UAM2• 1
Universal Audio
Amplifier
Ramsey Electronics Model No. UAM2
• Whopping 20W output at 18V.
• Runs on 8V to 18V DC.
• SNR: 102dB at 15W into 8Ω, 18V
95dB at 10W into 4Ω, 12V
• THD + N: 1% at 15W into 8Ω, 18V
.2% at 10W into 4Ω, 12V
• Square board for screw mounting, or circular “break out” board for
attaching directly to speaker magnet.
• Line level input
• Adjustable gain: 12dB, 18dB, 23.6dB, 32dB
• Remote shutdown input
Need more audio “punch” for a project? Build your own
powered speaker or juice up that audio kit with this high quality
audio amp. Maximum 20 Watt screaming output for any
application; lower gain settings with the change of a jumper.
UAM2• 2
PARTIAL LIS T OF AV AILABLE KI TS :
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RAMSEY MINI-KITS
Many other kits are available for hobby, school, scouts and just plain FUN. New
kits are always under development. Write or call for our free Ramsey catalog.
UAM2 Universal Audio Amp
Ramsey Electronics publication No. UAM2 Rev. 1.1
October 2003
COPYRIGHT ©2003 by Ramsey Electronics, Inc. 590 Fishers Station Drive, Victor, New York
14564. All rights reserved. No portion of this publication may be copied or duplicated without the
written permission of Ramsey Electronics, Inc. Printed in the United States of America.
UAM2• 3
Universal Audio
Amplifier
Ramsey Publication No. UAM2
Manual Price Only $5.00
TABLE OF CONTENTS
Introduction to the UAM2 .................................. 4
UAM2 Circuit Description .................................. 4
“Learn-As-You-Build” Kit Assembly ...................6
Parts List ........................................................... 8
Assembly Steps ................................................. 9
Setup and Testing ...........................................11
Troubleshooting Guide .....................................11
UAM2 Parts Layout Diagram ...........................13
UAM2 Schematic ............................................. 13
Ramsey Kit Warranty .......................................15
KIT ASSEMBLY
AND INSTRUCTION MANUAL FOR
RAMSEY ELECTRONICS, INC.
590 Fishers Station Drive
Victor, New York 14564
Phone (585) 924-4560
Fax (585) 924-4555
www.ramseykits.com
UAM2• 4
INTRODUCTION
The UAM2 is a small, high quality audio amplifier that you can plug any line
level source into and get a whopping 20W out! So if you want, you can plug
your portable cd player in and run your big ol’ speaker! The board is made so
that you can mount it directly onto the back of a speaker or just use it as is
with the mounting holes. It puts out great quality sound with lots of power and
the active parts are all surface mount! You’ll be amazed when you fire it up,
20W is going through a tiny TSSOP IC, and it doesn’t even get warm. There
are 4 gain settings giving you a rough volume adjust, and also a shutdown
input so you can turn the UAM2 off without disconnecting the power.
UAM2 CIRCUIT DESCRIPTION
The UAM2 is built around the Texas Instruments TPA3001D1 audio
amplifier. It is a 20W audio amp in a 24 pin TSSOP package that we have
soldered onto the board for you. We know that many of our customers have
super skills, but we soldered it on for the sake of the ones that might have a
hard time with a small part like that. All the other parts are left for you to
solder, and if you have some surface mount experience it should be really
easy. If this is your first kit, it may be a little challenging, but if you work
slowly and carefully it should come out all right. The TPA3001D1 is a class D
audio amplifier. The “D” is the magic behind how a tiny chip can handle 20W
without going “poof”. If you already know how a class D amplifier works, you
may skip this section. If, however, this is your first exposure to class D amps
as it was for me when I designed this kit, keep reading and allow me to
enlighten you.
audio input
reference signal
outp
outn
differential
output
filter
output to speaker
comparator and
switch
UAM2• 5
First, your audio input is compared to a high frequency reference signal. This
generates two squarewave outputs. These outputs change phase in
response to the audio input.
When the audio input is 0 volts, the two outputs are nearly in phase and the
differential voltage is almost zero most of the time, just little spikes. But, when
the audio input is greater than zero volts, the two outputs are out of phase
and the differential voltage becomes greater, that is, its duty cycle increases.
The voltage is high a greater percentage of the time. This differential voltage
is filtered to produce a sine wave that is sent to the speaker. The magic of all
this is that the circuitry needed to carry out these operations can be digital
because all the waveforms are squarewaves; the voltage is either high or
low, on or off. until they go through the filter. This means that the circuitry
need only have switches to turn the voltage on and off. Switches don’t
consume power so a tiny chip can be used without getting hot. This is in
contrast to other types of amplifiers that have resistive elements in them
which burn up lots of power. They have to have big fat transistors in them
that can handle lots of heat. For more info on class D amps check out the
TPA3001D1 data sheet at:
http://focus.ti.com/lit/ds/symlink/tpa3001d1.pdf
Or a Georgia Tech site:
http://users.ece.gatech.edu/~mleach/ece4435/f01/ClassD2.pdf
audio input = 0 vo lts
audio input > 0
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