Ramsey Electronics UAM4 Manual 

UAM4 • 2 x 21W Output Power in Stereo Mode (8Ω, THD = 10%) • 1 x 42W Output Power in Mono Mode (4Ω, THD = 10%) • High Efficiency: Up to 87% • Filterless Class D Amplifier • Unique Patented Spread-Spectrum Mode • Programmable Gain (+22dB, +25dB, +29.5dB, +36dB) • Balanced or Unbalanced High Impedance Inputs • Shutdown and Mute Control • Integrated Click-and-Pop Suppression • Low 0.1% THD+N • Current Limit and Thermal Protection • Programmable Thermal Flag Need more audio “punch” for a project? Build your own powered speaker or juice up that audio kit with this high quality audio amp. 40 Watts of awesome output for any application! 40 WATT UNIVERSAL STEREO AUDIO AMPLIFIER

RAMSEY TRANSMITTER KITS • FM10A, FM25B FM Stereo Transmitters • AM1, AM25 Transmitter RAMSEY RECEIVER KITS • FR1 FM Broadcast Receiver • AR1 Aircraft Band Receiver • SR2 Shortwave Receiver • AA7 Active Antenna • SC1 Shortwave Converter RAMSEY HOBBY KITS • SG7 Personal Speed Radar • SS70A Speech Scrambler/Descrambler • TT1 Telephone Recorder • SP1 Speakerphone • MD3 Microwave Motion Detector • PH14 Peak hold Meter RAMSEY AMATEUR RADIO KITS • HR Series HF All Mode Receivers • DDF1 Doppler Direction Finder Kit • QRP Series HF CW Transmitters • CW7 CW Keyer • QRP Power Amplifiers 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. UAM4 40 Watt Universal Audio Amp Ramsey Electronics publication No. UAM4 Rev. 1.6 This Printing: November 2007 COPYRIGHT 2007 by Ramsey Electronics, LLC, 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, LLC. Printed in the United States of America.

Stereo Audio Amplifier Ramsey Publication No. UAM4 Manual Price Only $5.00 TABLE OF CONTENTS Introduction to the UAM4................................... 4 How It Works ..................................................... 4 “Learn-As-You-Build” Kit Assembly....................8 SMT Soldering....................................................9 Parts List.......................................................... 10 Pre-Assembly .................................................. 10 Assembly Steps................................................11 Using Your UAM4.............................................15 UAM4 Schematic..............................................18 Detailed Input/Output Information ....................21 Troubleshooting Guide .....................................25 Neat-to-Know Info.............................................29 Conclusion........................................................30 Specifications ...................................................31 UAM4 Parts Layout Diagram............................32 Ramsey Kit Warranty........................................35 KIT ASSEMBLY AND INSTRUCTION MANUAL FOR RAMSEY ELECTRONICS, LLC 590 Fishers Station Drive Victor, New York 14564 Phone (585) 924-4560 Fax (585) 924-4555 www.ramseykits.com

of 40 watts, 20 watts per channel in stereo mode, or 40 watts in mono mode. The UAM4 is designed to be configurable in a number of different ways to suit your requirements and allow you to experiment and learn about the capabilities of the Maxim MAX9708 amplifier integrated circuit. After you finish this kit, all you need to do is supply power, an audio signal and speakers and you are ready to go! HOW IT WORKS The UAM4 is a class D amplifier. The letter D is simply the next letter after C, and does not stand for digital. Class D and Class E amplifiers are sometimes mistakenly described as "digital" because the output waveform superficially resembles a pulse-train of a digital signal, but a Class D amplifier merely converts an input waveform into a continuously pulse-width modulated (square wave) analog signal. (A digital waveform would be pulse- code modulated.) Class D amplifiers are much more efficient than Class AB power amplifiers. As such, Class D amplifiers do not need large transformers and heavy heat sinks, which means that they are smaller and lighter in weight than an equivalent Class AB amplifier. All power devices in a Class D amplifier are operated in on/off mode. The term usually applies to devices intended to reproduce signals with a bandwidth well below the pulse switching frequency which is the case of the UAM4 is about 200kHz.. The heart of the UAM4 is the Maxim MAX9708 amplifier IC. The MAX9708 converts the input signal to a sequence of pulses whose averaged value is directly proportional to the instantaneous amplitude of the signal. The frequency of the pulses is typically ten or more times the highest frequency of interest in the input signal. The pulse frequency in the UAM4 is around 200kHz or 10 times 20kHz. The output of such an amplifier contains unwanted spectral components (that is, the pulse frequency and its harmonics) which must be removed by a passive filter. The resulting filtered signal is then an amplified replica of the input. For the UAM4 the filtering is handled by the patented technology of the Maxim MAX9807 amplifier chip and the speaker. The design uses a unique filterless modulation and spread- spectrum switching mode. This eliminates the need for large inductors and capacitors on the output. Typical class D amplifiers use a simple modulation method called ‘Fixed- Frequency Modulation’ (FFM). This simply means that a switching frequency is selected and that is the frequency at which the output is switched. The MAX9708 can use this method, but it also has a special method called ‘Spread-Spectrum Modulation’ (SSM). With this method the switching

of 200kHz. Using this method the MAX9708 is able to reduce the noise generated by typical class D amplifiers and as such, the need for large filters described above is minimized. How this is accomplished is beyond the scope of this manual, but interested readers can find information on the web by searching for ‘spread spectrum’ and checking the Maxim web site at “www.maxim-ic.com” for the MAX9708 data sheet. The main advantage of a class D amplifier is power efficiency. Because the output pulses have a fixed amplitude, output devices (MOSFETS, in the case of the MAX9708) are switched either on or off, rather than operated in linear mode. This means that very little power is dissipated by the transistors, except during the very short interval between the on and off states. The MAX9708 is capable of achieving up to 87% efficiency. The wasted power, the remaining 13%, is low because the instantaneous power dissipated in the transistor is the product of voltage and current, and one or the other is almost always close to zero. The lower losses permit the use of a smaller heat sink while the power supply requirements are lessened too. A TOUR OF THE UAM4 Now let’s take a quick tour of the signal path from input to output. Looking at the schematic (pg. 18) you will notice a large rectangle in the middle. This represents the MAX9708 and aside from a transistor, LED and zener diode, it is the major active component in the UAM4. The input signal(s) are applied to the left and right inputs at the right side of the schematic. These inputs have the advantage of being able operate in either balanced or un-balanced modes. Read on for explanations of unbalanced vs. balanced signals. Unbalanced Signals Most home entertainment audio devices (at least the ones that don’t use optical connections) are using unbalanced signals. Unbalanced means there is a signal line for each signal (or channel), and a common ground for them all. This is fine for consumer audio, but sometimes problems with noise on the signal and/or ground loops can occur. There is only one signal line available, so any noise that manages to get onto that line is amplified and passed to the output, in this case the speakers. Balanced Signals In the case of a balanced input signal, each input actually has two signal lines which are opposite in phase or polarity. That means that when one line increases the other decreases. The amplifier input uses both of these signals by amplifying the difference between them to produce an output. If the signal on both lines is the same the amplifier essentially doesn’t have anything to amplify. The advantage of this is that it is very unlikely that any noise on both lines would be out of phase and therefore the amplifier will essentially reject