Acoustic protection circuit and turn-on delay. Speaker protection device based on scheme A

We checked its performance, evaluated the sound quality of the main channel. It's time to add an accidental short circuit protection module to it, so that all the work does not go to waste, due to inevitable accidents during its operation. We will also collect the rest of the low-power ULF channels for connecting rear speakers.

PROTECTION AS UMZCH

Initially conceived to use the scheme of protection against BRIG , but then reading reviews about triac protection I wanted to try it. The protection units were made at the very end, then it was tight with finances, and triacs and other components of the circuit turned out to be quite expensive for us, so I returned to relay protection. I remind you that all schemes are review.

As a result, three protection units were assembled, one of them for a subwoofer amplifier, and the other two for OM channels.

On the web you can find a large number of protection block diagrams, but this scheme has been tried by me repeatedly. In the presence of a constant voltage at the output (above the permissible), the protection instantly works, saving the dynamic head. After power is applied, the relay closes, and when the circuit is triggered, it should open. Protection turns on the head with a slight delay - this, in turn, is additional insurance and a click after turning on is almost inaudible.

The components of the protection unit may deviate from the specified, the main transistor can be replaced with our KT815G, used high voltage transistors MJE13003- I have a lot of them, in addition, they are quite powerful and do not overheat during operation, so they do not need a heat sink. Low power transistors can be replaced by S9014, 9018, 9012, even on KT315, best option - 2N5551.

Relay for 7-10 Amperes, you can pick up any relay for 12 or 24 Volts, in my case 12 Volts.

Protection blocks for OM channels are installed near the transformer of the second inverter, the whole thing works quite clearly, at maximum volume the protection can work (falsely) extremely rarely.

LOW POWER AMPLIFIERS

For a long time I decided which amplifier to use for low-power acoustic systems. As a cheap option, at first I decided to use microcircuits TDA2030, then I thought that 18 watts per channel was not enough and switched to TDA2050- a powerful analogue of 32 watts. Then, comparing the sound of the main options, the choice fell on your favorite microcircuit - LM1875, 24 watts and the sound quality is 2-3 orders of magnitude better than the first two microcircuits.

I dug into the network for a long time, but I did not find a printed circuit board for my needs. Sitting at the computer for several hours, our own version was created for a five-channel amplifier on microcircuits LM1875, the board turned out to be quite compact, the board also provides a block of rectifiers and filters. This unit was completely assembled in 2 hours - all components were in stock by then.

VIDEO AMPLIFIER

The sound quality of these microcircuits is very high level, finally discharge hi-fi, the output power is decent - 24 watts of sine, but in my case the power was increased by increasing the supply voltage to 24 volts, in which case you can get about 30 watts of output power. On the main amplifier board, I had space for a 4-channel amplifier on TDA2030 but for some reason I didn't like it...

The LM board is attached to the ULF main board through racks in the form of tubes and bolts. Power for this unit is taken from the second inverter, a separate winding is provided. The rectifier and filter capacitors are located directly on the amplifier board. As rectifier diodes are already traditional KD213A.

I did not use chokes to smooth out high-frequency interference, and there is no need to use them, since they are often not installed even in fairly branded car amplifiers. As a heat sink, I used a set of duralumin blanks 200x40x10 mm.

A cooler is also attached to the board, which simultaneously drains warm air from this block and blows off the heat sinks of the inverters. We have completely figured out the electronics of the audio complex - let's move on to Regards - AKA KASYAN.

Discuss the article HOME AMPLIFIER - VLF AND PROTECTION UNIT

This acoustic protection project was borrowed from one of the Portuguese sites. In addition to DC protection, the unit delays the connection of speakers to the output of the power amplifier by approximately 3 to 10 seconds, while eliminating clicks when the amplifier is turned on. Schematic diagram:

The circuit uses a relay for a voltage of 12 Volts with one group of switching contacts capable of holding a current of 6 ... 8 Amperes.

In the original article, the following images of the printed circuit board were given:

And the view of the PCB board format:

Using the image data, we drew the protection board in the Sprint Layout program. LAY6 format looks like this:

Photo view of the printed circuit board for protecting acoustics LAY6 format:

Foil fiberglass one-sided. We slightly reduced the size of the board, now it has become 45 x 75 mm.

A conventional parametric stabilizer is used as a power supply for the circuit, the stabilization voltage is 12 volts. The circuit is shown below:

We hope it will not be difficult for you to calculate the value of the current-limiting resistor for the zener diode, it is indicated by an arrow in the diagram. Its value will depend on what voltage you will have after diode bridge. The PSU can also be implemented on the LM7812.

Connecting the protection and acoustics unit to the power amplifier is shown in the following image:

List of elements of the acoustic protection unit circuit:

Relay 12 Volt - 2 pcs.
Transistors 2SC945 - 2 pcs.
Transistor 2SC9013 - 1 pc.
Diodes 1N4007 - 5 pcs.
Electrolytic capacitors 220 uF/ 50V - 2 pcs.
Resistors 10 kOhm - 4 pcs.
Resistor 1 kOhm - 1 pc.
Resistor 39 kOhm - 1 pc.
Connectors 2 Pin - optional
Trimmer resistor 220...500 kOhm - 1 pc.
Zener diode 12 Volt 1 Watt - 1 pc. (for example imported 1N4742A)

Acoustic protection unit board assembly:

Link to download the archive with the scheme and printed circuit board LAY6 format will appear on the same page after clicking on any line ad block below, except for the line “Paid advertising”. File size - 0.3 Mb.

Speaker protection is a must, and if you do not use it, you can lose your acoustics due to a malfunction of the bass amplifier. There are many schemes that provide protection for speakers. This article presents a working circuit, tested by time and sound lovers, which is an approximate copy of the protection of the speaker system of the BRIG amplifier.

The circuit provides protection against DC voltage at the output of the low-frequency amplifier (in case of its malfunction), and also provides a delay in connecting the speakers until all transients in the amplifier and power supply are over. Without such a delay, when the amplifier is connected to the network, clicks, pops, ringing, etc. are heard in the speakers.

Key Features of Speaker Protection

DC supply voltage from +27V to +65V.

Speaker connection delay time from 1 second to 3 seconds.

DC voltage sensitivity at the protection input is ±1.5V.

Speaker protection circuit

A voltage regulator is assembled on the elements VD5, VD6, VT5, R13, which provides a wide range of supply voltages. On VT5, you need to install a small radiator. Diodes VD3 and VD4 are necessary to eliminate interference from the self-induction of the relay winding during switching. Transistors VT3, VT4 are control relay windings K1 and K2. Diodes VD1 and VD2 protect transistors VT1 and VT2 from breakdown if a negative voltage appears at the input of the circuit. Electrolytic capacitors C3 and C4 directly affect the delay time, the larger the capacitance, the longer the time.

Circuit elements

All resistors must be 0.25W, resistor R13 can be set to 0.5W, especially when the supply voltage of the circuit is 40V and higher. Electrolytic capacitors should be rated for one and a half times the voltage of the circuit supply (I set it to 63V). Although only C5 has a supply voltage of the circuit, and on the remaining electrolytes there are units of Volts.

Instead of BDX53, you can use BD875, KT972. The pin layout of all transistors is different, so be careful when replacing.

The 2n5551 transistor is very common and is present on many shelves, but it can still be replaced with KT3102, BC546, BC547, BC548. The location of the pins is also different.

Don't dream, act!

Audio power amplifiers with direct connection pose a danger to speakers. Almost all failures internal components amplifiers lead to a significant (according to Murphy's laws, up to the supply voltage) offset at the output. As a result, expensive loudspeaker systems can fail, and it would be reckless not to provide the amplifier with a protection circuit that disconnects the load when a constant potential appears at the output of the amplifier. The protection should operate when the constant potential at the amplifier output is exceeded ± 1.5 V, or when low-frequency oscillations with a frequency below 2 ... 3 Hz appear.
Practice shows that it is necessary to use simple and reliable speaker protection circuits based on electromagnetic relays.

Scheme for protecting the acoustic systems of the amplifier "Brig-001"

On fig. 1 shows a time-tested scheme for protecting acoustic systems from constant displacement of the Brig-001 amplifier. The input of the protection circuit is connected to the output of the power amplifier, and the output of the amplifier is connected to the normally open contacts of relay K1. After power is supplied to the protection circuit, after some time, determined by the time constant R6, C2, the composite pair of transistors VT2, VT3 open, relay K1 is activated, and connects the amplifier output to the speakers with its contacts. Turn-on delay allows you to eliminate transients in the amplifier at the moment of turn-on, perceived as unpleasant to the ear claps, destructive to acoustic systems.

Rice. 1. Scheme for protecting the acoustic systems of the amplifier "Brig-001"

When a positive polarity DC voltage appears at the amplifier output of any of the channels, the transistor VT1 opens, which shunts the base circuit of the composite transistor to a common wire. In this case, the current through relay K1 decreases so much that it releases the contacts and disconnects the speakers from the amplifier. Capacitor C1 prevents relay K1 from being actuated by the AC output voltage.
If a voltage of negative polarity appears at the output of the amplifier, it will go through the divider R6, R7 to the base of the composite transistor, as a result, relay K1 will release and disconnect the load from the amplifier.

The case of the appearance of bipolar voltages equal in absolute value at the outputs of the amplifier is taken into account by choosing different values ​​of the resistors R1 and R2.
Thus, the speaker system is protected from direct voltage of any polarity at the output of the amplifier.

A similar speaker protection scheme has worked in one of my amplifiers for more than two decades, and has never failed, although for about half of the specified period the amplifier worked at entertainment events.

The proposed device can be used both for this project and for independent design of audio frequency amplifiers.

Advantages:
simplicity and reliability;
almost complete absence of false positives;
versatility of application.

Flaws:
There is no circuit to turn off the speakers in the event of a power failure.
This disadvantage was brought in for the sake of simplicity and reliability of the device.

The protection circuit has second-order passive infrasonic low-pass filters (C3, C5, R10, R12 and C4, C6, R11, R13, respectively) and emergency DC voltage sensors at the amplifier output (VT2, VT4, VT6 and VT3, VT5, VT7) . If the voltage of any polarity is more than 1.5 V, the corresponding key opens (VT2 or VT3 for the positive polarity of the constant voltage and VT4, VT6 or VT5, VT7 - negative). In case of an accident, the base of the composite transistor VT8, which controls the electromagnetic relays K1 and K2 connected in series, is reliably connected to the common wire through the low-resistance anti-ringing resistor R5, opening the connection of the speaker outputs through the relay contacts.

The integrating circuit R1, C2 in the base circuit of the transistor VT1 provides a delay in connecting the speakers when the power is turned on (for a time of 1.8 s), thereby preventing the penetration of noise into the speaker system caused by transients in the amplifier.
The protection scheme is universal and can be used with other UMZCH. In the table on the right upper corner diagrams fig. 5 shows the ratings of R6, R7, which must be changed in accordance with the supply voltage Up of the amplifier.

Specifications:
Supply voltage, V= +25...45
Turn-on delay time, s= 1,8
Protection threshold, V= more than ±1.5
Output current for relay supply, mA= up to 100
PCB dimensions, mm= 75x75

Details of the upgraded circuit of the speaker protection device.

VT1 ... VT3, VT6, VT7 - Transistor BC546B (TO-92) - 5 pcs.,
VT4, VT5 - Transistor BC556B - 2 pcs.,
VT8 - KT972A transistor - 1 pc.,
VD1 - Zener diode KS212Zh (BZX55C12, 12V / 0.5W, DO-35 case) - 1 pc.,
VD2 - Diode 1N4004 - 1 pc.,
K1, K2 - Electromechanical relay (1C, 12VDC, 30mA, 400R) BS-115C-12A-12VDC - 2 pcs.,
R1 - Res.-0.25-220 kOhm (red, red, yellow, golden) - 1 pc.,
R2 - Res.-0.25-1 m (brown, black, green, golden) - 1 pc.,
R3, R4 - Res.-0.25-11 kOhm (brown, brown, orange, golden) - 2 pcs.,
R5 - Res.-0.25-10 Ohm (brown, black, black, golden) - 1 pc.,
R6 - Res.-0.25-2.2 kOhm (red, red, red, golden) - 1 pc.,
R7 - Jumper,
R8 ... R11 - Res.-0.25-22 kOhm (red, red, orange, golden) - 4 pcs.,
R12, R13 - Res.-1-22 kOhm (red, red, orange, golden) - 2 pcs.,
C1, C2 - Cond.47/25V 0511 +105 °C - 2 pcs.,
C3 - C6 - Cond. 47/50V 1021 NPL (47/25V 1012 NPL) - 4 pcs.,
Terminal block 2k pitch 5mm for TB-01A board – 5 pcs.

After completing the assembly, do not rush to turn on the device, but check the installation in accordance with the diagram (Fig. 6). In this case, pay special attention to the absence of jumpers between the current-carrying tracks, cold soldering (insufficient soldering of the contact of the element with the printed circuit board). If there are any, remove them with a soldering iron. Check the correct installation of polarized electrolytic capacitors, transistors, diode and zener diode.
The appearance of the speaker protection device, assembled by nephew Alexei, is shown in the abstract of the article. I have an intermediate version of the protection device with the RES22 relay.
To cut and remove insulation from wires (cables), it is better to use a special tool (Fig. 9).

Rice. 9. Pliers for stripping wire and crimping lugs - an assistant when installing an amplifier

Turn on!

The first inclusion is always significant. I turn on the amplifier, I hear the click of the triggered relays of the protection device, then silence. Although I “driven” all the nodes separately, I once again measure the supply voltages and zeros at the outputs: everything is in order.
I am distracted by business and only after half an hour I start listening. The amplifier sounds good, delivering about 20 watts to a 6 ohm load.
Works cleanly and transparently, delivering listening pleasure. However, we should not forget that the amplifier is not a system entry level(the best of the simple) and there is room to grow and develop.

Let me remind you once again that you can use and instead; in this case, the supply voltage of the bipolar source should be ±22 V for , ±16 V for , and ±12 V for TDA2006.

I strongly advise everyone to repeat this project to gain experience and build a good amplifier for the radio complex. It is no coincidence that I chose the slogan “Don’t dream, act!” as the motto of the project. .

There are many options for protecting speakers from DC voltage, clicks when turned on and off. The most advanced of them are assembled on microcontrollers, control a large number channels, have additional functions, for example - Datagor whale

Convenient, functional and small-sized as devices on specialized microcircuits. Unfortunately, they are not always available, and it can take a long time for them to be delivered by mail.

I was wondering which scheme discrete elements It's simple, cheap, functional, and needs minimal tweaking. I bring to your attention the scheme that most meets, in my opinion, these requirements.
Since the article is intended mainly for beginner radio amateurs, I will try to describe in detail even simple things.

AU protection prototype - A. Kotov's scheme

At first glance, there is a wide choice of circuits, but upon closer examination, it turns out that they have disadvantages - a lot of parts, scarce parts, low sensitivity, the need for tuning, performance in a narrow range of supply voltages, etc.

It turned out to be the most suitable.

However, this scheme is not without drawbacks:
- there is no quick shutdown of the speakers when the amplifier is turned off,
- strictly defined supply voltage,
- all consumed current flows through the LED,
- operating mode with "torn off base" VT10.
In addition, there is no voltage diagram and tuning recommendations, no PCB drawing.

Advanced speaker protection device circuit

These shortcomings are easily eliminated, here is my modified version.

The numbering of parts of A. Kotov's scheme has been preserved and continued.
I want to note the advantages and features of the scheme:
- the turn-on delay is optimal 4 seconds, determined by the R5C3 chain,
- circuit D5R8R9C4 when disconnected from the network allows you to quickly de-energize the relay and turn off the speaker,
- after the protection is triggered (the relay is turned off), the capacitor C3 discharges quickly, and charges slowly through the resistor R5, so there will be no fast chaotic switching,
- the device operates in a wide voltage range, from the relay operation voltage (and plus 2 V) to 36 V (limit for TL431),
- practically the only resistor that requires selection - R7 serves to extinguish the excess voltage for the relay, the values ​​​​of the remaining resistors may differ several times and do not require replacement in a wide range of supply voltages,
- all elements, except TL431, operate at very low currents, which ensures high reliability,
- the use of TL431 provides the key mode of operation of the relay,
- the voltages on capacitors other than C4 are very small, no more than 2.5 V, which allows the use of low voltage capacitors, so I tested the option with single polar capacitors C1 and C2 for low voltage,
- any LED is suitable (bright is better) because the current through it is set by a resistor,
- the sensitivity is very high (about 1 V), it is better to make it rougher, for this, the board has pads for SMD resistors (gray in the diagram).

Own PSU

If you power the ultrasound from the main power supply amplifier (like A. Kotov), ​​when the network is turned off, the relay will not release immediately due to the large capacities of the power supply and a click, crack, etc. is possible. Here, due to very small capacity C4 \u003d 1-4.7 uF the relay releases immediately.

You can take a change from the transformer of the main ULF power supply, then you may have to change the R8R9 divider to reduce the voltage.

For the "versatility" of this circuit, you need a power supply with a low-power transformer with low voltage secondary winding. I used a transformer ~ 230/12 V, 2 VA. The power supply is made on a board of the same width as the protection unit, it is convenient to place them on one board.

The presence of a separate power supply unit allows you to use the protection unit with any amplifier, including a mock-up one, which is especially convenient because speakers are at increased risk in this case.

Applied parts and setup

Installed relay "OMRON G2R-2" for 12VDC in a transparent case. This was not done by chance - although it has larger dimensions than similar ones in a non-separable opaque case, it can be opened and the contacts cleaned. When using a non-separable relay, I recommend that you carefully cut its case in advance so that the cover can be removed from it and put in place. I especially advise in the case of a used relay.

Sealed relays are usually smaller and therefore easy to install with minimal PCB modifications. Since I placed the relays and screw terminals quite tightly, when repeating the board, you need to make sure that the sizes of the terminals are identical, in otherwise slightly tweak the circuit board. You can do without clamps, it is even more reliable, but inconvenient, especially when setting up amplifier layouts.

If there are no installation errors and serviceable parts, the circuit starts working immediately, you only need to calculate the current limiting resistor through the relay winding.
For example, +18 V supply, 12 V relay with a resistance of 280 ohms. Relay operating current 12V/280Ω = 43mA.
It is necessary to extinguish 18V - 12V - 2V (voltage drop across the open TL431) = 4 Volts.
4 V / 43 mA = 100 ohms. Resistor power 43 mA x 4 V = 170 mW, i.e. you need a resistor of 0.25 W or more. This resistor is “worth” on the board, this is done so that you can install resistors of different sizes and with a power margin of up to 2 watts.

All diodes, except for the shunting relay winding, are almost any low-power ones, you just need to remember that the stripe marking on the case of KD522 and other Soviet diodes is the opposite of imported marking.

In case of problems in operation, first of all, it is necessary to check the correct installation of parts, especially diodes, transistors and TL431. Then check the quality of the rations (I soldered the leads of the diodes poorly), for this you need to rinse the board well and inspect the solderings with a magnifying glass (or with a good eye).
Then check the modes direct current, the voltages at the bases of the transistors must correspond to those indicated in the diagram ± 0.1 V.

Since among beginners there is a passion for gigantomania and amplifiers with a power of hundreds of watts and with an amplifier supply voltage of the order of ± 50 V, it must be remembered that the greater the power of the amplifier, the greater the currents flow through the relay contacts, with high voltages increases the likelihood of an arc between the open contacts of the relay.

In this case, any relay with one group of contacts can be installed on this board, this relay will be intermediate and control another, more powerful relay with contacts designed for more current and with an increased distance between open contacts. It will be possible to bring larger wires to this powerful relay.

The versatility of this protection node with “its own” power and that it can be connected to the outputs of the bridge (usually increased power) amplifier. The common wire is connected not to the common wire of the amplifier, but to one output of the amplifier, and one input of the protection node to the second output of the bridge amplifier.

When installing the protection unit in a finished structure, there is no need for a separate power supply (for a conventional, non-bridged amplifier).

Total

I made two copies - with conventional resistors and SMD, the board allows you to do this. Impressions from the devices are very good. The board length can be reduced by 1-2 cm, especially with SMD resistors, but I prefer wide tracks that allow for repeated re-soldering of parts and forgiving offsets when drilling holes; sufficient spacing between tracks.

We must not forget that such a device protects only low-frequency heads from constant voltage and all heads from transient processes in the amplifier, including when amplifiers fail, and does not protect RF heads during overloads and excitation of amplifiers. At the same time, this circuit solution allows you to connect sensors for overheating, limiting (clipping), excitation for the safety of all speakers.

In addition (as used in some amplifiers) you can control the connection of one or more pairs of loudspeakers to the output of the amplifier using a switch on the front panel of the amplifier, while not having to run high-current signal circuits through this switch.