Power amplifier electronic circuits-tube audio rf amplifiers

Electronic Amplifier Circuits-Power amplifier, audio amplifier designs and circuits

June 2nd, 2010

Microphone Pre-amplifier Circuit

Circuit Description

Here is the circuit diagram of three input microphone preamplifier. This is a mic mixer preamplifier centered on the high gain operational amplifier IC LM 348. This IC LM 348 is a quad operational amplifier IC that is it has four operational amplifiers embedded in this chip. This IC has also got some advanced features such as very high gain, class AB output stage and very low input supply current of 0.6 mA for each op-amp.

The 3 channels of mic input require three amplifiers. The three op-amps (IC1b, IC1c and IC1d) out of four in the IC LM 348 are used here as input amplifiers for the corresponding channels. This three input amplifiers are made in this circuit work as non-inverting amplifiers. The operational amplifier IC1a is the output amplifier in this circuit. IC1a is wired as inverting amplifier here. The output from each input amplifiers are given to the inverting terminal of output op-amp. IC1a mixes the signals from each channel and produces the required output.

Circuit diagram

Microphone Pre-amplifier Circuit

Microphone Pre-amplifier Circuit

Notes

  • Use a good quality PCB to assemble this circuit.
  • IC LM 348 operates from a dual power supply. A +12/-12V DC dual supply is used here for powering the circuit.
  • The gain of individual channels can be adjusted by using potentiometers R5, R6 and R7.
June 2nd, 2010

Capacitance Meter Circuit

Circuit Description

The circuit diagram of simple capacitance meter has been published here. The core part of this circuit is the frequency to voltage converter IC LM 2917 developed by National Semiconductors. This IC LM 2917 is a monolithic IC having a very high gain. This IC has got its primary application in tachometers. It can also be used for other applications as well.

This is a capacitor measurement circuit that displays capacitance by using a meter M1. The capacitor Cx whose capacitance is to be measured is connected between the pin2 of the IC and ground. The capacitance Cx will be proportional to the output voltage of the IC. At the output pin (pin4), a resistor R2 (10K) is connected as load. The voltage across this is displayed through a voltmeter (M1) which is connected across R2.

Circuit Diagram

Capacitance Meter Circuit

Capacitance Meter Circuit

Notes

  • Use a Vero board to assemble this particular circuit.
  • Use a suitable holder to mount the IC LM 2917.
  • Capacitance values from 0.01uF to 0.1uF can be measured using this circuit.
  • Potentiometer R1 (200K) can be used for calibrating this circuit.
  • Use a 10V FSD voltmeter in place of M1.
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