HOW TO CHOOSE AN AMPLIFIER
At its heart, all you want is a straight wire with gain. But with so much more on offer, how do you start compiling a short-list of potential amplifiers for your hi-fi system?
Traditionally, an amplifier’s job was simply to take the small signals from your sources and make them big enough to drive your speakers. That’s what amplification is. And in the world of hi-fi purism, that may be still pretty much all an amplifier does — those expensive often hulking mono power amps, for example, may have just a single input at one end, and outputs to a loudspeaker at the other, aiming as best as they can for the classic definition of “a straight wire with gain”.
Of course back when Quad’s Peter Walker (supposedly*) came up with that phrase, it was assumed that the wire itself didn’t affect the sound — whereas these days that’s a whole other discussion.
But amplification is the heart of an amplifier, and generally responsible for the bulk of its price and certainly its weight, thanks to the transformer/s inside which provide the juice for that stepping up of signal size. This we can call the ‘power’ section of an amplifier.
Then there is the pre-amplifier section, where switching of sources and processing of sound takes place. Here the functionality can be far more diverse, with the available facilities varying from almost none on a minimalist power amp to extraordinary versatility on the modern breed of smart amplifier. Processing lets you play with the sound, originally the function of all the knobs that adorn analogue amps, these days often digitally tweaked via software and app control. Inputs may include phono-level analogue, line-level analogue, balanced analogue, and a variety of digital inputs of different types. The modern amp, and still more so its audio-visual equivalent the AV receiver, can seem simple from the front yet baffling round the back. So how do you decide what you need?
Inputs
While it’s the quality of amplification that will ultimately bring you beautiful music, your first question should be whether any given amplifier will allow you to connect and easily select between your available sources. And you probably need several more inputs than you think, to build in flexibility for the future.
This decision may be simplified by the trend in audio systems towards both minimalism and streaming. You might choose a smart amplifier (see below) which has built-in abilities to stream music from the internet and/or direct streaming from a phone, tablet or computer via Bluetooth or AirPlay. If that’s all you need, then you may not need any physical inputs at all. But in a more traditional system, with other sources, you need to start counting. In the olden days this meant largely line-level analogue inputs on RCA sockets, and occasional XLR balanced inputs capable of receiving the higher signal levels from high-end or professional sources.
But with most sources now being digital, it may be digital inputs that you’ll be needing most. Do you want to connect a PC or Mac to play direct from computer? Then look for a USB-B socket. Do you want to plug in a CD player? It may have an analogue output, but it may also have a digital output as well, in which case you can compare which unit has better quality digital-to-analogue conversion — the DAC inside the CD player, or the DAC inside your amplifier? Choose whichever solution you prefer.
If you’re planning to play your TV and movie sound through your amplifier, then an optical input may be most reliable, though some amplifiers include an HDMI socket which can connect to an ARC-equipped input on your TV to play sound back to the amplifier. Just be aware that ARC doesn’t always work reliably, so that the optical socket is a near-essential standby.
Phono input
If you’re using a turntable, or play to get one in the future, then look for a phono input, which accepts the lower level of a phono cartridge signal directly and applies the equalisation required. There are two types of phono input, the more common moving magnet (as used on most affordable turntable), and moving coil, an even lower signal requiring a different level of pre-amplification and pre-emphasis.
“While it’s the quality of amplification that will ultimately bring you beautiful music, your first question should be whether any given amplifier will allow you to connect and easily select between your available sources.”
However, if you’ve set your heart on a particular amplifier which lacks a phono input, there are workarounds. Some turntables, even quite high-end ones (see the Clearaudio model reviewed this issue), may have a phono stage built in, so that they plug into any analogue line-level input. Or you can use a separate standalone phono stage, the isolation of which may provide sonic advantages when dealing with these tiny signals.
Outputs
The most obvious outputs on an amplifier are the sockets for the loudspeakers. These can be of varying quality, from small unsteady spring-clip terminals which can accept only bare speaker wire, up to magnificently solid terminals capable of accepting spade connectors and banana-plugged cables as well. You may find speaker sockets which have been ‘filled in’ with little red and black plastic bungs, blocking where you’d plug in banana plugs. That’s because the European Union legislated against such plugs and sockets after someone in Scandinavia managed to plug their speaker cables into the similar mains power sockets there. The plastic bungs can be removed with a bit of effort (sometimes sticky tape or Blu-tac can be useful).
Some stereo amps also have two sets of speaker terminals — usually labelled zone ‘A’ and ‘B’ or ‘1’ and ‘2’ — which allow you to run two pairs of speakers at the same time (in different rooms, for example), although usually only with a single volume control. Doubling up speakers can have a detrimental effect, as essentially the amp’s power is being shared multiple ways and potentially into different impedances. We’d normally discourage such simultaneous use except in rare occasions (Cambridge’s CXA81, pictured below, is a notable exception), but switching between two sets of connected speakers is entirely acceptable use of such facilities.
There may also be various other outputs using RCA-type sockets. A subwoofer output can be useful if you’re using small speakers and fancy adding bass with an external subwoofer. Tape outputs are getting relatively rare, and tape returns even rarer, even though these fixed (not affected by the volume control) line-level outputs can be useful for many other purposes.
Pre-out sockets provide a line-level signal which is affected by the amplifier’s volume control, and if you’re looking to record, these will be no use. But if you’re considering biamping, where the preamp’s output is chained on to an additional power amplifier, they’re essential.
One of the most common inclusions is a 3.5mm (minijack) or 6.3mm (full-sized) headphone output. We prefer full-size sockets, because it’s far easier to add a little adaptor to a minijack headphone cable than it is to go the other way. But we see why minijack headphone sockets are becoming more prevalent, because the use of home-style headphones is declining. In that regard, you may want to find an amplifier which can play to headphones via Bluetooth, as can many of the new breed of “smart amps”.
Smart amps
We define smart amps as being those which have streaming abilities built in — not only Bluetooth, but a module which can access the likes of Spotify, Tidal and internet radio, often also playing files from shared storage on a computer or a networked-attached hard-drive (NAS).
Such facilities almost certainly require an app to navigate such wonders, and we always express mild concern if a product can only be operated by app — because we reckon a good amplifier should last for decades, and what chance an app will still be available and compatible for whatever devices we’re using in 20 years? Hence it can be wise to check such functionality can operate from the front panel as well as via app, or at least consider one of the established systems in this regard, such as (in alphabetical order) Bluesound/BluOS, HEOS, MusicCast or Sonos, all of which also offer the possibility of multiroom operation with other compatible equipment.
For the same reason we also believe that every amp should have a physical remote control, not only app operation. Note that some smart amps in particular don’t supply a physical remote, or have it as an optional accessory.
Also offering some degree of streaming and multiroom are Chromecast and AirPlay, even the simple inclusion of Spotify Connect, which streams that service direct from the internet rather than via your phone.
Integrated or pre-power combination?
Do you go for an integrated amplifier or separate pre/power boxes? The former is the most simple, convenient and spacesaving option, packing both pre- and power amplification into one chassis. This means everything has been tuned together, saving you the work that goes into matching separate amplifiers.
Two-box amplifiers, on the other hand, involve splitting the control hub from the power amplification, the idea being to keep digital and switching circuitry away from the electricallypure power amplifier section (and to a lesser extent, vice versa).
The most obvious way of selecting pre- and power amps that work together well is by sticking within one brand. If you plan to mix-and-match, be aware some pairings will work better together than others. A good dealer is your friend here.
Power ratings and amplification types
With your connections and form factor decided, you now face a market’s worth of different approaches to styling, different amplification types and circuits, and the different ways of rating those circuits in terms of watts. Not to mention the joys of synergy between components, and especially amp-speaker interaction. For those extensive and interesting cans of worms, we will deliver a separate primer in an upcoming issue!