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Introduction

Problem: At the moment my computer uses a pair of small active speakers that do not produce very good sound, also when I want to plug my mp3 player into then I have to unplug them from the back of my computer first which usually consists of a lot of wire untangling and takes a while. Solution: To solve the problem I am going to build an amplifier which will take four separate inputs and be able to switch between them. It will produce good sound quality through external, passive speakers Specification for Amplifier: 1. It must use an op-amp amplifier 2. It must have four inputs 3. It must have a volume control 4. It must have a bass control 5. It must have a treble control 6. It must be able to switch between inputs 7. It must have stereo speaker outputs 8. It must include a power supply. 9. It must have a maximum size of 300x150x250mm 10. It must be completed by 28th March 2007. 11. It must have a mains power switch. There are various ways in which I can approach this task. I will draw three system block diagrams to show different ways in which I could build my amplifier. Solution 1:- Description:- This is a basic amplifier system. It has four different audio inputs. ...read more.

Middle

x Resistance x Frequency (cut off) I decided on a value for my resistor, 220k?. So: Capacitance= 1 2? x 220k x 15 Capacitance = 48nF Tests:- High pass filter at 40hz:- The output is still 5v, as it should be. High pass filter at 20hz:- The output is just under 5v, as it should be if it is to be cut down to 2.5v at 15hz. High pass filter at 15hz:- At 15Hz it has cut the voltage down to about 3.5v, not quite half but close enough - it is cutting the voltage down. High pass filter at 5hz:- At 5hz the filter has cut the voltage down to a little over 1v, the filter is doing what its meant to be doing. This shows me that my high pass filters are working, giving me a cut off point of 15hz. I will now test my low pass filter. This filter should give me a cut off point of 25khz. To achieve this I will use a 220k? resistor. To calculate the capacitor I used this formula:- Frequency (cut off) = 1 2? x Resistance x Capacitance So: Capacitance = 1 2? x 220k x 25k Capacitance= 28pF. I will test this filter with frequencies from 10khz to 30khz. Low Pass filter at 10khz: It is giving an output at 5v, as it should Low Pass filter at 20khz: It is still giving an output of 5v, as it should. ...read more.

Conclusion

After connecting this and checking all of my power connections I turned the power supply on. Within seconds one of my op-amps started smoking and emitted a small pop. Presumably it has blown, but, as I don't have a spare one to hand I can't check. All the power wires were correct, there was not a short circuit on the board and the op-amp was fitted the right way around. I cannot understand why it blew in the circuit as I had tested the circuit using a signal generator and oscilloscope previously, when it had worked, I had also tested it on the prototype board. Bar the fact that the system doesn't work I am pleased with it. All of the PCB boards were etched very well, and the soldering was good (at least there were no faulty connections or places where solder crossed between tracks). Parts List:- Part Price Each Quantity Total NE5532 Op-Amp �0.34 2 �0.68 12pF Capacitor �0.10 2 �0.20 470nF Capacitor �0.07 6 �0.42 330k Resistor �0.01 2 �0.02 2k2 Resistor �0.01 2 �0.02 22k Resistor �0.01 4 �0.04 220k Resistor �0.01 2 �0.02 NPN Transistor �1.05 1 �1.05 PNP Transistor �1.06 1 �1.06 Diode �0.14 2 �0.28 44k Variable Pot �0.30 2 �0.60 100k Variable Pot �0.37 1 �0.37 Togle Switches �0.56 4 �2.24 TOTAL �7.00 Sources of Information:- - GCSE Electronics Booklets. - Success in Electronics by Tom Duncan. - Rapid Electronics Catalogue 2006 - www.rapidonline.co.uk - www.howstuffworks.com Word Count: 2,455 ?? ?? ?? ?? Rowan Griffin GCSE Electronics ...read more.

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