1.  We always hear about various classes of amplifiers, how are they classified ?
Amplifiers are classed by their mode of operation. The majority of amplifier manufacturers adapt any one of the major modes of operation : Pure A, Class B, Class AB, Class D and Class G. Each of this class of operation is to respond to switching of the amplifier and the relative distortion levels. Many of today's car amplifiers are using Class AB, D and G technology. Latest news from the famous UK brand : GENESIS takes one step further to develop a Class A/AB 475 Special Edition to optimize the result of sound quality. The different classes of operation each have advantages and disadvantages, and the designer will choose the most suitable for the product being developed
2.  What is Class A amplifier ? Many audiophile commented that Class A amplifiers sound sweet, harmonious and warm and lack of transistor's harshness , is it true ?
Yes, it is true that Class A amplifiers sound sweet, warm and harmonious and lack of transistor's harshess but they also have some disadvantages. Class A amplifier is also known as Linear amplifier. In a true Class A amplifier, the transistor of the positive and negative rails are always " on " at the same time, regardless of whether the output is positive, negative or zero. the unused power is then dissipated as heat. This means that a lot of power gets wasted as heat. Hence, these amplifiers run hot and ventilation must be seriously considered during the installation. It is a relatively inefficient mode of operation in terms of current/power consumption. As you can imagine, a big Class A amplifier needs massive heat-sinks to maintain thermal stability or the output devices will overheat. Hence, most of the Class A amplifiers are not designed for high power of output. However, the advantage of such amplifiers is the transistors is permanently turned on and readily respond to the incoming signal hence no lag and low distortion levels. Class a amplifiers are always not cheap
3.  I have not seen any Class B car amplifier in the market, who is using it ?
Yes, we hardly see Class B car amplifier in the market. Class B designs are used principally in low lost amplifiers. some cheap amplifiers use Class B such as portable transistor radios. In a true class B design, the positive and negative rails are completely off until a signal comes through. If the signal is positive, the positive block rail output device is powered on. Conversely, when the signal changes to negative, the positive rail turns off and the negative rail output device turns on. The two rails are never on at the same time. There is no power loss when there is no signal, but the handoff between the positive side and the negative side is a bit rough, the result is distortion. The transition from one to the other causes crossover distortion that is obvious at lowe levels. The benefit is small power supplies, high efficiency and very little heat generated. Therefore, Class B should never be used for serious sound quality reproduction.
4.  What are the differences between Class class A, Class B and Class AB
Most amplifiers choose the middle ground-Class AB. In this mode of operation, when there is no signal, the positive and negative rails are both " on " a little bit and both faucets are " on " a little. Some power is wasted, but not nearly as much as in a straight Class A. When the signal goes positive, the negative rail stays on for a brief time while the signal gets bigger. Once the signal is strong, the negative rail shuts off, as in Class B. In a similar way, when the signal goes negative, the positive rail stays on until the negative signal is sufficiently strong. This over-lap prevents the crossover distortion present in a straight Class B design. The drawback to Class AB is that the overlap, known as bias, has to be adjusted for every channel on the amp. It is an acceptable compromise with comparable distortion levels to Class A yet runs cooler than Class A. The needs of power supply design are less so it reduces the cost of manufacture without compromising much the sound quality. However, the sound is not as sweet, harmonious and warm as Class A.
5.  What is so good about the Class A/AB 475 Special Edition, developed by renowned Brand : GENESIS of United Kingdom
Genesis' Class A/AB 475 Special Edition takes one step further as compared to other modes of amplifier, trying to combine the good from both Class A and Class AB designs while seeking to eliminate the drawbacks from each. At low levels, the amplifier is practically running in Class A till the sudden transients come in, the burst of power comes from Class AB. This amplifier has a number of improvement and modifications over the standard Genesis Series 3's 4- channel. The power has been up-rated from 4 x 50 watts to 4 x 75 watts (RMS @ 4ohm), 4 x 125@ 2ohm, 2 x 250 @ bridge 4 ohm. The output devices used are the same Sanken output transistors as that normally only find in the premium Genesis Dual Mono Extreme and Dual Mono Class A ( DMA ). To improve the sound further, which is to improve the signal to noise ratio, the crossovers were removed as they can be a major source of noise. the result is an outstanding > 110dB signal to noise ratio when most amplifiers are struggling to achieve the magical 100dB range. We understand that Genesis Class A/AB 475 Special Edition is a limited edition developed exclusively for the Singapore market and is not available in other locations.
6.  Nowadays,I noticed that many High End CD players come with " Time Alignment" technology, what is the purpose of this technology ?
The distance between the listener and the speakers in a car vary widely due to the complex speaker placement. This difference in the distances from the speakers to the listener creates a shift in the sounds image and frequency characteristics. This is caused by the time delay between the sound reaching the listener's right versus the left ear. To correct this, Time alignment technology is able to delay the audio signal to the speakers closest to the listener. This effectively creates a perception of increased distance for those speakers. The listener can be placed at an equal distance between the left and right speakers for optimum staging.
7.  I noticed that many audio CDs are labelled " 18 bit CD" or " 24 bit CD " etc. , what is the significance of the different Bit in CD recording ?
This is the " sound " compression rate specified for encoding. The higher the bit rate, the higher the sound quality, but also the larger the files. Therefore, 24 Bit CD has a better sound quality reproduction than 18 bit or lower bit CD, but you need a headunit with the equivalent bit processor to achieve the optimum reproduction of sound, for example, DENON DCT-1 or DCT-100 head unit is equipped with 24 bit processor.
8.  What is MP3?
MP3, whose official name is " MPEG-1 Audio layer 3", is a compression standard prescribed by the ISO, the International Standardization Organization and MPEG which is a joint activity institution of the IEC. MP3 files contain compressed audio data. MP3 encoding is capable of compressing audio data at extremely high ratios, reducing the size of music files to as much as one-tenth their original size. This is achieved while still maintaining near CD quality. The MP3 format realises such high compression ratios by eliminating the sounds that are either inaudible to the human ear or masked by other sounds. MP3 files that can be played back by this device have the file extension " mp3"
9.  What is WMA ?
WMA, or " Windows Media Audio ", is compressed audio data. WMA is similar to MP3 audio data and can achieve CD quality sound with small files sizes. Audio data is compressed using software with WMA codes. WMA files that can be played back by this device have the following file extension : " wma"
10.  I intend to add in a subwoofer into my audio system, how much power do I need from a subwoofer amplifier , please advise ?
The appropriate power for a subwoofer amplifier mainly depends on how much power is used for the rest of the system and the subwoofer crossover frequency used. Notice that less than half the power in music is above 300 Hz. This means tht at least half the power in music is below 300 Hz. To make sure you are covered, used the rule of thumb : THE SUB AMP POWER SHOULD EQUAL 1.5 TIMES THE POWER TO THE FRONT SPEAKERS. For example, suppose you are using a 50W x 4 amp to drive your main speakers. The rule of thumb says you should use a sub amp that can provide roughly 1.5 x(50 watts +50 watts)= 150 watts to your sub. This could mean a 75W x 2 amp driving a dual voice coil sub or an amp that produces 150 watts when bridged to a single sub.