Tesla puts it together

Now we’re getting to the core of understanding how power in our hi-fi system is transferred from the wall and in the next few posts we’ll start to understand how we convert this power into music. First let’s wrap up our little history lesson on why we use AC power at all.

If you’ll remember, Tesla was getting ready to change the world from DC to a new form of DC called AC, something we use in our homes to power our stereo systems to this day.

Nikola Tesla was poised to build his AC power system based on the idea that each home or block of homes would connect to a very high voltage AC main line through a transformer – the transformer reducing the high voltage to a lower and more usable voltage for the home.

As we’ll remember, transformers only work when the power that feeds them is moving between plus and minus rapidly – something we call Alternating Current or AC. But Tesla had a problem and in a matter of only a few days he solved that problem and created the modern power grid still in use today.

The problem he had was generating the AC and once generated using it directly to make a motor work. In those days, dynamos or generators as well as motors were all generating and running off of DC. The dynamos that generated the DC and the motors than ran from DC were essentially the same things – each used in reverse of the other. This was sort of the same thing we’ve seen before with coils and magnets – if you spin a motor it makes electricity and if you put electricity into a motor it spins.

It was known even by Michael Faraday a decade earlier how to generate AC – one simply used a physical magnet connected to a hand crank in close proximity to a coil of wire. When you spun the magnet (a long straight bar of metal turning end to end) it would change the magnetic field from plus to minus and what came out of the coil was AC. But no one knew how to make a practical design for that and, perhaps more importantly, no one knew how to use that AC to make a motor.

Over the course of only a few weeks, Tesla saw the entire system in his head and in one of the great strokes of genius figured out the modern power grid, invented the AC motor, the AC dynamo, the efficient AC power transformer, and the system that would make it all work. Tesla’s grasp on the fundamentals of coils, electricity, magnetism and the efficient means to use all those elements together is unmatched since the genius of Michael Faraday who set all this in motion.

Within but a few years time, Westinghouse and Tesla’s new power system took over the modern world and sent Edison home to work on other projects like the phonograph, the motion picture camera and the thousands of innovative products he invented or brought into the world – but power was not to be his fame – it was Tesla who would make the leap necessary to build the world’s power grid – still in use today with but few changes.

Edison never gave up the fight for DC, even inventing the electric chair to prove just how dangerous AC power was. Edison personally electrocuted hundreds of animals and more than his fair share of condemned prisoners in public showings around the country – all in an effort to prove to the world AC was not to be used. But in the end AC survived even to this day.

Here’s a picture of Edison personally strapping in the first victim of the electric chair he invented to prove how bad AC was.

So, now you understand why AC is what comes into our homes and why.

Paul McGowan – PS Audio, Intl.

Artist tools

A few readers have asked me to back off on being uber technical and get back to writing more about sound and high end audio from a listener’s perspective rather than a designer’s and I’ll definitely do that but I did want to finish up on our little series about DACS.

One thing to remember is that while most of us just want to use our equipment as black boxes and not really care what’s inside, I think it’s always good to have some level of understanding about their workings to help make buying decisions. After all, an informed buyer is usually better equipped to make a choice that will bring greater musical joy than one without any understanding at all.

The first choice a designer has to make when it comes to the output analog stage of a DAC concerns gain: how loud the output of the DAC needs to be. This is an interesting dilemma for a number of reasons and one of the primary ones concerns what I just wrote about: making smart choices when it comes to purchasing your audio equipment.

Loud sounds better than soft. Sorry, it’s just human nature and those of us having been around long enough have watched the audition process too many times to ignore it. Most users will always pick the louder DAC than an identical sounding one with less gain. I have heard this described as sounding “more powerful” and “bigger” by those that don’t gain match their audition pieces.

Secondly, the designer also has to determine use case: does the DAC have an internal volume control and if so is it likely to be used with or without a preamplifier? This is a tougher choice as an increasing number of DACS have built in volume controls.

If the user is going directly into a power amplifier, as we ask people to do with our PWD, then that unit must have enough gain to drive the amp without turning the DAC all the way up. Why? For two reasons: the first and most important is that you have enough volume to play all recordings at maximum level with any given amplifier. The second is the age old misconception that when a volume control is nearing the end of its range the sound can become “strained” as if it were a gas pedal on a car and taxing the engine. Like it or not, as designers, we have to give enough gain so people don’t panic that they’re running out “room” and straining the system – despite the fact they are not.

As I have written in past posts, this is completely wrong but the ideas remain for new users and older ones as well. Think of the volume control more like the car’s brake, as opposed to its gas pedal.

Once the designer has figured out what gain they want, the next step is how will the output stage work and sound – in other words, what kind of configuration will it be? We’ll cover some of that tomorrow.

The one thing you might want to take away from this article is the following: whenever you audition a new piece of gear, do your best to first gain match as closely as you can to whatever your reference is. Don’t be fooled by a “louder is better” decision.

Paul McGowan – PS Audio, Intl.