Sachin Sruthi 2-Channel IC Type Audio Gainer

12V DC Single Power Supply 6-Channel gainer from Extreme Amps Company

6-Channel Gainer with 12V DC Single Supply

6-Channel Gainer board from Crystal Audio

12V Single Supply Transistor Bass and Treble Board

12V to 36V DC Supply Bass, Treble Board from Extreme Amps

Crystal Dual Supply Bass Treble Board

Velan Audios 12V Bass, Treble, Mid Control BT

3D option Bass, Treble Board from Crystal Audio

NC Bass, Treble Board with gainer from Crystal Audio