Nobsound AV-525 HiFi Hybrid Stereo Valve Tube Amplifier

1. Introduction

The Nobsound AV-525 is a versatile HiFi hybrid stereo amplifier designed to deliver clear, warm, smooth, and delicate audio. It combines the rich sound characteristics of vacuum tubes with the power and efficiency of transistors. Featuring multiple analog and digital audio inputs, including Bluetooth 5.0, USB, Coaxial, Optical, and RCA, it is compatible with a wide range of audio devices. The amplifier also includes a dedicated low-frequency output for active subwoofers, allowing for the creation of 2.1 channel audio systems with enhanced bass. Its elegant design, complete with dual VU meters and an LED display, makes it a perfect addition to any home or desktop audio setup.

2. Key Features

• Multiple Audio Inputs: Supports Bluetooth 5.0, USB (U-disk), Coaxial, Optical, and two groups of RCA inputs, ensuring compatibility with MP3 players, phones, tablets, computers, CD players, and more.
• U-disk Playback: Supports lossless audio formats such as APE, FLAC, WAV, and WMA for high-fidelity music playback.
• 2.1 Channel System Support: Features a dedicated low-frequency output for connecting an active subwoofer, allowing you to build a powerful 2.1 channel audio system.
• Tone Control: Independent treble and bass controls enable fine-tuning of the sound to match personal listening preferences.
• Hybrid Design: Utilizes EL84/6K4/5726 tubes for pre-amplification and WY2P tube for rectification, combined with 4PCS Toshiba 5200 and 4PCS 1943 transistors for robust power amplification.
• High Power Output: Dual toroidal transformers provide a stable maximum output of 100W per channel, capable of driving all home passive speakers.
• Elegant Aesthetics: Exquisite black panel with retro vacuum tubes, dual VU meters, and an LED display for real-time working status, offering a luxurious and attractive appearance.

3. Package Contents

Please check the package carefully for the following items:

• 1x Nobsound AV-525 Tube Amplifier
• 1x Power Cord
• 1x Remote Control (batteries not included)

4. Controls and Interfaces

4.1 Front Panel Controls

• Power Button: Turns the amplifier on or off.
• U-disk Input: USB port for connecting a U-disk (USB flash drive) for music playback.
• Input Select Button: Cycles through available audio inputs (BT, USB, COAX, OPT, RCA).
• Play/Pause Button: Controls playback for U-disk and Bluetooth sources.
• Next Song Button: Skips to the next track for U-disk and Bluetooth sources.
• Bass Knob: Adjusts the low-frequency output level.
• Treble Knob: Adjusts the high-frequency output level.
• Volume Knob: Controls the overall output volume.
• VU Meters: Visual indicators of audio signal levels. Note: These meters will primarily work with large dynamic music and significant bass effects.
• LED Display: Shows the current input source and other operational status.

4.2 Rear Panel Connections

• Subwoofer Output: RCA output for connecting an active subwoofer.
• Speaker Output: Binding posts for connecting passive speakers (4-16Ω).
• AC 110-120V / 220-240V Input Select Switch: Voltage selector for power input. Ensure this is set correctly for your region before connecting power.
• Radiating Fan: Internal cooling fan for optimal performance.
• Bluetooth Antenna Port: For connecting the included Bluetooth antenna.
• Optical Input (OPT): Digital audio input for devices like TVs, game consoles.
• Coaxial Input (COAX): Digital audio input for devices like CD/DVD players.
• RCA Inputs (CD/DVD): Two sets of analog RCA inputs for various audio sources.
• Power Input: For connecting the power cord.

5. Setup Instructions

1. Unpacking: Carefully remove all components from the packaging and verify against the "Package Contents" list.
2. Placement: Place the amplifier on a stable, flat surface with adequate ventilation. Ensure the radiating fan at the rear is not obstructed.
3. Voltage Selection: Locate the AC voltage select switch on the rear panel. Set it to either "AC 110-120V" or "AC 220-240V" according to your local power supply. Incorrect voltage selection can damage the unit.
4. Speaker Connection:
   • Connect your passive speakers to the "Speaker Output" binding posts on the rear panel. Ensure correct polarity (+ to + and - to -) for each speaker. The amplifier supports speakers with an impedance of 4-16Ω.
5. Subwoofer Connection (Optional):
   • If using an active subwoofer, connect its input to the "Subwoofer Output" RCA jack on the rear panel.
6. Audio Source Connection:
   • Bluetooth: Screw the included Bluetooth antenna into its designated port on the rear panel.
   • Digital Inputs (Optical/Coaxial): Connect your digital audio source (e.g., TV, CD player) to the "OPT" or "COAX" input jacks using appropriate cables.
   • Analog Inputs (RCA): Connect your analog audio source (e.g., CD player, DVD player) to one of the "CD" or "DVD" RCA input pairs.
   • USB (U-disk): Insert a U-disk containing audio files into the "U-disk Input" USB port on the front panel.
7. Power Connection: Once all audio connections are made and the voltage switch is correctly set, connect the power cord to the amplifier's power input and then to a wall outlet.

6. Operating Instructions

1. Power On: Press the "Power" button on the front panel to turn on the amplifier. The vacuum tubes will glow, and the LED display will illuminate.
2. Select Input Source: Press the "Input Select" button on the front panel (or use the remote control) to cycle through the available input sources (BT, USB, COAX, OPT, RCA). The selected input will be shown on the LED display.
3. Adjust Volume: Rotate the "Volume" knob clockwise to increase the volume and counter-clockwise to decrease it. Start with a low volume level and gradually increase it to a comfortable listening level.
4. Tone Control: Use the "Bass" and "Treble" knobs to adjust the low and high frequencies according to your preference.
5. U-disk Playback:
   • Insert a U-disk with supported audio files (MP3/WAV/APE/FLAC/WMA) into the front USB port.
   • Select "USB" as the input source.
   • Use the "Play/Pause" and "Next Song" buttons on the front panel or remote control to manage playback.
6. Bluetooth Pairing:
   • Select "BT" as the input source. The LED display will indicate Bluetooth mode.
   • On your mobile device, search for Bluetooth devices and select "Nobsound AV-525" (or similar) to pair.
   • Once paired, you can stream audio wirelessly to the amplifier.
7. VU Meters: The dual VU meters will dynamically respond to the audio signal. For noticeable movement, ensure you are playing music with a large dynamic range and significant bass content.
8. Power Off: Press the "Power" button again to turn off the amplifier.

7. Specifications

8. Troubleshooting

If you encounter any issues with your Nobsound AV-525 amplifier, please refer to the following common problems and solutions:

• No Power:
  • Ensure the power cord is securely connected to both the amplifier and a working wall outlet.
  • Check the AC voltage select switch on the rear panel is set correctly for your region.
  • Verify the wall outlet is supplying power.
• No Sound:
  • Check that the correct input source is selected on the amplifier.
  • Ensure speakers are correctly connected to the "Speaker Output" terminals with correct polarity.
  • Increase the volume level on the amplifier and your audio source.
  • Verify that your audio source is playing and its volume is not muted or too low.
  • For digital inputs (Optical/Coaxial), ensure the source device is configured to output audio in a compatible format (e.g., PCM stereo, not Dolby Digital or DTS).
• Distorted Sound:
  • Reduce the volume level on both the amplifier and the audio source.
  • Check speaker connections for loose wires or incorrect polarity.
  • Ensure speaker impedance matches the amplifier's supported range (4-16Ω).
  • Try adjusting the Bass and Treble controls to a neutral position.
• Bluetooth Connection Issues:
  • Ensure the Bluetooth antenna is securely attached.
  • Make sure the amplifier is set to "BT" input mode.
  • Unpair and re-pair the amplifier from your device's Bluetooth settings.
  • Move your Bluetooth device closer to the amplifier to ensure a strong signal.
• U-disk Playback Issues:
  • Ensure the U-disk is formatted correctly and contains supported audio formats (MP3/WAV/APE/FLAC/WMA).
  • Check that the U-disk is properly inserted into the USB port.
  • Try a different U-disk to rule out a faulty drive.

9. User Tips

• VU Meter Activation: The VU meters are designed to respond dynamically. For them to show significant movement, play music with a wide dynamic range and prominent bass frequencies.
• Remote Control: The amplifier includes a remote control for convenient operation. Remember that batteries are not included and need to be purchased separately.
• RMS Power: While the amplifier is rated for 100W+100W at 4Ω, the RMS (Root Mean Square) power, which represents continuous power handling, is typically slightly lower than peak or maximum power. For detailed RMS specifications, refer to the full technical datasheet if available, or consider the rated output power as a strong indicator of its capabilities for home audio use.

10. Maintenance

• Cleaning:
  • Always disconnect the power cord before cleaning.
  • Use a soft, dry cloth to wipe the exterior surfaces of the amplifier.
  • Do not use liquid cleaners, aerosols, or abrasive chemicals, as they may damage the finish or internal components.
• Vacuum Tubes:
  • The vacuum tubes can get hot during operation. Avoid touching them.
  • Over time, vacuum tubes may degrade and require replacement. If you notice a significant change in sound quality or tube performance, consult a qualified technician or the manufacturer for replacement options.
• Ventilation: Ensure the amplifier has proper ventilation to prevent overheating. Do not block the radiating fan or place the unit in an enclosed space without airflow.

11. Warranty and Support

This Nobsound AV-525 amplifier comes with a standard manufacturer's warranty. Please refer to your purchase documentation for specific warranty terms and conditions. For technical support, service, or inquiries regarding replacement parts, please contact the Nobsound Official Store or your authorized dealer.