Douk Audio ST-01 PRO HiFi Bluetooth 5.0 Vacuum Tube Amplifier User Manual

1. Introduction

This manual provides detailed instructions for the safe and efficient operation of your Douk Audio ST-01 PRO HiFi Bluetooth 5.0 Vacuum Tube Amplifier. The ST-01 PRO is an upgraded version of the ST-01, featuring U-disk input and adjustable VU meter sensitivity. It combines a DAC and amplifier, offering multiple digital audio inputs and powerful output for an enhanced home audio experience.

2. Safety Information

• Ensure the power supply voltage matches the requirements of the amplifier (DC 18-30V).
• Do not expose the unit to rain, moisture, or extreme temperatures.
• Avoid placing the unit near heat sources or in direct sunlight.
• Do not open the amplifier casing; there are no user-serviceable parts inside except for the vacuum tubes.
• Disconnect power before making any connections or performing maintenance.
• Keep out of reach of children.

3. Package Contents

Please check the package for the following items:

• 1x ST-01 PRO Amplifier
• 1x DC 24V Power Adapter (optional, may vary by region)
• 1x Remote Control (batteries not included, requires 2*AAA batteries)
• 1x USB Cable
• 1x Bluetooth Antenna
• 1x User Manual

4. Product Overview

4.1 Front Panel Controls

The front panel features essential controls and indicators for easy operation.

Figure 1: Front Panel Layout (ST-01 PRO)

1. VU Meter: Displays audio signal level, providing a vintage visual experience.
2. Input Channel Indicator: Lights up to show the currently selected input (BT, RCA, OPT, COA, PC-USB).
3. Power Switch / Input Switch / Volume Knob:
   • Press to power on/off.
   • Rotate to adjust volume.
   • Press briefly to cycle through input sources.
4. Bass Knob: Adjusts the low-frequency output.
5. Treble Knob: Adjusts the high-frequency output.
6. Infrared (IR) Receiver: For remote control commands.

4.2 Rear Panel Connections

The rear panel provides all necessary audio input and output ports.

Figure 2: Rear Panel Layout (ST-01 PRO)

• BT (Bluetooth Antenna Port): Connect the provided Bluetooth antenna here.
• USB (U-disk Input): For playing lossless audio files from a USB flash drive (ST-01 PRO only).
• RCA (L/R Audio Input): Connect analog audio sources using RCA cables.
• COA (Coaxial Input): Connect digital audio sources using a coaxial cable.
• OPT (Optical Input): Connect digital audio sources using an optical (Toslink) cable.
• PC-USB Input: Connect to a computer for use as an external DAC.
• LINE OUT (3.5mm AUX Output): Connect to another amplifier, active speakers, or a subwoofer.
• SPEAKER OUTPUT (Banana Speaker Jacks): Connect passive speakers.
• DC 18V-30V Power Input: Connect the DC power adapter.

5. Setup Instructions

5.1 Unpacking and Placement

1. Carefully remove all components from the packaging.
2. Place the amplifier on a stable, flat surface with adequate ventilation.
3. Ensure the vacuum tubes are securely seated in their sockets.
4. Attach the Bluetooth antenna to the BT port on the rear panel.

5.2 Connecting Speakers

The amplifier supports passive speakers with an impedance of 3-8Ω.

1. Connect your passive speakers to the "SPEAKER OUTPUT" banana jacks on the rear panel.
2. Ensure correct polarity: connect the red (+) terminal of the amplifier to the red (+) terminal of the speaker, and the black (-) terminal of the amplifier to the black (-) terminal of the speaker.

Figure 3: Amplifier connected to passive speakers.

5.3 Connecting Audio Sources

Choose one of the following input methods:

• Bluetooth 5.0: Pair your Bluetooth-enabled device (phone, tablet, etc.) with the amplifier.
• USB (PC-USB): Connect the amplifier to your computer using the provided USB cable. The amplifier will act as an external sound card. (Supports XP/W7/W8/W10/MAC/Linux).
• U-disk (ST-01 PRO only): Insert a USB flash drive (max 64GB) containing MP3, WAV, WMA, FLAC, APE audio files into the USB port on the rear panel.
• Coaxial/Optical: Connect digital audio sources like TVs, CD players, or game consoles using coaxial or optical cables.
• RCA: Connect analog audio sources such as CD players, tuners, or preamplifiers using RCA cables.

Figure 4: Multiple digital audio inputs.

5.4 Power Connection

1. Ensure all audio connections are made before connecting power.
2. Connect the DC power adapter to the "DC 18V-30V" input on the rear panel.
3. Plug the power adapter into a suitable wall outlet.

6. Operating Instructions

6.1 Power On/Off

Press the main volume knob on the front panel to power the unit on or off.

6.2 Input Selection

Briefly press the main volume knob to cycle through the available input sources (Bluetooth, RCA, Optical, Coaxial, PC-USB, U-disk). The corresponding input indicator on the front panel will light up.

Alternatively, use the "MODE" button on the remote control to select the input source.

6.3 Volume Control

Rotate the main volume knob clockwise to increase volume and counter-clockwise to decrease it. You can also use the volume up/down buttons on the remote control.

Note:

• When the volume is turned down to minimum, the BT/(USB) indicator will flash.
• When the volume is turned up to maximum, the PC-USB indicator will flash.
• The indicator of the current input channel will go out during adjustment but will light up again when adjustment stops.

6.4 Tone Control (Bass/Treble)

Use the "BASS" and "TREBLE" knobs on the front panel to adjust the low and high frequencies to your preference. The adjustment range is ±6dB.

Figure 5: Tone control knobs.

6.5 VU Meter Sensitivity Adjustment (ST-01 PRO only)

The ST-01 PRO features a sensitivity adjustment for the VU meter located on its bottom. This allows you to match the VU meter's response better with different input signals for optimal visual effect.

Figure 6: VU Meter with sensitivity adjustment.

6.6 U-disk Playback (ST-01 PRO only)

Insert a USB flash drive containing supported audio formats (MP3, WAV, WMA, FLAC, APE) into the USB port on the rear panel. Select the U-disk input using the input switch. The amplifier will automatically begin playback.

6.7 Remote Control

The included remote control allows for convenient operation from a distance. It can control power, input selection, volume, and mute functions.

Figure 7: Amplifier with remote control.

Note:

• The remote control requires 2*AAA batteries (not included).
• Point the remote control towards the IR receiver on the front panel.

7. Specifications

8. Troubleshooting

• No Sound:
  • Check all cable connections (power, speakers, audio sources).
  • Ensure the correct input source is selected.
  • Verify volume levels on both the amplifier and the audio source.
  • Check if the amplifier is muted (if applicable via remote).
• Distorted Sound:
  • Reduce the volume level.
  • Check speaker impedance compatibility (3-8Ω).
  • Ensure audio cables are not damaged or loose.
• Bluetooth Pairing Issues:
  • Ensure the amplifier is in Bluetooth input mode.
  • Delete previous pairings on your device and try pairing again.
  • Move your device closer to the amplifier.
• VU Meter Not Responding (ST-01 PRO):
  • Adjust the VU meter sensitivity on the bottom of the unit.
  • Ensure an audio signal is present.
• Remote Control Not Working:
  • Check and replace AAA batteries.
  • Ensure there are no obstructions between the remote and the amplifier's IR receiver.
  • Point the remote directly at the IR receiver.

9. Maintenance

• Cleaning: Use a soft, dry cloth to clean the exterior of the amplifier. Do not use liquid cleaners or solvents.
• Vacuum Tube Replacement: The amplifier uses pluggable 6K4 vacuum tubes. These can be replaced with compatible tubes such as 6J1, 6J2, 6J3, 6J4, 6J5, 6"1N, 6*4N, 6*5N, 5654/5654W, 5725, 6AK5, EF95, 6BA6, 403B. Ensure the amplifier is powered off and unplugged before replacing tubes. Handle tubes carefully as they can be fragile.

10. User Tips

• Power Supply: The amplifier typically includes a DC 24V power adapter. Ensure it is connected correctly. The unit operates within a DC 18-30V range.
• Mobile Phone Connectivity: For PC-USB input with mobile phones, Android devices may require an OTG cable, and iOS devices may require a camera kit. These accessories are not included.
• Tube Rolling: Experimenting with different compatible vacuum tubes (e.g., 5654/5654W) can subtly alter the sound signature to suit personal preferences. Always ensure the amplifier is off and unplugged before swapping tubes.

11. Warranty and Support

For warranty information, technical support, or service inquiries, please refer to the seller's policies or contact the manufacturer directly. Keep your purchase receipt as proof of purchase.

12. Product Demonstration Video

Watch this video for a visual demonstration of the Douk Audio ST-01 PRO amplifier's features and operation.

Video: Douk Audio ST-01 PRO Amplifier in action, showcasing its design, connections, and VU meter.