Re: [Phys-l] amplifier

[John Denker <jsd@av8n.com>]

On 04/02/2008 06:16 AM, John M Clement wrote:

> You can reverse the phase digitally 

Definitely.

OTOH flipping the wires is in some ways more "physical".
It depends on the audience.  See below.

>  Audio Cleaning Lab 

Or, if you want to save $35.00 you can use sox:
  http://sox.sourceforge.net/

It is a "Swiss army knife" for sound files.  It is standard 
on Linux boxen and also available for free for windows.

Flipping phase is the easiest thing in the world:  just
set the volume to a negative number on one channel.  Sox
allows this.

====================================

If you prefer the "physical" route, I would recommend building
a box sorta like this:
  http://www.av8n.com/turbid/paper/img48/box20.jpg

That is, just get a smallish chassis box and mount a couple
of standard jacks on it.  Then leave open one side of the
box so you can complete the circuit using alligator clips.
Soldering a small loop of wire onto the jack terminals makes
them easier to grab.

  In the picture the circuit is already completed by resistors.  
  You would want to omit the resistors.  

Such a box is cheap and easy to make, and gets re-used a lot.
Also it sets a good example for the kids, showing that you 
can flip the phase (and insert voltmeters, and do a lot of 
other things) without having to cut the wires.