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Amplifier PT2399 debugging guide

更新時間: 2020-12-08 18:00:35

Loudspeakers are used in subway broadcasting, traffic control, football matches, etc. However, there are some problems when using loudspeakers, such as reverberation, howling, and the size of the loudspeaker. Therefore, it is necessary to do the amplifier debugging, and PT2399 is the key component.

Before understanding the debugging of the loudspeaker PT2399, we first understand several basic concepts in the loudspeaker system.

1. Reverberation

When sound waves propagate in the hall, they are constantly reflected by the walls. Even after the sound source stops sound radiation, there will still be a sense of sound. 

However, because the energy of the sound waves is constantly absorbed by the surrounding walls and other obstacles, it is the sound source After the vibration is stopped, the sound can only be maintained for a limited period. This phenomenon is called reverberation, and the maintained time is called reverberation time.

2. Echo

It is a single fixed reflected sound, its intensity and time difference are large enough to distinguish it from the direct sound, and it can distinguish the syllables. The echo and the original sound are at least 50ms apart before they can be felt.

3. Artificial reverberation

Repeatedly superimpose the sound several times and gradually attenuate it to get the reverberation effect.

4. Howling

After the microphone is picked up, the sound is amplified by the mixer, peripheral equipment, power amplifier, and speaker. 

This sound enters the microphone through direct radiation or acoustic reflection, which causes the entire sound reinforcement system to generate positive feedback, causing the acoustic and electrical signals to self Encourage, the speaker then whistle, the principle is very simple: when the MIC is very close to the speaker, the sound of the speaker is captured by the MIC. 

At this time, the MIC transmits the sound to the amplifier, and the amplifier transmits the sound to the speaker. When the sound becomes louder. The louder sound is captured by the MIC again... and so on.

It can be seen from the above content that debugging the loudspeaker is mainly to eliminate howling. How to eliminate howling?

Generally speaking, the frequency of howling is relatively high. The simplest method is to attenuate the frequency of howling and attenuate the frequency of howling through an RC circuit. 

Generally, the series resistance should be less than 10K, and the capacitor should be less than 104 to achieve better results. Besides, a capacitor of 103 or less on the feedback resistance of the triode amplifier circuit or the operational amplifier circuit can also play a role in eliminating howling...

PT2399 debugging reverberation and how to eliminate howling

The following picture shows the PT2399 reverberation circuit

PT2399 reverberation circuit picture

If the MIC signal directly enters the PT2399, the sound is not loud enough, so it is necessary to add a level of amplification before entering the PT2399. The 103 capacitors can be added to the amplifying feedback resistor R40 to eliminate howling.

The following figure shows the circuit of the reverberation part

the circuit of the reverberation part

  • To eliminate the interference of the reverberation circuit on the radio and other circuits, single-point grounding is adopted.

  • The resistor R31 connected to the 6th pin adjusts the reverberation time, increasing the reverberation time will increase, otherwise, it will decrease.

  • The capacitors C37 and C36 connected between the 9th, 10th and 11th, and 12th pins are used to adjust the reverberation effect. Generally, 683~104 are sufficient, and generally do not need to be changed too much. If the two capacitors are the same size.

  • The capacitors C38 and C26 connected between the 13th, 14th, and 15th and 16th pins are also used to adjust the reverberation effect. Generally, 681~102 are used, and there is no need to change too much. If the two capacitors are the same size.

  • The R44 and C40 connected to the 14th pin form an RC circuit, which can adjust the howling of the reverberation. Adjusting the resistance and capacitance can effectively suppress the howling.

  • C29 and C28 are the coupling capacitors of the reverberation circuit, which can adjust the clarity and fullness of the reverberation sound. Reducing the capacitor can reduce the low-frequency sound of the reverberation sound, making the sound clearer, but too small. The reverberation is thin and not loud enough.

  • If the shouting voice is too deep, you can reduce the input capacitor C20 and the output capacitor C31.

The above is the amplifier PT2399 debugging guide, I hope it will be helpful for you to debug the amplifier. If you need to find other electronic components, you can find them in the search box on the Jotrin website.

ラベル: PT2399


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