Headphone Amplifier, Equalizer, and Sound StageAbstract

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 circuitsProblem Statement

Current Portable Audio Devices

•Have insufficient power to drive high end headphones

•Lack equalization control

•Have stereo localization

Problem Solution •Provide 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 objectives •Enhance musical listening experience

•User friendly interface

Functional requirements •Input 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 constraints •Must 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 considered Several passive and active circuits were tested for each element of the system.

Testing considerations Each 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

Estimated Personal Effort Requirements

195.5

184.5191

183

Bohlen, Brandon

Chenoweth, Thomas

Fast, Travis

Nelson, Cory

Other Resource Requirements

$20.00

$50.00

$10.00$25.00

$40.00 IC chips and LEDs

Pots and Switches

Case

Poster Expenses

PCB creation

Semester 1 Break Semester 2

Deliverable 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

Project Plan

Bound Project Plan

Design Report

Bound Design Report

Project Poster

Final Report

Bound Final Report

IRP Presentation

Class Presentation date varies

Weekly Email Reports

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Deliverable Schedule

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

LEFTEQ

RIGHT EQ

BALANCE

SOUND STAGE

LEFTPOWERAMP

RIGHTPOWER AMP

POWER SUPPLY

STEREO

INPUT

STEREO

OUTPUT

The green lines represent components with ganged controls.The red lines represent power supply lines

EQ CONTROLS VOLUME

Block Diagram of End Product