audio power amplifier

* 1. Introduction to project functions

• 1. Function description
• AUX audio input + Bluetooth input two-in-one 20Wx2 output analog power amplifier
• 6N2 is the pre-amplifier + LM1875x2 post-amplifier
• Vacuum tubes have the advantages of large input dynamic range and fast conversion speed; LM1875 is also an old friend of everyone, with ultra-low distortion rate, good output power, and protection against overload and overheating. As the core of this circuit
• Adding Bluetooth diversified input methods, the transmission distance and efficiency are good.
• Parameter Description
• 1. In the power supply part, the main power supply is connected with a 3P terminal block. 2 input fuses to prevent overload and short circuit.
• Main power supply range: AC12-18V
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• The preamp filament and Bluetooth board are powered.
• Adopt DC-DC solution and use LM2596 to step down to +6.3v to power the 6N2 filament
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• The Bluetooth board is powered by the filament, which is filtered by LC and then dropped by D4 to power the Bluetooth board.
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• The preamplifier is a 6N2 from Dawn. There is a certain change in the timbre, and there is also a certain improvement in the listening experience. The circuit has not been added with any mixing or polishing, and is basically original.
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• The peripheral circuit of LM1875 is basically designed according to the official circuit diagram.
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• The M18 Bluetooth version is a ready-made module purchased from Taobao. It has LC filtering added to the power supply and four control buttons.
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• Interface description
• The main power supply interface is JL301 terminal block, and the power switch is added to the input end of the transformer.
• Audio input methods, wired input and wireless input. Manual switching mode, turn on or off Bluetooth SW1
• 2.0 dual channel, still uses two 2P binding posts, connected to two full-range speakers, recommended impedance 4-8 ohms, power 20 watts x2
• function test
• The long-awaited express delivery and PCB finally arrived. After welding, they fell directly into the ditch and could not work properly. After some analysis. I found that on the schematic diagram, VEE and GND were short-circuited.
• Texture description, corrected in schematic.
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• Question 2: The PCB library package of 6N2 Xiaojiujiao is wrong (the pin position is wrong)
• Texture description and library packaging have been updated. PCB needs to be updated.
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• Question 3: LM1875 self-oscillates (suspected to be caused by covering all the GNDs together). In this version, I used a button SW7 (also the preamp use/cancel button) to directly pull up to eliminate the oscillation, but this way the speaker will There is DC loss
• Personal testing found that after pulling up, you can’t hear any self-noise and it doesn’t affect the music playback. Everything is normal.
• Welcome to leave a message in the comment area and think of ways to reduce or eliminate self-excitation in PCB design.
• Finished product display
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• Two 1875s and a CPU radiator are enough for heat dissipation. The speaker used in the picture is eight ohm and 15 watts.
• Note: The PCB has not been updated, and the 1875 self-excitation cannot be used in the front stage yet .
• This time is a pure post-level test .
• Friends are welcome to correct mistakes in the comment area, thank you in advance.

*2. Project attributes

first public

Try combining tubes and transistors

Experience tube + classic LM1875

See if you can create a different spark

* 3. Open source agreement

1. Embrace open source, share, and have unlimited happiness !

2. Open source agreement GPL3.0

*4. Hardware part

*5. Software part

*6. BOM list

*7. Contest LOGO verification

* 8. Demonstrate your project and record it as a video for uploading

More details: https://diy.szlcsc.com/posts/06c94d90c2c447dfbd9ed7339ff4a5b1