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Video: How to Choose an Amplifier

Amp features to consider


This in-depth video walks through the major points to consider when choosing a new amplifier. It answers the questions: How many channels do you need? How much power should you get? What are the important features to look for? And why do some amplifier brands cost more than others?

Amplifier Channels

Zak: When you're shopping for an amplifier the first question to ask yourself is,
"How am I going to use it?"
"Am I going to power a sub or two subs?"
"One pair or two pairs of speakers, or maybe subs and speakers?"

Knowing this helps you make the first decision: which type of amp to buy based on how many output channels and how much power you need. So then let's take a look at the different types of amplifiers based on the number of output channels they have. Mono amps have one output channel. They're usually used to power subwoofers. And depending on the amp and the impedance of the subwoofers you can connect one, two or even more subs to just one mono amp.

Ken: 2-channel amps offer more versatility. You can use the two output channels to power a pair of speakers like the ones in your car's front doors. And most 2-channel amps can also be bridged. This combines the output of the two channels into a single channel. It's a great way to power a subwoofer.

Zak: 4-channel amps give you the most options. They're perfect for powering a couple pairs of speakers. You can also enjoy the best of both worlds by using two of the amp's channels to power a pair of full-range speakers in the front of the car while bridging the output of the other two channels to drive a sub. You'll get clean highs and powerful lows out of one package.

Amplifiers don't stop at four channels though. 5-channel amps let you power your entire system with just one amplifier. They have four channels for powering your front and rear speakers and a fifth, higher-powered channel for powering your subwoofers. Plus, a 5-channel amp takes up less space and it's easier to install than two separate amplifiers. A 5-channel amp is a good investment if you want to build a system that has a lot of flexibility and room to grow.

How Much Power?

Ken: You know, one of the questions our advisors get a lot is "How much power should my amp have"?

Zak: That's a really good question. It's important though, before you start comparing amp power ratings, that you don't compare apples to oranges. There's two different kinds of power ratings out there: peak power and RMS power.

Ken: Peak power is what the amp can produce for a very limited burst of power. It's often the number you'll see on the box but it's not very useful. It's better to look at RMS ratings.

Zak: Yeah, RMS power is the measure of the amp's continuous power output. It's much better to look at the RMS numbers when you're shopping.

Ken: And if you really want to be sure about an amp's power rating, compare amps that have a CEA-2006 power rating. Now, this standard establishes specific guidelines for how the amp's power is measured. So amps with this kind of power rating have all been measured on a level playing field.

Zak: But once you're aware of all this you still need to figure out just how much power you need to drive your speakers. The first thing to remember is that it's better to have more power.

Ken: Right. You want your amp to be able to play all your music, loud and soft, without distortion, and be able to handle sudden changes in volume easily.

Zak: Yeah, and more power gives you just that. It's something that we call "headroom."

Ken: As a starting point consider the RMS power ratings of your speakers or subs. Match or better yet, exceed the speaker power ratings with your amplifier.

Zak: For example, to get that headroom, if you have a subwoofer that handles 200-watts RMS, power it with an amp that puts out 250-watts RMS.

Ken: It'll drive it cleanly and without distortion, especially when the volume is cranked and it'll do it better than an amp with less power. More power is always better.

Amplifier Features

Zak: Depending on the kind of amp you're getting and how you're going to use it, there are some features built into most amps that you should think about while you're shopping.

Ken: These can include high- and low- pass filters, bass boost, and speaker-level inputs. High-and low-pass filters have an important job to do. They make sure that your amp is only boosting the frequencies that you want it to. High-pass filters strip away the low frequencies from the signal the amp is boosting. You'll use the high-pass filter when the amp is powering smaller speakers like those in the front doors of your car. This way your amp will direct its energy to making the vocals and instrumentals sound their best.

Zak: Low-pass filters do just the opposite. They take out the highs so you're only amplifying the lows. You'll want a low-pass filter when you're using the amp for powering a sub, that way the amp can concentrate its power on kicking out the low notes.

Ken: We should mention one other type of filter, the subsonic filter. A subsonic filter blocks ultra low frequencies that you can't hear from getting to the subwoofer. This lets the sub operate more efficiently.

Zak: Yeah and there's a couple other important things to look for in your filters. Some filters are variable. They let you select the frequency for the filter. Others are fixed, meaning that they limit you to a specific frequency.

Ken: Variable filters let you tailor the output of your amplifier more precisely than you can with a fixed high-or low-pass filter. And there's one other feature to look for: a bass boost.

Zak: Yeah, a bass boost augments the low frequency output of the amp so you get a bigger bass output with your subs and your larger speakers.

Ken: A bass boost frequency can be fixed or variable and the amount of boost can be fixed or variable too.

Zak: Yeah kind of like the filters we talked about. Variable bass boosts give you some more choices in how you tailor the sound that your amp puts out so keep an eye out for this feature if you're planning to amp subs. Now besides the number of speaker output channels we talked about earlier, amplifiers have other outputs and inputs that you may want to look for.

Ken: The first is speaker-level inputs. Most amps get their signal from the receiver through RCA inputs which are connected to your stereo's preamp outputs. The factory radios rarely have preamp outputs so if you're connecting your amp to a factory radio the amp will need speaker-level inputs like these. They'll let you tap into your car's speaker wires for the signal your amp requires.

Zak: If you're going to put together a system with multiple amps, you might want to think about an amp like this one. The reason is it has preamp outputs so you can send a signal into the amp and then out again and into another amp without having to run any extra cables all the way from the stereo.

Amplifier Build Quality

Ken: Another question we hear a lot is "Why should I buy a more expensive amp"? "What am I getting for my money"?

Zak: Again, a good question. To answer it we're going to look under the hood of two amps. One is a more entry-level and affordable amp and the other one costs a little bit more. So what are you getting for that money?

Ken: These are both mono amps of similar power built for driving subs. This one is an entry level amp that sold for about $200. It's a good amp but right away you can see a basic, generic circuit board with a lot of exposed metal traces and wires. That can let noise into the system. It's got small FETs, or Field Effect Transistors, underneath these small heat sinks. That can let them heat up and create distortion. The capacitors are small and the coil is small so you don't have a lot of reserve energy for when you crank the volume.

Zak: Now over on this side, we have an amp from Rockford Fosgate priced in the $300 range. On the inside you can immediately see what you're getting for that extra money. You've got this high-quality, custom-built circuit board tying everything together. You've got larger, beefier components throughout and you've got this vented heat sink that goes all the way around the outside and that's going to keep the amp running cool and much more efficiently. Overall, you're getting a better built amp which equals better performance and better sound.

Amp Wiring

Ken: But we haven't talked about one of the most vital factors in amp performance: amp wiring.

Zak: Your amp depends on a steady supply of power to operate at its peak, and that's why you should invest in a high-quality amp wiring kit when you buy the amp.

Ken: If you use too thin or cheap wiring to hook up your amp, you're starving it of the power it needs to do its work.

Zak: Yeah, the bottom line is that you're not going to get the performance that you paid for.

Ken: To see all the amps we carry, go to crutchfield.com/amps and be sure to check out which wiring kits we recommend.

Zak: To learn more about choosing the right amplifier, go to crutchfield.com/ampguide.

Ken: And for personal one-on-one help, call 1-800-555-9408.

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