EE 420L Engineering Electronics II Lab

Lab 7 - Design of an audio amplifier

Francisco Mata Carlos

 email: matacarl@unlv.nevada.edu

 4/3/19

Pre-lab:

review lab 6

Lab description:

Design an audio amplifier (frequency range from roughly 100 Hz to 20 kHz) assuming that you can use as many resistors, ZVN3306A transistors, and ZVP3306A transistors as you need along with only one 10 uF capacitor and one 100 uF capacitor. Assume that the supply voltage is 10 V, the input is an audio signal from an MP3 player (and so your amplifier should have at least a few kiloohms input resistance), and the output of your design is connected to an 8-ohm speaker (so, ideally, the output resistance of your amplifier is less than 1 ohm).

The gains values are based from Lab 6 push-pull calculations, which are shown below

First set up:

The first design we used was the one given in the lab, which is the push-pull amplifier (shown below). We used this set up and connected to our 22-ohm speaker and realized the sound was too low. So, we changed the sourced resistance (RS1) and the gain resistor (R1).

First design used with 22-ohm speaker
Input and output
Current through RS1 and Rspeaker1
Power dissipation on the output, RS1 and R1
Experimental result The yellow trace is the input, blue is the output, and the pink trace is the output without an amplifier
Comments: This design was first used with the 22-ohm speaker, which gave us a result with very little volume.

Second set up:

Second design used with 22-ohm speaker RS1=2k, R1=50k With a frequency range starting at 100Hz
Input and output
Current through RS1 and Rspeaker1
Power dissipation on the output, RS1 and R1
Experimental result
click here to see video playing “Split” by Tiesto and the Chainsmokers using the amplifier
Input and output at 100Hz, RS1=2k, R1=50k Gain of about 1 Power supply at 10V	Input and output at 20KHz, RS1=2k, R1=50k Gain a little higher than 1 Power supply at 10V
Input and output using the same size resisors, but using the power supply at 5V
Theoretical values
Comments: The input and output signals above have thick traces because of noise after increasing the voltage on the power supply. However, the noise minimizes as the power supply was turned down to 5V as we can in the oscilloscope picture above. The value for RS1 was reduce to 2kΩ in order to have a smaller voltage drop across RS1 and have a higher voltage on the left side of R1, which was increased even higher by the amplifier and the 50k resistor. By making those changes the 22-ohm speker was much louder.

Note:

One of the issues that was noticed after all the simulations were done was the power dissipation by the transistors. The power dissipation from our design were between 1W and 1.6W. However, according to the datasheets from the transistors, the maximum power dissipation for the N-channel and P-channel at 25°C is 625mW for both. This means that the design will work for only a certain amount of time because the transistor will keep heating up until they burn out. Thus, for future reference the current through the transistors needs to be reduced in order for the desing to work under the maximun power dissipasion. To increase resistance one can add mosfets in series to increse the “L” or adding resistors in series.

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