Senior design may06 01 headphone amplifier equalizer and sound stage
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Senior Design May06-01: Headphone Amplifier, Equalizer, and Sound Stage Design Review Presentation Project Team Information Team Members Brandon Bohlen EE Cory Nelson EE Tom Chenoweth EE Travis Fast EE Clients John Lamont Ralph Patterson III Presentation Outline

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Senior design may06 01 headphone amplifier equalizer and sound stage l.jpg

Senior Design May06-01:

Headphone Amplifier, Equalizer, and Sound Stage

Design Review Presentation


Project team information l.jpg
Project Team Information

Team Members

Brandon Bohlen EE

Cory Nelson EE

Tom Chenoweth EE

Travis Fast EE

Clients

John Lamont

Ralph Patterson III


Presentation outline l.jpg
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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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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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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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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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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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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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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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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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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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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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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Approach used

There are five product components

Preamplifier

Balance control

5-band equalizer

Sound stage

Power amplifier


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Preamplifier

  • Gain of 10 dB

  • High-pass filter implementation

    • Reduces noise

  • Dual in-line packages

    • Reduces size


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Balance

  • One channel can be completely cut while the other channel remains constant


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Equalizer

Three different equalizers were built and tested

Baxandall

Resonant frequency

Graphic equalizer


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Baxandall equalizer

  • Circuit used in last year’s amplifier project

  • Could not modify into 5-band equalizer


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Resonant frequency equalizer

  • Capable of having 5-bands

  • Never could get to work as desired


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Graphic equalizer

Best of both worlds

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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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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Sound stage

Loudspeaker emulation

Time-delay

Cross-feed


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Sound stage

Two sound stage circuits were considered

Ohman cross-feed

Brungart

Pinna filter

Time-delay


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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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Brungart sound stage

  • Time-delay

    • Fourth order Bessel 150us time-delay

  • Pinna-related filter circuit

    • Mimics ear canal resonance curves

  • Cross-feed

    • Buffer, current-adder


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Brungart sound stage

  • Sound stage was tested for audio qualities


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Brungart sound stage

  • Pinna-related filter wasn’t considered aurally pleasing

  • Sound stage implemented with only the time-delay circuits


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Power amplifier

  • Similar to pre-amp

  • Available gain of 20 dB


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Accomplishments

  • Researched, tested and chose circuits to use in final product

  • Ordered casing and parts

  • Created final circuit on breadboard






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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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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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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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Closing summary

  • Problem

    • 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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