1) NESTPRO BS12

Nestpro BS-12 is an amplifier with 4 channels and 2 volume control. 
The amplifier can support up to 200 internal tweeters.
The amplfier has AC & DC power supply which can be use with solar panel / battery to supply the power and it is Built in Blower Fan.
If you could like to use it as an external calling it would be suitable.