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					Car Audio Amplifier
Midterm Presentation
28 February 2005

Team Members
Car Audio Amp Group
Stephan Sykes
Team Leader Power Supply

Dwayne Custer
Amplifier

Jacob Fulper
Documentation

Dr. Ray Winton
Faculty Advisor

Darius Boyce
Input/Output

Presentation Overview
I. II.

Introduction Amplifier
A. B.

Selection Functionality On/Off Switch Output Relay

Jacob Fulper Dwayne Custer Darius Boyce Stephan Sykes

III.

Input/Output
A. B.

IV.

V.

Power Supply Conclusion

I. Introduction


Project Goal


The car audio amplifier will allow music enthusiasts to listen to their MP3 player, or other headphone audio device, through their car speakers.

I. Introduction

1.

Advantages Over Competition
Size – This device will be much smaller than most existing car audio amplifiers. Width ≤ 4”, Length ≤ 6”, Thickness ≤ 2” Cost – This device will cost less than most existing car audio amplifiers. Projected production cost: ≤ $15 Projected retail price: ≤ $45 Sound Quality – This device will provide the listener with higher quality of sound than its cheaper competitors, which include the FM transmitter and the cassette adapter.

2.

3.

II. Amplifier
Car Battery Portable Audio Player Power Supply On/Off Relay Amplifier

Car Stereo

Block Diagram

Speakers

II. Amplifier – Selection
Class A B AB D Advantages Very low distortion Much more efficient than A Low distortion, good efficiency Very high efficiency Disadvantages Very inefficient Very much distortion Requires more circuit elements Small bandwidth

II. Amplifier – Functionality
Input

Input Buffer/Filter

Voltage Gain Element

Current Gain Element

High Level Block Diagram for the Amplifier

II. Amplifier – Functionality


Input Buffer/Filter – Maximally Flat, Audio Range (20Hz-22kHz)

II. Amplifier – Functionality


Voltage/Current Gain Elements
Power = Voltage x Current  Output Voltage Gain of 5  Class AB final stage  Output current gain = 560k

Vin V+

V+

RL V-

V-

II. Amplifier – Functionality


Voltage and Current Gain Elements Final Output

III. Input/Output
Car Battery Portable Audio Player Power Supply On/Off Relay Amplifier

Car Stereo

Block Diagram

Speakers

III. Input/Output – On/Off


The amplifier will only be on when the audio player is plugged into the jack.
Portable Audio Player “ON” “OFF” On/Off 5V Switch (Jack) 0V 5V 0V Power Supply ±7V 0V

Logic

Audio Signal In

Amplifier

Audio Signal Out

III. Input/Output – Output Relay


To prevent damage, the car stereo will be disconnected from the speakers when Car Stereo the amplifier is on.
5V 0V Relay Audio Signal Out

Amplifier Signal Car Stereo Out Out

5V 0V

Logic

5V 0V

Power Supply

Speaker

Amplifier “ON” Amplifier “OFF”

±7V
0V

Amplifier Audio Signal In

IV. Power Supply
Car Battery Portable Audio Player Power Supply On/Off Relay Amplifier

Car Stereo

Block Diagram

Speakers

IV. Power Supply


Every amplifier circuit requires an independent power supply to function.


The following criteria define the requirements of the power supply:

2Ω 2Ω 2Ω 2Ω 12W 12W 12W 12W
PL=4 x 12W=48W

0.5Ω 48W
RL=2||2||2||2=0.5Ω

VS(opt)  2RL PL  2  0.5  48  6.92V  7V

IV. Power Supply


Power supply requirements (continued):
It should be noted that the amplifier needs voltage rails of ±VS(opt), which is ±7V.  The actual efficiency of the amplifier will be greater than 70%, but… …the power supply will be designed to handle a worst case efficiency, η, of 50%.


PS=PL/ η=48/0.5=96W  PD=PS-PL=96-48=48W (Worst Case)  ISmax=PS/VS(opt)=96/6.92=13.9A≈14A


V.
Portable Audio Player

Conclusion – Recap
Car Stereo On/Off Switch (Jack) Logic Relay Power Supply

Amplifier

Car Battery

Speakers

Acknowledgments



  

Dr. Ray Winton Dr. James Harden Mr. Nishant Chandra Mr. Charles Simmons (Raytheon) Crutchfield New Media, LLC

Any Questions?


				
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