electronics-amplifier tutorial

This is a simple microphone preamplifier circuit which you can use between your microphone and stereo amplifier. This circuit amplifier microphone suitable for use with normal home stereo amplifier line/CD/aux/tape inputs.

The circuit is based on a low noise, high gain 2 stage PNP and NPN transistor amplifier, using DC negative feedback through R6 to stabilize the working conditions quite precisely. Output level is attenuated by P1 but, at the same time, the stage gain is lowered due to the increased value of R5. This unusual connection of P1, helps in obtaining a high headroom input, allowing to cope with a wide range of input sources (0.2 to 200mV RMS for 1V RMS output).

P1         : 2K2 Potentiometer
R1,R2,R3   : 100K
R4         : 8K2
R5         : 68R
R6         : 6K8
R7,R8      : 1K
R9         : 150R
C1         : 1µF/63V
C2,C3,C4   : 100µF/25V
C5         : 22µF/25V
Q1         : BC560C
Q2         : BC550C 

This is a 3 stage discrete Microphone amplifier circuit with gain control.The first stage built around Q1 operates in common base configuration. This is unusable in audio stages, but in this case, it allows Q1 to operate at low noise levels and improves overall signal to noise ratio. Q2 and Q3 form a direct coupled amplifier.

As the signal from a dynamic microphone is low typically much less than 10mV, then there is little to be gained by setting the collector voltage voltage of Q1 to half the supply voltage. In power amplifiers, biasing to half the supply voltage allows for maximum voltage swing, and highest overload margin, but where input levels are low, any value in the linear part of the operating characteristics will suffice. Here Q1 operates with a collector voltage of 2.4V and a low collector current of around 200uA. This low collector current ensures low noise performance and also raises the input impedance of the stage to around 400 ohms. This is a good match for any dynamic microphone having an impedance's between 200 and 600 ohms.

Source

This Circuit of microphone preamplifier has a high quality and using a single power supply, suitable for dynamic or electret microphones. The op-amps Used Can be any low noise, high performance type, eg LM471, NE5534, TL071, OPA 371 etc.

Skema rangkaian op-Amp mic preamplifier

The design is a non-inverting amplifiers design, the input is applied to the non-inverting input of the op-amp pin 3 Which is in most cases. The input impedance is 23.5k, the overall voltage gain is determined by R2 and R1 and with the values of R2 and R1 on the circuit diagram the voltage gain (for mid band, 1KHz) is approximately 27.2dB.

Op-amp feature high gain bandwidth products, have a fast slewing rate and have extremely low noise. It is difficult to achieve the same performance using discrete components. Finally the overall signal to noise ratio has been calculated, the source was a 1k impedance microphone generating a 1mV pk-pk sine wave. An impressive result of 110dB S/n at 1KHz is achieved. In practice this figure will be lower and determined by the quality of the microphone used.

This microphone amplifier circuit is very simple, consisting of two levels. with wide dynamic regions, small noise, and can with a long cable about 50 meters. The battery supply is a good compromise: in this Manner The input circuit is free from mains low frequency hum pick-up and connection to The amplifier is more for simple, of due To The absence of mains cable and power supply. Using a stereo microphone the circuit must be doubled. In this case, two separate level controls are better than a dual-ganged stereo potentiometer. Low current drawing (about 2mA) ensures a long battery life.

List Component

P1: 2K2 Potentiometer
R1,R2,R3: 100K 1/4W Resistors
R4: 8K2 1/4W Resistor
R5: 68R 1/4W Resistor
R6: 6K8 1/4W Resistor
R7,R8: 1K 1/4W Resistors
R9: 150R 1/4W Resistor
C1: 1uF 63V Polyester Capacitor
C2,C3,C4: 100uF 25V Electrolytic Capacitors
C5: 22΅F 25V Electrolytic Capacitor
Q1: BC560C 45V 100mA PNP Transistor
Q2: BC550C 45V 100mA NPN Transistor