Friday, March 14, 2014

Some Unknown Facts About Today's Stereo Amplifiers

By Marta McBrian


When selecting a brand new amplifier, you almost certainly will take a look at the technical specifications. One often found parameter is the frequency response. This specification although critical isn't going to tell the full story relating to how well the amplifier is going to sound. You might not completely understand the way in which the frequency response is calculated. I will describe what precisely this specific expression means. I hope you will be able to make a much more well informed buying decision. An amplifier is only able to function within the specific frequency range. Any kind of signals outside this range are going to be eliminated. As such the frequency response gives a significant hint concerning if a particular amplifier might be appropriate for a particular application. Ordinarily a lower and upper frequency are shown, just like 20 Hz - 20 kHz. This spec indicates that the amplifier has the ability to amplify music inside that frequency range. It may seem the greater the frequency response the better the amplifier. That, however, may not necessarily be. You should look at the specs much more carefully so that you can adequately interpret them all.

A large frequency response doesn't imply the amp has good sound quality. By way of example an amplifier with a frequency response between 30 Hz and 15 kHz may sound a lot better than another amp having a response between 10 Hz and 30 kHz. Moreover, each producer, it seems, utilizes a different way of specifying the lowest and highest frequency of their amps. Normally, the frequency response shows the standard operating range of the amp. Within this range, the amp gain is largely constant. At the lower and upper cutoff frequencies the gain will drop by at most 3 decibels.

It appears there are numerous methods that companies employ whilst specifying the frequency response. The most common method is to describe the frequency response as the frequency range within which the amp will have quite constant gain with a greatest decrease of 3 decibel (dB). Ordinarily the decline in gain is highest at the lower and upper frequency. However, many suppliers ignore this convention. They push the lower frequency and upper frequency to where the amplifier barely provides any gain. In addition, these figures tell almost nothing about how linear the amp is operating inside this range. A complete frequency response graph, however, will show whether there are any peaks and valleys and also show how the frequency response is to be understood. Peaks in addition to valleys might result in colorization of the audio. Preferably the gain of the amp ought to be linear throughout the entire working range.

This change is most obvious with many digital amplifiers, also referred to as Class-D amplifiers. Class-D amplifiers employ a lowpass filter within their output in order to reduce the switching components that are created by the internal power FETs. A varying speaker load will impact the filter response to some amount. Generally the lower the loudspeaker impedance the lower the maximum frequency of the amplifier. Also, the linearity of the amplifier gain will depend on the load.

Mostly current digital or "Class-D" amplifiers can have changes in the frequency response with different loads. The main reason is the fact that Class-D amps employ switching FETs as the power stage which produce a lot of switching components. These components are removed using a filter which is part of the amplifier. A varying loudspeaker load is going to impact the filter response to some amount. Normally the lower the speaker impedance the lower the highest frequency of the amp. In addition, the linearity of the amplifier gain will depend on the load. Some amps integrate feedback in order to compensate for changes in gain because of different attached loads. A different strategy is to offer specific outputs for different speaker impedances that are attached to the amplifier power stage via audio transformers.




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