Pre-amplifier for subwoofer.

Graphic arts Submitted by homemade amplifier

works in the 2+1 standard (stereo + subwoofer). It is made on the basis of a popular (and most importantly cheap) microcircuit, which gives an output power of about 30 W 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 generated through a second-order low-frequency active filter. Signal components above 200 Hz are cut off, after which the signal is sent to a low-frequency power amplifier. The circuit can be powered with 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 InL, passing through a filter high frequencies

, consisting of C1 (1uF) and R1 (100k). The values of these elements ensure that the cutoff frequency of this filter is around 1.5 Hz, which effectively cuts out the DC component and very low frequencies. Next, the signal goes to the op-amp amplifier U3A (NE5532), and 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 preamp U3A from the op amp U4A (NE5532) frequency control system.

Tone block operation Frequency adjustment is built in a classical way, elements that make changes to the signal characteristics are in a negative loop feedback

When any of the sliders of potentiometers P1A or P2A are moved from their middle position, this will lead to a change in the values of X1 and X2, and, consequently, the gain value becomes different from -1 and begins to depend on frequency. Please note that the values of X1 and X2 always depend on frequency, so it is fixed only in the case of X1=X2.

Potentiometer P1A is responsible for adjustment low frequencies. For high signal frequencies, capacitors C20 and C21 are conductors, so adjusting with a potentiometer has no effect at these frequencies. Potentiometer P2A allows you to adjust the treble, and thanks to capacitors C17 and C18, it does not affect the bass adjustment. For low frequencies, capacitors C17 and C18 represent an open circuit due to which the potentiometer is disconnected from the circuit and its influence on regulation becomes negligible.

The signal from the output of the tone control unit 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 around -2 (-33k/15k). From output U5A, the signal through filter R17 (100P), C3 (1uF) and R4 (100k) enters the input of the UMZCH power amplifier.

The cutoff frequency of the filter for the 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 designated by the letter “a”, and the potentiometers and operational amplifiers are marked “B”.

An additional module is a adder and an active low-pass filter made using an operational amplifier U6 (NE5532). The signal isolated 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 input of U6A. 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 an amplifier with adjustable gain in the range of 0-2.2. The second operational amplifier (U6B) is an active low-pass filter. The values of the elements are selected so that the system operates as a second-order Butterworth filter with a cutoff frequency around 200 Hz. The signal from the filter output through circuit C24 (220nF), R5 (100k) goes to 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 the 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 to each of the four op-amps is smoothed using capacitors C9-C16 (100nF).

Operation of the UMZCH unit

The power amplifier is built on the basis of 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 W. Capacitor C8 (1uF) cuts off the DC component of the signal and at the same time represents a high-pass filter at the input. R20 (22k) determines the resistance at the input of the power amplifier.

The feedback circuit is 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 amplifier input. Resistor R19 (2.2 Ohm) and capacitor C32 (470nF) prevent the amplifier from self-excitation. 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 onto a common printed circuit board. First of all, you need to solder all the jumpers. Then you can start soldering the resistors. All of them are 0.25 W. Next, attach the sockets for the operational amplifiers. At the very end, place voltage stabilizers, electrolytic capacitors and potentiometers on the board. When installing potentiometers, care should be taken that they are in line - for aesthetic reasons. Metal housings of potentiometers must be connected to ground using wires. This causes shielding of the variable housings, reducing interference and AC hum when the potentiometer knobs are touched.

All three TDA2050 can be placed on a common heatsink, which will have the potential of the negative power bus. To avoid this, use insulating washers. You must be careful not to short the heatsink to the metal chassis of the amplifier.

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.

Launching and setting up the scheme

When starting up for the first time, do not insert operational amplifiers into the sockets and after turning on the power, check that each socket has the correct supply voltages. Then you can stick them in place. The volume potentiometer should be turned to minimum (all the way to the left), and a signal from an mp3 player or computer should be supplied to the input. The amplifier works well with both speakers acoustic systems) with a resistance of 4 and 8 ohms.

TDA2050, TDA2030 or TDA2040 microcircuits operate as output power amplifiers, providing output power of 14, 20 or 30 watts per channel, respectively. Not all amplifier chips have to be the same. You can install the weaker ones as a stereo ULF, and leave the more powerful amplifier for the subwoofer.

Voltage stabilizers U1 and U2 provide symmetrical bipolar voltage at a level of +/-15 V. You can successfully use stabilizers for a voltage of 12 V or even 9 V. 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 voltage than +/- 18 V. The 7815 and 7915 stabilizers may not want to work properly with a low voltage drop. Download PCB files

Discuss the article STEREO AMPLIFIER WITH SUBWOOFER AND LPF

Fans of music or watching movies on a large home theater screen are undoubtedly interested in receiving high-quality sound. Therefore, it is important which preamplifier to choose so that the result does not disappoint you, and what characteristics to pay attention to when choosing an audio device.

When listening to music on a CD player, you also need an amplifier, because the signal they deliver is very weak level. 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 Integrated, which combines everything in one housing, is currently the most common. A separate device circuit consisting of a preamplifier is considered more expensive and of higher quality. Amplifiers can be tube or transistor.

It is the preliminary version that can give a true music lover the sound that he would like to hear - cleaner and higher quality, truly alive.

When choosing from the category of expensive multi-channel digital systems, you can choose an AV processor. And when choosing among amplifiers, it is better to give preference to a preamplifier, which is best investment money. The processor is able to properly adjust parameters and surround sound 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 records, a cassette deck and other options. An AV processor can be used as a preamplifier. Preamplifiers are more effective when paired with digital audio systems, where they are paired with power amplifiers. This allows the owner of professional acoustics to avoid the pitfalls of recording music when playing and neutralize the frequency resonances inherent in the room.

In order for the preamplifier for a 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 set its output to the maximum level, and at the input to the power amplifier to the minimum level. The sound 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 combine well. You can connect the preview to active speakers, but good sound can only be obtained by using high-quality studio models.

As a rule, the preamplifier plays the role of a control controller, which allows you to adjust the volume and timbre of the audio system, switches sound sources and prepares a signal for the power amplifier. Unlike the latter, the preamplifier is placed in plain sight.

If you choose a high-quality pre-amplifier, then this is a “High End” technology, 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 source. 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 similar device can bring a lot of pleasure to true music lovers.

Subwoofer amplifier for TL074 and TDA7294.

This amplifier circuit for a subwoofer based on TL074 chips, on which the filter is assembled, and TDA7294 in the final stage, was found on one of the Turkish sites, at least this is how Google translator determined the language of the article text. The amplifier will produce 70 watts of power into an 8 ohm load with a supply voltage of ±35 volts. See the image below for the main parameters of the TDA7294:

Schematic diagram of an amplifier for a subwoofer:

Board source, PCB format:

Source board, location of elements:

Using the above pictures, we drew a printed circuit board in the Sprint Layout program, LAY6 board format looks like this:

Photo view of the LAY6 amplifier board format:

The board is designed to be made from one-sided foil fiberglass laminate. Size 98 x 56 mm.

Below is a snapshot printed circuit board subwoofer amplifier assembly:

You can download the amplifier circuit for the subwoofer on TL074 + TDA7294 using a direct link from our website, which will appear in the center of the same page after clicking on any line of the advertising block below except for the line “Paid advertising”. File size – 0.9 Mb.

To connect a subwoofer to a signal source, one ULF is not enough. We also need a block that will process the signal before it is amplified by ULF. If the signal source does not contain a separate low-frequency line output to the subwoofer LFE (Low Frequency Effect), then you first need to isolate the subwoofer signal using a adder.

The signal must then be amplified to the desired level.

Next, you need to cut the signal from below using Subsonic - a device designed to cut off infra-low frequencies below 20 Hz, which are especially harmful to the speaker, especially since nothing can be heard there, but the amplitude of the diffuser at these frequencies is maximum and there is a high risk of hitting the speaker coil and leaving the speaker out of service.

After this, the signal should be cut from above 125-150Hz using a low-pass filter. To coordinate the subwoofer with the rest of the speakers, you will need the last node - the phase control.

Below is a diagram of a pre-amplifier for a subwoofer, it is made on 4 op-amps: on the 1st op-amp a pre-amplifier is assembled to amplify the input signal, on the 2nd op-amp there is a 2nd order subsonic with a cutoff frequency of 17 Hz, on the 3rd op-amp there is a low-pass filter with a cutoff frequency of 150 Hz and on the 4th op amp – phase shifter.

The device does not require adjustment. The gain can be adjusted by resistances R5 and R4:

Power is supplied from integrated positive and negative voltage stabilizers 7815 and 7915. If you have a stabilized bipolar power supply of 15V, then they can be excluded along with capacitors C10, C11, C14, C15.

Capacitances C11, C13, C15, C17, C18, C19 are power supply filters; in the circuit they have a minimum capacitance of 0.1 µF, but if possible they can be increased to 0.22-0.47 µF. C18, C19 are op-amp power supply filters and should be located in close proximity to the microcircuit (if you use your own board layout).

If the device is located at a distance of up to 70mm from the power supply, then capacitors C10 and C14 can be eliminated by using the power supply filter as them.

For stable operation of banks 7815 and 7915, the minimum capacitance of C14 and C15 is 10 µF. For stable operation of the op-amp, the minimum capacitance of C12 and C16 is 47 µF.

The circuit uses the following variable resistors: P1 - double group A (linear), and P2 and P3 - group B (inverse logarithmic). The resistance of the signal level regulator P3 depends on the input resistance of the subsequent stage, in our case the power amplifier. The resistance of the regulator P3 must satisfy the condition:

Rout. signal source< R регулятора < R входн. усилителя

In practice, the input impedance of amplifiers lies in the range of 22k-200k, in most cases the input impedance of amplifiers is 100k.

Device circuit board:

The PCB layout in Spilnt-Layout format can be downloaded from here.

When listening to music on a CD player, you also need an amplifier, because the signal they produce is at a very weak level. 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: pre-amplifiers, integrated amplifiers and power amplifiers. Integral, which combines everything in one housing, 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 can be tube or transistor.

It is the preliminary version that can give a true music lover the sound that he would like to hear - cleaner and higher quality, truly alive.

When choosing from the category of expensive multi-channel digital systems, you can choose an AV processor. And when choosing among amplifiers, it is better to give preference to a preamplifier, which is the best investment. The processor is able to properly adjust parameters and surround sound 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 vinyl record player, cassette deck, or other options. An AV processor can be used as a preamplifier. Preamplifiers are more effective when paired with digital audio systems, where they are paired with power amplifiers. This allows the owner of professional acoustics to avoid the pitfalls of recording music when playing and neutralize the frequency resonances inherent in the room.

To adjust the sound on the preamplifier, you should set its output to the maximum level, and at the input to the power amplifier to the minimum level. The sound 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 combine well. You can connect the preliminary version to active speakers, but good sound can only be obtained using high-quality studio models.

If you choose a high-quality pre-amplifier, then this is a “High End” technology, 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 source. 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 bring a lot of pleasure to real music lovers.