DOUK AUDIO A1 PLUS Valve Tube Preamp User Manual

DOUK AUDIO A1 PLUS Valve Tube Preamp

PANEL

13 PLUS front and back panel

1. Power switch/Volume knob (Anti-clockwise rotate to off/Vol-; Clockwise rotate to on/Vol+)
2. Headphone output
3. PHONO GND interface
4. PHONO input (red: right channel; white: left channel)
5. AUX input
6. RCA output (red: right channel, white: left channel)
7. Power interface (DC 12V)
8. MM/MC switch; MC mode impedance setting

Operation steps

1. Insert the vacuum tubes into the sockets of T3 PLUS. (please check if the pins of the tube are deformed)
2. Make sure the volume is at the minimum.
3. Connect active speakers or an amplifier to the RCA output of T3 PLUS, a headphone also can be connected to its headphone out. (Stereo RCA and 3.5mm headphone jack can output at the same time. )
4. PHONO IN: Connect the turntable to the phono input of T3 PLUS, select MC/MM mode, and adjust the matching impedance.
   • AUX IN: Connect an audio source to AUX input of T3 PLUS. (AUX input with priority, please make sure the AUX cable has been pulled out if want phono input.)
5. Connect the power adapter to T3 PLUS and then plug the power cable into the socket.
6. Clockwise rotate the knob to power on and adjust the volume according to your preferences and enjoy music.
7. After use, anti-clockwise rotate the knob to power off and then disconnect the power adapter.

Parameters

FAQ

• Q: Why are all cables connected but there is no sound?
• A:
  • Check the LED below the tubes: If it can light up normally, please check if the corresponding input mode is selected. 2 If it cannot light up, please use another DC 12V power supply to detect whether the fault is the power supply or T3 PLUS.
  • If the indicator light is on but there is no sound, the power supply is normal. Please continue to check according to the order of audio signal transmission: audio source → audio cable → preamp/decoder → amplifier → speaker.
  • If all is fine, please check whether the audio source is muted, paused or the volume is too small.
• Q: Why is the sound distorted? How to adjust the treble, bass, and main volume?
• A: Maybe the input amplitude is too large. If the volume of the audio source and T3 PLUS both are turned to maximum, it is easy to cause distortion. Please turn down the volume of the audio source or T3 PLUS. In general, adjust the volume of the amplifier to about 60%, then fine-tune the volume of the preamp (distortion will be greatly reduced in this way); the treble and bass are usually adjusted according to the music style/device types/personal preference.
• Q: Why is there a loud current sound or buzzing sound on the speaker?
• A:
  • Please use the original power supply. Many power supplies in the market have interference, which will cause current sound.
  • When using an unshielded signal cable with no load, there will be interface signals. Please use the shielded signal cable or unplug it.
  • If there is still noise after eliminating the above situations, please confirm whether it is external noise or internal noise. Disconnect all inputs and only retain the power supply and power cable. If the noise disappears, it is from audio input; if the noise is still there, it is possibly caused by a power supply or the internal of 13 PLUS.
• Q: Why is there no sound output when using MC or MM mode?
• A: AUX input is with priority, please unplug the AUX input cable, otherwise there will be no sound.
• Q: Can I replace the vacuum tube without turning off the power?
• A: No, because T3 PLUS Is working under high pressure internally, it will be damaged if the tubes are plugged during its work.
• Q: Why is there a thumping sound when switching on/off?
• A: Please confirm the on-off sequence is correct, normally it follows the order of signal transmission when turned on: audio source → preamp / DAC → amplifier → speaker. (The sequence is reversed when switching off. The internal capacitors will be discharged for a while after shutdown. If turn off the preamp first and then turn off the amplifier, impact sound will be easily caused which may damage the amplifier or speaker in severe cases).
• Q: How does the vacuum tube work when the supply voltage of the vacuum tube preamp is only 12V?
• A: In addition to the high-voltage power supply of the transformer, vacuum tubes also use positive and negative voltage supplies (it depends on the function of the vacuum tube in the circuit), we also have some products that adopt the step-up power supply.
• Q: Why is the sound not clear every time the vacuum tube preamp starts to be used?
• A: Unlike transistors, vacuum tubes are sensitive components that need to be warmed for a while before entering normal working status. Generally, It’s better to warm up for about 15 minutes.
• Q: Why is there a faint sound even when the volume is turned up to the maximum without vacuum tubes?
• A: The preamp is for audio signal amplification, other components such as capacitors or resistors will still produce a weak signal coupling although no vacuum tubes are plugged in. Please install the vacuum tube correctly before use.
• Q: How long is the service life of vacuum tubes? Can I replace them by myself?
• A: The service life of the vacuum tubes is about 4000-4500 hours, they are not easy to break as long as not damaged by external forces. Before replacing, please confirm the model that can be replaced.
• Q: The vacuum tubes of T3 PLUS can be replaced by what model?
• A: Default 6A2 vacuum tube, can be replaced by: 6J1, 6J2, 6J3, 6J4, 6J5, 6K4, 6″ 1N, 64N, 65N, 5654/5654W, 5725, 6AK5, EF95, 6BA6, 403B, etc.
• Q: What should be paid attention to when using vacuum tube devices?
• A: The vacuum tube is a high-resistance component, easy to interfere with, so it should be as far away as possible from RF interference or electromagnetic interference sources and avoid vibration; The vacuum tube will generate heat when working, so it should be well-ventilated and heat dissipated.
• Q: Can I replace or upgrade the op-amp by myself?
• A: Commonly used replaceable op amps: 2604 / 2134 / Muse02, etc. (dual op-amps are generally available), different op amps have different sound effects. (According to the actual product models).
• Q: What is the difference between MM/MC? How to determine which type of phono cartridge is?
• A: MM: Moving-magnetic cartridge; MC: Moving-coil cartridge You can check the product model to determine the type of phono cartridge (MM cartridges are commonly used in the record players produced currently)…
• Q: What is RIAA?
• A: RIAA is a unified standard for the recording and playback of vinyl records issued by the Recording Industry Association of America, the currently produced phonograph and vinyl records basically must follow this standard.
• Q: What is the function of the phonograph GND? Why are not all phonographs grounded?
• A: Phonograph GND is to connect the phono cartridge or phonograph shell to the signal GND of the preamp, to avoid inductive loads such as phono motors from interfering with audio signals. (Old-fashioned phonographs usually with a GND wire or GND terminal, and new-style connect the GND wire to the negative pole of the single cable directly, the effect of both ways is the same).
• Q: How to check and avoid the current sound/interference sound from the phonographs?
• A: Due to the unique design and structure, as well as the characteristics of the direct contact between phonograph cartridges and records to read signals, the background noise of the phonograph will be more obvious when compared with phones and computers. Besides its background noise, uneven placement, record aging, cartridge wear and dust on the surface, etc. also can result in current noise (Please clean the record or replace the cartridge regularly).
• Q: Why is the sound distorted and broken?
• A: Please confirm whether the type of phono cartridge and phono preamp is matched; whether the phono output mode is correct (some phonograph with built-in phono preamp, the LINE/PHONO input switch in the correct position or not); whether the gain of preamp is adjusted too high; whether the impedance is matched (for MC cartridge); whether the GND is connected well, etc.
• Q: Can the phono preamp be used as a common audio preamp?
• A: Phono preamp is designed for vinyl record players, the amplification times are larger than the common audio preamp. If used as a common preamp, lots of distortion will be caused, and even the amplifier and speakers will be damaged.
• Q: Why is the sound very low when the headphone is connected to the headphone amplifier?
• A: Please confirm whether the impedance, plug type, and other parameters of the headphones are compatible with the headphone amplifier, or whether the input signal is too low.
• Q: Why is the sound from the headphones distorted after connecting to the headphone amplifier?
  A: Please confirm the volume of the audio source and headphone amplifier. If the volume is too high and exceeds the power that the headphones can bear, distortion will be caused.

Warning

1. Please do not open the shell by yourself, improper operation may cause a risk of electric shock.
2. Please use the regular manufacturer’s switching power supply, otherwise, there will be a risk of damage to T3 PLUS.
3. Please do not use T3 PLUS in a high-temperature and humidity environment.
4. Please do not unplug or plug the vacuum tube when T3 PLUS is on, otherwise, the tubes or T3 PLUS will be damaged.
5. Please do not replace mismatched vacuum tubes, otherwise, the tubes or T3 PLUS will be damaged.
6. The default 12V power adapter and T3 PLUS will be damaged if the voltage exceeds 12V.

Contact information

• Website: www.doukaudio.com.
• Email: nobsound@doukaudio.com.
• WeChat/Whatsapp: +86-17704028602
• Address: Room 1329, Wang Cheng Building, Long Guan East Road,
  • Long Hua District,
  • Shen Zhen,
  • Guang Dong,
  • China,
  • 518000

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