Classics JLH1969 Single-ended Class A Amplifier Base On HOOD1969 Headphone Amp DIY Kit/Finished Board

Introduction: In 1969, United Kingdom engineer John Linsley Hood published the famous JLH single ended Class A power amplifier at Wireless World, which achieved excellent listening experience with its simple circuit. It quickly became popular worldwide, and there were countless imitators of the JLH1969. This headphone amplifier is designed based on the architecture of the Base on JLH1969, with rich even harmonics creating a beautiful and unique charm. It is also the circuit closest to the sound of an electronic tube, with warm, sweet, delicate, and durable sound, while perfectly reflecting both dynamics and sound field. Due to being a Class A circuit and with a static current adjustment of 220mA, this headphone amplifier has strong current driving capability, even headphones like K701, which are well-known for their high current, can be well driven. Heating of Class A circuits is also inevitable, and a slight temperature sound is better. Input voltage: AC 18V (Transformer power not less than 40W) Frequency characteristics: 12Hz --- 50KHz (+ 0db, -1db) 12Hz --- 120KHz (+ 0db, -3db) SNR:>98db Conversion rate:> 35V/uS Quiescent Current: 220mA Weight About 2.2kg Size: 107mm * 110mm (W*H) Debugging method: Step 1: Adjust the power supply voltage: Measure the voltage at+21V and GND, adjust the 2K blue adjustable resistor, and adjust the voltage to DC 21V (NOTE: The input voltage must be AC 18V. If your input voltage is lower than AC 18V, the+21V voltage position voltage needs to be 3-3.5V lower than the rectified voltage to ensure reliable operation of LM317, otherwise there will be serious noise.) Step 2: Adjust the static current: Measure points "A1" and "A2", connect the multimeter to the current "mA" position, adjust the 10K blue adjustable resistor to adjust the current to around 220mA, and then short-circuit these two points with wires. Step 3: Adjust the midpoint voltage: Measure the two points "V1" and "GND", connect the multimeter to the voltage position, adjust the 200K blue adjustable resistor to adjust the voltage to half of the+21V voltage. If the voltage at the+21V position is not 21V during the first adjustment step, it doesn't matter as long as the difference is not significant. NOTE: We have DIY kit or finished board (Optional) ◆ DIY kit ---- All parts need you to solder and test it. ◆ Finished board ---- All parts have been welded and tested OK.