1. Design Review Presentation
Senior Design May06-01:
Headphone Amplifier, Equalizer, and Sound Stage
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2. Project Team Information
Team Members
Brandon Bohlen EE
Cory Nelson EE
Tom Chenoweth EE
Travis Fast EE
Clients
John Lamont
Ralph Patterson III
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3. Presentation Outline List of definitions
Problem statement and proposed approach
Operating environment
Intended user(s) and use(s)
Assumptions and limitations
End product
Approaches considered and used
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4. Presentation outline cont.
Accomplishments
Schedules and hours worked
Resource requirements and project costs
Project evaluation
Lessons learned
Risk and risk management
Closing statements
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5. Acknowledgements
Professors Lamont and Patterson III for their time and continued advice throughout the year
Ken Uhlenkamp for his work with the power supply
Jason Boyd for his help with the PCB layout
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6. List of Definitions
Audiophile – a person who is enthusiastic about high- fidelity sound reproduction.
mp3 – an audio compression format used for the playback of digital audio in home computers and portable devices.
PCB – a printed circuit board is an insulated board containing conductive strips that connect components into a compact circuit.
Sound stage – a circuit that simulates three-dimensional sound reproduction for headphone listening. The purpose of this circuit is to provide the user with an aural experience that sounds more like listening to two loudspeakers in a small room, rather than the typical binaural headphone experience.
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7. Problem statement
Design an amplifier for portable audio devices that has a 3-band equalizer, sound stage simulation and balance control built in for an enhanced user experience.
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8. Proposed approach
Research, test, and analyze results for multiple circuits and decide the optimal circuit combination to meet the client’s requirements.
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9. Operating environment
Intended mainly for desktop use
Car compatible
Sustains a wide temperature range
-30o F to 120o F
Susceptible to random vibration
Not intended for mobile use
7.75” x 6.3” x 2.5”
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10. Intended User(s) and Use(s)
General public
Specifically audiophiles
Use in conjunction with a portable audio source, such as a CD or MP3 player
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11. Assumptions Product will drive headphones or self- powered speakers
Must at least have a 3-band EQ with ±20dB amplification
A battery supply that has a voltage rating of ±4.5 V
Product must run for a minimum of 8 hours
End product must stay under $150
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12. Limitations The system must at a minimum include: 3.5 mm input jack
Two headphone jacks
one 3.5 mm (1/8” mini)
one 6.5 mm (1/4”)
Volume control
Balance control
Power switch and LED indicator
3-band equalizer controls
Sound stage by-pass switch indicator
Labels for all controls
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13. End Product
A completely encased prototype of a portable audio device capable of driving a set of high-fidelity headphones with a sound stage offering the user the ability to adjust a 5-band equalizer
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14. 2/24/2019 7:00 PM

15. Approach considerations
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16. Approach used There are five product components Preamplifier
Balance control
5-band equalizer
Sound stage
Power amplifier
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17. Preamplifier Gain of 10 dB High-pass filter implementation
Reduces noise
Dual in-line packages
Reduces size
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18. Balance
One channel can be completely cut while the other channel remains constant
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19. Equalizer Three different equalizers were built and tested Baxandall
Resonant frequency
Graphic equalizer
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20. Baxandall equalizer Circuit used in last year’s amplifier project
Could not modify into 5- band equalizer
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21. Resonant frequency equalizer
Capable of having 5-bands
Never could get to work as desired
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22. Graphic equalizer Best of both worlds Problems
Passive LC filter network
Only one op-amp per channel
Controllable Q and center frequencies
Problems
Inductors required for audio frequencies were not practical for this project (large, heavy)
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23. Graphic equalizer
Solution: simulate induction using gyrators to invert the phase properties of a capacitor
Allows for any inductance value to be realized for the filters
Added quiescent current draw of each gyrator
Best compromise based on current draw vs. performance
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24. Graphic equalizer
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25. Sound stage Loudspeaker emulation Time-delay Cross-feed
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26. Sound stage Two sound stage circuits were considered Ohman cross-feed
Brungart
Pinna filter
Time-delay
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27. Ohman cross-feed Passive style cross- feed with time delay
Saves on current draw
Time delay set to be variable with maximum of 300 μs delay.
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28. Brungart sound stage Time-delay Pinna-related filter circuit
Fourth order Bessel 150us time-delay
Pinna-related filter circuit
Mimics ear canal resonance curves
Cross-feed
Buffer, current-adder
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29. Brungart sound stage Sound stage was tested for audio qualities
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30. Brungart sound stage
Pinna-related filter wasn’t considered aurally pleasing
Sound stage implemented with only the time-delay circuits
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31. Power amplifier Similar to pre- amp Available gain of 20 dB
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32. Accomplishments
Researched, tested and chose circuits to use in final product
Ordered casing and parts
Created final circuit on breadboard
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33. Schedule
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34. Hours
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35. Resources required
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36. Project costs
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37. Project evaluation Project completed successfully
Design requirements were met
Cost exceeded requirements, but was deemed acceptable
Within size limitations
Provides user with a unique listening experience
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38. Lessons learned Gained knowledge about audio schematics
The importance of decoupling the audio signal
Have backup circuit choices
Importance of breadboard testing vs. PSpice simulations
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39. Risk and risk management
Anticipated
Loss of a team member
Circuit inadequacies
Many circuits were tested
All circuits were listened to in breadboarding
Unanticipated
Out of stock or discontinued parts
Different packages were ordered
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40. Closing summary Problem Solution
Design an amplifier for portable audio devices that has a 5-band equalizer, sound stage simulation and balance control built in for an enhanced user experience.
Solution
Designed and built a functional prototype that includes an amplifier, equalizer, sound stage simulator and balance control.
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41. Questions?
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