Microphone amplifier

The preamplifier amplifies the output signal of a microphone, so that it can be. The further amplified by a power amplifier The circuit provides an output signal line. With two transistors, it is not difficult to build such a circuit. The amplifier produces little noise. In the shown embodiment, the circuit is suitable for microphones 500 and 600 Ω. 200 Ω R1 microphones should be reduces to 220 Ω and C1 should be increased to 4.7 uF. The gain is set by R2. If the average declared value of 22 K? Can be used. The maximum gain is about 200times.

• R1 = 470 Ω
• R 2 = 22 K?
• R3 = 12 K?
• R4 = 47 k
• R5 = 820 Ω
• R6 = 100 Ω
• R7 = 1 k
• R8 = 100 k
• C1, C4 = 2.2 V μF/16
• C2 = 47 V μF/16
• C3 = 470 nF
• T1 = BC 549C
• T2 = BC 547B

Microphone Preamplifier

This is a good pre-amplifier for microphones that can be. Used in, for example, mixing consoles The circuit operates with a dual op-amp type NE 5532. The amplifier must be adjusted. Simply plug the power and control over P1 such that half the supply voltage (6 V) on pin 3 of IC1 state. P2 is then adjusted to the desired volume.

• R1 = 8,2 kW
• R2, R4, R5, R6 = 10 kW
• R3 = 1 k
• P1 = 4.7 K?
• P2 = 100 k
• C1, C2, C4, C6 = 10 uF
• C3 = 470 nF
• C5 = 100 nF
• IC1 NE = 5532

Phono/line adapter

In older amps usually have a phono input is available. Today, it is used less and less, and therefore it would be useful if the input can be. Used as line input With this circuit it is. the circuit is actually an attenuator and a filter. The signal is attenuated to the level of a phono-receiving element, and filtered to the RIAA equalization is undone in the amplifier. On 'in' is the line signal, and is connected to the phono input 'from' the amplifier.

• R1 = 1 M 1%
• R2 = 82% 1 K?
• R3 = 1 k 1%
• C1-C4 = 1 nF 1% Styroflex

Peak Indicator

This indicator can be used, or to see if you can get the sound output. Damaged speakers with P1 lets you set the limit at which D1 LED lights. The potentiometer is 100k here, you can experiment. Themselves with other values ​​if you could turn a logical port on the LED or opto coupler would use, you can turn it so that the signal between the preamp and power amp would fall away. Or that the signal to the speakers with the aid of a relay would be turned OFF.

• R1 = 680 Ω
• R2 = 1.2 K?
• P1 = 100 k linearly
• B1 = 4 x B250C1000 or 1N4003
• D1 = LED
• T1 = 2N3904

Amplifier circuit TDA 1524A

Description

This amplifier can control the volume, balance and tone controls take over. The circuit operates a specially designed IC, LM 1036. The advantage is that few external components are necessary, and that may be, which are cheaper. Used for controlling monopotmeters speaks scheme for itself. S1 loudness can be adjusted. In the position shown, the loudness. Moreover, the IC TDA 1524A Philips same capabilities.

Circuit Diagram

Part list:

• R1-R4 = 47 k
• P1-P4 = 47 k
• C1 = 47 uF
• C2, C3 = 470 nF
• C4, C5, C16 = 10 nF
• C6, C7 = 10 uF
• C8, C9 = 390 nF
• C10-C13 = 220 nF
• C14, C15 = 4.7 uF
• IC1 = LM 1036

VU meter

This circuit can control analog moving coil meters, for use as a VU meter. The circuit is left connected to the line terminals of the amplifier. VU meter works pretty simple. T1 and T2 increase the signal strength. The signal is then rectified by the two diodes and applied to the meter. The capacitors C3 and C4 ensure that the voltage is slightly flattened and the meter responds less quickly.  After building the circuit, it must be calibrated. For this purpose, the VU meter connected to a tone generator which delivers 0.3V at 1000 Hz. Then P1 is fully open, that is to say that the wiper of P1 is located at the entrance. Then P2 is so cut that regulates the meter full deflection. P1 is then adjusted so that meter reads 0.5 mA (= half the maximum). 

For a stereo VU meter circuit to be built twice.

• R1 = 1 M
• R2 = 820 Ω
• R3 = 2,2 kohm
• P1, P2 = 100 k
• C1 = 330 nF
• C2 = 22 uF
• C3 = 1 uF
• C4 = 470 uF
• T1, T2 = BC 547B
• M1 = 1 mA meter

Subwoofer filter LM 741

Description for Subwoofer filter LM 741:

     If you like I want some more bass in your stereo, you can switch a subwoofer there. This is a speaker that only reflects the bass. Below is a circuit to ensure that the subwoofer gets really only the bass. 

This circuit is used between the signal source (mixer, CD player) and the amplifier. It is an active filter, better than passive filters which are generally mounted behind the amplifier. The circuit is mono because the bass for both channels are equal. The human ear can not yet determine the direction of this bass. 

The first 741 is used as a mixer amplifier. The gain is adjustable with P1. Then, the signal is applied to a second of the order Butterworth-filter. C A(C1 + C2) and C B (C3) can be calculate using the following formulas: where F k , the crossover frequency (the frequency at which filter stops the transmission of sound), pi = 3.1416, R = R3 = R4, F k in Hertz, and C. F. As shown, the filter is now set at 240 Hz. , the supply voltage must be symmetrical, + and - 12-15 V. A suitable diet is the Symmetric mini power supply . If you would like a better sound would have you two 741's replaced by an NE5532. The picture for the layout to be printed at 150DPI (= + / - 33x33mm).

Circuit Diagram:

subwoofer filter lm741 circuit diagram

Part-list:

• R1, R2 = 47 k
• R3, R4 = 4.7 K?
• R5, R6 = 100 Ω
• P1 = 47 k logarithmically
• C1-C3 = 100 nF
• IC1, IC2 = LM 741

Layout and PCB:

Subwoofer filter LM741 layout and pcb

Datasheet for LM741 and NE5532:
LM741 Operational Amplifier - Download
NE5532 Operational Amplifier - Download