This is a voice changer/pitch shifter circuit built into an industrial megaphone. 
It's loud and its crazy.
<a href="http://casperelectronics.com/wp-content/uploads/VP4/megaphoneVP4.jpg"><img src="http://casperelectronics.com/wp-content/uploads/VP4/megaphoneVP4-257x300.jpg" alt="" title="megaphoneVP4" width="300" height="360" class="alignnone size-medium wp-image-808" /></a>

<a href="http://casperelectronics.com/wp-content/uploads/VP4/phoneprofile.jpg"><img src="http://casperelectronics.com/wp-content/uploads/VP4/phoneprofile-300x199.jpg" alt="" title="phoneprofile" width="300" height="199" class="alignnone size-medium wp-image-809" /></a>
<strong>
CONSTRUCTION:</strong>
The circuitry and especially the control interface were far too large to fit inside the megaphone housing so I built an external control module which clips to the users belt. </p>
The entire device (megaphone and sound manipulation circuitry) are all battery powered off the same supply so I had to use a connection cable between the phone and control box which could send audio and power. <br>It passes audio from the mic on the phone down to the audio circuit, then send it back up to the phone amp and speaker. I also had to send power from the phone batteries to the sound circuit. I used an insulated XLR cable which worked well. 
<a href="http://casperelectronics.com/wp-content/uploads/VP4/prototyping.jpg"><img src="http://casperelectronics.com/wp-content/uploads/VP4/prototyping-300x199.jpg" alt="" title="prototyping" width="300" height="199" class="alignnone size-medium wp-image-810" /></a>

<a href="http://casperelectronics.com/wp-content/uploads/VP4/VPmegaPrototyping.jpg"><img src="http://casperelectronics.com/wp-content/uploads/VP4/VPmegaPrototyping-300x199.jpg" alt="" title="VPmegaPrototyping" width="300" height="199" class="alignnone size-medium wp-image-811" /></a>

<strong>SCHEMATIC:</strong>
Here's the latest schematic as of 2010. Still needs some work, but it's functional
<a href="http://casperelectronics.com/wp-content/uploads/VP4/VP4_schm.jpg"><img src="http://casperelectronics.com/wp-content/uploads/VP4/VP4_schm-300x192.jpg" alt="" title="VP4_schm" width="300" height="192" class="alignnone size-medium wp-image-813" /></a></p>

Old schematic below as of 2008. lots of weird stuff going on in there... but it took me a long time to hand draw and its fun to look at so I'm including it anyway:

<a href="http://casperelectronics.com/wp-content/uploads/VP4/VP4schematic.jpg"><img src="http://casperelectronics.com/wp-content/uploads/VP4/VP4schematic-300x225.jpg" alt="" title="VP4schematic" width="300" height="225" class="alignnone size-medium wp-image-812" /></a>