The JBL 6010B is a highly reliable, conservatively rated amplifier, designed for professional sound engineering applications where a high degree of performance is required. The circuitry has been carefully designed to reduce the possibility of failure within the specified environmental and electrical conditions. A protective circuit is utilized in this amplifier which makes it virtually impossible to damage it under any conditions of overload, including shorted or grossly mismatched load, inductive load at low frequencies, capacitive load at high frequencies, excessive input signal, white noise or installation errors. The JBL 601 OB can be overdriven by at least ten times normal input voltage, from 4(5-12 kHz, and eventually produces square waves increasing in RMS value up to about 160W at which point the output actually begins to decrease. The DC fuse is intended as a protective device for the power supply in the event of output stage malfunction. It is not intended to protect the output transistors which are guarded by the special circuitry provided. As an indication of high frequency stability, the JBL 601 OB draws only 30% more power from the AC line at 12 kHz, 100W, than at 1 kHz for at least one hour without malfunction or entering the "protect" mode. In the event of fan failure, the thermal switch will activate if the heat sink temperature exceeds 200° F. The hum and noise level is extremely low—at least 85 dB below maximum output. The 6010B amplifier is designed for maximum flexibility in varying input and output arrangements. A standard unbalanced 50K input is provided which can be converted to balanced line bridging or matching with the installation of the accessory 5195 transformer. A low cut filter switch reduces the possibility of damaging horns. All the power outputs are balanced and the bridging output unbalanced.