The computers had evolved a lot in the last years. Long time ago, they were just some big machines capable of doing just some simple operations. Now they can come in very small sizes (the laptops) and can do a lot of sophisticated operations. Along with the development of the computers, all its components had developed too. And here you can include the computer speakers. Today you can find all sorts of speakers, in different sizes and shapes, with different powers and characteristics and also with different prices. The audio playback chain of a computer includes many devices, and one of them is the audio amplifier. This is a component that amplifies low power audio signals (signals of frequencies between 20 to 20.000 hertz) to a level suitable for the speakers. Other components of this audio chain may be low power  audio amplifiers which can do different things such as pre-amplification, tone control, equalization, mixing or effects. The input signal to an audio amplifier may have just a few hundred watts, the output signal may get to thousands of watts.

The audio amplifier was invented a long time ago in 1909 by Lee de Forest. After making the first amplifier he was able to make the first AM radio. The first amplifiers were based on vacuum tubes, and they were capable to achieve some pretty good quality. The amplifier from our days are based on other technologies (transistors and other devices), but there are still some people who prefer the tube amplifiers, due to the warmer sound they can give. The amplifiers based on transistors became available to most of the people in the 1960's.

The most important parameters for an audio amplifier are the frequency response, noise, gain and distortion. When the gain is too high it can happen that the noise and distortion get too loud , and the gain is too low, the distortion may also reduce. Many years ago most of the amplifiers and preamplifiers had filter circuits for equalization and tone adjustment, because of the quality of recordings, playback technology and speakers that was not perfect. But the technologies had evolved and the source materials and speakers have a much better quality these days, so there is no need for filter circuits anymore. Because of the modern devices such as CD / DVD players, there is also no need for a preamplifier. If you do not have an external amplifier, you should know that there are many of them in your computer. For example the sound card from your computer contains several audio amplifiers and also a stereo or home theatre audio system.

The computer speakers and speaker amplifiers for a computer can be a tricky subject. Most of the speakers give you their total power for all the speakers. But some speakers with a big total power may sound very poor when compared to some speakers with half the power but with a good amplification. The difference can be also made by the size of the speakers, the current and even the speaker cables. So that's why you don't have to look just at the total power in watts when choosing some speakers. A good way to test the speakers that you want to buy is to play some music at all the volume levels (either if you are in a store). You should begin with the lower levels and go as high as possible. The sound quality may be the same through all the volume levels. The poor speakers will pop or have distortion at higher volumes, especially on the lower frequencies.

Now let's talk about some of the speaker amplifiers for computers on the market. One if them is the MS - 4V Surround Sound Amplifier with 8 ohms per Zone Speaker Impedance. The technical specifications for this product are:

-Power rating: 75 W RMS maximum input per channel
-Switch type: 12-position light touch silent rotary switch "make before break"
-Terminal type: toggle quick disconnect 20-14 AWG wire capacity
-Frequency response: 20 to 20 KHz + / - 1 dB
-Speaker impedance: 8 ohms per zone
-Total attenuation: - 42dB; full clockwise position is straight-through, full counter clockwise position is off
-Attenuation by step: top seven steps are -3 bB per step, lowest four steps are - 6dB per step
-Dimensions (W x H x D): 429 x 56 x 260mm
-RMF (W x H x D ): 438 x 45 x 260mm

Another amplifier is the AD-7500N 5.1 Surround Sound Amplifier with Hi-Fi Playback Function. If you are interested in the technical specifications for this product, here they are:

-Hi-fi playback function
-High quality digital karaoke
-Dolby AC-3 (Dolby Digital) / DTS 5.1-channel input ready port
-Six DSP modes: rock, classic, church, hall, theater, and live
-5 CH high-power hi-fi power amplifier
-Main-function infrared remote control
-VFD
-Microcomputer intelligence operating system
-Perfect protection function
-Signal-to-noise ratio: ≥ 80dB (A Weighted, bypass)
-Distortion: ≥ 0.5% (1 kHz, 20 W)
-Frequency response: 20 Hz~20 kHz (± 1 dB) (L, R, C, and surround sound channels)
-Maximum voltage gain: ≥ 40 dB
-Microphone signal: (no-delay signal)

-Maximum voltage gain: ≥ 65 dB
-Band width: 50 Hz ~ 20 kHz (± 3 dB)
-Distortion: ≤ 0.8% (without delay)

-Tone circuit
-Bass peaking attenuation amount: ± 6 dB (100 Hz)
-Treble peaking attenuation amount: ± 6 dB (10 kHz)
-Delayed electrical circuit: Delay time: 20ms ~ 200ms
-Pitch electrical circuit:

-Bass peaking attenuation amount: ± 8 dB (100 Hz)
-Treble peaking attenuation amount: ± 8 dB (10 kHz)

Power output: ≥ 80 W (4 ohms)
Voltage of power supply: 220 V ± 10 % / 50Hz

If you are interested in an amplifier for your subwoofer, one of them is the MSI-200 A Subwoofer Amplifier with Load Impedance of 4 ohms. The technical specifications are:

-AC input voltage: AC 115 / 230 V
-Amplifier type: Class AB
-Output power THD 1 % 50 Hz RL=4 ohms > 205 W
-Output power maximum RL= 4 ohms > 220 W
-Noise at Vin=0: < -70 dB
-Frequency ( 6 dB): 15 - 70 Hz
-T.H.D at output power 170 W: 0.04%
-Input sensitivity at 200 W, 50 Hz: 300 m Vrms
-Load impedance: 4 ohms
-Short circuit protection: no
-Thermal protection: no
-Fuse rating at AC 115 V: 5 A
-Power auto on: yes
-Auto on input sensitivity: < 5 m Vrms
-Auto on time: >  40 minutes.

Let's present just one more amplifier, the AV-1068 B AV 5.1 Amplifier. The technical details for this one are:

-2 ch Amplifier
-Virtual 5.1 Surround
-4 DSP Mode
-3 x Stereo Input & 1 x 5.1 Input
-Digital Karaoke Function
-Treble / Bass Tone Control
-Electronic Volume Control
-Total Output Power: 90 W
-Power Output (1 kHz, 2 %THD, Per Channel)
-Total Output Power : 90 W
-Frequency Response : 20 Hz - 20 KHz
-Norminal Impedance : 8 ohms
-THD (rated condition) : ≤ 2%
-Input Sensitivity/Impedance : 250 mV / 47 kohms
-Signal-to-Noise (Line-in) : 80dB
-Tone : Control Treble ± 10 dB, Bass ± 10 dB
-Power Consumption : 250 W
-Product Dimension (HWD) : 120 x 430 x 330 mm
-Net Weight : 5.1 kg
-Carton Dimension (HWD) : 192 x 491 x 400 mm
-Gross weight : 6 kg
-CBM : 0.038
-20 fts container : 740 pcs
-40 fts container : 1530 pcs
-40 ftsHiQ container : 1790 pcs

If you are interested in other audio amplifiers you can find many of them on the internet, or at specialized stores.