Amplifiers

What Is Amplifier Gain?

What Is Amplifier Gain?
Axiom’s A1400-8 multichannel amplifier seen
from the inside. The gain stages are right
at the top of this picture. Each board is two
channels.

An audio amplifier can boost the small incoming audio signal’s voltage by increasing its voltage, and current. The degree to which the amplifier magnifies the low-level input signal compared to its output signal is the amplifier’s gain, and it is expressed in decibels (dB) because it’s a ratio of the amplifier’s output divided by its input.

In amplifier discussions, we don’t normally talk about the specifics of an amplifier’s gain because it involves writing formulae and a background in engineering, mathematics, and an understanding of logarithms. However, the following explanation should help you understand the concept of amplifier gain.

For illustration, let’s consider a typical line-level audio input signal from your CD player that averages about 0.5 volts. That isn’t nearly enough power to drive the voice coils of your loudspeakers; the signal’s magnitude will need to be amplified or increased. When you connect the 0.5-volt AC audio signal from the CD player to any line-level input jack of your stereo amplifier or AV receiver, it will increase that 0.5-volt signal to an output signal of, say, 40 volts. If you divide 40 volts by 0.5 volts, you get 80. So you could say your amplifier or receiver has a voltage gain of 38 dB.

If you were so inclined, you could express this as a formula. If you know the amplifier gain in dB and the strength of the input signal, you could use this information to determine the output power of the amplifier. Or, not knowing the gain, you could measure the input signal strength and the amplifier’s output power, and thus determine the amplifier’s gain, always expressed in dB. For some audio signals that are extremely weak, like those from a moving-magnet (MM) phono cartridge (often 5 millivolts, which is 5/1000th of a volt) or even smaller, from a moving-coil (MC) cartridge (typically about 0.2 millivolts), a preamplifier will be necessary to raise the tiny input voltage to the 1-volt or 2-volt range in order to drive the input stage of most amplifiers. To do that, the preamp will need at least 40 dB or more of gain. Engineers will often talk of “adding an extra gain stage” to an amplifier in order to accommodate a very small audio input signal.

Amplifiers

More in Amplifiers

Rogue Audio Pharaoh

Rogue Audio Pharaoh Tube Hybrid Integrated Amplifier Review

Home Theater ReviewJune 22, 2015
Yamaha A-S2100 and CD-S2100

Yamaha A-S2100 Integrated Amplifier Review

Home Theater ReviewJune 8, 2015
Perla 50 Signature Integrated Amplifier

Perla Audio Signature 50 Integrated Amplifier Review

Home Theater ReviewMay 21, 2015
Denon HEOS Drive

Denon HEOS Drive Multi-zone Amplifier

Brian MitchellMay 20, 2015
Parasound 275 v.2 Stereo Amplifier

Parasound 275 v.2 Stereo Amplifier Review

Home Theater ReviewApril 8, 2015
NAD M27 Amplifier

NAD M27 Seven-Channel Amplifier Review

Home Theater ReviewMarch 18, 2015
Krell Solo 375 Monoblock Amplifier

Krell Solo 375 Mono-Block Amplifier Review

Home Theater ReviewMarch 16, 2015
Raven Audio Nighthawk Integrated Amplifier

Raven Audio Nighthawk Tube Integrated Amplifier Review

Home Theater ReviewMarch 4, 2015
image.jpeg

Outlaw Audio Model 5000 Amplifier Review

AudioholicsFebruary 17, 2015