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.
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 £150 7.5kg 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.
Power Supply
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.
Build Quality
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 £1500
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.
Bass Management
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.
Necessary Features
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 (upscaling) 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.
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.
By: Gene DellaSala
Contributors: Clint DeBoer
Refreshed & updated for the UK by Gavin Duffy 2007
© 2004 Originally published online at www.audioholics.com/buying-guides/how-to-shop/av-receivers-buying-guide