High-performance power amplifier driven by operational amplifier

High-performance power amplifier driven by operational amplifier

Due to the limitation of the voltage of the op amp, the power of the traditional op amp drive power amplifier is difficult to increase. This power amplifier uses voltage conversion current to directly drive the power amplifier tube for power amplification, so the output power mainly depends on the final power amplifier tube and power amplifier power supply, and the speaker has no on / off impact sound. The whole machine does not add any compensation capacitor, which is original and has little phase shift. Due to the use of op amps for constant current amplification, it is easy to replace op amps with different performances, and there are more options for sound. This article designs a simple and practical power amplifier driven by an op amp.
The circuit is shown in Figure 1. IC1 and T1, IC2 and T2 respectively constitute a current negative feedback absorption constant current source, which is responsible for the voltage and current conversion and amplification of the positive and negative half cycles of the audio signal, so that the base currents of T3 and T4 are only affected by IC1, T1 and T4. IC2 input voltage control, that is to say, as long as the input of the op amp is a constant voltage value, the current flowing through the collectors of the final tubes T3 and T4 is also a constant value. W1 and W2 (multi-turn potentiometer) are used to adjust the quiescent current and output zero point of T3 and T4 respectively. IC3 and R1, R2 and R5 form a quasi-current negative feedback circuit, as long as the resistance of R3, R4 or R2 and R6 is changed accordingly. Can change the size of the gain. The power amplifier protection circuit (Figure 2) adopts the method of cutting off the total power supply. The advantage is that when the power amplifier fails, it not only protects the speaker, but also protects the final stage tube. The working principle is: when the power is turned on, T6 is electrically turned on, J is self-protected, and the power remains on. When the DC component of the output zero point of the power amplifier is greater than ± 0.24V, IC4 or IC5 outputs a high level, so T5 is saturated and turned on, T6 is turned off, relay J is released, and the total power is cut off, thereby achieving the protection function of the speaker and the power amplifier tube .
High-performance power amplifier driven by op amp

The debugging of this machine is relatively simple. First adjust W1 and W2 to the minimum position, then slowly adjust W1 and W2 to make the upper pressure drop of R8 and R7 to 40mV (200mA). Measure the output point, and then fine-tune W1 or W2 to control the output voltage below 5mV. Then, after preheating for half an hour, adjust it again, then you can connect to the speaker test. Subjective evaluation, the amplifier has a high signal-to-noise ratio, full bass, elasticity, and slender and smooth treble.
The op amp adopts dual op amps such as NE5532 or AD827, and the power tubes 2SB674, 2SD667, etc. are selected for T1 and T2. The final power amplifier tube can be selected from the three-conductor pair tube 2SC2922, 2SA1216 or 2SC3281, 2SA1302 and other audio pair tubes, and the resistance is 1 / 4W metal. Membrane resistance.

6V AC DC wall mount switching power adapter produced by Shenzhen Juyuanhai Electronic Co.,Ltd were certificated by UL/TUV. It is a small power supplies that used for many consumer products and home appliances, like smart phone, tablet, camera, Bluetooth speaker, aromatherapy diffuser, LED lighting, stage lighting, security, etc. All our power supply have over voltage protection, over current protection and short circuit protection, 100% burn in test and high voltage test during production to make sure high quality. 

6V AC DC Switching Power Adapter

6V AC DC Switching Power Adapter,AC DC 6V 1.5A Charger Adapter

Shenzhen Juyuanhai Electronic Co., Ltd. , https://www.powersupplycn.com