Something Old? Something New?
Sony have taken out a patent on a speaker system. Nothing new in that you may think but there you'd be wrong! This speaker is the first of a new generation of 'digital' speakers.
To understand how it works though, we have to understand how audio signals can be digitally encoded.
Sound consists of a pressure wave that travels in air. If a suitable transducer, a microphone, picks these signals up, its output will consist of an electrical voltage whose amplitude will rise and fall in sympathy with the pressure wave (the sound) that impinges on it. If this signal is examined on an oscilloscope, a complex ever-changing voltage level will be seen. Conventional audio equipment operates with amplified levels of this original voltage.
There is, however, another way in which this signal can be encoded. Before describing this in detail it will be as well to define just what we are trying to encode. Sound levels in a live concert can vary by a ratio of 10,000:1 in amplitude. This is known as the signal's dynamic range.
The frequency range that must be covered extends from 20Hz to 20kHz, a thousand to one ratio. Digital recording works by sampling the waveform at a very high frequency and encoding its instantaneous amplitude.
Now computers cannot count in tens like us, they only know two numbers, 0 and 1. 1 represents a high voltage level and 0 an absence of voltage.
At first sight this seems extremely limiting but in fact a computer can count quite easily with just these two levels. In our conventional number system (decimal) large numbers are represented by thousands, hundreds, tens and units, i.e. powers of ten. The computer equivalent uses powers of two (binary). For example, consider the computer number 1001100. Note that only 0 and 1 appear. The key to translating this back to a decimal number is shown below:
There are several ways one can acquire a decent hi-fi system. The most obvious (and expensive) is to trail around hi-fi stores and, after listening to various combinations, part with your well earned cash. Another way, is to assemble the projects featured in this and other magazines. A third, very much underestimated method, is to assemble a stereo system from ready made modules, many of which are excellent in value and performance.
One such module I have recently come into contact with is an interesting example of this approach. Bi-Pak have established an excellent reputation over the years for the reliability and performance of their amplifier modules so it was with great interest that I received the new S453 FM tuner module.
Like it's predecessor, the S450, this module consists of two PCBs, one of which holds the guts of the tuner, and the other the four 100k multiturn presets which control the varicap tuning.
Also in common with the S450, tuning is accomplished by means of four pushbuttons. Although this means that only four FM stations can be selected, this isn't a major drawback. For those who wish to experiment it is not too difficult a problem to add further stations by using a separate switch bank.
One of the great things about this tuner is its small size, the large PCB is only 125 x 80mm. The tuning PCB is 45 x 80mm. Adding the unit to an existing installation is simple since the unit requires a supply voltage between 18-25V and has a current consumption of 45mA. In many cases a suitable supply rail will already be available and the tuner can then be run via a simple network consisting of a dropper resistor and decoupling capacitor.
So much for the mechanics. Now, how does it sound? To find out I built the module together with a simple PSU into a Verocase in which it was a fairly tight fit. After the usual, debugging exercise, in my case the elimination of an earth loop, I was most impressed with the performance. While it is not the most sensitive tuner that I have ever tested, adequate stereo reception of all the major stations with good signal to noise ratio was obtained. Stereo separation was extremely good (Bi-Pak quote 30dB). What is more important though is a tuner's ability to produce a good stereo sound stage with the subtle depth of effects intact. This the tuner can do. Technically the unit employs a discrete front end with an IC limit/demodulator stage. Stereo decoding is carried out by the ubiquitous PLL IC. Stereo operation incidentally can be bypassed by fitting an external switch.
In conclusion, a fine product which can be recommended for those who wish to obtain a good tuner and are prepared to do some mechanical work themselves. The price is £19.53 exclusive of VAT and should be available during August from Bi-Pak Limited.
Feature by Jeff Macaulay
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