While many receivers today have decent amplifiers built into them, there are always compromises that have to be made because a receiver has to perform many tasks such as digital-to-analog audio conversion, preamplification, video switching, etc., in addition to amplification, all in one box. Having the amplification isolated from all of those other electronics along with its own power supply is always a good thing. Also, many receivers have power ratings that are not indicative of their true performance and may not be able to deliver their rated power in real-world situations. For instance, a receiver may be rated at 100Wpc into an 8-ohm load with 0.1% THD (Total Harmonic Distortion) at 1kHz, but it will not perform as well if a speaker’s impedance drops below 8 ohms (which they often do) or if all the channels are driven simultaneously. Total harmonic distortion is also often much higher at the frequency extremes than it is at 1kHz, where the measurement is typically taken for receivers. Thus, separate power amplifiers, even if they have the same published power ratings as a receiver, are almost always more powerful and better sounding because they are more conservatively rated.

Do I have to buy a five-channel amp?

You do not necessarily have to upgrade all five channels of amplification at once. Many companies offer less expensive three-channel versions of their multichannel power amplifiers that can be used to drive the front three channels. These channels are arguably the most critical, and many will argue that they should have, at a minimum, similar high-quality amplification and speakers. Other than the advantage of cost savings, adding power amplification to only the front channels of a receiver will often result in better sound from the rear channels. By relieving the receiver of the burden of amplifying the front channels, there will be more power available to the rear channels, which should now be able to play louder and more clearly. You might even consider adding power amplification to just the left- and right-front channels if finances are especially tight or, as is often the case, you find an especially good deal on a new or used two-channel amplifier.

What improvements can I expect when I upgrade my receiver with a separate power amplifier?

Increased Dynamics -- Dynamics are the ability of a system to differentiate both very quiet and very loud passages with good resolution and little distortion. This increase in dynamics will be most evident when the system is asked to play very loud. The sound should not distort as much during these demanding passages. Distortion is generally the harsh sound that you hear when systems are pushed beyond their limits. Many people think that this is caused by their speakers being strained, but more often than not it is actually the amplifier that is being driven into distortion.

Better Bass -- Better amplification will result in bass that is "tighter" and more defined. By this we mean that the pitch of individual bass notes will become noticeable and it will no longer be just an indistinct low-frequency rumbling that is often associated with inferior low-frequency reproduction. More accurate bass may actually seem like a lack of bass because it is less present and does not linger like inaccurate bass, which we often describe as boomy, flabby, or slow. Good bass is quick, responsive, and appears and disappears very quickly, which may actually seem like a lack of bass when compared to poor bass! Even though a speaker may be capable of reproducing plenty of high-quality bass, it will usually require a capable amplifier to control it.

These are just the two most common and obvious improvements that you may notice after adding a power amplifier, but with very high-quality amplifiers, you will also notice many of the attributes that audiophiles often describe in high-end two-channel systems. For instance, there will be more detail and depth to the sound that will bring you closer to that feeling of "being there." The better the quality of the amplifier, the more you will notice these more subtle improvements in the sound.

Why should I upgrade with a power amplifier?

For one thing, upgrading a receiver with power amplifiers does not require throwing anything away, having to try to sell off any surplus equipment, or, worse yet, relegating equipment to the attic or crawl space. Also, receivers also make pretty good processors and are more economical than standalone processors, which usually cost much more. Finally, there are many surprisingly good five-channel amplifiers out there starting in the $1000 to $1500 price range and some stereo amplifiers going for $500 or less. Because power amplifiers have so few moving parts, they are quite reliable and make excellent candidates for upgrading through their purchase on the used market.

I still fondly remember my first power amplifier. It was a two-channel THX-certified unit that I used to drive the front channels from my Pro Logic receiver that was connected to an outboard Dolby Digital/DTS decoder. I received a smoking deal on that amplifier because it was a dealer demo. To this day, it is one of the most cost-effective upgrades that I have ever made. Since that time, I have owned three different multichannel amplifiers and this is still my favorite method of upgrading my home-theater system.

Stay tuned

If you do not have the requisite outputs on your receiver to add a power amplifier or you do not wish to upgrade your system in this manner, remember that this is just one of many ways that you can upgrade your system. In upcoming months we will be investigating other ways of upgrading your home-theater system.

...Roger Kanno
roger@hometheatersound.com