An issue has recently come up, where people want to use a laptop for ChurchBells, and the laptop has no proper LPT (printer) port.
This breaks down into two issues, actually.
The first issue is one of reducing the expense of electrical power when the music is not playing. The reason I provide an amp relay feature is to accommodate old vacuum tube amps, which have a very high idle current. Solid state amps (except for the studio monitor amps found inside of super high end recording studios) are class AB, and as such use only a "bug-light" worth of electricity when in the idle mode. If a solid state amp was provided as a part of a bell tower, even in the tape cartridge days, it is most likely class AB. Class A amps were the exception, intended for extremely high fidelity use in a recording studio. (I have one such Class A studio monitor; it is a monster!) Pretty much all home stereos are in the class AB category, and usually use less electricity than a small light bulb. If you want, you can measure your amplifier's idle current using an AC ammeter (like a fluke DVM set to AC current measurement). You will then see why the amp relay is intended for tube amps.
The second issue is one of making sure the system stays operational even during a city wide power outage. For cthis, there are three methods you could use:
#1: Put a small UPS (uninterruptable power supply) just on the
amplifier, so that it too will operate during a power blackout. The
idle current is small and will not quickly drain the UPS.
#2: Get a fairly new (and pretty powerful) car stereo, about 100 watts RMS per channel, running from batteries kept on charge. They have gotten really good lately at even further minimizing the idle current on car stereos to avoid putting any noticeable strain on the car battery.
#3: Get a Class D amplifier(s) and run it from batteries that you keep on charge. This is a little more expensive, and it may take a while for the savings in electricity to pay for the difference. I will be researching this option and get back to you. There is a company that makes really great sounding class D amps. They make the chips, actually, but they have demo boards for sale that use the chips, which I have used on the beach to great effect as battery powered PA systems.