G4 Metal Gate. It's great for metal style drop D tunning it's all have 4 knobs control give you "ton of brick" sounds toggle switch use with scoop/boost mid let you control the sound of metal.
Use Mosfet clipping with silicon diode to compress out gain sound great for the guitarist who likes style of metal.

The Controls:
GAIN: Adjust Gain control
BASS: Adjust Bass frequency
HI: Adjust Hi-Mid frequency
LEVEL: Adjust Output level
Toggle Switch: Scoop/Boost Mid frequency
Complete bypass (True bypass)
Supply Voltage Range: 9 -12V DC, 15mA