1. Headphone Amplifier, Equalizer, and Sound Stage Abstract Some portable media devices, such as mp3 players, have insufficient power to drive top-of-the-line headphones, which have an impedance of 32 to 600+ ohms. Sound quality on these mp3 players on headphones is sub par. Headphones do not implement a sound stage, where the left and right channels aren’t localized to each ear. Speakers would allow the user to hear audio from the left channel in their right ear, and vice versa, creating a 3D sound, but headphones don’t incorporate this. Including this sound stage, see fig. 1, will help to create a more realistic sound for the user to experience. Equalizers are a common sound element that is lacking in these mp3 players. Adding an equalizer would allow the users to adjust the sound to their own preferences. To fix these problems a combined amplifier, equalizer and acoustic simulator device will be developed. The end product will be a small, user-friendly device. Headphone Amplifier, Equalizer, and Sound Stage Acknowledgement Ken Uhlenkamp Professors Lamont and Patterson Provided a carefully regulated power supply for the project Providing time and expertise about audio circuits Problem Statement Current Portable Audio DevicesHave insufficient power to drive high end headphones Lack equalization control Have stereo localization Problem SolutionProvide gain and buffer stages to help drive high end headphones Provide a 5-band equalization circuit Incorporate sound stage simulation Operating Environment It should be portable enough to be carried It should work at a desk or in a car Intended Users and Uses User: General audio enthusiast Use: Gain more control over portable audio experience Assumptions The output impedance will range from 32 to 600+ Ohms The manufacturing price of the product should not exceed $75.00 The product will run for 8 hours before requiring a recharge Limitations There is a finite budget of $150.00 The system must run on 120 Volts AC, 12 Volts DC, and on an internal 9 Volt power supply The system will at a minimum include these controls: a volume control, a balance control, a power switch, 3-band equalizer controls, a variable time-delay control. Expected End Product An encased device that includes: a 3.5 mm input jack on the front and back panels, two headphone jacks (one 3.5 mm and one 6.5 mm), a volume control, a balance control, a power switch, 5-band equalizer controls, a separate 3-band preset “easy” equalizer controls, a variable time-delay control with bypass switch built in, and a pilot light, all of which will be labeled. The device will include a carefully regulated, rechargeable power supply designed by another team from Cedar Rapids and optimized by Ken Uhlenkamp. The end product layout should be similar to the front and back panel diagrams shown below. May0601 Team Information Team Members:Brandon Bohlen, EE Thomas Chenoweth, EE Travis Fast, EE Cory Nelson, EE bbohlen@iastate.edu tomcheno@iastate.edu tfast@iastate.edu nels0398@iastate.edu Client:Faculty Advisors: References: http://www.headwize.com Iowa State University ECpE Department Senior Design Program John Lamont Ralph Patterson III Project Requirements Design objectivesEnhance musical listening experience User friendly interface Functional requirementsInput from 3.5mm audio source and output to 3.5mm or 6.5mm jacks Amplification control to drive varied impedance outputs 5-band equalization control will be provided Variable time delay and cross feed circuit control will be implemented Design constraintsMust not exceed 8” x 8” x 2” Proposed approach Problem definition Product design Breadboard implementation Client listening test PCB board design Final product test End product demonstration Technical Approach An educated trial and error process was used to choose the separate circuits for each module. A series of circuit options were chosen from previously designed circuits and tests of these circuits gave us the final circuits. Technologies consideredSeveral passive and active circuits were tested for each element of the system. Testing considerationsEach circuit was listened to by a variety of listeners. Listening to the circuits to determine the best was the only test that would yield the best combination for our system. Estimated Resources Website: http://seniord.ece.iastate.edu/may0601/index.html Closing Summary There is a niche market for a device that will amplify, equalize, and provide a more realistic, “ open ” sound for a portable audio device. This result of this project will provide a product that will fill this niche market. The project will be completed beginning with research, progressing to design, simulation and testing, and concluding with building a working prototype in a self-contained casing. The final prototype will essentially be a ready-to-use production model. The product is intended to allow the user to have more control more control over and provide a more pleasurable listening experience. This product will integrate three currently available products into a single unit, providing a more convenient and cost- effective experience for the user. Milestones Figure 1 LEFT PREAMP RIGHT PREAMP LEFT EQ RIGHT EQ BALANCE SOUND STAGE LEFT POWER AMP RIGHT POWER AMP POWER SUPPLY S T E R E O I N P U T STEREOOUTPUTSTEREOOUTPUT The green lines represent components with ganged controls. The red lines represent power supply lines EQ CONTROLS VOLUME Block Diagram of End Product