Why did the engineer break up with his girlfriend?
Because he was always trying to find the "next great thing," but she just wanted to settle for a "stable relationship"!
Ok, the other one is that engineers tell lame jokes.
In our continuing story of how I came to design the original Moving Coil Amplifier for PS Audio, we just got ourselves up to date on the difference between a moving magnet cartridge and a moving coil cartridge. The MM has lots of unwanted mass at the end of its cantilever in the form of a hunk of magnetized iron, while the MC solves this problem by replacing that iron blob with a lightweight pair of copper coils.
Engineering, at its core, is all about the art of side stepping the side effects of your decisions.
Swapping the magnet's position from the tip of the cantilever to the sides of the cartridge solved one major problem—the unwanted sonic sluggishness of too much mass—while creating an entirely new problem—low gain.
A typical MM cartridge produces a few millivolts of output in response to moving within the grooves of a record. These tiny voltages then need to be amplified loud enough to be heard over your loudspeakers. The typical preamplifier has a gain of about 10 (meaning, 1 volt coming in could get boosted as high as 10 times—or 10 volts out). A phono cartridge, on the other hand, has to have quite a bit more gain—by a factor of 100. So, a MM phono preamplifier has a gain of 1,000.
And the trick with this is noise. The more gain a preamplifier has the more noise goes with it. Doing just the math, a phono preamplifier should have 100 times more noise (hiss) than a preamplifier. Unfortunately, no one would accept that level of hiss coming through their speakers. No, in fact, we audiophiles want to hear…wait for it…
Nothing. Nada!
So, the art of designing a phono preamplifier isn't for the faint of heart. All kinds of tricks of the trade need to be emnployed to keep us audio nut jobs happy. We turn the level of a preamplifier up to listening levels and we expect to hear…nothing but music.
But then comes the Moving Coil cartridge. Less mass. Better sound. Lower output.
Lower output by a factor of 30!
So now, we need 30 times more gain just to get to the level of the MM.
More tomorrow.
