Created by Created November 13, 2011 Last modified June 07, 2017 Tags

### Summary

A one-transistor amplifier, intended to amplify audio picked up by a piezoelectric transducer.

### Description

This models the amplifier circuit described in detail at http://www.nerdkits.com/videos/sound_meter/ .

Vpiezo and Cpiezo in series represent a piezoelectric element that's being vibrated mechanically by sound waves, and is generating a voltage as a result. R1 and R2 represent a 100K potentiometer. Together with RE, these set up a 100uA bias collector current for transistor Q1. CE provides extra amplification.

#### A few things to try in CircuitLab

This circuit highlights several cool features of CircuitLab simulations that you can quickly try. Load this circuit with the "Open in editor" button above, and then click the "Simulate" tab to get started.

##### DC

Run the DC simulation to quickly get a sense of the bias currents, etc.

##### DC Sweep

See how the circuit varies of our power supply isn't really at 5V.

##### Time

Take a look at how a sine wave input looks, and how distorted it is at the output. You can adjust the amplitude of the sine wave source (Vpiezo) and re-run to see how distortion varies with amplitude.

##### Bode

Run the frequency-domain analysis to see a plot of the gain of the amplifier. As-is, it's about +38dB in the passband. That's a voltage gain of 10^(38/20) = 79. Notice that our hand calculations indicated a gain of about 88, so that's pretty close!

Now remove CE, and re-run the Bode analysis. The gain is now about +15.7dB, or a voltage gain of 10^(15.7/20) = 6.1 That's pretty close to the 6.7 we calculated by hand.

#### More Common Emitter Amplifier info

• Take a look at the third video here for another example about simulating a common emitter amplifier