In shows, audio video and lighting power often come from different supplies or even different phases.
You have to be very careful when doing show control - you get hum when you connect things together.
Audio isolation transformers are quite useful.
ARTcessories makes an isolation transformer ( the ART DTI ):
http://www.8thstreet.com/product.asp...dio_Processors
The manufacturers website is :
http://www.artproaudio.com/
