Introduction

In the last two labs we were learning and reviewing many of the fundamentals of electronic circuit analysis. In this lab we'll try to put these basics together, along with a few new ideas to have fun building a fairly high-quality audio amplifier for a compact disc player. The main goal in making the CD audio amp is to take a relatively small signal from the CD player $(V_S \approx 0.5V)$,with relatively high source resistance $(R_S \approx 1K)$,and amplify it sufficiently to drive a speaker, which is usually described as an $8\Omega$ load. A good quality amp will be able to deliver five to ten watts average power to the load, without distorting the original signal. In other words, the signal supplied to the speaker (load) should be an exact replica of the original signal coming from the CD player. Therefore, the hi-fi will amplify all frequencies equally over the audio range which is 20Hz to 20kHz. Any unwanted deviation from the original signal is considered distortion. To achieve this audio amps usually have two basic stages: (1) a pre-amp stage which increases the voltage of the original signal and (2) a current or power amp stage which makes sure the amp can source enough current so the load does not sag the voltage at the output. There are also peripherals such as tone control circuits, and of course the audio amp requires a strong enough power supply to power the circuit.