AV Receivers Buying Guide
The purpose of this guideline is to educate the consumer about Home Theater A/V Receivers to assist them in purchasing the best product for their money when buying time is evident.
Definition of a Receiver
A basic receiver is an all in one box component with an integrated preamp, tuner, and power amp. With the advent of home theater upon us, we are now blessed with A/V receivers. These receivers have everything a basic receiver has with an added processor to decode Dolby Prologic, Dolby Digital and even DTS. They also house multi channel power amplifiers, DSP processing and plenty of Audio/Video inputs/outputs to act as a control center for all of your components in your home theater setup.
What are Watts?
Watts are a unit of power defined as voltage (V) times current (I) or V*I or I^2*Z or V^2/Z where Z is impedance. Usually receivers are rated in RMS power or "Root Mean Squared". This is the typical power your receiver can provide for a given characteristic impedance.
It is important when comparing power ratings between receivers to verify they are being measured uniformly. For example, typical mass market receivers rate each amp at 0.7% THD @ 1 KHz as opposed to full bandwidth under acceptable THD audible limits ( < 0.1%) creating the illusion of more power to the unknowing customer. This is why a $300 15lbs mass market receiver appears to deliver as much power or more than a receiver twice the price and weight. In addition some companies take it one step further and rate their amps at 6 ohm loads to give the illusion of more power when compared to similarly priced receivers from other manufacturers rated at 8 ohm loads.
There are more important concerns in judging an amp than power specs rated into a resistive load given at the back of a user manual of the receiver. Loudspeakers present a reactive load to the amplifier that can increase the current demand as much as several times that demanded by a trivial resistor. Since it is the current, not the voltage, that actually drives the speaker cone, output current capability is the limiting factor in most amplifiers. It is important to verify the amplifiers behavior when it is presented with 4 and 2 ohm loads; its output should increase substantially over the 8-ohm value. Receivers typically publish specifications of dynamic power under 4 and 2 ohm loads for the amp. If the receiver can deliver about double the power or more in 1Ö2 the nominal load, it is usually a good indication that it's amp sections are dynamic enough to drive moderately efficient speakers to satisfactory undistorted levels (90-100 dB) in an average size living room. Some manufacturers also claim their amps are "high current" designs and publish peak current capabilities in excess of nominal operating conditions. Interpret these numbers with a grain of salt. There is no standardized method by the FCC to make this type of measurement. Therefore the manufacturer can make any claims they desire without backing them up. In addition, these measurements are usually instantaneous figures and not continuous.
Weight does! Good linear power supplies are heavy and costly. Forget power numbers for a moment. First take a glance at the receiver you are interested in. Look inside it if you can. Observe the power supply section. A good 5 channel receiver should have a power supply capacitance of at least 30,000uF with a large and heavy transformer. The heatsinks should be moderately thick and occupy a great deal of real-estate, housing at least 2 discrete output devices per channel with smaller biasing devices to help maintain class AB operation. Now open up that spec sheet again and look for numbers such as Damping Factor, Dynamic Power in 8/4/2 ohm loads, Power for all channel driven at full bandwidth (20Hz to 20KHz) with THD < 0.1%. These numbers are a starting point in judging the quality of the power supply and amp section.
Quality of construction and workmanship play a vital role in creating an excellent receiver. A receiver built with bad parts is a bad receiver. Take note of the connectors on the backplane. Are they flimsy? Do the speaker terminals accommodate 12 gauge wire? How do the controls on the front feel? Are they well laid out? If you plan on spending $2600 on a receiver, ask yourself this question: Is the front door panel (if there is one) metal or cheap flimsy plastic? If not, it makes you wonder what else they skimped on internally.
Sound Matters Most!
Before deciding on a receiver you plan on buying based on the specifications you have read, take some time to listen to the product thoroughly. Many mid to low priced receivers packed with features, nice lights and cool face plates suffer from a common problem, terrible preamp/processor sections. This can easily be ascertained by asking the salesperson to leave the showroom for a few minutes so you can be alone with the receiver to get to know it better. At this point, the room is quite silent, hopefully. Switch the receiver onto a 5 channel mode with no source running. Turn the volume control up about half way and balance all channels using the test tone. Now walk around the room and listen for airplane noises. Assuming you are not near an airport, you should not hear any. If you do, than this is a good indication that the receiver has a noisy preamp section. In a seated position midway between all speakers, listen for excessive background noise. Usually the rear channels are most obvious. If you can clearly hear hissing or white noise from any speaker while seated, than avoid this receiver as it will annoy you in the long run when playing 5 channel sources.
If the receiver passed the noise test, move on to quality of the DAC's and ADC's. You should compare the fidelity of sound of the internal DAC's with that of the CD/DVD player you are using in your system. When switching from analog to digital inputs on the receiver, you should notice similar or better fidelity. If you don't this may imply the DAC's in the receiver are not as good as the ones in your CD/DVD player. This may present a problem to those who enjoy listening to DSP modes or want to really reproduce excellent 5 channel DD/DTS surround. If the DAC's in the receiver are weak than you may have to rely on the DAC's in the CD player while listening to music in DSP modes. Doing this would involve a D/A conversion from your CD player to a A/D conversion in your DSP processor and finally a D/A conversion before the signal gets amplified. This process will manipulate the source 3 times as opposed to one. This should be avoided if possible as it will result in loss of fidelity.
Two Channel Fidelity
All right, so the receiver passed the noise test, what next? The amplifiers. In order for the receiver to be a winner, it has to deliver quality power for your speakers in the room size you are in and listening levels you are accustomed too. Pick speakers in the showroom as close to the ones you own or plan on buying. Put on a bass heavy CD. Listen to the bass notes for strain, boominess and lack of impact. If the receiver shares these characteristics, it is attributed to a weak power supply. This will be a problem for those with large tower speakers who demand bass output without the use of a powered subwoofer. Next listen to the midrange and high frequency spectrum. The midrange should have good balance throughout the 200Hz - 4KHz bandwidth free from excessive boosting or attenuation within the frequency spectrum. The high frequency spectrum above 4 KHz should sound airy, natural and not overly bright. Receivers which tend to sound bright must be carefully mated with speakers with a subtle nature in the high frequency spectrum.
Surround Sound Performance
Surround sound performance is a very critical issue that you must pay careful attention to. Listen to all of the surround formats available on the receiver (IE.DPL,DD,DTS) and verify there is no center channel bleed over into the other surround channels. You can accomplish this by listening to a movie with the center channel speaker on and the other speakers off. Familiarize yourself with the voices that are emanating from the center speaker. Now disconnect the center channel and reconnect the front speakers. Listen for bleed over of the voices to the main speakers. Next turn on all 5 channels and listen to a particular movie passage. Pay attention to how the sounds shift from one speaker to the next. Listen to this passage repeatingly until its familiarity is burned in your head. Compare its sound characteristic with the different receivers using the same speaker set-up to determine which receiver decodes the information best.
In spite of the fact that Surround Receivers have been on the market for quite some time, many of them still don't handle bass management correctly. Illustrated below is a proper bass management scheme a receiver should exhibit.
A Note About Bass Management
Some receivers may offer you the option to mix the bass output of your large main speakers with the subwoofer. While this is not proper according to the Dolby Digital and DTS specifications, it may be desirable in some cases for an increased bass boost.
Aside from quality amplifiers and power supplies, features are one of the most important concerns when purchasing a receiver. You want the receiver you choose to purchase not only to sound good but to provide you with the features you need/desire. It is always better if you can buy a receiver with many A/V inputs and outputs both analogue and digital, and plenty of component / HDMI video switching. Does the receiver have the ability to upconvert all analogue inputs to component or HDMI? If it doesn't, you will have to use multiple cables/inputs on the display in order to view all of your components.
Does the On-Screen Display (OSD) pass through the component video or HDMI ports? Are the on-screen displays (if this feature exists on the model you choose) intuitive? If not, you will be scratching your head often when attempting to optimize the performance of the system. Is the remote control complete with all function keys necessary to properly operate your system? And, is it easy to operate? If not, you will be investing in a multi-brand remote after many frustrating hours.
What Doesn't Matter?
Impedance Selector Switches
This so called feature, used by some manufacturers, is designed to prevent overheating of the receiver or damage to its output transistors because of excessive current flow. The manufacturer accomplishes this in one of 2 ways: 1) Stepping down rail voltage supplied to the power amp or 2) feeding half the signal strength to a voltage divider of power resistors. Both of these methods severely limit dynamics and current capability of the power amp. This results in an audible decrease in bass capability and dynamics transient sound because the 4 ohm setting effectively increases the receiver's output impedance. Unfortunately many manufacturers put these features on their products to ease customer concerns with driving low impedance loads and for safety reasons when getting UL approvals. Note: In order to meet UL requirements, a receiver cannot be rated down to 4 ohms without having this switch onboard. Receivers without this switch are usually rated down to 6 ohms. In most cases, well designed receivers can easily handle 4 ohm loads safely and efficiently. It is highly recommend to keep the impedance switch set to 8 ohms regardless of your speakers impedance and make sure your receiver has plenty of ventilation.
Take your time when evaluating receivers. I recommend that you pick 3 top contenders based on your budget, needs and personal tastes and spend extensive time listening and evaluating them. If possible bring them home for direct comparison in your personal listening environment. Be sure however that your retailer has a good return policy for full refund without restocking fees. Choosing a receiver is a matter of personal taste. However, there are many poorly designed products in the marketplace and it is the intent of this document to help you avoid buying one of these units. Use this as a guideline not a Biblical source when choosing the receiver that is right for your needs. Good luck and happy listening.