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 • 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
Presentation outline cont. Accomplishments Schedules and hours worked Resource requirements and project costs Project evaluation Lessons learned Risk and risk management Closing statements
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
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.
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.
Proposed approach • Research, test, and analyze results for multiple circuits and decide the optimal circuit combination to meet the client’s requirements.
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”
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
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
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
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
Approach used There are five product components Preamplifier Balance control 5-band equalizer Sound stage Power amplifier
Preamplifier • Gain of 10 dB • High-pass filter implementation • Reduces noise • Dual in-line packages • Reduces size
Balance • One channel can be completely cut while the other channel remains constant
Equalizer Three different equalizers were built and tested Baxandall Resonant frequency Graphic equalizer
Baxandall equalizer • Circuit used in last year’s amplifier project • Could not modify into 5-band equalizer
Resonant frequency equalizer • Capable of having 5-bands • Never could get to work as desired
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)
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
Sound stage Loudspeaker emulation Time-delay Cross-feed
Sound stage Two sound stage circuits were considered Ohman cross-feed Brungart Pinna filter Time-delay
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.
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
Brungart sound stage • Sound stage was tested for audio qualities
Brungart sound stage • Pinna-related filter wasn’t considered aurally pleasing • Sound stage implemented with only the time-delay circuits
Power amplifier • Similar to pre-amp • Available gain of 20 dB
Accomplishments • Researched, tested and chose circuits to use in final product • Ordered casing and parts • Created final circuit on breadboard
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
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
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
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.