Analysis of several classic and simple sound card microphone amplifier circuits

This article mainly analyzes several sound card microphone amplifier circuits, and hope it will be helpful to your study.

Super simple sound card microphone amplifier

It is used to amplify the front end of a collective microphone with a computer sound card, and a single-tube Class A radio follower, which is simple to make. The reason for the production is that the sensitivity of the microphone end of the sound card is too low and it is difficult to speak. After debugging, the sound is clear and the effect is good by pressing the lighter 3 meters away from the microphone.

The triode is any low-frequency small power tube, such as C1815, C945, 9014 and the like. Too high frequency, beta, and power is not good. It is recommended that the value of the input and output capacitors should not be too large. For voice purposes, the value in the figure is sufficient.

The 75k resistor is responsible for the microphone bias voltage. Use a high internal resistance multimeter to measure the positive of the microphone. It should be 0.2~1V. Otherwise adjust. The voltage is high, the gain is large, and the noise is large. vice versa.

The 680K resistor determines the operating point and feedback, from 500K to 1M, the larger the gain, the higher the distortion. Small is the opposite.

The 47K variable determines the operating point of the triode. For different tube types, the power supply voltage needs to be changed accordingly, and the front and rear stages are involved. Adjust to minimize distortion and maximize gain.

The voltage can be 5~15V. Of course, the work point must be adjusted accordingly. High voltage, low distortion and high gain. Do not take the power supply from the 5V~12V output of the computer power box. If there is square wave interference from the host, use an external independent power supply. Even mobile phone chargers are available.

Light-emitting diodes are used for protection; it is best not to omit it for work instructions.

The shell can be an ordinary serial port box, the circuit is too simple, direct lap welding. Note that the ground wire should not form a loop to avoid interference and self-excitation.

After debugging, consider the issue of mechanical strength. The space in the serial port box can be filled with sealed silica gel.

The connector is directly glued to the half of the serial port box with epoxy resin (two-component glue). Note that the glue should be less and just add it to a few key stress points. Too much, it is troublesome to stick the movable contacts.

The sensitivity of the dynamic microphone is too low, it is too reluctant to connect to this amplifier, try using an op amp when you are energetic. If you want to use 1.5V power supply, you can remove the light-emitting diodes, recalculate the next few bias resistors, ensure that the transistor b, e 0.6V, microphone bias 1V, ,,, gain and distortion. I personally think that the 5V solution is more convenient, and the distortion and gain are more compromised. There are old and used chargers everywhere, and you can grab one to get power. You can also connect to USB to get power in emergency.


Unexpectedly found:

1. It was thought that the microphone input of the sound card is monophonic. This time it was discovered that a newer sound card chip supports dual-channel mic. I had known that I had chosen a larger parallel port box to directly do the stereo speech amplifier.

TDA2822 making microphone amplifier circuit

This circuit has few external components and is simple to make, but the sound quality is unexpectedly good. Adopt a dual-channel audio amplifier integrated circuit. Its main features are high efficiency and low power consumption. The typical quiescent current is only about 6mA. The integrated circuit has strong voltage adaptability (1.8V～15V DC). Even if it is used at 1.8V low voltage, it will still have about 100mW. The power output, the specific circuit is shown in the figure.


The electret microphone MIC converts the picked-up sound signal into an electric signal, and introduces it from the foot ② of U1 through C2 and W, and after U1 audio amplification, it pushes the speaker to pronounce. This machine is connected to a BTL output circuit, which is good for improving sound quality and reducing distortion. At the same time, the output power is also increased by 4 times. When 3V power supply, its output power is 350mW.

Resistors R1 and R2 are all 1/4W metal film resistors, W is a small carbon film potentiometer, C2 is best to use monolithic capacitors, if there is no good quality ceramic capacitors, C1, C4, C3 use high-quality withstand voltage 16V , Electrolytic capacitor with small leakage current, MIC uses high-sensitivity electret microphone. K selects small button switches or toggle switches, etc. U1 selects TDA2822M or TDA2822, or D2822 can be used instead. It is made according to the numerical value in Figure 1. Generally, it can work normally without debugging.

Electret microphone detection:

For example, use the RX 1O0 gear of the MF47 multimeter to measure the Great Wall CZⅢ electret microphone. When the black test lead is connected to the core wire and shell of the electret microphone, the pointer of the multimeter points to 3kΩ. When blowing hard, the pointer points to the value of 4kΩ (also The resistance of the microphone becomes smaller). If you blow hard and the pointer of the multimeter swings very small, you can swap the two test leads and try again. If the pointer of the multimeter still swings very small, it means that the electret microphone is damaged.

When the electret microphone is used, the drain D must be connected to the positive pole of the power supply through a 4.7~10kΩ resistor, and then connected to the amplifier circuit, as shown in the figure.


Add amplifying circuit to the microphone

The electronic components are as follows: resistance R1 is 1kΩ, resistance R2 is 1MΩ, and R3 is also 1kΩ. The triode vT is 9014, the capacitor c1 is 4.7uf, and the c2 is 4.7uf, and a battery of No. 5 is enough.


1. The working principle of the amplifying circuit

Figure 1 is a circuit diagram of the entire microphone amplifier circuit. It can be seen from Figure 1 that the entire circuit only has six or seven originals. Let’s talk about the working principle. The resistor R1 is responsible for providing the working voltage to the microphone, R2 and R3 are responsible for providing the bias voltage to the transistor, and the capacitor C1 is responsible for coupling the signal from the microphone to the transistor for amplification, and the amplified signal passes through the capacitor. After C2 is coupled, it is sent back to the positive pole of the microphone line, which is the outermost shielding layer of the microphone line (that is, the outer layer of copper mesh). Figure 2 shows the materials or electronic components that we use when making them.

2. Precautions like making

The specifications of the electronic components required by the entire amplifying circuit are as follows: the resistance R1 is 1KΩ, the resistance R2 is 1MΩ, the resistance R3 is 1KΩ, the transistor VT is 9014, the capacitor C1 is 4.7μF, the capacitor C2 is 4.7μF, and the battery uses the general No. 5. The battery is sufficient, and it can be used normally for about half a year. The finished circuit board after making is shown in Figure 3.

Pay attention to the following points in the production process:

1. The pins of the triode must be connected correctly, otherwise it will not be able to magnify. The pin distinction is as follows: the lead of the triode is facing down, the flat side is facing itself, followed by E (emitter), B (base) and C (Collector); 2. The microphone head is also polarized (see Figure 4 for specific distinction);

3. The polarity of the coupling capacitor can be distinguished by marking. The pin with an arrow and marked "-" is the negative pole, and the positive pole is generally not marked.

Since there are few components, it can be directly welded on the shed. After the circuit board is completed, it can be directly installed in the base of the microphone, and the power lead of the circuit board can be connected to the battery slot reserved for the microphone.

Third, the effect test

After trial, the effective distance of the microphone can reach 5~6 meters, and with the voice input function of Office Word 2003, the effect is also very obvious, and it can be accurately recognized when speaking about 1 meter away from the microphone.