Douk Audio U3 Mini Pure Class A Headphone Amplifier User Manual

1. Introduction

Thank you for choosing the Douk Audio U3 Mini Pure Class A Headphone Amplifier. This ultra-compact, high-fidelity desktop stereo amplifier is designed to provide exceptional audio performance for a wide range of headphones, including high-impedance models. Featuring an innovative circuit design and a replaceable op-amp, the U3 delivers a warm, delicate, full, and mellow sound with ultra-low distortion. This manual provides essential information for the safe and effective use of your amplifier.

2. Safety Information

Please read and understand all safety instructions before operating this device. Keep this manual for future reference.

• Do not expose the device to water, moisture, or extreme temperatures.
• Use only the provided power adapter or a recommended high-quality power adapter (DC 5-20V, above 5W).
• Ensure proper ventilation around the amplifier to prevent overheating.
• Do not attempt to open or repair the device yourself. Refer all servicing to qualified personnel.
• Keep out of reach of children.
• Avoid listening at high volume levels for extended periods to prevent hearing damage.

3. Package Contents

Please check the package for the following items:

• 1 × Douk Audio U3 Headphone Amplifier
• 1 × DC 5V Power Adapter
• 1 × 6.35mm to 3.5mm Headphone Adapter

4. Specifications

5. Setup

Follow these steps to set up your Douk Audio U3 Headphone Amplifier:

1. Connect Audio Source: Connect your audio source (e.g., CD player, DAC, computer) to the L/R RCA input jacks on the rear panel of the U3 amplifier using an RCA cable.

   

2. Connect Headphones: Plug your headphones into the 6.35mm headphone jack on the front panel. If your headphones have a 3.5mm plug, use the included 6.35mm to 3.5mm adapter.

   

3. Connect Power: Connect the provided DC 5V power adapter to the DC 5-20V input jack on the rear panel, then plug the adapter into a wall outlet. Ensure the power switch is in the 'OFF' position before connecting power.

6. Operating Instructions

1. Power On: Flip the power switch on the rear panel to the 'ON' position. The power indicator light on the front panel will illuminate.
2. Adjust Volume: Turn the volume knob on the front panel clockwise to increase the volume and counter-clockwise to decrease it. Start with the volume at a low level and gradually increase it to a comfortable listening level.

   

3. Power Off: When finished listening, flip the power switch on the rear panel to the 'OFF' position.

7. Maintenance

• Clean the device with a soft, dry cloth. Do not use liquid cleaners or aerosols.
• Keep the amplifier away from dust and direct sunlight.
• Store in a cool, dry place when not in use for extended periods.
• Ensure all connections are secure and free from debris.

8. Troubleshooting

No Sound:

Ensure the amplifier is powered on and the power indicator is lit. Check all audio cables (RCA and headphone) are securely connected. Verify the audio source is playing and its volume is not muted or too low. Adjust the U3's volume knob.

Distorted Sound:

Reduce the volume on both the amplifier and the audio source. Ensure your headphones' impedance is within the supported range (18-600Ω). Check for loose connections or damaged cables. Try a different audio source or headphones to isolate the issue.

Power Indicator Not Lit:

Check if the power adapter is correctly plugged into both the amplifier and the wall outlet. Ensure the power switch on the rear panel is in the 'ON' position. Try a different power outlet. If using a third-party power adapter, ensure it meets the DC 5-20V input requirement and provides sufficient current (e.g., 1A for 5V, 0.5A for 12V).

9. User Tips

• Power Adapter: For optimal performance, especially with higher impedance headphones, consider using a high-quality power adapter with a higher voltage (up to 20V DC) and sufficient current (e.g., 1A for 5V, 0.5A for 12V). The DC plug size is commonly 5.5mm outer diameter with a 2.1mm inner diameter.
• Headphone Compatibility: The U3 amplifier is capable of driving a wide range of headphones, including high-impedance models up to 600 ohms, such as HD580/HD600/HD650, K701/K702/Q701, DT880/T70/T90, and SR225/SR325/RS1e.
• Op-Amp Rolling: The U3 features a pluggable op-amp socket design, allowing users to easily upgrade or swap the TI-NE5532 op-amp with other compatible models to customize the sound signature to their preference. This offers significant DIY fun and playability.
• Volume Control: Even with low-impedance headphones (e.g., 32 ohms), the U3 provides ample power, often requiring only half of the maximum volume for a loud listening experience.

10. Frequently Asked Questions (FAQ)

Q: What is the recommended power adapter for the U3?

A: The U3 supports a DC 5-20V input. We recommend an original high-quality power adapter above 5W. For a 5V adapter, ensure the current is above 1A. For a 12V adapter, ensure the current is above 0.5A. The DC plug typically has a 5.5mm outer diameter and 2.1mm inner diameter.

Q: Can I use 250-ohm or 600-ohm headphones with this amplifier?

A: Yes, the U3 amplifier is designed to easily drive most high-impedance headphones, including those with 250 ohms and up to 600 ohms impedance.

Q: Are the op-amps replaceable?

A: Yes, the U3 features a pluggable op-amp socket design, allowing you to upgrade or replace the original TI-NE5532 op-amp with other compatible models for sound customization.

Q: Does this amplifier work with headsets that have a microphone?

A: The U3 provides a standard 6.35mm (or 3.5mm with adapter) stereo audio output for headphones. It does not have a dedicated microphone input, so microphone functionality from a headset will not be supported through the amplifier.

11. Warranty and Support

Douk Audio products are designed for reliability and performance. For any technical support or warranty inquiries, please contact the official Douk Audio customer service or your authorized dealer. Please have your product model and purchase information ready.