A application a Signal amplifier circuit diagram with set input-output ratio, specifically the AC signal amplifier in common electronic circuits. The most these amplifiers will fed back some signal to the input again. To reduce amplify rate down affects to reduce a distortion rate and reduce also the noise signal. The feedback signal may through resistor, transistor or diode Depends on circuit design.
But circuit is presented to use series of resistor adjustment and only 4 diodes, and can set a signal amplifier ratio between input and output.
The circuit in Figure 1 amplifier sets the ratio between input and output. As signal amplifier for simple alternating current. By use the op-amp (IC1) is signal amplifier. And by some signal will be feed back through the diode and has potentiometer-VR1 about of 50 Kohms. To selects the output signal to come out three different models.
If adjust VR1 clockwise until the input impedance or Ri has value about 12Kohms cause the output impedance or Ro has value about 36Kohms will cause ratio between signal input and output is Exponential form or if Ri has value equal Ro or around 24 Kohms ,the output appears as a linear form. And if Ri has value 36 Kohms, The Ro has value of 12 Kohms, the output is logarithm form. As graph in Figure 1
The diode is a silicon type work in a high sensitivity switching form. The power supply so depends on the amplifier circuit that use op-amp types. In circuit use the OP-AMP number-LF351 has JFET is input of amplifier section which is low noise signal. We can use power supply from +9V to +18V. We can replace The potentiometer with fixed resistors in series
How to builds
This project is not used many components so can assemble on the universal PCB board as Figure 2. In the assembly circuit, Starting equipment lowest first to Beautiful and easy to the assembly. Start from Diode and then resistors and sort of high continuously.
For the device has various polarity should be careful in the assembly circuit.
The components list
VR1: 50K, standard horseshoe-shaped resistor
D1-D4: 1N4148, 75V 150mA Diodes
IC1: LF351, Wide Bandwidth JFET Input Operational Amplifier
The universal PCB board.