![]() Just why does it take such a long time for a high performance (low signature – high musicality) piece of audio electronics to burn-in? Try doing it without these electrolytic capacitors and the signal will be far worse than sh*t. Sorry to upset the “all capacitors are sh*t” brigade, but they ought to try getting a proper education. ![]() Yes, even if the input, output and negative feedback network are DC coupled. So the bass and some of the midrange of the signal flows in an electrolytic capacitor, period. OK, you’ll have heard of bypassing, but that’s a smaller (film usually) capacitor which can’t do the bass end, and quite often doesn’t do the midrange either (depending on the impedance of the load). What through? The electrolytic capacitor! It then has to return to the power rail(s) to complete the other leg of the circuit. The output of an amp is delivered to the load from the power rail(s) and then to ground. And because they connect the signal between the power rails, you have a case of electrolytic capacitors in the signal path – try doing it without them.Ī lot of people who’ve been fed misinformation may detest this fact and argue against it, but all currents flow in circles – to make a light bulb work requires two wires to make the circuit, doesn’t it? To get the high value of capacitance required and still have room in the case for the rest of the parts means using electrolytic capacitors. How do you short the power rails together at signal frequencies but not at DC? Yes, a capacitor again! A short circuit would achieve this but then there’d be no power, just a blown fuse or a burnt offering… The AC resistance (impedance) between the wires of a DC supply must be zero or as near as damn it. Most people see ground as being the negative (usually) wire in a two wire supply (the middle wire in a three wire supply), but in actual fact the ground is both wires! (or all three in a three wire supply). The return wire in an audio circuit is called ground. ![]() Remember, the minimum number of wires to make a circuit is two. Now, the signal is a two wire thing too - the wire that carries the signal and the wire that carries its return. Enter the capacitor again - placed across the supply after the regulator, the charge on it makes the resistance tiny at audio signal frequencies. Whether battery or voltage regulator, each exhibit some output resistance which would steal power from the load. Often in the precision circuits of preamplifiers the DC has to be far smoother, so a voltage regulator is placed after the large value capacitor. A very large value, often 1,000 micro farads or many times more, is needed to “smooth” the rectified waveform to “flat” DC. This frequency is reduced to give an acceptably low ripple voltage on the DC by the property of the capacitor. What we need is a waveform-less voltage, otherwise we’d hear the twice mains frequency waveform (and a lot of distortion). This produces a waveform of one polarity operating at a frequency twice that of the mains supply. In most cases it is derived from the AC (alternating current) mains by means of a transformer and rectifier. The type of voltage is DC (direct current). For tube amps the voltage can be in the region 200 to 500 volts. Let’s just concentrate on the two wires – three just makes it harder to explain.Īcross these two wires will be a voltage of 3 to 36 volts, depending on the design, for a preamp circuit, and in the region of 80 to 100 volts for most solid state audio power amps. Most people realize that it takes two wires to make a light bulb work.įew realize that it takes two or three wires to make an electronic circuit work. It is a lengthy explanation, so as usual I’m doing it in stages. Here is the first part of my long awaited article on burn-in.
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