Group 1 Audio Amplifier Final Presentation

Amplifier ProjectTeam

Murphy, Allen – Pre-Amp builder Toshua, Ruben – Power Amp tester Ahluwalia, Akshay - Pre-amp tester

Enzerillo, Richard – Power Amp builder Lorenzo, Charles – Power Amp builder

Procedure

• Build a Pre Amp and Power Amp from a supplied parts kit

• Testing of Both units• Final Hook up of both circuits• Detailed Reports to analyze our circuits

Pre-Amp Test DataDC TestingV=12VCurrent w/o AC: 4.2mACurrent w/ AC at minimal signal: 4.0mA

AC TestingV=1VFrequency (in Hz): Output Voltage (in Volts):100 4500 0.61000 0.362000 15000 2.610000 4.815000 6.8

100 500 1000 2000 5000 10000 150000

1

2

3

4

5

6

7

8Output Voltage (in Volts):

Output Voltage (in Volts):

Pre-Amp Assembly

The pre-amplifier circuit was constructed as per the schematic that was provided. The images below provide views of the assembly process at approximately the halfway point and at completion. Upon the advice of the lab instructor, two additional 1 μF capacitors were added in order to stabilize the signal (see figure 2). Note that during unit testing a third 0.1μF signal-stabilizing capacitor was added across the positive and negative voltage inputs (ports 8 and 4, respectively) of the LM833 op-amp chip.

Figure 1Circuit construction - phase I

Amplified AC signal out

AC signal in

Additional capacitor for signal

stabilization

-12V DC Input for

LM833 chip

+12V DC Input for LM833

chip

Additional capacitor for signal stabilization

LM833Op Amp

chip

Circuit construction - phase II Figure 2

Pre-Amplifier Unit Testing

Prior to handing the pre-amplifier circuit over to the tester, unit testing was conducted in order to verify that the circuit was working correctly. 12 volt positive and negative power were supplied for the LM833 chip by the DC power terminals of a protoboard. AC signals of low, medium and high frequency produced by a function generator were used as input to the pre-amplifier and the resulting input and output wave forms were visually checked with an oscilloscope. The potentiometer in the circuit was also rotated in both directions to verify that the amplitude of the output signal was adjusted appropriately. The images below document the unit testing process:

Figure 3 Pre-amp circuit and test equipment

Figure 4 Test 1

Figure 5 Test 2

Figure 6Test 3 Test 3

Power Amp

Power Amplifier

TESTING DC

1st DAY

Revising the circuit for any bad connection. The BD139 was connected directly the Vcc and through the 220ohms resistor.

Zero voltage was measured for the output with no input signal. 7.02mA and -7.04mA were drawn from the power supply when the amp was on but with no

input signal.

Testing AC

11.19mA and -4.68 were drawn with an input signal and it was different from DC. I had a distortion of 1.2 v and it was 600mV of a period. I multiply by 2 Volts/Div and it gave me

1.2v I Fixed the distortion by adding two 100uF capacitors in the –12Vcc and the +12Vcc and also to

ground. 2nd Day of troubleshooting the power amp:

BJT Transistor beta measured

An isolation on this wave. And that was the problem.

NPN PNP BD139=BDC=160 BD140= BDC=240 BD139=BDC=180 MJE2955= BDC=50 MJE3055=BDC=300 BC559= BDC=220 BC559= BDC=300

Beta: 50*160=8000

240*200=48000 40000 of difference

The problem was that the beta from positive circuit was 8000 and the negative circuit was 48000. It was too high and 40000 was the difference from positive circuit. So I switched the MJE2955 transistor with a higher beta of 300. 160*300=48000 and they matched with negative circuit.

3rd Day Measure the Frequency

I did all the measurement again from the beginning like the first day of the testing.

This time the current with no input was even higher (64mA and -64mA) With the input amplifying and the voltage peak to peak was 16v and the current

drawn was 260mA and -250.8mA

The picture below is the input and the output. Input is the small wave Output is the big wave.

28.8

29

29.2

29.4

29.6

29.8

30

30.2

0 5 10 15 20

Y-Values

Y-Values

Frequency Input Output Av dB 100Hz 440mV 12v 27 29 500Hz 390mV 12.4v 32 30 1KHz 400mV 12.5v 31 30 2KHz 420mV 12.4v 30 30 5KHz 430mV 12.4v 29 29 10KHz 420mV 12v 30 30 15KHz 400mV 11.8v 30 30 20KHz 380mV 11.6v 31 30

The table and the graph