What’s In An Amplifier?

Written by Kevin Ray

am proud to say that I have been a contributing writer for The Bluffton Breeze magazine since its third printing four years ago. When I was deciding what to write about in this month’s edition of Bluffton Technical, it occurred to me that I have never written about the important role amplifiers play in a quality audio system. I’ve written a great deal about surround processors which are the nerve center of any home theater system, but I have never focused on the power amplifier which is the taskmaster that controls the loudspeaker. Shame on me!

You may not know this, but speakers do not readily accept being controlled by an amplifier’s signal. In fact, they resist being controlled. Speakers are cantankerous, and just like any hard-headed teenager; they talk back to the amplifier by returning signals. Some amplifiers are not capable of handling a rebellious speaker. In these cases an amplifier will become unstable when pushed, and will send severely distorted signals. In severe cases an amplifier can literally destroy itself by attempting to deliver a signal during a high demand situation.

So, what does an amplifier require to whip a rebellious speaker into submission? The answer lies in the balance between an amplifier’s power supply and its output stage. The power supply gives the amplifier its potential to deliver power. The output stage transfers this potential to the loudspeakers. A good power supply enables an amplifier to deliver sufficient power to each channel or to all channels at once without faltering or distorting.

Now the question becomes how to choose a power amplifier that meets your needs and budget. The first thing you should do is visit a reputable custom installation business and talk to their sales specialist. This person is more likely to listen and be more attuned to your specific needs than the majority of the big box store sales representatives who sell a little bit of everything, and are less likely to possess the same knowledge as a custom installation sales specialist.

The custom sales specialist should tell you that an amplifier should be able to power all of your speakers at once, and at volume levels that you consider to be your maximum. If you live in an apartment complex, your power output needs should be far less than someone who loves a lot of volume, and has no worries about disturbing the neighbors.

Judging how much power is enough power can be challenging because most manufacturers rate amplifier power delivery differently, and comparing specifications can be very confusing.

Factors to consider:

“RMS” (Root Mean Square): This is an engineering term that isn’t a lot of help, and defines “average long-term power” rather than “peak” power.

Number of channels driven: Make sure that the “watts per channel” is for all five channels working at once; not just two as some manufacturers like to do to boost their amplifier’s rating.

Bandwidth: This is the range of frequencies that an amplifier will produce its rated power. A rating of 100 watts per channel at 1 kHz means very little. Ratings based on “frequency extremes” such as 20 Hz (low bass) to 20 kHz (very high treble) mean something because these frequency ranges are within the normal human hearing range.

Distortion: A good amplifier reproduces the signal sent to it by the processor without altering or coloring it in any way. Any alteration by the amplifier is called distortion. Distortion figures under 1% are desirable. .03% is excellent. Just make sure that these figures are based on all channels being powered simultaneously.

Impedance: This is the measurement of how much a speaker resists an amplifier’s signal, and this is measured in ohms. Manufacturers can also use this to deceive unknowing buyers. For instance, an amplifier advertised to produce 200 watts per channel may only produce 150 watts per channel if connected to the most commonly used speakers which are 8 ohms; not the less common 6 ohm speakers which 200 watts per channel really represents.

The bottom line is that some manufacturers will advertise specifications that look good on the surface, but lack the specific information that is necessary to make an informed decision. The chances are pretty good that if the manufacturer provides all of the information necessary to make an informed decision, they are probably proud of their specifications, and are likely to produce a high quality amplifier that produces consistent power that is clean, and makes even the most cantankerous speaker do what it’s told.

If all of this is just too much to digest, but you love truly good sound and don’t want to make a mistake when purchasing equipment, visit a custom sales specialist. More than likely, they don’t sell anything that doesn’t at least meet the minimum requirements discussed in this article.

This article provided by Kevin Ray of Custom Audio Video, LLC. Member CEDIA (Custom Electronic Design & Installation Association)