Pop quiz

November 29, 2016
 by Paul McGowan

What do airplane wings, teeter totters, balancing scales, subtraction, gravel sorters, batteries, stereophonic sound, and balanced audio have in common?

They all rely on differences.

  • Airplane wings can lift tonnage by the differences in air pressure between the top and bottom surface.
  • Put two equal weight people on a teeter totter and nothing happens.
  • Place two identical objects on a balance beam scale, even if they are massive, and you get nothing.
  • 6-6=0.
  • Pea gravel doesn’t come naturally—only rocks having a common size are sorted through an appropriate filter.
  • Attach two wires of a lightbulb to the + terminal of a battery, you get nothing—moved to the opposite pole, light.
  • We create the phantom third channel of stereophonic sound from elements common to left and right—differences are filtered out of the center.

I am sure there are many more examples of difference amplifiers and common element sorting filters.

You can begin to grasp how a difference amplifier, responsible for eliminating common noise in cables, separates one from the other.

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4 comments on “Pop quiz”

  1. Paul, this makes ‘real good’ sense
    The difference between the polarities and all things in-between.
    So finally begin to understand the 3rd channel.
    On a good recording and playback system, the ‘music’ becomes LIVE!!
    All that music, channel separation and yet the full sound is there.

  2. Paul I suppose with all being said it would make no sense then to have a balanced cable between two components that are single ended with adapters. My reason for asking is because I needed a three meter cable between pre and pwr and thought having a balanced cable would cut down on any noise. I have replaced the cable with a special three meter RCA type.

    Thanks for the posts Paul.

    1. Using an adapter certainly cuts out many of balanced potential benefits because the second wire inside the balanced cable is being ignored. Some adapters do an interesting this, though. Instead of tying the ground wire of the cable to the chassis ground, instead, it is connected to the second input of the balanced amplifier, giving a sort of quasi benefit – but that’s mostly home brew that does that.

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