Balance control: Enables the volume bias to be directed to either the left or the right, compensating for unbalanced recordings, hearing deficiencies or odd speaker placement.

Bi-amplifying: A process by which the high and low frequency drivers of a speaker are amplified by two pairs of independent power amps. This can be achieved with a combination of an integrated and an add-on power amplifier or with one pre-amplifier and two stereo power amplifiers. By driving the bass and treble separately, you will hear a more impressive sound-stage with greater scale and more control over the entire frequency range. Your speakers will need to be biwireable to enable biamplification - most speakers over £100 are biwireable these days.

Bridging: A feature which allows a stereo power amplifier to be converted into a far more powerful mono amplifier. For example the Rotel RB971 is 70 watts per channel in stereo mode, but can be switched into a mono amplifier of 210 watts! Then you would add another identical amplifier and run one speaker off each amplifier. The result: better dynamics and greater power.

DB25 connector: A serial interface found on some products which allows control using the RS232 interface of your computer. The socket looks like this.

Headphone socket: Very useful for private listening. Many separates do not have their own independent headphone outputs, so having such a connection on your amplifier ensures that all components in your system can be heard through headphones.

Inputs: The more the merrier! When buying an amplifier you should consider the number of components you already own and those you intend to buy in future. Most amplifiers have three or four "line level" inputs. These can be used for most components excluding turntables. Turntables must be connected to a "phono" input. If there is no such input, a line level input can be converted into a phono type with the addition of an external phono pre-amplifier. Line level inputs include: CD, tuner, tape, video, aux, MiniDisc and DAT. See also Tape loop.

Integrated amplifier: Unless referred to as "pre" or "power" amplifiers, all the amps on this site are integrated types. These are the most common single box amplifiers which most people have, containing both the pre-amplifier (with volume and input control) and the power amplifier (with speaker outputs) in the one box.

Ohms: A measure of resistance. Amplifiers do not have a resistance, but they often quote optimal resistances which they can drive. For example an amplifier might quote an ideal speaker loading of 4 to 8 ohms. This means the amp can drive speakers which present loads of between 4 and 8 ohms. See also Watts.

Phono stage/input: The input specifically designated for turntables. Because record players have a much lower signal level compared to other components, amplifiers are often built with phono stages which have extra circuitry to compensate for this. Some amplifier's phono stages are switchable between "moving magnet" (MM) and "moving coil" (MC) type cartridges. The vast majority of turntables have MM cartridges fitted. Moving coil type cartridges tend to be pricier (typically from £100 upwards) and are usually custom fitted on more expensive turntables. All of the decks on this site have MM cartridges fitted unless we specifically state otherwise. Likewise all of the amps with turntable inputs have MM cartridge inputs - those with both MM and MC are quoted as such.

Pre-amplifier: Sometimes referred to as the "control" amplifier, these are responsible for volume, tone and input facilities and have a large bearing on overall sound quality. To run speakers, a pre-amplifier has to be used in conjunction with a power amplifier.

Pre-out/Main-in loop: Found on some integrated amplifiers. This is a pair of sockets which separate the pre and power sections of your amplifier. This enables easy connection to extra power amps, home cinema processors and graphic equalizers.

Power amplifier: Designed to boost an unamplified signal to run speakers. Often available with many channels (for example a home cinema power amplifier might drive five speakers) and often bridgeable providing huge power. Power amplifiers require a pre-amplifier to control volume, input etc. 

Record output switch: This is a very useful feature for those who make a lot of recordings. Sometimes you may wish to record from one source whilst listening to another. This switch enables you to do this without having to make wiring changes to your system.

Remote switching: allows a device to be remotely activated and shut down by a control device. For example, the Rotel RB1070 power amplifier has remote switching. When connected to a pre-amplifier with remote switching control (such as the Rotel RC1070 pre-amplifier) the power amplifier can be activated and shut down by simply turning the pre-amplifier on and off.

You would find this particularly useful if you had the power amplifier away from your main hifi (maybe near to the speakers, in another room or under the floor). This enables the larger power amplifier to be effectively hidden and yet safely controlled.

Speaker outputs: Measured in pairs - i.e. one pair of speaker outputs will drive two speakers (left and right). Some amplifiers have two pairs of speaker outputs. It you wish independent control over two pairs of speakers, look for "switchable" speaker outputs so that you can turn each pair of speakers on and off separately. In the absence of such a feature you could alternatively add a speaker switching box.

Tape loop: A tape loop is a group of two pairs of sockets; tape in (left and right) and tape out (left and right). Both are required to enable connection of a recording device (e.g. cassette recorder, MiniDisc recorder, DAT recorder) for playback and recording in stereo. For instance, if you have a cassette recorder and a MiniDisc recorder and wish to retain full functionality on both, you should buy an amplifier with two tape loops. If this isn't possible, we have a range of switching boxes which can convert one loop into two, three or even four!

Tape loops can also be used for connecting a graphic equalizer or add-on home cinema processor to an amplifier.

THX: is a specification of performance. Products with this badge are certified as having met certain stringent performance criteria as set out by Lucasfilm - George Lucas' film company. This is not to say that non-THX products are inferior (there are many products which would qualify but have not applied for the certification), but it is another guarantee of performance which is fast becoming very desirable in the home entertainment industry.

For more information visit the THX homepage.

Tone bypass/defeat: Commonplace on many amplifiers today, this is a switch which bypasses the tone controls of the amplifier. By having less electronics in the signal path, there is less chance of the signal degrading or for noise to be introduced.

Tone control: Split into bass and treble, these allow you to adjust the higher and lower frequencies of the sound to suit your needs.

Watts: A measure of power - the higher the wattage, the greater the power of the amplifier. Wattages are measured into a load - that is to say that the figure is dependant on the speakers the amplifier is driving. An amplifier that outputs 50 watts into 8 ohm speakers, will output 100 watts into 4 ohm speakers as they have half the resistance. All amplifier ratings quoted on this site are into an average 8 ohm load except where specified. This is because, typically, the average speakers’ load is 8 ohms.

Contrary to popular belief, it is easier to damage speakers with an underpowered amplifier than an overpowered amplifier. Every amplifier has a point at which it runs out of power. At this point it wont get louder, instead the sound will harden up and distort - this noise is often referred to as "clipping" and is produced by the amplifier, not the speakers. However it is this "clipping" which most commonly damages speakers and leads to "blown" speaker drivers.

XLR/Balanced connections: These connections are used when long cable runs are necessary. You may have your power amplifier near to your speakers, or maybe hidden in the crawl-space below your floor, and wish to run a long connection from the pre-amplifier in a remote location. Balanced connections ensure that the signal loss is minimised thereby maintaining the best sound quality.