Trick questions

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I asked a fundamental question in yesterday's post. If the power supply of a piece of equipment is not in the signal path, how could it have an affect on the sound?

The question, of course, is a trick one. For the power supply IS in the signal path as much or perhaps more than the amplification circuitry itself. I started the conversation with this 'trick' question because I wanted to engage those who still believe in this often used misconception. What's interesting to me is how many folks just kind of take for granted the role the power supply takes and assume it is separate and not a 'real' part of the signal path. I recall years ago getting into heated debate with an engineer who told me it was as obvious as the nose on my face that power supplies and amplifiers are independent systems that, when the power supply is appropriately designed, hasn't any bearing on the sound quality. The conversation went something like this:

"The signal is modulated by the amplifier and that signal passes only through the amplification circuitry. As long as the power supply is adequate, there should be no difference from one to another."

"Yes," said I, "but if you look at a schematic you'll note the power supply is in series with the amplifier's output. It's fed from that supply."

"True," he said, "but note that the power supply doesn't move and its only job is to remain a rock solid source of power for the amplifier to work on the musical signal. As long as that supply is steady, regulated and clean, there can be no difference in sound between various types."

So perhaps that's a good place to start our discussion; the role power supplies play in our circuits. What does a power supply actually do? A power supply replaces that that could be handled by a battery. Batteries are DC (direct current), stereo circuits require DC but what comes out of our home's wall sockets is AC. Remembering back to our prior discussions on the difference between DC and AC, we'll recall that AC is like a battery - only it changes from plus to minus 50 or 60 times a second (depending on the country you live in). AC is used without conversion for lightbulbs, heaters and motors and not much else. Anything we stereo buffs would be interested in requires conversion to DC before its useful. So, the first task of any power supply is to convert the AC into DC and this is where the trouble starts. But I digress.

Primary function of a power supply is converting AC to DC.

Secondary function of a power supply is to make the DC as clean and free of AC as possible.

Tertiary function of a power supply, to provide the appropriate voltage levels the preamplifier requires.

Tomorrow we look even closer.

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Paul McGowan

Founder & CEO

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