Physics 104
Amplifier Lab
Introduction
In this experiment you'll build and test an inverting amplifier.

Apparatus
breadboard              741 or 411 operational amplifier    speaker
oscilloscope              function generator 
various resistors        digital multimeter

Procedure

Mount your op amp chip on the breadboard such that each pin is in its own hole, and such that the body of the chip straddles a gap on the breadboard, and each pin is in one of the vertical columns of holes that are electrically connected. The "pin-out" diagram is sketched below:


Connect wires from the +5v and -5V power supplies on the breadboard to the appropriate pins of the chip. Measure the resistance of all of your resistors. Using the 11 k and 110 k resistors and consulting the diagram below, wire up an inverting amplifer with a gain greater than 1 (Rf > R).

    

Now use the I/O BNC connector on the breadboard to bring in a signal from your function generator, say a 1 kHz sine wave, 0.1 volts peak-to-peak. Display this signal on your oscilloscope as well, and then use an I/O BNC connector on the board to measure the output of your amplifier on the second channel of the scope. Turn on the breadboard power. Note: When the breadboard is on, the power supplies are all operative, so be careful not to connect "ground" to any of the power supplies with a wire. This way you'll avoid getting a "zap" or shorting out the power supply.   

1. Measure the gain of your amplifier to two significant digits, using the voltage cursors on the oscilloscope. Note whether or not the signal is inverted.

2. Repeat this gain measurement at the following frequencies: 10 kHz, 100 kHz, 1 MHz, and 10 MHz.

3. Go back to 1 kHz and change the input waveform amplitude to 1 volt. What happens to the output?

4. Test out your amplifier with a 1 kOhm feedback resistor and a 100 Ohm input resistor, using as input a 1 kHz wave with 0.1V amplitude. Determine the output and input voltage as before.

5. Finally, add a second resistor to the circuit as follows:


where R1 = 100 Ohm, Rf = 1 kOhm, and R2 =  50 Ohm.  Feed the output of the circuit to both an oscilloscope and a speaker.  Set your input amplitude to 0.01 V, increase it by 0.01 V until the output starts to "clip."  What does this sound like before and after the output "clips"?

When you are done, please turn off the breadboard and measure the resistances of your resistors with the DMM, while they are unplugged from the circuit.

Analysis
1. Create a table showing the gain of your amplifier circuit as a function of frequency and compare it to the expected theoretical value. Was the output signal inverted? How did the gain change with frequency, or did it?

2. How can you explain the output of the amplifier in part 3. above (hint: think about the power supplies)? What does it sound like when the output "clips"?  Why?

3. How can you explain the input voltage in part 4. above (hint: think about input resistance)?

4. How can you explain the sound before and after the voltage "clips" in part 5?

Conclusion
Be sure to conclude with a statement regarding what you learned in the lab.