The 4558D Op Amp is a dual high gain operational amplifier internally compensated and constructed on a single silicon chip. It's high voltage gain (100 dB typ.), good input impedance (5 MΩ typ.) and versatile power supply (± 4 to 18 Volts) make it perfect to fit in pedal circuit designs. This is the same chip used in our Mean Screamer Overdrive Pedal.