Audio


Posted on Feb 5, 2014

This lab will demonstrate the theory and operation of non-inverting amplifiers as well as their practical application to amplify the signal of a microphone. We will construct a non-inverting amplifier to increase the output signal of a microphone, and use this circuit to measure the performance of a loudspeaker Electret capsule microphones are ver


Audio
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y popular due to their decent performance and low price. The simplest way to imagine the microphone`s operation is to view it as a resistor whose value varies when a sound wave hits it. If a bias current flows through this varying resistance, it will create a small voltage that must be amplified for useable purposes. Build the circuit in Figure 4 shown below. In the above circuit, R4 provides the bias current for the microphone. Capacitor C1 prevents the DC voltage across the microphone from being amplified, while allowing the AC signal to pass to the amplifier. Resistor R2 provides a DC bias current path for the TL081 but also creates a high-pass filter with C1, whose cut off frequency can be determined as: The simulation shows that the circuit has a gain of 40 dB as predicted and its low frequency roll-off occurs around 15. 9 Hz. The upper frequency roll-off is created by the bandwidth of the opamp itself. For small signals, the easiest method to predict the bandwidth of the amplifier is to use the gain/bandwidth product (GBW) specified by the manufacturer. The TL081 has a GBW of 3 MHZ, by dividing this number by our gain of 101, we can predict the 30 kHz bandwidth of the amplifier seen in the simulation. The Bode application included with the myDAQ can be used to verify the operation of the circuit once it`s built. Be sure to install the capacitor with polarity in the correct orientation and care should be taken when...




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