The Hafler DH-500 is a two channel audio power amplifier designed to the very highest performance standards. It is available as a kit, or factory assembled. Its power rating of 255 watts per channel is very conservative, and it can deliver appreciably higher powers into impedances below the rated 8 ohms. You must be very cautious in the application of this amplifier, as its output capability is more than most speakers can safely tolerate. We urge you to read the “Operation” section of this manual so your speakers will be reasonably protected. The best protection is still common sense in choosing program levels which your speakers can tolerate. The DH-500 combines power MOSFET technology with a uniquely simple and effective circuit which reduces all types of distortion at all power outputs, over the entire audio spectrum, to levels where the finest test equipment has great difficulty in measuring it. The DH-500 sets a new high in reliability and resistance to abusive operating conditions at such high powers. This is one of the direct benefits of the power MOSFET’s ability to current limit under abnormal conditions. Where the conventional bipolar transistor must be protected by special circuits from entering “thermal runaway” when it gets hot due to heavy signals, tending to get even hotter, the MOSFET self-corrects to reduce the current, and thus the heat under the same conditions. You thus gain the dual advantages of simpler circuitry and the elimination of one of the chief causes for distorted signals imposed on the music-the sound of the actuation of complex protective circuits. The speed-measured as the slew rate-of the DH-500 delivers unmatched transient linearity, revealing the most delicate nuances of the music. In refining the basic Hafler MOSFET circuit the overall open loop gain was reduced by using more local feedback in the input stage. This required less compensation to stabilize the circuit, with the result that it was faster overall. With the built in bandwidth limitation at the input, all other stages are free of any transient overload.