PSU AES Amplifier Design Project (2007-2009)

- Sponsored by Penn State’s Audio Engineering Society, student section

- Additional funding provided by Penn State’s Electrical Engineering Dept., Fall 2008

Team Members:
   - Devin Ott (Project Manager, Chief Designer)
   - John Mihalic
   - John Tortorice
   - Ryan Sarver

- Joe Everly

- Steve Beirs

My Role as Project Manager:

• Led a team of students in the design & construction of a high-fidelity audio power amplifier.

• Founded the project in September 2007; sponsored by PSU AES; additional funding from PSU EE Dept.

• Designed and prototyped preamp circuits, filters, power supplies, discrete transistor amps, protection circuitry, audio switching circuits, sensor circuits.

• Designed, fabricated, and assembled the final 50-watt power amplifier and printed circuit board.

• Designed system integration of PIC MCU.

Documentation on this page has been organized into sections:

Project Overview (Sept 2007)

50-Watt Power Amp (Dec 2008)

Headphones Amp (April 2008)

Preamplifier Circuitry (Jan 2009)

Power Supply (April 2008)

Embedded PIC Microcontroller (Aug 2009)

PicBasicPRO Source Code (Aug 2009)

NOTE: I am still in the process of adding documentation.

*Check back soon to see more updates.

Project Overview:

Introduction:

This project was created and sponsored by the Pennsylvania State University (PSU) student chapter of the Audio Engineering Society (AES) to provide students with an opportunity to gain real world engineering experience as members of a student-led development team challenged with the design & construction of a hi-fi audio power amplifier application.

Design Specifications:

High-power low-THD stereo amplifier (max 50W per channel into 8-ohm load)
3 stereo inputs & switching circuit
Bass & treble tone controls w/ optional bypass switch
L/R channel balance
Automatic output current-limiting (3 amps max)
Automatic thermal shutdown
Automatic output DC protection
Delayed-start power-up sequence
Delayed power-down sequence
LED indicator for output voltage-clipping, output current-limiting, power-up sequence, thermal shutdown, etc.
Front-panel LCD screen w/ multiple display options; also indicates operating state of each amplifier channel.
Low-THD Stereo headphones amplifier

PSU AES Amp Design Project (2007-2009) Return to Top
Project Overview (Sept 2007)
50-Watt Power Amp (Dec 2008)
Headphones Amp (April 2008)
Preamplifier Circuitry (Jan 2009)
Power Supply (April 2008)
Embedded PIC Microcontroller (Aug 2009)
PicBasicPRO Source Code (Aug 2009)

50-watt Power Amplifier Monoblock

Design Features: *More information coming soon!

• Low Total Harmonic Distortion (THD) = 0.0169% @ 1kHz

• Temp Sensor - monitors temperature of heatsink, provides a good estimate of MOSFET junction temperature.

• On-board power relay - allows the external MCU to turn off the amplifier if the heatsink exceeds a predetermined threshold temperature.

• On-board output relay - allows the external MCU to connect/disconnect the loudspeaker load from the amplifer.

• Automatic DC offset protection - the amplifier's output relay is automatically opened if a DC offset greater than +/-0.7V exists on the output

o Prevents expensive loudspeaker damage if a fault occurs within the amplifier.

o This protection circuit is entirely housed on-board for maximum response speed if fault occurs.

• "DC offset" logic signal is sent to the MCU to indicate "DC offset" on the LCD to inform the user of a possible fault.

• Amplifier output current is internally limited to approximately 3 amps.

Fabricated Product:

Schematic (all circuits on PCB)

PCB Layout: November 2008

Simulation & Layout Software:

National Instruments’ Multisim & Ultiboard v10.0.1

Screen Captures:

THD measurement data:

Vout = 25Vpeak

load = 10ohm test load (made of 5-watt 1ohm resistors)

Power Amp Prototype: Spring 2008

PCB Etching: Fall 2008

Stereo Headphones Amplifier

Prototype:

Preamplifier Circuitry

Schematic:

Prototype:

Preliminary Filter Designs:

Unregulated Power Supply: for L/R Power Amps and Preamp Circuits

Power Supply Schematic: for the entire project

Diagram of Power Distribution: Illustrates how the MCU controls the Power Relay &

Output Relay of Each Amplifier Channel

• Notice that the MCU circuitry has an independent power supply

o Allows the high-power ±30V supply to be shutdown while application is in STANDBY mode.

o Allows the MCU to continue running even if a catastrophic fault occurs in the ±30V supply.

Embedded Microcontroller: PIC18F4620

Links: some essential references for the design & implementation of our PIC MCU system.

PIC18F4620

PIC18F4620 Datasheet

PICBasic Pro Compiler

PICBasic Pro Compiler Manual

20x2 LCD Display

20x2 LCD Display Manual

Hitachi HD44780U (LCD-II) Dot Matrix Liquid Crystal Display Controller/Driver

Preliminary Summary:

Microcontroller Pin-out & Pin Assignments:

I/O Pin Assignments & Signal Routing info between PCB cards in the chassis:

Sketch of Front Panel:

Microcontroller DESIGN NOTES: developing source code in PicBasicPRO

· Setting the FET/Heatsink Temperature thresholds: THERMAL WARNING (T>85°C), THERMAL SHUTDOWN (T>90°C)

· Setting Output Clipping thresholds: Vout(max) = 29Vpeak, Iout(max) = 2.9Apeak

· Measuring Analog Input voltages & mapping them to numerical values.

· Organizing LCD Display modes & content

· A single DISPLAY button (momentary-contact) is used to cycle through the 6 display modes.

· Fundamentals of working with the Hitachi HD44780 LCD Driver/Controller.

· The 20x2 LCD we purchased is driven by the HD44780.

· We configured the LCD for a 4-bit parallel interface for data transfer with our Microcontroller.

· Some general configuration settings for our PIC MCU.

· Some additional design specifics

Microcontroller SOURCE CODE: in PicBasicPRO

· We apologize; this is NOT the complete source code. Presented here is a collection of PicBasicPRO code segments with unformatted notes/comments scattered within describing additional code to be included.

Click the link below to view the unfinished SOURCE CODE:

PicBasicPRO_AmpProject_SOURCE-CODE.pdf

…Or Scroll down to see a preview.

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