HTA professional series power amplifiers are high-performance units employing state-of-the-art power MOSFET technology. The characteristics of power MOSFETS make them ideally suited to power amplifier design, providing far superior performance and reliability compared to other types of transistors. They afford higher efficiency, reduced heat, simpler overall design, reduced size and weight. The Model HTA125A supplies 125 watts (RMS continuous output) at less than 0.5% total harmonic distortion from 20 to 20,000 Hz. An input signal of only 500mV is required for full rated output. The input impedances are: high-impedance (50,000 ohms) unbalanced; low-impedance (500/600 ohms, balanced or unbalanced) with optional accessory transformer Model TL600. Line bridging can be achieved with an optional transformer Model TL100. Residual hum and noise is at least 90dB below rated output and the output regulation is better than 2dB from no load to full load. The HTA125A can drive a variety of load impedances: outputs include 4 ohms, 8 ohms, 25 VCT and 70 volts. It is capable of safely driving any recommended load continuously.The HTA125A is thermally protected to prevent damage due to excessively high temperatures; however, the amplifier will deliver the full rated power output continuously, even at +131ºF (+55ºC). Additional failure protection devices include electronic overload limiting, short circuit protection, and a Slo-Blo fuse. Electronic shutdown circuitry is automatically activated if an overload or short circuit occurs and a front panel overload shutdown LED illuminates. Once the cause has been rectified, the unit automatically resets. The power on/off switch, located on the front panel, illuminates when the power is on.The rear panel contains an input level control, input and output connections, the AC line fuse, and an auxiliary receptacle. A low-cut filter switch is located internally.