Of course, the mysterious young man is Fu Xin, regardless of Fu Xin's lack of interest in revealing his identity or participating in the search for the mysterious young man, he is huddled with the workers at this time, tackling a new product, tape recorder!

The military's order for signal boosters was about to run out, and Fu Xin had to find a new way out at this time, and he thought of the legendary "eight major items", televisions, washing machines, sewing machines, tape recorders, cameras, motorcycles, video recorders, and refrigerators. In order of importance, television sets are steadily in the first place, and the rest are in slightly different order in everyone's minds.

Fu Xin thought about coming, thinking about going, Fu Xin chose the tape recorder, this big guy, is currently the most suitable for the production of Huaxing Electronics Factory.

Fu Xin chose a cassette recorder, although this kind of big guy came out of the Dutch Philips company in the sixties, but this kind of guy has not become obsolete until the 21st century. In the Chinese market, which has just opened its door, it is an advanced large-scale item.

Cassette recorders record sound based on the mutual conversion of acoustic, electrical, and magnetic. Because the vibration of sound can produce a current with strong and weak changes, and the changing current causes a change in the surrounding magnetic field, try to record the corresponding magnetic field change on the tape to achieve the purpose of recording sound.

When recording, the switch connected to the microphone and recording amplifier is closed, and the switch connected to the speaker and amplifier is disconnected. The voice produced by the speaker is converted into an electrical signal through the microphone, amplified by the recording amplifier, and then enters the recording head. The recording head converts the electrical signal into a magnetic signal and records the magnetic signal on a moving tape.

When playback, the switch connected to the speaker and amplifier is closed, and the switch connected to the microphone and recording amplifier is disconnected. The magnetic tape with the recorded magnetic signal is moving, and a weak electrical signal is constantly induced on the playback head, and after being amplified by the playback amplifier, the electrical signal has enough power, and then it pushes the speaker to make a sound.

If you want to clear the magnetic signal from the tape, you need to wipe the sound. At this time, let the wiping head contact with the moving tape, so that the ultrasound electrical signal from the ultra audio oscillator enters the trowel head, disrupting the original magnetic signal on the tape, which is the wiping.

The working principle is very simple, and in the future, it will be learned in junior high school physics, but to convert the simple working principle into a product, it is not so simple, at least the workers and masters of Huaxing Electronics Factory think so. At that time, Fu Xin proposed to build a cassette recorder, and many of them thought it was incredible. When will the factory also have the ability to produce one of the "eight major pieces"?

Although many people were skeptical, Fu Xin still insisted on doing it, because he believed that he could make it. The cassette recorder is composed of eight parts: ultra-audio oscillator, recording amplifier, playback amplifier, wiping head, recording head, playback head, microphone and speaker.

Among them, Fu Xin, who is the most important circuit of the working principle of the ultra-audio oscillator, recording amplifier and playback amplifier, probably remembers, and the army also understands the tape recorder, Fu Xin is confident that he will make this tape recorder.

"Brother Jun, don't you see if it would be better to add a bias voltage oscillator behind this capacitor behind the LM381 low-noise dual preamplifier." Fu Xin pointed to the capacitor behind the LM381 low-noise dual preamplifier in the circuit diagram and said, he vaguely remembered that there was a bias voltage oscillator in this place.

"Biased voltage oscillator? Yes, why didn't I think of it, yes, there should be a bias voltage oscillator here, so that the frequency response of the recording amplifier head can be compensated! The army patted his head and said, then took out a small bias voltage oscillator and connected it to the back of the LM381 low-noise dual preamplifier. Fu Xin also added a bias voltage oscillator to the circuit diagram.

"Alright, now try the sound quality." After a while, the army took out a cassette tape, because there was no casing, for fear of falling, the army carefully put the tape on the magnetic head, turned on the power supply, pressed the switch, and seven or eight people stared at this extremely ugly experimental object.

"The instrument is running normally, the data is normal, and it meets our design requirements, and now the recording is stopped. Let's start playing. Fu Xin looked at the tape to the end, signaled Lin Mo, the female college student who was interning next to him, to stop singing, and commanded the army.

The army carefully disconnected the recording light, connected the playback switch, and the tape recorder began to make sounds, at first, the recorded sound was normal, which made everyone show happy expressions, but after a while, the tape recorder made a "rustling" murmur.

"No, the sound is distorted, I think this LM387 two-channel preamp needs to add a capacitor here." Fu Xin took out the circuit diagram again, pointed to the back of the LM387 two-channel preamplifier on the circuit and said.

"And how much capacitance should we add?" Zhang Daquan next to him asked. He is a seventh-level worker in the original electronic components factory, and he must also know some technology.

"Let's make a micro method, don't be too big!" Fu Xin frowned, rang for a moment, and then stretched out.

"Okay, then I'll try." After speaking, the army picked up a zero-point micromethod capacitor and connected it between the LM387 two-channel preamplifier and the sliding rheostat. Then use the instrument to detect that there is no problem with the connection, glanced at Fu Xin, and saw that Fu Xin nodded at him, the army no longer hesitated, picked up the tape, connected the sound and opened the light, and debugged it.

After a while, the tape came to an end, during which there were no accidents, and Lin Mo's voice was clearly played from this "ugly" tape recorder. There was a round of applause.

After the applause, Fu Xin said: "Okay, the last test, reverse the tape and try the wiping function." ”

The basic principle of the sound wipe is to make the magnetic flux on the tape no longer change or make the residual magnetic flux of the tape gradually decrease until it reaches zero, so as to achieve the purpose of eliminating the sound produced by the old signal. Generally, DC and AC wipes are used more.

When a point on the tape is gradually close to the wiping head, it will be subjected to the gradually increasing high-frequency wiping magnetic field, and the hysteresis loop gradually increases, and when it reaches the gap of the wiping head, it is affected by the greatest effect of the wiping magnetic field, and the magnetic layer is saturated and magnetized. There is no magnetic field left on the tape, so as to achieve the purpose of wiping.

The ultra-audio oscillator selected by Huaxing Electronics Factory on the tape recorder is the RC oscillator, which is an oscillator with resistance and capacitor as feedback and frequency selection elements, and its outstanding feature is that it can produce a very low oscillation frequency.

"Let's go!" With Fu Xin's order, the army began its own movements, and everyone present held their breath.

The machine continued to run normally until it was almost the end, when the army disconnected the switch, and there was no accident, and the data tested on the various meters showed normal.

"Rewind the tape and record! Lin Mo, you are ready. Fu Xinchao said to Lin Mo, who was standing behind him.

With Fu Xin's order, the army pressed the switch, Lin Mo began to sing, and the tape recorder also began to operate, and everyone did not dare to make a sound, for fear of making noise.

After a period of time, Lin Mo sang until her mouth was dry and her voice was a little hoarse, and Fu Xin signaled her to stop.

Fu Xin took a deep breath and said, "Let's play!" ”

The army began to move in his hands, and Lin Mo's crisp singing voice came out of the tape recorder.

"It worked!" This was the thought in everyone's minds, and then applause and cheers rang out in this simple laboratory. Because of this success, it means that Huaxing Electronics Factory has added a profitable product, which has the shortest cooperation with Fu Xin, and it has been more than two months, and they have figured out Fu Xin's temperament.

Fu Xin, he has a bite to eat, he will never treat you badly, he is not so possessive of money, so when the factory settles wages on the 10th of every month, many people receive very high bonuses!

"That's it! All right! Fu Xin opened his arms and swung up and down to tell everyone to stop.

"Everyone has worked hard in this month, and I decided to invite everyone to the cafeteria for a big meal today, how about it?" Fu Xin shouted happily.

"Good!" Smiles of joy appeared on everyone's faces.

Fu Xin said: "But before that, I want everyone to put forward some opinions and suggestions, our tape recorder is still the first product of the laboratory, and it is impossible to sell it to the market." Everyone thinks about what humanized improvements we should make in addition to packaging it in a shell. ”

"Director Fu, I have an idea." In the crowd, because his voice had been singing non-stop before, Lin Mo raised his hand and said.

Fu Xin immediately looked over and said, "Classmate Lin Mo, you have worked hard today, I decided to give out an extra bonus." If you have any suggestions, please mention them, and if they are good, we will definitely accept them. ”

Lin Mo did not refuse Fu Xin's kindness, and said in a hoarse voice: "Hmm! I wondered if it would be a bit of a hassle to rewind the tape when we just erased the tape, and if it would be better if we could just erase the tape without rewinding. ”

Fu Xin thought about it and was right, but this problem seemed to have not been solved in the products of the 21st century, so he said: "Lin Mo, your suggestion is very good, but we can't solve the technical problems on this for a while, but thank you!" You have a good suggestion. We will do our best to solve this problem you raised in the future research and development! ”

"Oh!" Lin Mo studied economics and didn't know much about technology, so he only had an "oh".

"Do you have any good suggestions?" Fu Xin asked. (To be continued.) )