Introduction
This manual provides essential information for the proper setup, operation, and maintenance of your Douk Audio Nobsound 12AX7 12AU7 Vacuum Tube Preamp HiFi Preamplifier (Model DJ417F). Please read these instructions carefully before using the device to ensure optimal performance and longevity.
Product Features
- Improved circuit design for enhanced audio performance.
- Equipped with Shuguang 12AX7 (ECC83) * 2, 12AU7 (ECC82) * 2, and 6Z4 * 2 vacuum tubes. Note: Tube models may vary based on supply chain, but performance remains consistent.
- Features a robust scaffolding design with a reasonable, regular, and symmetrical device layout, ensuring strict adherence to grounding principles.
- Incorporates Power Transformers 76 * 40 H250 0.35 sheets and a Japan ALPS 16 A-type audio potentiometer for precise control.
- Constructed with a full aluminum chassis and elegant wood side panels.
- Offers 4 sets of stereo L/R RCA audio inputs and 1 set of RCA output for versatile connectivity.
Package Contents
Upon unpacking, please verify that all items listed below are present and in good condition:
- 1x Nobsound Vacuum Tube Preamp
- 6x Vacuum Tubes (2x 12AX7, 2x 12AU7, 2x 6Z4)
- 1x Power Cord
Image: The packing list for the Nobsound Tube Preamp, illustrating the main unit, six vacuum tubes, and the power cord included in the package.
Setup Instructions
1. Tube Installation
The vacuum tubes are typically packaged separately to prevent damage during transit. Carefully insert each tube into its corresponding socket on the top panel of the preamplifier. Ensure the pins align correctly with the socket holes and gently push down until the tube is seated firmly. Avoid forcing the tubes, as this can bend or break the pins.
Image: A close-up view of the six vacuum tubes (12AX7, 12AU7, 6Z4) that need to be installed into the preamplifier.
2. Audio Connections
Connect your audio sources (e.g., CD player, DAC, turntable with phono preamp) to the RCA input jacks on the rear panel. The preamplifier features four stereo RCA inputs. Connect your power amplifier or active speakers to the single stereo RCA output jacks.
Image: The rear panel of the Nobsound tube preamplifier, highlighting the multiple RCA input pairs, a single RCA output pair, and the AC power inlet.
3. Power Connection
Connect the provided power cord to the AC inlet on the rear panel of the preamplifier, then plug the other end into a suitable wall outlet. Ensure the voltage matches the device's requirements (100V-115V AC).
Operating Instructions
1. Power On/Off
Locate the toggle switch on the front panel. Flip the switch to the 'ON' position to power on the preamplifier. The tubes will begin to glow. Allow a few moments for the tubes to warm up before expecting full audio performance. Flip the switch to 'OFF' to power down the unit.
2. Input Selection
Use the rotary input selector knob on the front panel to choose your desired audio source. Rotate the knob to cycle through the available inputs (Input 1, Input 2, Input 3, Input 4). Please note that the physical labeling on the rear panel for inputs may not correspond sequentially with the front selector knob; refer to the physical connections you have made.
3. Volume Control
Adjust the main volume using the large rotary knob on the front panel. Start with a low volume setting and gradually increase it to a comfortable listening level.
Image: The front panel of the Nobsound tube preamplifier, displaying the power toggle switch, input selection knob, and master volume control knob.
Maintenance
Tube Replacement
Vacuum tubes have a finite lifespan and may require replacement over time. If you notice a degradation in sound quality, increased noise, or if a tube fails to light up, it may be time to replace it. Always ensure the unit is powered off and unplugged before attempting to remove or install tubes. Allow tubes to cool completely before handling. When replacing, use tubes of the same type (12AX7, 12AU7, 6Z4) or compatible equivalents. Handle new tubes with clean gloves to avoid leaving skin oils on the glass, which can shorten their lifespan.
Cleaning
To clean the exterior of the preamplifier, use a soft, dry cloth. Avoid using liquid cleaners, aerosols, or solvents, as these can damage the finish or internal components. Ensure the unit is powered off and unplugged before cleaning.
Troubleshooting
- No Sound: Check all audio cable connections. Ensure the correct input source is selected. Verify that the power amplifier or active speakers are turned on and functioning. Confirm that the volume knob is not set to minimum.
- Humming or Buzzing Noise: This can often be caused by ground loops. Ensure all components are plugged into the same power strip or wall outlet. Try using a different power cord. Check for proper grounding of the unit; some users have found improvements by ensuring the AC outlet ground is connected to the chassis.
- Distorted Sound: Ensure all connections are secure. Check if the input signal level is too high, causing clipping. If tubes are old or faulty, they can cause distortion; consider replacing them.
- Unit Not Powering On: Verify the power cord is securely connected to both the unit and the wall outlet. Check the power switch position. If the unit has a fuse, inspect it for damage and replace if necessary (consult a qualified technician if unsure).
Specifications
| Parameter | Value |
|---|---|
| Input Sensitivity | 400mv |
| Voltage Output | 2V (RMS THD <0.03%) |
| S/N Ratio | 94dB |
| Frequency Response | 12Hz-50KHz (-0.5dB) |
| Input Impedance | 200Kohm |
| Output Impedance | 600ohm |
| AC Input | 100V (115V) |
| Power Consumption | 30W |
| Dimensions (W-D-H) | 320 * 170 * 120 mm / 12.6 * 6.69 * 4.72 in (Add tube height) |
| Net Weight | 3.5 kg / 7.72 lb |
| Item Model Number | DJ417F |
| Date First Available | June 28, 2018 |
Official Product Video
Video: An official product video from Douk Audio demonstrating the Nobsound 12AX7 12AU7 Vacuum Tube Preamp in an audio setup, showcasing its appearance and functionality.
Warranty and Support
For warranty information, technical support, or service inquiries, please refer to the documentation provided with your purchase or contact Douk Audio customer service directly through their official website or the retailer where the product was purchased. Keep your proof of purchase for warranty claims.
