A Buying Guide for Amplifiers

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A Buying Guide for Amplifiers

When the average audiophile thinks of amplifiers, the first word that comes to mind is power. While it may seem wise to choose the most muscular product on sale, amps cannot act as a cure all for an insufficient satellite speaker set and a weak subwoofer. An amplifier needs to work harmoniously with the rest of the sound system and its key role is to control unruly sound waves. Loudspeakers can transform a tight, tonal bass into a vibrating, decayed boom when they're not reined in by an amplifier with the right damping capacity. When levels of restraint, tone, and wattage are perfectly integrated with a system that is finely honed for its purpose, sound quality will far outweigh the benefits of pure clout. Fortunately for second hand buyers, some of the most legendary amplifiers were manufactured four decades ago, making these some of the most viable products to repurpose.

Refining the Search

Amplifiers can focus on sectioned off portions of a sound system such as the subwoofers or speakers. The three basic types of amplifiers come with their own advantages in terms of performance and sound quality, with each serving a distinct set of listeners.

Two Channel Amplifiers

Configured specifically to deliver high quality sound to the speakers and subwoofers. Circuitry types are split into Class A and Class AB. The former funnels constant power into the system, while the latter generates less heat by delivering power only when an audio signal exists.

Four and Eight Channel Amplifiers

Versatility is the primary goal of these amplifiers. Four channel amps deliver sound to four corner speakers using independent crossovers. They can handle the entire system and are thus particularly power and space efficient.

Mono Channel Amplifiers

These control the subwoofers in isolation so that ohm load is sent to multiple subwoofers. This generates the optimum bass tones through an energy efficient system.

Three and Five Channel Amplifiers

These hybrids combine the benefits of mono channel amps' bass frequencies with two channel amps' mid-range outputs. Installation is simplified by unfussy wiring.

Choosing Power Ratings

Power alone will not achieve tone clarity but without it, subwoofers produce limp bass and tweeters generate tones too weak to resound over the middle ranges. Generally, speakers need to have the same impedance levels and ohm load as the amplifier to prevent distortion. When amplifiers have less power than their speakers, they can cause damage to the system.

Ohm load of one speaker

The wattage displayed on the back of the speakers refers to the amount of power they can handle and not their output. Amplifiers with a higher wattage than the speakers' capacity will produce a weak sound. Maximum performance is achieved when ohm loads and wattage match.

Ohm load of parallel and series speakers

The total ohm load of all speakers collectively adds up to the optimal ohm load and wattage of the amplifier required.

The Effects of a Mismatch

Complex speaker set ups with extensions and multiple connections need to be matched in terms of wattage and ohms using Ohm's Acoustic Law, which claims that the human ear can separate individual tones and frequencies. Mathematical equations controlling the suitability of amps to speakers ensure that the amplifier exploits the speakers' clarity and frequency, cutting out distortion and isolating every harmony. The effects of mismatches vary according to the type of circuitry and imbalance that exists.

Speakers with higher impedance loads than the solid state amp's minimum.

The amplifier's full output is not exploited, resulting in lower volume and less power.

Speakers with lower impedance loads than the solid state amplifier's.

Current flow may rise, leading to amp shut downs. Alternatively, amps without circuitry protections will overheat and catch fire.

Speakers with higher or lower impedance loads than tube power amps.

Output tubes and transformers become damaged. Tube power amps must match speaker impedance precisely.

The simplest and most efficient way to match amps with speakers is by choosing an amplifier that has double the power capacity as the speakers' total IEC power rating.


Every amplifier has a maximum volume before which sound begins to distort. The technical term for this top tier is headroom. While wattage plays a role in determining this level, several other factors are more influential.

Gain Stages

Solid State

When speaker impedance rises, the amplifier pushes out more power. Since the voice coil is able to adapt to the speakers, bass and high frequencies are restrained and mid frequencies receive the most oomph. Solid state amps are preferred by guitarists and acoustic music fans. They are a budget-friendly option and are easily transported.


These are small, digital amplifiers that simulate the sound of tube amps. Their portability and featherweight prices make them a favourite choice for novice musicians.

Tube Amplifier

Glass tubes control the amp's imput, generating a clear, tonal sound that is ideal for true audiophiles who refuse to accept anything less than professional quality sound. They are hefty pieces of equipment that come with premium prices.


Those who appreciate the traditional quality of analogue choose valve amps for their warm tone and nostalgic distortion. They achieve more volume per watt than tube amps do but they are also prone to deterioration. Vintage musicians and fans of blues adore valve amps enough to tolerate their need for frequent valve replacements.


As their name suggests, these amplifiers combine the features of other types to obtain a specific sound. Circuitry, valve power and digital modelling can be merged into a single hybrid to suit fussier audio-addicts.

Signal Strength

Music and film sound effects do not occur on a single level. Transient peaks can create problems when the amplifier in use has only enough power to cope with average levels. Peaks can reach up to 25 decibels higher than the median volume, so it is advisable to choose wattage in accordance with the peak headroom required. Peaks are more demanding of power than average levels are.


Unique Demands of Peak Levels

Ideal Peak Levels


Headroom is artificially created to prevent transient overloads.

Maximum peak level of 18dBu


Peak levels need to tolerate volume without distorting.

Peak levels between 18dB and 22dBu


Studio environments need to maintain quadruple the amp's IEC power rating in peak transient capability.

Peak levels between 22dBu and 28dBu, or 6 dBs higher than the IEC power rating

The Art of Decision Making

Don't exchange quality for affordability.

Saving on an amplifier in order to pay for a costly speaker system is counterintuitive, since speakers are only as good as their amps. Amplifiers tend to cost double what speakers do, and those with insufficient power are likely to damage speakers.

Avoid weak links

High quality sound can only be achieved when the entire system is built of excellent components. The amp, cables, and head unit are the foundation stones of a great system and none should be weakened by compromise.

Don't forget the cables

Cables determine how well the signal is transported to and from the amplifier. Poor compression or low quality analogue can distort sound quality as severely as a poorly chosen amplifier can. HDMI, DVI and Multichannel RCA cables are all options that deliver high quality signals in analogue or digital format. Gauge wire needs to be thick enough to cope with high voltage amplifiers.

Find Amplifiers on eBay

eBay's amplifiers suit every brand of listener from vinyl fans to digital buffs, musicians to cinemaphiles. The Electronics & Technology tab on the home page offers a Sound & Vision category which leads to two options for disparate shopping preferences: Those who have a brand in mind can shop from the Brand tab, while those choosing according to specifications can enter the TV & Home Audio Accessories page. Typing 'amplifiers' into the Search tab on the home page gives audiophiles a list of available options for vehicles, home entertainment and stereo systems. Compression is a facet that can destroy even the most potent amp, and cables that resolve the dilemma can be found through the search tab.


The ultimate amplifier is able to deliver every frequency and tone individually so that the sound seems to surround the listener from every angle. The appropriate amplifier for any given room will deliver authentic tone to every pocket of the space. Audiophiles who understand the difference between noise and distortion have grasped the value of organic sound. Master volume and saturation go hand in hand, ensuring that input is identical to output. Well-chosen amplifiers take command of tone while simultaneously allowing the listener to exert his own control through layering, which is achieved with the twist of a knob or the touch of a button. Many of the sounds that make legendary pieces of music so magical last for only a fraction of a second. It is the amplifier that makes sure that every crest, wave, and tine is delivered to the speakers precisely as the musician intended.

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