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.