Fosi Audio Box X2 Phono Preamp User Manual

1. Introduction

The Fosi Audio Box X2 is a versatile tube phono preamplifier designed for MM (Moving Magnet) turntables. It converts phono signals to line-level signals, ensuring clear and high-fidelity sound. Additionally, it functions as a tube preamplifier with a 3.5mm AUX input, allowing connection to various audio sources. The device features switchable gain modes and replaceable vacuum tubes for sound customization.

Image 1: Fosi Audio Box X2 Phono Preamp. This image displays the compact black unit with two glowing vacuum tubes on top, and the front panel showing input and gain controls.

2. Package Contents

• 1 x Box X2 Phono Preamp
• 2 x Vacuum Tubes (6J2)
• 1 x RCA Cable
• 1 x DC 12V Power Adapter
• 1 x User Manual

Image 2: Package Contents. This image illustrates all items included in the Box X2 package: the preamp unit, two vacuum tubes, an RCA cable, a power adapter, and the user manual.

3. Product Overview & Control Functions

Front Panel

• IN (3.5mm AUX Input): Connect external audio sources such as phones, tablets, or computers.
• PHONO BOX X2 (Gain Adjustment Switch): A multi-function knob that serves as the power switch and allows selection between 39dB, 42dB, and 45dB gain settings.

Rear Panel

• DC 12V Input: Power input for the device.
• AUDIO OUTPUT (RCA L/R): Connect to your amplifier or active speakers.
• MM INPUT (RCA L/R): Connect your MM turntable.
• GND (Grounding Post): Connect the grounding wire from your turntable to reduce hum and noise.

Image 3: Rear Panel Diagram. This diagram clearly labels the DC 12V input, RCA audio outputs, MM turntable inputs, and the grounding post on the rear of the unit.

4. Setup Instructions

1. Install Vacuum Tubes: Carefully insert the two provided 6J2 vacuum tubes into their respective sockets on the top of the Box X2. Ensure the pins are properly aligned with the socket holes. Apply gentle, even pressure until the tubes are fully seated.
2. Connect Turntable: Connect your MM turntable to the "MM INPUT" RCA jacks on the rear panel of the Box X2 using an RCA cable. If your turntable has a grounding wire, connect it to the "GND" post on the Box X2.
3. Connect to Amplifier/Speakers: Connect the "AUDIO OUTPUT" RCA jacks of the Box X2 to a line-level input on your amplifier or directly to active speakers using an RCA cable.
4. Connect Power: Plug the DC 12V power adapter into the "DC 12V" input on the rear panel, then plug the adapter into a wall outlet.
5. Power On: Turn the multi-function knob on the front panel from "OFF" to your desired gain setting (39dB, 42dB, or 45dB). The tubes will glow blue, indicating the unit is powered on.

Tube Installation Video

Video 1: How to install Amp/Preamp tubes. This video demonstrates the correct procedure for inserting the vacuum tubes into the Fosi Audio Box X2, ensuring proper alignment of the pins to avoid damage.

5. Operating Instructions

Using as a Phono Preamplifier

• Ensure your MM turntable is connected to the "MM INPUT" and the Box X2 is connected to your amplifier/active speakers via "AUDIO OUTPUT".
• Select the appropriate gain setting (39dB, 42dB, or 45dB) using the front knob. Higher gain settings will increase the output volume.
• Play your vinyl records.

Using as a Tube Preamplifier (with 3.5mm AUX Input)

• Connect your audio source (e.g., phone, tablet, PC) to the "IN" 3.5mm jack on the front panel.
• Ensure the Box X2 is connected to your amplifier/active speakers via "AUDIO OUTPUT".
• The gain settings will affect the output volume from the 3.5mm input as well.
• Play audio from your connected source.

Image 4: Connection Diagram. This diagram illustrates how to connect various audio sources (turntable, phone, laptop) to the Box X2 and then to active or passive speakers.

6. Maintenance

• Cleaning: Use a soft, dry cloth to clean the unit. Avoid using harsh chemicals or abrasive materials.
• Tube Replacement: The vacuum tubes are replaceable. Compatible models include 6K4, 6J1, 6J4, GE5654, 6AK5, 66, etc. Different tubes may produce varying sound characteristics.
• Storage: Store the unit in a cool, dry place away from direct sunlight and extreme temperatures.

7. Troubleshooting

If you encounter issues with your Fosi Audio Box X2, refer to the following common troubleshooting steps:

No Sound or Weak Sound

• Check Power: Ensure the power adapter is securely connected and the unit is powered on (tubes should glow).
• Check Connections: Verify all RCA and 3.5mm cables are securely connected to the correct input/output jacks.
• Gain Setting: Adjust the gain switch to a higher dB setting (42dB or 45dB) to ensure sufficient signal amplification.
• Tube Seating: Gently re-seat the vacuum tubes in their sockets. Sometimes loose tubes can cause intermittent sound or no sound.
• Test Tubes: If one channel is weak or silent, try swapping the tubes between sockets. If the problem moves with the tube, the tube may be faulty. If the problem remains in the same channel, the unit may have an internal issue.

Hum or Noise

• Grounding: Ensure your turntable's grounding wire is securely connected to the "GND" post on the Box X2.
• Cable Quality: Use high-quality, shielded RCA cables to minimize interference.
• Proximity to Electronics: Move the Box X2 away from other electronic devices that may cause interference (e.g., Wi-Fi routers, power supplies).

Tube Troubleshooting Video

Video 2: How to troubleshoot a Tube Amp/Preamp. This video provides visual guidance on common troubleshooting steps for tube amplifiers and preamplifiers, including checking tube functionality and re-seating.

8. Specifications

9. Warranty and Support

Fosi Audio products come with a standard warranty. For detailed warranty information, technical support, or service inquiries, please visit the official Fosi Audio website or contact their customer service directly. Keep your purchase receipt for warranty claims.

For additional support and resources, you may visit the Fosi Audio Store on Amazon.