When to Add a Power Amplifier to an A/V Receiver

The question often comes up on our forums asking what benefit a user may see from connecting an external amplifier to their A/V Receiver.  The answer depends on many factors including:

• Listening habits - how loud you listen.
• Room size - big rooms require more power to achieve high sustained SPLs (Sound Pressure Levels).
• Speaker Load - some speakers present a more difficult load impedance than others; efficiency also plays an important role.
• Bass management – if you’re running your main speakers full range, they will typically demand more power for bass heavy passages.   

Let's assign a point system to determine if you may benefit from an external amplifier, or if you would be better served by saving your cash. Please keep in mind this is not a biblical source.  I didn’t use any fuzzy math to come up with these guidelines.  They are in fact just guidelines based on common sense and experience, so please use them as such.

How to find your Total Score?

Add up the points from each column of the above table to find your Total Score.  Your Total Score can be as low as 0 points or up to +7 points depending on your conditions.

• If Total Score is 0-4, you can probably get away with your current A/V receiver amp section.
• If Total Score is > 4, then it is time to consider adding a separate power amp to your system.  If you score a +7 and feel your score should be even higher, we really want to hear from you in our forums!
  

A Detailed Look at your Conditions

So what are your listening habits like?  Do you often listen at ear-bleeding levels that would send your mother-in-law out of your room in a hysterical rage, or do you listen at levels where you can still have a comfortable conversation? 

How big is your room?  Did you cram all your equipment into a small bedroom, stuffing your TV and subwoofer in the closet to accommodate everything, or do you have a dedicated theater room that can seat more than two people?

What kind of speakers do you have?  It’s a good idea to study your speaker’s impedance graph and sensitivity rating.  Speakers that dip into the 4 ohm range at low frequencies tend to demand a lot of power from an amplifier. 

Are you running your speakers full range, or are you running bass management and redirecting the low frequency content to a dedicated powered subwoofer?  If you’re running them full range, than add a point to your total score to determine if you may need an external high power amplifier.

If you're fortunate enough to own an A/V Receiver that has preamp outputs to connect an external amplifier, then doing so is quite straightforward.  You simply connect a pair of RCA terminated line-level cables from the front or main channel preamp outputs of your A/V receiver to the inputs of the external two-channel power amp.

Yamaha RX-A2020 AV Receiver Backpanel - notice the highlighted main front left/right preamp outputs

What an External Power Amplifier Will Do For Your System

Not all output ratings are created equally.  An amplifier rating really depends on many things like the bandwidth it’s being rated at, the impedance it’s being tested at, and the specified distortion level.  Some A/V receivers current limit when driving low impedance speakers meaning they will deliver similar or slightly less power into a 4 ohm load than they will into an 8 ohm load. While you'll find many A/V receivers rated to deliver ~100 watts per channel into an 8 ohm load, relatively few are able to deliver big output into 4 ohm loads, particularly when driving 5+ channels worth of loudspeakers. Conversely, finding a separate amplifier capable of driving complex 4 ohm loads with authority isn't too difficult, and isn't necessarily an expensive proposition either.  Keep in mind that doubling power will not only give you roughly 3dB more acoustical output, but it will also take off some strain from your A/V receiver’s power supply that is being tasked to power five or more loudspeakers.  This will clean up the sound and provide a nice shot of adrenaline that your system just may be in need of.  Adding external amplification isn't just about making things louder, it's also about preserving dynamic range of the music to avoid unwanted compression. 

Graphed below you can see the relationship between perceived double loudness vs frequency.  If you want to calculate how much more perceived loudness you can potentially achieve by adding external amplification simply pull out the scientific calculator and plug in the following:

dB(gain) = 10*log (Pext amp / Preceiver)  where dB is log base 10 and P is power in watts

So if you're running a 100 watt/ch AV Receiver and upgrade to a 500 watt/ch external amp, then you simply plug into the formula as follows:  dB(gain) = 10* log(500/100) = +7dB

Equal Loudness Curves - courtesy of Hyperphysics

Editorial Note about Equal Loudness:
It takes 10dB of added output to double perceived loudness in midrange region (500Hz to 3kHz band) but much less (around 3-4dB) at bass and high frequencies.  For more information on the relationship between loudness and the DB, please check out our article The Decibel (db) Scale and Audio Rules 101

Emotiva UPA-200 (left pic) two-channel amplifier; Outlaw Audio Model 2200 Monoblock Amplifier (right pic)

Do All Amplifiers Sound the Same?

Well, we discuss this topic in great detail in the video below so you're gonna have to watch it to get our take.  Of course we encourage you to voice your opinion on our forum too.

Do All Amplifiers Sound the Same?

What to Do with Unused Receiver Amps

Some may fear that adding an external amp will in a sense "waste" the unused internal amplifiers of the AV Receiver.  Our answer to that is to simply reroute them.  Most modern AV Receivers allow you to reroute them to power speakers in another zone or to add height channels to do a full 9.1 speaker configuration.  Another option would be to power a second set of speakers in another room from the main zone if your receiver doesn't have multi-zone capabilities. You can turn them off by toggling the main speaker A or  B switch.  Fear not as there is always a use for those unused amplifier channels. 

Yamaha AV Receiver GUI for Speaker Assignments

Conclusion

Power is cheap these days so it certainly won’t hurt to add an external amplifier for the main front left/right channels of your A/V system if your conditions call for it.   Some great and affordable options include those from Emotiva (UPA-200 costs only $349 and pumps out 200 watts into 4 ohms x 2 channels) or the Outlaw Audio (M2200 Monoblock for $379/ea delivers 300 watt into 4 ohms).  Of course if the budget allows, it's always a good idea to buy more power.  Please share your experiences in what adding external amplification has done to elevate the sound quality or listening experience in your A/V system.