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Wednesday, 5 March 2014

Uncovering The Truth About Modern Stereo Amplifiers

By Marta McBrian


When choosing a new amplifier, you probably are going to take a glimpse at the technical specifications. One often found specification is the frequency response. This specification whilst significant does not tell the entire story relating to how good the amp will sound. You may possibly not understand fully precisely how the frequency response is measured. I am going to discuss what precisely this particular expression means. I hope you will be able to make a much more well informed buying decision.

An amp will magnify an audio signal which is inside the frequency response range. If the frequency range is 20 Hz to 20 kHz as an example, the amp can amplify any signals with a frequency greater than 20 Hz and less than 20 kHz. You might think the greater the frequency response the higher quality the amp. That, however, will not necessarily be the case. You need to consider the specifications far more closely so that you can correctly understand these.

The truth is, an amp which has a frequency response from 10 Hz to 30 kHz may actually have much lesser audio quality than an amp that has a frequency response from 20 Hz to 15 kHz. Different companies appear to use different ways to establish frequency response. Ordinarily, the frequency response displays the standard working range of the amp. Inside this range, the amp gain is essentially constant. At the lower and upper cutoff frequencies the gain will drop by no more than 3 decibels. On the other hand, a number of companies push this standard to the limit and tend to list a maximum frequency where the amplifier will hardly create a signal anymore. Also, merely reviewing these 2 figures won't say a lot about the linearity of the frequency response. A complete frequency response chart, on the other hand, will show whether there are any kind of peaks or valleys and also show the way the frequency response is to be understood. You can even desire to ask for a phase response diagram which also offers important clues regarding the sound quality.

You also want to look at the conditions under which the frequency response was determined. You normally are not going to find any specifics about the measurement conditions, however, in the manufacturer's data sheet. Actually amps could have different frequency responses depending on the loudspeaker that is attached.

Various amplifier topologies offer a way to compensate for variations in the amplifier gain with various loudspeaker loads. One of those techniques utilizes feedback. The amplifier output signal following the internal lowpass is input to the amplifier input for comparison. If not designed correctly, this technique could potentially cause instability of the amp though. One more method is to offer dedicated outputs for different loudspeaker impedances that are connected to the amplifier power stage by way of audio transformers.




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