Speaker protection device. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Speakers

 Comments on the article

In life, situations are not uncommon when, for one reason or another, speaker systems are connected to audio frequency amplifiers whose power exceeds the maximum allowable for the system, which, on the one hand, often allows you to get better sound quality, increase the dynamic range, on the other hand, increases the risk damage to dynamic heads due to overload.

This is especially true when using speakers at school, student, youth parties, where acoustics are often connected to the first working amplifier that comes across, which is "more powerful". In order to prevent damage to the AU when power exceeding the rated power is supplied to it, it must be equipped with an overload protection unit built into the AU and not requiring an additional power source. A schematic diagram of such a device, designed to protect speakers with a power of 10 ... 35 W, is shown below.

In addition to shutting down the speaker in case of overload, this device also protects its dynamic heads from damage in the event of failure of the amplifier transistors and the appearance of a constant voltage at its output. The device is connected to the output of an audio frequency power amplifier. The AC voltage is rectified by the diode bridge VD1. Resistor R1 eliminates the influence of the device on the operation of the power amplifier. The rectified voltage is smoothed by oxide capacitors C3, C2.

As long as the power at the output of the amplifier does not exceed the maximum allowable for the AC, the voltage at the terminals of the capacitor C2 is small, the zener diode VD3 is closed, therefore, the trinistor VS1 is also closed. In the microcurrent mode, SCRs of this type are controlled, i.e., they can be closed by removing the control voltage. Since VS1 is closed, transistor VT2 will also be closed. The contacts of the relay K1 are closed, 100% of the power will be supplied to the dynamic heads of the AC.

As soon as the power at the output of the amplifier exceeds that allowed for the AC, the voltage at C2 will increase so much that the zener diode VD1 opens, the trinistor VS1 and the transistor VT2 open, the relay contacts K1 open, the power supplied to the AC will be limited by resistors R11-R13. These resistors act as a load on the power amplifier, which improves the stability of the amplifier in the event of a loudspeaker shutdown, in addition, these resistors reduce sparking between the relay contacts when they are closed and opened.

When the overload protection is triggered, the HL1 LED lights up. Transistor VT1, the emitter junction of which operates as a micropower zener diode with a stabilization voltage of 7 ... 12 V, protects the field-effect transistor from breakdown of the gate insulator. As soon as the voltage at the output of the amplifier decreases, the zener diode VD3 will close, VS1, VT2 will close, the contacts of relay K1 will close, full power will again be supplied to the AC. Resistor R8 introduces a small hysteresis that prevents the relay contacts from cycling at a constant output power slightly above the threshold. Resistor R9 reduces the current through the relay winding when its contacts open, capacitor C6 accumulates enough energy necessary for reliable operation of the relay.

When the structure is placed inside the speaker cabinet, the structural elements operate in conditions of sufficiently strong vibrations in a wide range of sound frequencies created by dynamic heads, in addition, in some cases, an alternating magnetic field from dynamic heads should be taken into account. The printed circuit board should be located at the maximum distance from the open magnetic systems of the dynamic heads.

The device uses fixed resistors MLT, Cl-4, C2-23 or imported analogues. It is desirable to use the tuning resistor R3 in a closed case, for example, SP4-1, SPZ-16v, SP5-16A, SPZ-19a, SP4-3. After tuning, the rotary axis of the resistor should be fixed with a drop of paint. Capacitor C1 film polyethylene terephthalate K73-17, K73-9 or similar. C4 - ceramic K10-17, KM-5, oxide capacitors - K50-35 or imported analogues. Capacitor C3 can be made up of two 470 uF capacitors (this is provided on the printed circuit board).

If necessary, capacitor C6 should also be used for an operating voltage of 100 V. In case the device is used with amplifiers that have a supply voltage of the output stages of more than ±50 V, oxide capacitors must be for a voltage of 160 V, the power and resistance of resistors R1, R2 , R9 also needs to be increased. Capacitors C3, C6 are installed parallel to the printed circuit board and additionally fixed to it with wire ties. The diode bridge can be replaced with a similar low-power one, for example, DB103-DB107, RB153-RB157, or made up of four rectifier diodes with an operating voltage of at least 100 V. Instead of KD243A, you can install any of the KD243, KD247, KD208, KD105, 1N4002-1N4007 series.

The zener diode 1N4738A can be replaced with KS175A, KS175Zh, KS126K, LED - with any other. Instead of the trinistor KU112A, you can use KU 112 AM in the TO-92 package. Field-effect n-channel transistor IRF9540 in this design can work without a heat sink. Its maximum drain-source voltage is 100 V, the domestic analogue is KP785A. Instead of this transistor, you can use IRF9634, KP796A, having UCH MAX\u250e 315 V. Instead of KT312A, you can use any of the KT315, KT9014, SS1 series. Relay K29 - REK-4.501.56, passport DUSCH950. The winding resistance of this relay is about 15 ohms, stable switching of contacts occurs at a voltage of 7 V, the minimum holding voltage is XNUMX V. A relay of this type was used in the remote control modules of domestic USCT televisions. When replacing, you should take into account the fact that the contacts of this relay must switch a significant current.

The device can be mounted on a 140x50 mm printed circuit board, where all elements are installed, except for the LED. On pic.2 the printed circuit board is shown from the side of the conductors.

On the mounting side, it is desirable to cover the board with three or four thin layers of epoxy glue. Each next layer is applied after the previous one has hardened. The board is attached to the AC case from the inside with five M3 screws or self-tapping screws. If possible, it is desirable to close it with a blank thick-walled (> 0,5 mm) casing, which will also reduce the likelihood of device failure due to vibrations in powerful speakers, as well as reduce the likelihood of relay contact bounce.

Two copies of these devices made by the author are used in conjunction with 15AC-220 acoustic systems that use 25GDN-3-4 dynamic heads. These systems begin to wheeze and rattle at more than 40 watts of input power. The protection threshold is set to 25 W. These speakers are powered by the Orbita UM-002 stereo amplifier, which is capable of developing power above 50 W at a 4 ohm load. The other two copies are installed in self-made sealed speakers, assembled on 10GDSh-1 broadband heads, powered by a Corvette 50U-068 C amplifier. The threshold for switching on the protection is also set to 25 W based on the operation of the amplifier for a load of 4 ohms. If, when working with powerful speakers (> 35 ... 5O W) and a powerful amplifier, the trinistor closes at too low a power for this case, the resistance of resistors R4 and R7 can be doubled.

This device can be modified by installing a thermistor with a negative TCR resistance of 2 ... 3,3 kOhm at 4,7 ° C instead of a constant resistor R25, which should be rigidly fixed through a gasket made of thermally conductive rubber on the magnetic system of a powerful low-frequency head. In this case, with a strong heating of the magnetic system, the device will turn on protection at a lower output power of the amplifier.

Author: A. Butov, p. Kurba, Yaroslavl region; Publication: cxem.net

See other articles Section Speakers.

Read and write useful comments on this article.

<< Back

Latest news of science and technology, new electronics:

Artificial leather for touch emulation 15.04.2024

In a modern technology world where distance is becoming increasingly commonplace, maintaining connection and a sense of closeness is important. Recent developments in artificial skin by German scientists from Saarland University represent a new era in virtual interactions. German researchers from Saarland University have developed ultra-thin films that can transmit the sensation of touch over a distance. This cutting-edge technology provides new opportunities for virtual communication, especially for those who find themselves far from their loved ones. The ultra-thin films developed by the researchers, just 50 micrometers thick, can be integrated into textiles and worn like a second skin. These films act as sensors that recognize tactile signals from mom or dad, and as actuators that transmit these movements to the baby. Parents' touch to the fabric activates sensors that react to pressure and deform the ultra-thin film. This ... >>

Petgugu Global cat litter 15.04.2024

Taking care of pets can often be a challenge, especially when it comes to keeping your home clean. A new interesting solution from the Petgugu Global startup has been presented, which will make life easier for cat owners and help them keep their home perfectly clean and tidy. Startup Petgugu Global has unveiled a unique cat toilet that can automatically flush feces, keeping your home clean and fresh. This innovative device is equipped with various smart sensors that monitor your pet's toilet activity and activate to automatically clean after use. The device connects to the sewer system and ensures efficient waste removal without the need for intervention from the owner. Additionally, the toilet has a large flushable storage capacity, making it ideal for multi-cat households. The Petgugu cat litter bowl is designed for use with water-soluble litters and offers a range of additional ... >>

The attractiveness of caring men 14.04.2024

The stereotype that women prefer "bad boys" has long been widespread. However, recent research conducted by British scientists from Monash University offers a new perspective on this issue. They looked at how women responded to men's emotional responsibility and willingness to help others. The study's findings could change our understanding of what makes men attractive to women. A study conducted by scientists from Monash University leads to new findings about men's attractiveness to women. In the experiment, women were shown photographs of men with brief stories about their behavior in various situations, including their reaction to an encounter with a homeless person. Some of the men ignored the homeless man, while others helped him, such as buying him food. A study found that men who showed empathy and kindness were more attractive to women compared to men who showed empathy and kindness. ... >>

Random news from the Archive Hearing aid that reads lips even through a mask 09.09.2022 Engineers from the University of Glasgow have created a hearing aid that lip-reads words even through a mask on the interlocutor's face. The device uses artificial intelligence - the radar scans the movements of the lips and determines what sound they are typical for. For open faces, the accuracy is 95%, for closed faces, 83%. The new hearing aid will also use traditional sound amplification technology. The scanner will help people hear well both in normal conditions and in noisy environments. Prior to this, the effect of a cocktail party for the hearing impaired was provided by devices that read lips with the help of a camera. But the video recording of the interlocutors could violate their privacy. "Approximately 5% of people in the world have a hearing impairment - that's 430 million people. Hearing aids have changed the lives of many of them," said Kammer Abbasi, co-author of the development.

Other interesting news:

▪ radio controlled genes

▪ Viagra against malaria

▪ Smart bidet from LG Uplus

▪ The ovary was printed on a 3D printer

▪ Dual use battery

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ section of the site Stories from the life of radio amateurs. Selection of articles

▪ article Basic principles of geology. History and essence of scientific discovery

▪ article Which animals have the most genes? Detailed answer

▪ citrus article. Legends, cultivation, methods of application

▪ article A device for checking telephone sets. Encyclopedia of radio electronics and electrical engineering

▪ article Domestic coaxial cables. Encyclopedia of radio electronics and electrical engineering

Leave your comment on this article:

All languages ​​of this page

Arabic	Hebrew	Polish
Bengali	Hindi	Portuguese
Chinese	Italian	Spanish
English	Japanese	Turkish
French	Korean	Ukrainian
German	Malay	Vietnamese

Home page | Library | Articles | Website map | Site Reviews

www.diagram.com.ua
2000-2024