It's sometimes hard to remember how to figure current or power or whatever when you have two of the other parameters. Here's a useful reminder. E-mail me at bob_lee at qscaudio dot com if you'd like a PDF version of it.
Quasi-Balanced Interconnections
Sometimes you need to put a signal from an unbalanced source into a balanced input. Here's how to do it with the least risk of creating a ground loop.
Last On, First Off Switch
When you turn your audio system on or off, it's important to have the amps come on last and shut off first. You can use two double-pole power switches (make sure they have adequate current and voltage rating, and make sure your construction complies with all electrical codes; consult a licensed electrician if necessary) to ensure that this happens. Mount the two switches in different parts of the rack, such as one in front and the other in back. When you turn one switch on--either one--the mixer and processing gear will turn on, but the amps will stay shut off until the second switch is turned on. When you shut off either switch, the amps will shut off immediately, but the mixer and processing will not until you shut off the other switch as well.
