.
• Put your device close to the BOX X3.
• Replug the power adapter.

5. How to distinguish Power Switch and Volume Control?

• Power switch means turn the power switch knob clockwise for one time to power on the BOX X3. Adjusting the volume means turning the volume control knob clockwise to adjust the volume.

6. How do you switch between inputs?

• The BOX X3 supports three inputs: MM turntable input, 3.5mm AUX Input and Bluetooth Input. The priority of switching between the three inputs: Bluetooth input >3.5MM AUX Input >MM Turntable input.

7. Can I connect a headset and the active speakers to the BOX X3 3.5mm AUX input simultaneously?

• No, the BOX X3 is designed with a 3.5 MM AUX input, not the 3.5MM AUX headphone output. But you can connect to the powered/active speakers from the RCA output connectors.
Note: BOX X3 is a preamplifier, if you want to connect it to passive speakers, you need a power amplifier.

8. My turntable doesn’t have a ground wire connection. Does this need a ground wire hooked up for it to be able to work?

• No, it does not need a ground wire to operate. However, if your turntable has any ground loop, it will be piped and amplified through the BOX X3.

9. How to attach ground wire?

• There is a post to attach the ground wire.

10. Is the gain enough to support MC cartridge?

• No. It is for MM cartridge.

11. My turntable has a selectable built-in phono preamp or switch to the line. Can I still use this instead of my built-in pre-amp?

• Yes, deselect the preamp on your turntable.

12. Can I hook the BOX X3 to the power amplifier for my system?

• Yes. You can connect the BOX X3 to the power amplifier through the RCA output.

13. Can this work with my turntable and headphones?

• No, it’s not design for headphones, and the 3.5mm AUX connector on the front panel of the amplifier is input, not output.

14. Can I directly connect this phono preamp to the speakers?

• If your speakers are powered speakers, you can directly connect this preamp to the speakers. But you need to add an amplifier or receiver to the passive speakers.

15. What equalization is incorporated in this preamp?

• RIAA equalization

16. Can you hook a subwoofer to this unit?

• Yes, if your subwoofer is powered, you can connect the BOX X3 directly to the subwoofer, but you need add a sub amplifier between the BOX X3 and the subwoofer if your subwoofer is passive subwoofer.

17.Which vacuum tube can be replaced to the BOX X3?

• If necessary, tubes below are substituttions: 6K4/6J1/6J4/GE5654/6AK5/66*In vacuum tubes, etc. You can replace the vacuum tubes to DIY your stereo system.

18. Sound quality is not good?

• Make sure all the cables are fully connected.
• Adjust the treble and bass of the BOX X3 to achieve the right tone.
• Please try to change the sound source and cables to test.

19. Can it be left on all the time?

• The BOX X3 is designed with a power switch. It can stay connected safely without power consumption all the time, you only need to turn off the power switch on the BOX X3.

20. Why the BOX X3 came with a broken vacuum tube?

• Due to long-distance transportation, the vacuum tube may be damaged during transportation. If you find that the vacuum tube is damaged or other problems, please contact Fosi Audio after-sales email immediately, and we will replace the vacuum tube for you.

Any problems please leave a message to the customer support email address:

Warranty Information

  • All Fosi Audio products have an 18-month limited warranty on parts and labor from the date of purchase. Please contact us if you have any problems.

About Fosi Audio

  • Fosi Audio designs and builds innovative audio products with all your music in mind. Great sound, simple but elegant designs, high-quality materials, and truly useful features are what Fosi Audio is about. We sincerely hope you get as much enjoyment from our products as we’ve had to create them!

Our website:

Amazon store: 

Our Youtube channel: Fosi Audio

Our Facebook page: Fosi Audio

WhatsApp: +8613716612254

Call us: +49 33389171782

After-sale Service and Technical Support Email:




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