Pure DC current negative feedback power amplifier circuit made by LM3886TF

LM3886 TF is a new high-power audio amplification integrated circuit launched by NS Company in the United States. The TF behind it is a fully insulated package. Compared with LM1875T, it has larger power and can reach a maximum of 68W continuous without distortion at the rated operating voltage. Average power, it also has a relatively complete over-voltage, over-current and over-heat protection function. The most valuable thing is that it has the function of automatically resisting current shock when turning on and off, so that the speaker can work safely. The excellent performance of LM3886 has made it widely used in audio production in recent years. It is directly used in many finished power amplifiers as a power amplifier or as a subwoofer amplifier circuit. The new high-fidelity audio power amplifier integrated circuit LM3886TF introduced by the American NS Company (National Semiconductor Company) is used as the power amplification, and the operational amplifier NE5532 or AD 827 is used as the pre-linear amplification and tone amplification. Its features include: large output power (continuous output power 68W), low distortion (total distortion plus noise <0.03%), protection functions (including overvoltage protection, overheating protection, current limit, temperature limit, switching power supply The speaker has complete shock protection and squelch functions, few peripheral components, easy production and debugging, and stable and reliable operation. Because it is simple and practical to make power amplifier circuits, it is especially suitable for audiophiles and electronics enthusiasts.

The electrical parameters of LM3886TF are as follows:

The LM3886 can achieve a continuous average power of 68W when VCC=VEE=28V and a 4-ohm load, and an average power of 50W when VCC=VEE=35V and an 8-ohm load. Has a wide power supply voltage range VCC+VEE of 20V-94V;

Total harmonic distortion + noise: 0.03% at 60W 20Hz<f<20kHz AV=26dB

Slew rate (SLEW RATE): The value when VIN=2.0VP-P, tRISE=2ns is 19V/us

Total quiescent current: 50mA

Input bias current: 0.2uA

Gain bandwidth product: 8 MHZ

When talking about the playback quality of a power amplifier, the selection of components and the design of the circuit are very important, but another very important thing is the design of the circuit board. The PCB layout is unreasonable, no matter how good the circuit and the most audiophile-grade components It doesn’t help. For audio enthusiasts, AC noise and channel crosstalk are unacceptable. Before designing the LM3886 power amplifier, the first launched on this site, the author has studied some domestic and foreign products. Audio power amplifier circuit board, the simplest source of information is the PCB diagram of the recommended application circuit of some well-known semiconductor manufacturers, and strive to achieve the effect of turning the volume of the power amplifier board to the maximum, putting the ear close to the speaker, there is no humming effect, and the sound is Cross-traffic between paths is minimized.

The circuit adopts an integrated design that combines the front and rear stages. The width of the copper in high-current parts such as the power supply and output circuit is widened, and a pad is reserved to thicken the solder to reduce the resistance of the copper. The arrangement of components is more reasonable than the previous sample. And compact, considering the safety of the rear speakers, a relatively stable and reliable speaker protection function is added and a better quality relay is used, such as Japan's OMRON RELAY. It should be said that the now completed LM3886 power amplifier board is a board with complete functions and reasonable wiring. As long as the components are selected appropriately, I believe it will achieve satisfactory results if it is used to modify home audio. Reasonable grounding is required during wiring, and independent wiring is implemented at the front and rear. After the grounding of the left and right channel power amplifier ICs is separated, star grounding is required. This board is designed to combine the front and rear stages, but the wiring of the front and rear stages has been fully considered. Separation, careful enthusiasts can observe that the front stage of the PCB board and the high-current power amplifier rear stage have been separated by several separate ground wires, so that the phenomenon of electromagnetic interference is basically minimized. This can be verified in the audition. In order to maximize the excellent performance of LM3886.

Listen:

After assembling the sample, carefully check that the circuit is correct, then connect the power supply, signal line and speaker connector (note that the polarity is not wrong). The equipment is ordinary, the sound source is Xianke VCD, and the speaker is homemade. First, do not play it. For music, turn up the volume potentiometer after powering on, and put your ear close to the speaker. The result is that there is no hum, and the noise (the noise of the integrated circuit itself) is very small. You can't hear it at all from a little further away, which means that the wiring of this circuit has met the design. Reasonable, the measures of separate wiring of high-current rear stage and front stage and point grounding effectively reduce the cross-talk between front and rear stages. Then comes the exciting moment. Playing music gives people a refreshing feeling, which is different from the previous NE5532. Just like the king of op amps replacing the TL082, the excellent performance of the high-speed op amp AD 827 and the advantages of the LM3886 are fully utilized. The breath of the lips and teeth of the human voice is clearly audible, the sense of air is very realistic, and the extension of high and low frequencies is better than that of the NE5532. Personally It is believed that this is because the conversion rates of the two integrated blocks are very high, and the benefits of combining the two are naturally needless to say.