Fans of music or watching movies on the big screen of a home theater are undoubtedly interested in receiving high-quality sound. Therefore, it is important which preamplifier to choose so that the result does not disappoint you, what characteristics to look for when choosing an audio device.
When listening to music on a CD player, an amplifier is also needed, because the signal they provide is very weak. An amplifier is connected to help the speakers. It is capable of switching and receiving an audio signal, increasing it to the required volume.
Amplifiers are divided into three types: preliminary, integral and integrated, which combines everything in one package, is currently the most common. A separate device circuit, consisting of a preamplifier, is considered more expensive and of higher quality. Amplifiers are tube, transistor.
It is the preliminary version that is able to give a real music lover the sound that he would like to hear - more pure and high-quality, truly alive.
Choosing from the category of expensive multi-channel digital systems, you can stop at the AV processor. And when choosing among amplifiers, it is better to give preference to the preamplifier, which is the best investment. The processor is capable of properly adjusting the surround sound parameters and processing. As a result, you can assemble the following audio system, including a source (for example, a disc player), a preamplifier, an amplifier, and acoustics. Records, cassette deck and other options can serve as a source. An AV processor can be used as a preamplifier. Pre-amplifiers are more effective in conjunction with digital audio systems, where they are paired with power amplifiers. This allows the owner of professional acoustics to avoid music recording flaws when playing back and neutralize the frequency resonances inherent in the room.
In order for the preamplifier for the subwoofer to produce the desired sound quality, it is necessary to set the center frequency on its equalizer closer to one kilohertz, and set the midrange lower by half a decibel.
To adjust the sound on the preamplifier, you should bring its output to the maximum, and at the input to the power amplifier with a minimum level. The sound quality will be better if the output impedance of the preamplifier is lower than the input impedance of the power amplifier. Tube stereo amplifiers and transistor power amplifiers are well combined. It is possible to connect the preliminary version to active speakers, but good sound can only be obtained using high-quality studio models.
As a rule, the preamplifier acts as a control controller that allows you to adjust the volume and tone of the audio system, switch sound sources and prepare the signal for the power amplifier. Unlike the latter, the preamplifier is placed in plain sight.
If you choose a high-quality preamplifier, then this is a “High End” class technique, for example, “Evolution”, created by German designers. It achieves maximum neutrality by processing the input audio signal. The device has a perfect element base, a short signal path and a stabilized power supply. The preamplifier has a mono output for a subwoofer with satellite set-top boxes, a tuner and a universal phono preamplifier can be built into it. Undoubtedly, such a device can deliver a lot of pleasure to real music lovers.
The thing that we will now talk about, as the title of the article implies, is a homemade amplifier for a subwoofer, popularly called "Sub". The device has an active low-pass filter built on operational amplifiers and a combiner that provides signal input from the stereo output.
Since the signal for the circuit is taken from the speaker outputs, there is no need to interfere with the working amplifier. Receiving a signal from the speakers has another advantage, namely, it allows you to keep a constant ratio of subwoofer volume to stereo system.
Naturally, the subwoofer channel gain can be adjusted using a potentiometer. After filtering high frequencies and highlighting low frequencies (20-150 Hz), the sound signal is amplified using the TDA2030 or TDA2040, TDA2050 microcircuit. This allows you to adjust the bass output to your liking. In this project, any woofer with a power of more than 50 watts per subwoofer works successfully.
Filter circuit with UMZCH subwoofer
Schematic diagram of LPF and UMZCH subwoofer Description of the operation of the amplifier circuit
The stereo signal is fed to the In connector via C1 (100nF) and R1 (2.2M) on the first channel and C2 (100nF) and R2 (2.2M) on the other channel. Then it goes to the input of the operational amplifier U1A (TL074). Potentiometer P1 (220k), working in the feedback circuit of the amplifier U1A, controls the gain of the entire system. Further, the signal is fed to a second order filter with elements U1B (TL074), R3 (68k), R4 (150k), C3 (22nF) and C4 (4.7 nF), which works as a Butterworth filter. Through the circuit C5 (220nF), R5 (100k), the signal is fed to the repeater U1C, and then through C6 (10uF) to the input of the amplifier U2 (TDA2030).
Capacitor C6 ensures the separation of the DC component of the preamplifier signal from the power amplifier. Resistors R7 (100k), R8 (100k) and R9 (100k) serve to polarize the input of the amplifier, and capacitor C7 (22uF) filters the bias voltage. Elements R10 (4.7 k), R11 (150 k) and C8 (2.2 uF) work in a negative feedback loop and have the task of forming the spectral response of the amplifier. Resistor R12 (1R) together with capacitor C9 (100nF) form the output characteristic. Capacitor C10 (2200uF) prevents DC current from flowing through the speaker and together with the speaker resistance determines the lower cutoff frequency of the entire amplifier.
Protective diodes D1 (1N4007) and D2 (1N4007) prevent voltage spikes that may occur in the speaker coil. The supply voltage, within 18-30 V, is supplied to the Zas connector, the capacitor C11 (1000 - 4700uF) is the main filter capacitor (do not save on its capacity). Stabilizer U3 (78L15), together with capacitors C12 (100nF), C15 (100uF) and C16 (100nF), provides a 15 V supply voltage to U1. Elements R13 (10k), R14 (10k) and capacitors C13 (100uF), C14 (100nF) form a voltage divider for operational amplifiers, forming half the supply voltage.
Subwoofer Assembly
The whole system is soldered to. Installation should begin by soldering two jumpers. The order of installation of the remaining elements is any. At the very end, you should solder the capacitor C11 because it must be installed lying down (you need to bend the legs accordingly).
PCB for the device The input signal must be connected to the In connector using twisted wires (twisted pair). The U2 chip must be equipped with a large heatsink.
The circuit should be powered from a transformer through a rectifier diode bridge, the filter capacitor is already on the board. The transformer must have a secondary voltage in the range of 16 - 20 V, but so that after rectification it does not exceed 30 V. A subwoofer with good parameters should be connected to the output - a lot depends on the head.
Fans of music or watching movies on the big screen of a home theater are undoubtedly interested in receiving high-quality sound. Therefore, it is important which preamplifier to choose so that the result does not disappoint you, what characteristics to look for when choosing an audio device.
When listening to music on a CD player, an amplifier is also needed, because the signal they provide is very weak. An amplifier is connected to help the speakers. It is capable of switching and receiving an audio signal, increasing it to the required volume.
Amplifiers are divided into three types: preliminary, integrated and power amplifiers. Integral, which combines everything in one package, is currently the most common. A separate device circuit consisting of a power amplifier and a preamplifier is considered more expensive and of higher quality. Amplifiers are tube, transistor.
It is the preliminary version that is able to give a real music lover the sound that he would like to hear - more pure and high-quality, truly alive.
Choosing from the category of expensive multi-channel digital systems, you can stop at the AV processor. And when choosing among amplifiers, it is better to give preference to the preamplifier, which is the best investment. The processor is capable of properly adjusting the surround sound parameters and processing. As a result, you can assemble the following audio system, including a source (for example, a disc player), a preamplifier, an amplifier, and acoustics. The source can be a turntable, cassette deck, and other options. An AV processor can be used as a preamplifier. Pre-amplifiers are more effective in conjunction with digital audio systems, where they are paired with power amplifiers. This allows the owner of professional acoustics to avoid music recording flaws when playing back and neutralize the frequency resonances inherent in the room.
In order for the preamplifier for the subwoofer to produce the desired sound quality, it is necessary to set the center frequency on its equalizer closer to one kilohertz, and set the midrange lower by half a decibel.
To adjust the sound on the preamplifier, you should bring its output to the maximum, and at the input to the power amplifier with a minimum level. The sound quality will be better if the output impedance of the preamplifier is lower than the input impedance of the power amplifier. Tube stereo amplifiers and transistor power amplifiers are well combined. It is possible to connect the preliminary version to active speakers, but good sound can only be obtained using high-quality studio models.
As a rule, the preamplifier acts as a control controller that allows you to adjust the volume and tone of the audio system, switch sound sources and prepare the signal for the power amplifier. Unlike the latter, the preamplifier is placed in plain sight.
If you choose a high-quality preamplifier, then this is a “High End” class technique, for example, “Evolution”, created by German designers. It achieves maximum neutrality by processing the input audio signal. The device has a perfect element base, a short signal path and a stabilized power supply. The preamplifier has a mono output for a subwoofer with satellite set-top boxes, a tuner and a universal phono preamplifier can be built into it. Undoubtedly, such a device can deliver a lot of pleasure to real music lovers.
The presented homemade amplifier operates in the 2 + 1 standard (stereo + subwoofer). It is based on a popular (and most importantly cheap) microcircuit, which gives an output power of about 30 watts per channel with a 4 ohm AC load resistance and +/-22V power supply. The circuit is suitable for working with any standard audio signal source: mp3 player, smartphone or computer, as it is equipped with a preamplifier with tone controls. The signal to the subwoofer is formed through a low-pass active filter of the second order. Signal components above 200 Hz are cut off, after which the signal is fed to the bass power amplifier. The circuit can be powered by a voltage of no more than +/-25 V.
2.1 audio system amplifier circuit
The input signal is fed to the InP connector - the right channel, and the left channel to the InL, passing through a high-pass filter consisting of C1 (1uF) and R1 (100k). The values of these elements provide a cutoff frequency of this filter at a level of about 1.5 Hz, which effectively cuts out the DC component and too low frequencies. Further, the signal enters the op-amp amplifier U3A (NE5532), and the elements R6 (10k) and R11 (4.7 k) provide signal amplification at a level of about 1.5 (1 + 4.7 k / 10k). Capacitor C6 prevents excitation while C2 (1uF) decouples preamplifier U3A from the frequency control system built around the op amp U4A (NE5532).
Operation of the tone block
The frequency control is built in a classical way, the elements that change the signal characteristics are in the negative feedback loop of the U4A chip. On resistance X1 are capacitors C17 (4.7 nF), C20 (33nF) and resistor R7 (10k), "half" of potentiometers P1A (100k), P2A (100k) and elements R8 (10k) and R13 (3.3 k ). The resistance X2 is the capacitors C18 (4.7 nF), C21 (33nF), the resistor R9 (10k), the "half" of the potentiometers P1A, P2A and the elements R8 and R13. The figure below may help you understand:
When any of the sliders of the potentiometers P1A or P2A are moved from their middle position, this will change the value of X1 and X2, and, consequently, the gain value becomes different from -1 and begins to depend on the frequency. Note that the values of X1 and X2 are always dependent on the frequency, so only fixed if X1=X2.
Potentiometer P1A is responsible for adjusting the low frequencies. For high signal frequencies, capacitors C20 and C21 are conductors, so adjusting with a potentiometer has no effect at these frequencies. The P2A potentiometer allows you to adjust the high frequencies, and thanks to the capacitors C17 and C18, it does not affect the bass adjustment. For low frequencies, the capacitors C17 and C18 represent a trip, due to which the potentiometer is disconnected from the circuit and its influence on the regulation becomes negligible.
The signal from the output of the tone block goes through R12 (4.7 k) to the potentiometer for adjusting the volume P3A (100k) and then to the op-amp U5A (NE5532). Elements R14 (15k) and R15 (33k) set the gain to about -2 (-33k/15k). From the output of U5A, the signal through the filter R17 (100P), C3 (1uF) and R4 (100k) enters the input of the UMZCH power amplifier.
The cutoff frequency of the filter for a subwoofer can be calculated using programs or by changing the values of the elements experimentally.
The second channel of the preamplifier works similarly, the passive elements in it that appear are additionally marked with the letter "a", and the potentiometers and operational amplifiers are marked with "B".
An additional module is a combiner and an active low-pass filter made using the U6 operational amplifier (NE5532). The signal extracted in this part of the chain is used after appropriate amplification to drive the subwoofer. The signal from both preamplifier outputs goes through C22-C23 (220nF) and R2-R3 (100k) to the U6A input. Potentiometer P4 (220k) allows you to adjust the gain in relation to the main volume control P3. P4, R2 and R3 together with U6A form a variable gain amplifier in the range 0-2.2. The second operational amplifier (U6B) is an active low pass filter. The values of the elements are chosen so that the system operates as a second-order Butterworth filter with a cutoff frequency in the region of 200 Hz. The signal from the filter output through the circuit C24 (220nF), R5 (100k) enters the input of the power amplifier.
ULF power supply
The entire amplifier is powered by a bipolar voltage within 17-25 V. The supply voltage for operational amplifiers is formed using stabilizers U1 (78L15 / L12), U2 (79L15 / L12) and filtered using capacitors C4-C5 (100uF) and C7-C8 ( 47uF). In addition, the power supply of each of the four op amps is smoothed by capacitors C9-C16 (100nF).
Operation of the UMZCH node
The power amplifier is based on the popular U7 chip (TDA2050). This is probably the most common audio amplifier operating in class AB. With a total harmonic distortion of 0.5%, it allows you to achieve a power of about 30 watts. Capacitor C8 (1uF) cuts off the DC component of the signal and at the same time is a high-pass filter at the input. R20 (22k) determines the resistance at the input of the power amplifier.
Feedback circuit - resistors R21 (680R) and R22 (22k), changing their ratio leads to a change in gain, and a decrease in R22 or an increase in R21 causes a decrease in gain. In the datasheet of the TDA2050 chip, the manufacturer recommends that it be more than 24 dB. Capacitor C29 (22uF) cuts off the DC component at the input of the amplifier. Resistor R19 (2.2 Ohm) and capacitor C32 (470nF) prevent self-excitation of the amplifier. The UMZCH power supply is filtered by capacitors C26-C27 (2200uF) and C30-C31 (100nF). The other two channels work similarly.
Assembly
The circuit is soldered on a common printed circuit board. First of all, you need to solder all the jumpers. Next, you can start soldering the resistors. All of them are 0.25 watts. Next, fix the panels under the operational amplifiers. At the very end, place voltage regulators, electrolytic capacitors and potentiometers on the board. When installing the potentiometers, care should be taken to ensure that they are in line - for aesthetic reasons. The metal cases of the potentiometers must be connected to ground using wires. This causes shielding of the variable housings, reducing AC noise and hum when the knobs of the potentiometers are touched.
All three TDA2050s can be planted on a common heatsink, which will have the potential of the negative power rail. To avoid this, use insulating washers. You must be careful not to short the heatsink to the amplifier's metal chassis ground.
It is better to power the amplifier circuit from a transformer with a power of about 100 W and a voltage of 2x16 V, a rectifier and two capacitors that filter the alternating voltage.
Running and configuring the scheme
On first start up, do not insert any op amps into the sockets, and after turning on the power, check that each socket has the correct supply voltages. Then you can put them in place. The volume potentiometer must be turned to the minimum (all the way to the left), and a signal from an mp3 player or computer must be applied to the input. The amplifier works well with both speakers (speakers of acoustic systems) with an impedance of 4 and 8 ohms.
TDA2050, TDA2030 or TDA2040 microcircuits work as output power amplifiers, providing output power, respectively, of 14, 20 or 30 watts per channel. Not all amplifier circuits have to be the same. You can set those that are weaker as ULF stereo, and leave a more powerful amplifier for the subwoofer.
Voltage regulators U1 and U2 provide a symmetrical bipolar voltage of +/-15V. You can successfully use regulators for voltages of 12V or even 9V. This will not cause changes in the operation of the preamplifier. This procedure will be necessary if we want to power the amplifier with less than +/- 18 V. The 7815 and 7915 regulators may not want to work properly with a small voltage drop. Download PCB files
Discuss the article STEREO AMPLIFIER WITH SUBWOOFER AND LPF
To assemble an amplifier for a subwoofer with your own hands correctly, you need to stock up on free time and patience. Large expenditures of funds are not required. First of all, you need to purchase a power amplifier made on an integrated circuit. Next, we will analyze how to assemble an amplifier for a subwoofer with our own hands based on the TDA1562Q chip.
Below is a schematic diagram of the amplifier.
This circuit, in addition to the power amplifier, has a preamplifier made on a dual operational amplifier chip, which also plays the role of a frequency filter.
When powered by a car battery, the maximum output power of the amplifier will be about 50 watts, which is enough to drive an average subwoofer.
Required Equipment and Components
So, in addition to the above microcircuit, we need:
- operational amplifier TL 072 (can be replaced with TL 062, TL 082 or 4558 microcircuits);
- resistors with a power of 0.25-0.5 W;
- electrolytic capacitors (new!);
- non-polar capacitors - film;
- insulated wires;
- thermal paste;
- radiator with a dissipation area of at least 600 cm²;
- a sheet of one-sided textolite.
Of course, we will not do without a soldering iron, solder and some skill with all this.
Installation
Amplifier main board
The PCB diagram of the amplifier is shown below.
A printed circuit board can be made by etching textolite with a copper substrate with a solution of ferric chloride. It is easier to transfer the contact trace pattern onto the board from a glossy sheet of paper on which this pattern is printed using a laser printer. The nuances of this method can be easily found on the Internet on the relevant sites on electrical engineering.
We solder parts carefully, removing excess flux. This is especially true for microchips. The op-amp IC can be installed via the eight-pin panel.
Remember: overheating of semiconductor elements can lead to their failure!
The inductors L1 and L2 in the output filter of the amplifier are made of copper enameled wire with a diameter of 1 mm, by winding onto a cylindrical core with a diameter of 5 mm. The number of coil turns is 20.
The amplifier chip is mounted on a heat sink. It must be larger than 600 cm². The role of the radiator can be performed by the chassis of the car.
After installing all the elements, connect the wires.
Stabilization and power communication unit
In the above circuit, we used the simplest power supply circuit for the amplifier through a battery, however, for more stable operation of the amplifier, you can connect it through a stabilizer. You can assemble this device yourself (you can find a circuit for every taste on the Internet very easily), but the easiest way is to use a ready-made stabilization unit from an old amplifier or buy a new one.
In addition, the stabilization unit allows you to save car battery power.
Discharging is prevented by a relay with a separate REM terminal operating under a voltage of 12 V. The terminal is installed at the output of the car radio, so that the subwoofer starts working together with the music device.
To control the operation of the amplifier, you can install an LED in the power circuit of the device.
Final assembly of the device
After mounting the board, we carry out the final assembly of the amplifier and place it in the case. The case can be made independently from ordinary plywood using a jigsaw. A diagram is drawn on plywood according to the required dimensions, cut out with a jigsaw and fixed with sealant.
You can also purchase a case in a store or use an aluminum box, which will simultaneously act as a radiator.
When placing all the parts in the case, it is necessary to ensure free air circulation in it for better cooling of the parts.
The amplifier housing must be securely fixed in the vehicle interior.
Before installation, it is important to make sure that the polarity of the power supply is correct, otherwise the device will burn out immediately.
We figured out how to make an amplifier for a subwoofer, it remains to check its performance. This can be done at home, but in no case should the safety rules be neglected, otherwise you can get an electric shock or damage the device. Testing is as follows: the amplifier is powered through a battery and a speaker with a resistance of 20 ohms is connected. The amplifier is loaded and the power is checked.