Introduction
The Nobsound Douk Audio U4 Mini is a versatile HiFi audio device designed to enhance your listening experience. It functions as a Bluetooth 5.0 receiver, USB DAC, headphone amplifier, and stereo audio preamplifier. Featuring a classic 6N3 vacuum tube, it delivers a warm, clear, and smooth sound, effectively eliminating harsh digital artifacts. This manual provides detailed instructions for setup, operation, and maintenance to ensure optimal performance.
Product Features
- Multi-functional Design: Combines Bluetooth receiver, USB DAC, headphone amplifier, and preamplifier capabilities in one compact unit.
- Versatile Connectivity: Supports Bluetooth 5.0 and USB audio inputs, with Stereo RCA, 3.5mm AUX, and 3.5mm headphone jack outputs.
- Vacuum Tube Sound: Incorporates a 6N3 vacuum tube for a warm, clear, soft, and sweet audio signature, ideal for vocals, string instruments, and classical music.
- High-Quality Components: Features QCC3008 Bluetooth chip (supporting APT-X, APTX-LL), TDA1543 decode chip, 2704 USB chip, and MAX9722 headphone amplifier chip.
- Wide Compatibility: USB audio input is compatible with Windows, Mac, Linux systems, and Android smartphones with OTG function, offering plug-and-play convenience without drivers.
- Powerful Headphone Output: The MAX9722 headphone amplifier provides 300mW output, capable of driving most headphones with impedances from 16 to 600 ohms.
Package Contents
Please check the package for the following items:
- 1 x Douk Audio U4 Mini Headphone Amplifier
- 1 x 6N3 Vacuum Tube
- 1 x 12V Power Adapter
- 1 x USB Cable
- 1 x Bluetooth Antenna
Setup
- Tube Installation: Carefully insert the 6N3 vacuum tube into its socket on the top of the unit. Ensure it is seated firmly but do not force it.
- Bluetooth Antenna Connection: Screw the provided Bluetooth antenna onto the 'ANT' connector on the rear panel.
- Power Connection: Connect the 12V power adapter to the 'DC 12V' input on the rear panel, then plug the adapter into a power outlet.
- Audio Output Connection:
- For speakers or a power amplifier, connect the 'AUDIO OUT' RCA jacks to your audio system using RCA cables.
- For headphones, plug your 3.5mm headphones into the 'PHONE' jack on the front panel.
- Audio Input Connection:
- USB Input: Connect your computer (Windows, Mac, Linux) or Android smartphone (with OTG) to the 'PC-USB' port on the rear panel using the supplied USB cable.
- Bluetooth Input: Ensure the Bluetooth antenna is connected. The device will be discoverable for pairing.
Image: Rear panel showing 'AUDIO OUT' (RCA/3.5mm), 'PC-USB', 'ANT' (Bluetooth antenna), and 'DC 12V' power input.
Image: Illustrates USB compatibility with various operating systems including Windows, Mac, Linux, and Android devices.
Operating Instructions
- Power On/Off: Press the 'POWER' switch on the front panel to turn the unit on or off. The vacuum tube will glow when powered on.
- Input Selection: Use the 'SELECT' switch on the front panel to cycle between USB and Bluetooth inputs. The corresponding LED indicator (USB or Bluetooth) will light up.
- Bluetooth Pairing:
- Switch the input to Bluetooth. The Bluetooth LED will blink, indicating it's in pairing mode.
- On your source device (smartphone, tablet, etc.), search for Bluetooth devices and select "Douk Audio U4 Mini" to pair.
- Once paired, the Bluetooth LED will remain solid.
- Volume Control: Adjust the 'VOLUME' knob on the front panel to control the output level for both headphone and RCA/AUX outputs. Start with a low volume and gradually increase it to a comfortable listening level.
- Headphone Usage: When headphones are plugged into the 'PHONE' jack, the RCA/AUX outputs may be muted depending on the unit's design. Unplug headphones to resume output to speakers.
Image: Front panel showing Power switch, Select switch, Phone jack, Volume knob, and Power/USB/Bluetooth indicators.
Image: A user wearing headphones connected to the Douk Audio U4 Mini, demonstrating its headphone amplifier function.
Maintenance
- Cleaning: Use a soft, dry cloth to clean the unit. Do not use liquid cleaners or solvents.
- Vacuum Tube Care: The vacuum tube can become hot during operation. Avoid touching it. If replacement is needed, ensure the unit is powered off and cooled down before handling the tube.
- Placement: Place the unit on a stable, flat surface away from direct sunlight, heat sources, and excessive moisture. Ensure adequate ventilation around the unit.
- Storage: If storing the unit for an extended period, disconnect it from power and store it in a cool, dry place.
Troubleshooting
| Problem | Possible Cause | Solution |
|---|---|---|
| No sound output | Unit not powered on; incorrect input selected; cables loose; volume too low; headphones plugged in (muting RCA/AUX). | Check power switch; verify input selection; ensure all cables are securely connected; increase volume; unplug headphones if using RCA/AUX. |
| Bluetooth not connecting | Bluetooth input not selected; antenna not connected; device too far; already paired with another device. | Select Bluetooth input; ensure antenna is connected; move source device closer; disconnect from other devices and try pairing again. |
| Distorted sound | Volume too high; faulty cables; source audio quality issues; vacuum tube issue. | Reduce volume; try different cables; check source audio; ensure vacuum tube is properly seated. |
| No USB audio | USB input not selected; USB cable faulty; computer/phone not recognizing device. | Select USB input; try a different USB cable; check device manager on PC or audio settings on Mac/Android. |
Specifications
| Feature | Detail |
|---|---|
| Audio Input | Bluetooth 5.0, USB |
| Audio Output | Stereo RCA, 3.5mm AUX, 3.5mm Headphone Jack |
| Bluetooth Chip | QCC3008 (supports APT-X, APTX-LL) |
| Decode Chip | TDA1543 |
| USB Chip | 2704 (supports up to 16bit/96kHz) |
| Headphone Amp Chip | MAX9722 |
| Signal-to-Noise Ratio (SNR) | > 99 dB |
| Dynamic Range | > 99 dB |
| Headphone Output Power | 300mW |
| Headphone Impedance | 16-600Ω |
| Total Harmonic Distortion + Noise (THD+N) | 0.004% (RL> 10kΩ) |
| Dimensions (L*W*H) | 97 * 77 * 32mm (3.82 * 3.03 * 1.26 inches) |
| Unit Weight | 250g |
| Package Weight | 470g |
Image: Diagram showing the dimensions of the Douk Audio U4 Mini in millimeters and inches.
Image: Internal architecture diagram highlighting the MAX9722 (Amp), TDA1543 (Decode), 2704 (USB), and QCC3008 (Bluetooth) chips.
Warranty & Support
Nobsound products are designed for reliability and performance. For warranty information, please refer to the documentation included with your purchase or contact your retailer. For technical support, please visit the official Nobsound website or contact their customer service department. Please have your model number (U4 Mini or DZ077) and purchase details ready when seeking support.
