April 26, 2005

Headphone Amplifier & Equalizer

May05-01

Project Team Information• Team Members

– Jennifer Bruner, Electrical Engineering– Mike Dierickx, Electrical Engineering– Rachel Hager, Electrical Engineering– Kurtis Kenne, Electrical Engineering

• Advisors– John Lamont– Ralph Patterson III

• Client – Senior Design

Presentation Outline• List of Definitions• Problem Statement & Proposed

Approach• Operating Environment• Intended User(s) & Use(s)• Assumptions & Limitations• End Product• Approaches Considered and Used

Presentation Outline Cont.• Accomplishments• Schedules & Hours Worked• Resource Requirements & Project

Costs• Project Evaluation • Lessons Learned• Risk & Risk Management• Closing Summary

Acknowledgements

• HeadWize, specifically Chu Moy, for the audio schematics

• Jason Boyd, the brain behind the PCB layout and soldering

List of Definitions• Amplifier – The circuitry that allows one to

adjust the overall power and thus volume.• Cross-fed Delay Filter - A filter which

simulates a surround sound experience by combining both channels with time delay and attenuation in each ear.

• Equalizer – The circuitry that allows one to tune the relative power of individual frequency bands of an audio signal.

Problem Statement• Design a portable audio device capable of

driving a set of high-fidelity headphones with a soundstage offering the user the ability to adjust a 3-band equalizer.

Proposed Approach• Research and test audio schematics provided

by HeadWize and develop a design fitting the functional requirements set forth by the project advisors.

Operating Environment

• Encompasses all portable uses in both indoor and outdoor environments– Portability

• Dimensions no greater than 5” x 5” x 2.5”– Durability

• Extreme temperatures• Possibility of being dropped

Intended User(s) & Use(s)• General public

– Specifically enthusiasts of music• Use in conjunction with a portable audio

source, such as a CD or MP3 player

Assumptions• Drive a pair of high fidelity headphones

with an impedance range up to 32 ohms• Will use 3-band equalization with a max

of ±20 dB amplification• Equalization will be in stereo, but each

channel will not be equalized separately

Limitations• The device must have the capability to charge on 12

VDC, and operate on an internal power supply of six – 1.2 V (AA) NiMH rechargeable batteries

• The device will include at minimum a 3.5 mm input jack, a 3.5 mm headphone jack, a volume control, a power switch, 3-band equalizer, and a pilot light

• Since the device will be portable, it must be able to withstand extreme temperatures and be durable enough to withstand being dropped

• The MSRP (Manufacturers Suggested Retail Price) should not exceed $50.

End Product

• A completely encased prototype of a portable audio device capable of driving a set of high-fidelity headphones with a soundstage offering the user the ability to adjust a 3-band equalizer

• A users’ manual

Technical Approaches

Approach Considerations

Approach Used

• There are four primary components

– Amplifier

– Equalizer

– Soundstage Simulator

– Battery and Casing

Amplifier

• Should be superior to the digital “Class D” part contained in portable players

• Designed to have a voltage gain from zero (off) to about 2.5

• Guarded at the input by an AC couple to eliminate noise

Amplifier

Equalizer

• Both passive and active types• Chose an active “Baxandall” type with

about ±20 dB in each channel with centers at 300, 1050, and 1700 Hz

• This design was highly tunable, it can very nearly silence a band

Equalizer

Cross-fed Delay Filter

• Creates a proper “soundstage” using passive filters

• The soundstage is typically not present in studio recordings, but much more in symphonic or marching band tracks

Cross-fed Delay Filter

Headphone User

Cross-fed Delay Filter

Speaker User

Cross-fed Delay Filter

• The effect of hearing the path difference depends on both a time delay and a change in volume due to attenuation

• The volume change for a given path difference depends on the frequency of the sound

Cross-fed Delay Filter

Casing and Power Supply

• Power Supply wasdesigned by a previousteam finishing in December 2004

• Has 4.5, Ground, and –4.5 V, although currently other methods of power are being used

Casing and Power Supply

• Right now, casing has been chosen to accommodate the single 9 V cell

• Case for our first prototype has been chosen

Accomplishments

Accomplishments• Researched different audio schematics

published by various authors at www.headwize.com

Accomplishments• Ran PSpice simulations on selected

circuit schematic

Accomplishments• Completed breadboard testing

Accomplishments• PCB layout is complete and was

ordered using Orcad LayoutAll three layers Bottom Layer

Silkscreen Top Layer

Accomplishments• First Prototype PCB from Advanced

circuits www.4pcb.com $46

Accomplishments• Soldered surface mount components

onto PCB

Accomplishments• Encased PCB • Dimensions 5”x2.5”x1”

Accomplishments• Tested prototype with different types of

input

Accomplishments• Created users manual

Schedule and Resources

Project Schedule

Schedule• Power supply caused major delays

• Some tasks took longer than expected– Research– Parts and technology considerations– Breadboard implementation & testing

• Team finished on schedule

Hours Worked (To Date)

166Kurtis Kenne

164Rachel Hager

162Mike Dierickx

159Jennifer Bruner

Number of Hours

Team Personnel

Hours Worked (To Date)

Jennifer, 159, 24%

Rachel, 164, 25%

Kurtis, 166, 25%

Mike, 162, 26%

JenniferMikeRachelKurtis

Other Required Resources

$303.62Total:

$0.00Subtotal:

DonatedSoldering

Assembly Services:

$253.62Subtotal:

$89.25SMT and Case

$67.50Axial Lead

$46.87PCBs

Parts:

$50.00Project Poster

CostItem

Other Required Resources

$0 $20 $40 $60 $80 $100

PCBs

Axial Lead

SMT & Case

Item

Cost

Project Costs

$6,763.62$303.62Total:$6,510.00$0.00Subtotal:$1,660.00Kurtis Kenne

$1,640.00Rachel Hager

$1,620.00Mike Dierickx

$1,590.00Jennifer Bruner

Labor ($10 per hour):

$0.00$0.00Subtotal:DonatedDonatedSoldering

Assembly Services:

$253.62$253.62Subtotal:$89.25$89.25SMT and Case

$67.50$67.50Axial Lead

$46.87$46.87PCBs

Parts:$50.00$50.00Project Poster

With LaborW/O LaborItem

Project Evaluation

• Project Completed Successfully– Met design requirements– Product is durable and portable– Met expected cost– Provides unique listening

experience

Lessons Learned• Gained knowledge of audio

schematics• Importance of breadboard testing –

group knowledge of board layout• Set-back with the power supply• Issues with noise • Start testing earlier

Risk & Risk Management• Anticipated few problems with design layout

– Ran PSpice simulations– Breadboard testing

• Unanticipated problems with the power supply developed by previous senior design team– Sent power supply to get fixed– Fabricated device using a 9V battery supply

• Unanticipated noise during breadboard testing– Fixed some issues due improper grounding – Fabrication of PCB eliminated noise issues

Closing Summary• Problem

– Need a portable audio device capable of driving a set of high-fidelity headphones with a soundstage offering the user the ability to adjust a 3-band equalizer.

• Solution– Designed a device that includes an amplifier,

equalizer, and acoustic simulator, all placed into an economical package

• Result– Functional prototype was developed with

users’ manual

¿Questions?