6418 tube headphone amplifier

I am a freshman in high school and I like electronic production. Since I have never studied programming or digital electronics, I am currently mainly studying analog electronics. More interested in power amplifiers, switching power supplies, etc. 2. Headphones are an indispensable part of today’s young people. However, because headphones are divided into high and low impedances, the impedance of common headphones on the market is around 16 to 64Ω, while the impedance of fever headphones is usually several hundred ohms or even thousands of ohms. This makes the playback equipment not too flexible to deal with various headphones. So for 1. 6418 tube amp, the 6418 tube is used as the preamplifier, and the NE5532 or OPA2604 is used as the postamplifier. It is powered by a lithium battery and is only the size of a mobile phone. size.

  2. First of all, because the PCB integrates charging control, boost power supply, and power amplification, in order to make the size smaller, most components are made of patches. The size of the finished board is 810mmx510mm. Secondly, due to the high level of integration, filtering must be done between various parts to prevent mutual interference and noise. Next, the amp uses two stages of amplification. The signal coupling of the front and rear stages is essential. Here I use four capacitors and two resistors to make a voltage divider, and use them to tap the 0V reference voltage, so that we have a positive The negative power supply supplies power to the NE5532 behind it, so the front and rear stages can be coupled directly without the need for an audio isolation transformer or capacitor to couple the two signals. So the first difficulty is to adjust the anode resistance so that the front and rear stages can be perfectly coupled. The second difficulty is the impact of voltage on the circuit. Since Boost is used, the boost output will inevitably have noise. However, neither the tube nor the operational amplifier can operate at a lower voltage, so the voltage must be carefully adjusted to seek The balance in the middle. The third difficulty is the power supply of the electronic tube filament. The power consumption of the electronic tube filament is not large, so the lm7805 and a series resistor are used to reduce the voltage. The working voltage range of the filament is 1v to 1.5v. Too low voltage will cause cathode poisoning, and the voltage is too high. Will burn the filament. With a more conservative attitude, I used a 200Ω resistor and controlled the voltage to about 1.1v. Then there is the issue of output noise of the rear op amp. I used an RC filter for output filtering.

* 3. Then comes the charging and voltage boosting. The charging method uses TP4056. When it is fully charged, the green light is on, and when it is not full, it is a red light. This is the state when it is not full, and the red light is on.

When full, the green light is on. The boost uses MT3608, which adjusts the voltage to achieve the best working condition. This is the power supply part of the entire circuit. Next is the pre-amplification part of 6418. It is worth noting that there are no pin marks on the electronic tube. When installing the electronic tube, be sure not to install it upside down. Pins 1 to 5 of the electronic tube can be judged by the filament. The filament is pins 3 and 5.

Then there is the post-amplification part of ne5532. The positive phase amplifier of ne5532 is used here* 4. Project material list display:

* 5. Upload project pictures 5.1,           5.2. Other pictures of the project Welding of the charging part

* 6. Demonstrate your project and record it as a video for uploading 6.1. Official website of the video upload competition 6.2. Video title and link at Station B

  7. Is it the first public release? 7.1. Whether the project has been published or won an award before, please indicate: No 7.2. If the project is optimized on the original basis, please indicate the optimization part: None   8. Open source documents* 9. References

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