Most modern amplifiers audio frequencies (USC) built without dividing capacitors at the output. If a fault occurs in the amplifier emergence of a DC voltage at the output of USC can lead to costly damage of the speaker system. To protect them from the DC voltage of either polarity offer simple device (Fig. 1).

As a prototype of the derived scheme of the protection device amplifier "405" f."Quad", but the precautions taken to prevent inadvertent opening of the triac at a high slew rate of the output voltage, which is in the modern USC. Additionally introduced light indication of fuse failure, the flashing on the led when the protection is activated.

Non-contact protection of loudspeakers

Fig.1. Schematic diagram of the protection device speakers

When the output of USC DC voltage of either polarity more than 3...4 In, dramatically increases the voltage at the terminals of the capacitor C2, NW. The current flowing through the resistor R4, one of the diodes VD5, VD6 and one of the transistors VT1, VT2, opens the triac VS1. Open triac bypasses the output of USC until the blown fuse FU1. When the burn starts to blink the led HL1. The elements C1, L1 are designed to prevent unauthorized opening of the triac due to interference.

The fuse is chosen based on the maximum output of the amplifier and the resistance of the speaker system.

In the device, you can use resistors types S1-4, S2-23 MLT and other appropriate power. The Capacitor C1 - ceramic types K10-7, K10-17, km-5. Oxide capacitors C2, NW - type K50-16, C50-35. Both of the capacitor can be replaced by one non-polar, while the diode VD7, VD8 are excluded from the scheme. Diodes KDA can be replaced by CD (A, B), CD (A, B), CDA, 1N4148. HL1 led may be flashing or constant illumination, for example, AL307, CIPD, CIPD.

Transistor VT1 can be replaced by CTE, CT, CT, MPSA-43, 2N5550. VT2 is replaced CTE or any p-n-p transistor of the series CT, CT, 2SA709, 2SA910, MPSA-93. As a triac VS1 ideal CU with the indices D, e or TS-10, TS-16 and the other on the operating voltage of not less than 100 V.

The inductor L1 is wound wire sew-2 00,68 mm - 75 turns on a frame of thick paper with an outer diameter of 10 mm.

To check the assembled fuse node is temporarily replaced by an incandescent lamp at a voltage of 6...12 V and a current of 0.16...1 A. the Node is connected to the output laboratory power supply with adjustable output voltage 2...10 V. Gradually increasing the output voltage, at the moment of ignition of the lamp is determined by the threshold. If it is not more than 4, then the node is suitable for use with the automotive USC. When specified in the scheme of the capacitors C2, NW, delay protection operation will be about 1 s. If necessary, the delay time can be reduced to 0.2...0.5 s, taking these smaller capacitors.

Structurally, this unit may be placed inside USC and AC. In case of installation of the node inside the acoustic system, if the speaker has a filling of combustible material, for example, cotton wool, he should not come into contact with details of site protection.

For multichannel amplifier is going appropriate number of blocks.


  • D. Ataev, V. Bolotnikov. Functional units amplifiers high-quality sound reproduction. - Radio and communications, 1989, P. 111.
  • Author: A. Butov, S. CORBA, Yaroslavl region; Publication:

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