1 day ago · Low Cost 150 Watt Amplifier Circuit. In this project, we're building a simple 150 watt amplifier circuit. Description. This is the cheapest 150 Watt amplifier circuit you can make,I think.Based on two Darlington power transistors TIP 142 and TIP 147,this circuit can deliver a blasting 150 W Rms to a 4 Ohm speaker.Enough for you to get rocked?;then try out this.