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	WPI Technical Theatre Handbook: Power Amplifiers
	Power Amplifiers The outputs of a sound board are typically line level signals which can not directly drive speakers. Thus, a power amplifier must be used between the outputs of a mixer and the speakers. Power amplifiers come in a variety of sizes, each with different capabilities and features. Power amplifiers are functionally simple units. All amplifiers have a set of line-level inputs and a set of speaker-level outputs. Most have a power switch and volume controls as well. The outputs of a sound board are typically connected to the inputs on the amplifier, and speakers are connected to the speaker outputs. The job of the amplifier is to take the small line-level signal and boost it to the levels required to drive speakers. One characteristic of better amplifiers is that they more faithfully reproduce the small signal at the speaker outputs. Inexpensive amplifiers tend to color the sound by inaccurately reproducing the line-level signal at the speaker outputs. One important rating for amplifiers is the amount of power they can supply, specified in watts. Given sufficiently capable speakers, the more power an amplifier can supply the louder the overall sound system can be before it begins to distort6.2. System distortion is not desirable as it sounds bad and can damage speakers. It is important to note that some low-end professional equipment, and quite a bit of consumer gear is improperly rated. Knowing that the general public tends to buy amplifiers based solely on the number of watts they can produce, some companies go out of their way to artificially bloat these figures. Caveat emptor. The power rating for an amplifier is usually specified in terms of driving a certain load. The load (in most cases a speaker) has a characteristic impedance. Most speakers have an impedance of four or eight ohms, and not by accident, most amplifiers specify their ratings for four or eight ohm loads. It is important to pay attention to loading because it's possible to blow up an amplifier if it is not rated to handle the load being driven. Use of information in this document implies understanding and agreement with the copyright and terms of use. Specifically, no warranty is expressed or implied regarding the accuracy of the information contained within. YOU USE THIS INFORMATION AT YOUR OWN RISK. All trademarks are property of their respective owners. You must obtain permission from the author before using the contents of The Handbook for anything other than private use.	Table of Contents [Whole book in PDF 5.3MB] Contents Introduction Goals Sources Methods Conclusions Costumes Introduction Procurement Fabrics Color Patterns Fitting Rehearsal Clothing Design How to Begin Color Practicality Documents The Set Introduction Set Pieces Platforms Flats Stairs Rakes Other Structures Floor Coverings Construction Materials Tools Finishing Painting Types of Paint Mixing Paints Applying Paint Draperies Design How to Begin Documents Computer-Aided Design A Typical Set Construction at WPI Rigging Introduction Common Rigging Hardware Rope Wire Rope Thimbles, Wire Rope Clips, and Swages Shackles, Turnbuckles and Hooks Chain & Rapid Links Slings Fly Methods Non-Counterweighted Pulley Systems Counterweighted Fly Systems Lifts Chain Motors Flying Set Pieces Lighting Introduction Lighting Instruments Scoops Cyclorama Lights Parabolic Reflector Cans Fresnel Spotlights Ellipsoidal Reflector Spotlights Automated Instruments Color Color Theory Primary, Secondary and Complementary Colors of Light Light Mixing Practical Use of Color Glass, Gelatine and Plastics Dichroic Color Filters Patterns Dimmers Dimmer History Cables and Connectors Lighting Boards Control Design Washes Specials Cyclorama Lighting Color Lighting Angle Simulating Exteriors Lighting Design Paperwork Shop Order Instrument Plots Focus Sheets Computer-Aided Lighting Design A Typical Lighting Hang at WPI Audio Introduction Input Microphones Converting Sound to Electricity Directionality Analog Tape Digital Audio Tape (DAT) Compact Disc (CD) Mini-Disc (MD) Digital Samplers Computer Sound Cards Mixing Boards Signal Processing Equipment Equalizers Compressors and Limiters Noise Gates Effects Processors Output Power Amplifiers Speakers Crossovers Cabling and Connectors Line-Level Speaker-Level Automation Design Creating and Obtaining Effects Editing and Processing Effects Designing the Sound System The Input Section Signal Processing The Output Section A Typical Audio Setup at WPI Power Introduction Basic Theory Power Feeds Power Distribution Boxes Power Protection Important Considerations Special Effects Introduction Animated Costuming Smoke and Fog Pyrotechnics Acknowledgements References List of Figures Index About this document ...

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