Design Review Presentation Senior Design May06-01: Headphone Amplifier, Equalizer, and Sound Stage 24/02/2019 19:00

Project Team Information Team Members Brandon Bohlen EE Cory Nelson EE Tom Chenoweth EE Travis Fast EE Clients John Lamont Ralph Patterson III 24/02/2019 19:00

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 24/02/2019 19:00

Presentation outline cont. Accomplishments Schedules and hours worked Resource requirements and project costs Project evaluation Lessons learned Risk and risk management Closing statements 24/02/2019 19:00

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 24/02/2019 19:00

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. 24/02/2019 19:00

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. 24/02/2019 19:00

Proposed approach Research, test, and analyze results for multiple circuits and decide the optimal circuit combination to meet the client’s requirements. 24/02/2019 19:00

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” 24/02/2019 19:00

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 24/02/2019 19:00

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 24/02/2019 19:00

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 24/02/2019 19:00

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 24/02/2019 19:00

2/24/2019 7:00 PM

Approach considerations 24/02/2019 19:00

Approach used There are five product components Preamplifier Balance control 5-band equalizer Sound stage Power amplifier 24/02/2019 19:00

Preamplifier Gain of 10 dB High-pass filter implementation Reduces noise Dual in-line packages Reduces size 24/02/2019 19:00

Balance One channel can be completely cut while the other channel remains constant 24/02/2019 19:00

Equalizer Three different equalizers were built and tested Baxandall Resonant frequency Graphic equalizer 24/02/2019 19:00

Baxandall equalizer Circuit used in last year’s amplifier project Could not modify into 5- band equalizer 24/02/2019 19:00

Resonant frequency equalizer Capable of having 5-bands Never could get to work as desired 24/02/2019 19:00

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) 24/02/2019 19:00

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 24/02/2019 19:00

Graphic equalizer 24/02/2019 19:00

Sound stage Loudspeaker emulation Time-delay Cross-feed 24/02/2019 19:00

Sound stage Two sound stage circuits were considered Ohman cross-feed Brungart Pinna filter Time-delay 24/02/2019 19:00

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. 24/02/2019 19:00

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 24/02/2019 19:00

Brungart sound stage Sound stage was tested for audio qualities 24/02/2019 19:00

Brungart sound stage Pinna-related filter wasn’t considered aurally pleasing Sound stage implemented with only the time-delay circuits 24/02/2019 19:00

Power amplifier Similar to pre- amp Available gain of 20 dB 24/02/2019 19:00

Accomplishments Researched, tested and chose circuits to use in final product Ordered casing and parts Created final circuit on breadboard 24/02/2019 19:00

Schedule 24/02/2019 19:00

Hours 24/02/2019 19:00

Resources required 24/02/2019 19:00

Project costs 24/02/2019 19:00

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 24/02/2019 19:00

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 24/02/2019 19:00

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 24/02/2019 19:00

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. 24/02/2019 19:00

Questions? 24/02/2019 19:00