Firestone Audio Cute Beyond Headphone Amplifier - Silver Circuit Design: OPA2227 for main amplifier, current boosters NPN/PNP power transistors Class: Class A amplifier Output Resistance: Extra low output resistance (Zo &lt; 0.05 ohms),high current capacity Frequency Response: 6Hz~300Khz ,-1dB at 100 ohms loading, very low noise Max. output: 6Vrms (with 24 VDC Power Supply)