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Product Specifications
Product Overview & Control Functions
Package Contents​
Quick Steup
Comparison Section
Warranty Information
About Fosi Audio

Product Specifications

Fosi Audio BOX X2 is a Hifi tube phono preamp for MM turntable that features the Multi-function Knob which contains Power Switch and Gain Adjustment Switch with DC 12V power supply. The BOX X2 supports MM turntable input, 3.5mm AUX 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, which will provide you with serious sound performance.  

Input Interface

MM turntable input, 3.5mm AUX input, 12V DC input 


Output Interface

RCA output



Active(powered) speakers, Amplifier


Voltage Range

AC 100V - 240V


DC Input Voltage



Output Voltage Level

600 Mv @3mV 1kHz



≥ 98dB





Frequency Range

Standard RIAA


Product Weight

0.66 lb/300g


Product Dimensions

4.66 inch*3.85 inch*1.29 inch (L118.5*W98*H33MM)

Product Overview & Control Functions

Package Contents​

Fosi Audio BOX X2 *1

Vacuum Tube *2

DC 12V Power Adapter *1

Quick Setup​

Step 1: Install the vacuum tubes into the BOX X2.

Note 1: The electronic tube is not divided into left and right; check the pins before installing the electronic tube. There is no deformation; if there is a deformation of the situation, you can use your hand to dial the right.

Note 2: Please note that electronic tubes are fragile and need to be handled gently.


Step 2(OUTPUT): Connect speakers to the BOX X2.

RCA output: Use the RCA cable to connect the RCA line output of BOX X2 to your active (powered) speakers. Or use RCA cable to connect the RCA line output of BOX X2 to your amplifier, then use the speaker’s wire to connect the amplifier to your passive speakers.


Step 3(INPUT): Connect the audio source (MM turntable input, 3.5MM AUX input) to the BOX X2.

(1): MM turntable input: Use the RCA cable to connect your MM turntable to the RCA inputs of BOX X2, then connect the ground wire of your MM turntable to the grounding post of BOX X2.

Note 1: The ground wire can be omitted if your MM turntable does not need to connect a ground wire.

Note2: MM Turntable Input can only be connected to the turntable and cannot be used as a standard preamplifier connected to other audio sources, such as CD players, TVs, etc.

(2): 3.5mm Input: Use a 3.5mm audio cable to connect the BOX X2 and your device.

Note: Once 3.5mm AUX plugs in, the MM input will automatically be interrupted so that the input mode will turn to 3.5mm AUX input.

Input priority: 3.5MM AUX input > MM turntable input.


Step 4: Connect the power adapter to BOX X2 and the socket.

Turn the Multi-function Knob ( Power Switch/Gain Adjustment Switch) clockwise for one time to power on the BOX X2.

Note1: The power adapter does not have a power indicator light, so connecting to the socket means power is on.

Note2: Before connecting the power supply, please ensure that the BOX X2 is in the “OFF” position when connecting to the power adapter. Otherwise, there is a “POP” click sound from your speakers.

When the connection is completed, please turn on the BOX X2 first, then turn on the amplifier (or powered speakers); at last, turn on your turntable or other audio sources, then enjoy.

Note: If you turn on the amplifier (or powered speakers) first, then turn on the BOX X2, there is a “POP” click sound from your speakers; typically, all the phono preamps have the same issues; please don’t worry about it, the “POP” click sound will not damage your amplifiers or speakers.


1: Getting a buzz when turning the BOX X2 on?

  • Please know that when no inputs are connected to BOX X2, the default input way is MM input mode, in this mode, the gain of the amplify is much more significant than in other input modes, so it’s expected that it will have some humming sound when no sound pass through.
  • Please unplug all the inputs from the BOX X2, then turn it on to check if the noise is still there or not.
  • If the noise disappears, it may be from the audio source or audio cable; please exchange the audio source and the audio cable to try again.
  • If the noise is still, the noise may be from BOX X2 or amplifier/ speakers:
  • Please exchange the audio cables and amplifier (powered speakers) to try and make sure that the noise is from which devices.
  • Please check whether the gain is too high; the bottom noise may be more prominent if the gain is too high.
  • Please make sure all the cables are completely pushed into the device; an incomplete 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 should connect to the 3.5mm AUX input on the BOX X2, not the phono input. Also, make sure the grounding wire is connected well with the BOX X2; please reconnect it to have a try.
  • Please keep this device away from other electronic devices, like the FM radio or WiFi router.
  • Please ensure the tubes are completely pushed into the socket; an incomplete connection will cause this issue.
  • Please reconnect the power adapter to the BOX X2 to try again.

Note: • If the noise persists, please contact us via email at BOX X2 is a preamplifier, not a power amplifier, and 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 X2, amplifier, or powered speakers are all turned on and working mode.
  • Please check whether the light of the vacuum tube is always on after power on, and check whether there is a problem with the vacuum tube.
  • Please check if the music in your audio source is paused.
  • Please make sure that you choose the correct input mode of the BOX X2; if the 3.5mm AUX input plug in, the MM input mode will be interrupted; at this time, if you want to use the MM input, you need to disconnect the 3.5mm AUX input first.
  • If the connection is proper, but the BOX X2 does not work, please try another power supply (Any DC12V power adapter can work with the BOX X2, you can use the power adapter of the WIFI router or camera) that is suitable for the BOX X2. If BOX X2 works after replacing the appropriate power adapter, it means that the power adapter is probably broken; please contact us to replace the power adapter; if BOX X2 still does not work after replacing the appropriate power adapter, it means that the BOX X2 is probably broken, don’t hesitate to get in touch with us to replace the BOX X2.

Note: Make sure that all the cables are completely pushed into the device.


3. How to distinguish between Power Switch and Gain Adjustment Switch?

  • Power switch means turning the power switch knob(multi-function knob) clockwise for one time to power on the BOX X2. Adjusting the gain means turning the gain adjustment knob (multi-function knob) clockwise to adjust the gain.

4. How do you switch between inputs?

  • The BOX X2 supports two inputs: MM turntable input and 3.5mm AUX Input.

The priority of switching between the two inputs: 3.5MM AUX Input> MM Turntable input.


5. 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 X2.

6. How to attach ground wire?

  • Here is a post to attach the ground wire.

7. How does grounding post work? Does my turntable have a fork spade-type terminal?

  • You can connect the fork spade type terminal to the grounding post.

8. Does this have an analog to digital conversion?

  • No. This product is a phono preamp/tube preamplifier.

9. Is the gain enough to support the MC cartridge?

  • No. It is for the MM cartridge.

10. My turntable has an optional built-in phono preamp or switches to the line. Can I still use this instead of my built-in preamp?

  • Yes, deselect the preamp on your turntable.

Note: Please confirm whether your turntable has a built-in phono preamp; if there is a phono preamp, and it cannot be deselected, then you can only connect 3.5 mm input and can not connect MM Turntable input.


11. Can I hook the BOX X2 to the power amplifier for my system?

  • Yes. You can connect the BOX X2 to the power amplifier through the RCA output.

12. Can this work with my turntable and headphones?

  • This can not work with headphones because it does not have headphones output.

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

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

14. What equalization is incorporated in this preamp?

  • RIAA equalization.

15. Can you hook a subwoofer to this unit?

  • Yes, if your subwoofer is powered, you can connect the BOX X2 directly to the subwoofer, but you need to add a sub amplifier between the BOX X2 and the subwoofer if your subwoofer is passive.

16. Which vacuum tube can be replaced by the BOX X2?

  • If necessary, the tubes below are substitutions: GE 5654 EF95, 6AK5, 6AK5W, 403A/403B, 6J1, 6J1P, 6J2, 6J3, 6J4, 6J5 vacuum tubes, etc. You can replace the vacuum tubes to DIY your stereo system.

17. Is the Sound quality not good?

  • Make sure all the cables are fully connected.
  • Adjust the gain of the BOX X2 to achieve the right tone.
  • Please try to change the sound source and cables to test.

18. Can it be left on all the time?

  • The BOX X2 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 X2.

19. Why does the BOX X2 come with a broken vacuum tube?

  • Due to long-distance transportation, the vacuum tube may be damaged during transport. If you find that the vacuum tube is damaged or has other problems, please contact Fosi Audio.

After-sales email immediately, and we will replace the vacuum tube for you.

If you have any problems, please leave a message to the customer support email address:

Comparison Section

Warranty and Maintenance

All Fosi Audio products have an 24-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!

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