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INTRODUCTION
The Hafler DH-220 is a two channel audio power amplifier designed to the very highest performance standards. It is available either as a kit, or fully assembled. trts I 15 watt per channel power rating is sufficient for driving all loudspeakers in home applications, and its design assures extremely iow distor- tion of all types. A combination of high performance, depend- ability, reliability, and moderate price is in the Hafler tradition of using the very latest technology to provide outstanding value.
The DH-220 circuit is a refinement of the DH-200 design, a Hafler landmark which has achieved worldwide recognition, and has elicited glowing reviews since its 1979 introduction. As in the DH-l l0 preamplifier, particular attention has been paid to component quality, using polypropylene or film capacitors wherever feasible, for example, for superior sound.
combining the latest power MOSFET technology with uni- quely simple and effective circuit topology reduces distortion of all types, and at all power levels, over the full audio frequency spectrum, to the vanishing point. In addition to its pace-setting .performance achievements, the conservative mode of opera- tion accomplishes a new high in long term reliability and excep- tional resistance to abusive operating conditions. This is one of the direct benefits of MOSFET utilization in overcoming a serious limitation of conventional transistors - their tenden.y to self-destruct under other than normal operating conditions. So rugged is the DH-220 that it can deliver more than ten amperes into a short circuit!
The speed - measured as the slew rate of this design delivers unmatched transient linearity, revealing the most delicate shadings, textures and nuances of the music, surpassing the capabilities of the most revealing loudspeakers anA cart- ridges by a wide margin. Coupled with its unconditional stabili- ty, and ability to deliver adequate power into any loudspeaker load, the result is absolute freedom from listening fatigue. The longer you listen to this phenomenal amplifier, the more certain you will be that you could not have made a better choice.
The oversized power transformer and bridge rectifier; the massive heat sinks; the conservative operating levels of the MOSFET output devices - all are evidence of the design efforts to achieve exceptional reliability simultaneously wit[ state of the art sonics and specifications. And this circuit is convertible to a high power monophonic amplifier with comparable stability and specifications.
The fully complementary, symmetrical push-pull circuit, which is direct coupled throughout (except al the input), incor- porates all silicon devices in a format which is directly related to the highly acclaimed DH-110 preamplifier. Its unique self- protecting output stage prevents the thermal runaway which is a common threat to solid state amplifiers. The ruggedness and conservative operation of the output stage allows the DH-220 to avoid the need for special protective circuits which could com- promise audio performance. Basic protective systems provide maximum security against malfunction damage to the amplifier or the speaker: the AC line fuse, B + fuses, thermal breikers, and loudspeaker fuses. Nothing hinders the essential purity of the audio signal.
Those who use these instructions to assemble the DH -220 kit will find that the left and right audio modules (printed circuit and heat sink assemblies) are preassembled and pretested. This greatly simplifies the kit assembly so that it can be done in only a few hours without special skills or know-how. Because of the modular arrangement, it is possible to operate on one channel if the other requires service, and avoids the need to return the en- tire amplifier in cases where only one channel is at fault.
Accessories for special applications include provision for monophonic use; a panel for standard 19" rack mounting; and an alternative power transformer for international Ae fine voltages.
Through advanced engineering geared to the audio perfec- tionist, and an efficient no-frills approach, Hafler is making high technology high fidelity affordable.
CONTENTS
O Copyright 1984, All rights reserved.
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The DH-220 is most likely to be installed out of sight in most applications, since its power may be controlled by the AC switching of most audio preamplifiers, like the Hafler DH-l10. If your control unit does not provide switching capacity sufficient for the amplifier's 7 amp needs (plus other equipment it is also switching), you should use the amplifier's own power switch. In that case, turn on the preamplifier first; then turn the amplifier on a few seconds ofter the preamp has been turned on, to avoid any unnecessary turn-on transients from some preamplifiers. Likewise, switch the power amplifier off first.
If the amplifier is to be installed close to a record player, you should first check its position for freedom from hum pickup by the cartridge from the field radiated by the power transformer of the DH-220. Although the design of the transformer minimizes such radiation, certain cartridges are more sensitive
than others, and require separation from the amplifier. Check at a comparatively high volume setting, and while swinging the tone arm throughout its arc. Often a few inches additional spac- ing will eliminate the problem.
Be sure to provide sufficient uentilation for the amplifier. Unobstructed air circulotion around the finned heat sinks and oboue the amplifier is important for long, trouble-free life. Never put anything on top of the cover perforations. It is normal for the top and the heat sinks to become warm in use.
It is expected that the amplifier will always be resting on its feet, which should be on a hard enough surface that air flow underneath is not obstructed. If it is mounted in a rack, or through a panel, the feet may be removed so long as adequate ventilation is provided through the bottom openings.
INSTALIATION
OPERATION
The red pilot lamp which is integral with the power switch glows whenever the amplifier is turned on. A blown AC line fuse
is the most likely cause if it is not illuminated when the amplifier
is switched on.
The pilot lamp also provides a high temperature indication. In
the unlikel"y eVent that the amplifier ceases to function, and the
lamp *blinks on and off steadily, it indicates that one of the ther-
mal'breakers has shut down the amplifier because of excessive temperature rise in a heat sink. When the heat has dissipated in
a few minutes, the amplifier should return to normal operation.
If the lamp again blinks, check for insufficient ventilation, or an
excessive input signal, or an input which may have dangerous
signal content (such as oscillation). Failing evidence of this, the
amplifier may have malfunctioned. Because of the very large heat sinks, it is highly unlikely that any normal signal will cause the amplifier to overheat.
Loudspeaker Fuse Selection
The DII-220 power amplifier is supplied with 2 amp fuses in the speaker lines. Experience has shown that since an overload
must exist for a few seconds for a fuse to blow, a2 amp fuse will protect most speaker systems, and only blow when overload oc- curs. Smaller fuses tend to blow too easily, and larger fuses do
not adequately protect.most speaker systems.
A pair of 5 amp fuses are also supplied as alternatives for the speaker fuse holders. These should be substituted if the power
output of the amplifier is to be tested, and these or intermediate
values may be used if the amplifier is to be operated at very high power levels into 4 ohm loads.
If the manufacturer of your speakers recommends a specific value of fuse for their protection, we suggest that you obtain
3AG fuses of that value and install them in the back panel.
l,oudspeaker Power Ratings
There are no u.S. standards for rating the power handling of loudspeakers. As a result, the manufacturers' usual "music
power" ratings, or suggested amplifier limits, are of only minimal help in determining safe operating levels with amplifiers which can deliver substantial amounts of power. You must take into consideration the type of music, and the levels you like, to provide long term trouble-free operation of your speaker choice, when you have a sizeable amplifier like the DH-220.
Connections
AC
The AC power cord should be plugged into 120 volts, 60 Hz, on the switched outlet of a preamplifier which can provide at least 7 amps, or 840 watts. Then the amplifier power switch may be left on, and it will be controlled by the rest of the system. Or, it may be plugged into a 120 volt wall outlet, and switched on and off independently.
If your line (mains) voltage is different, be sure you have the alternate power transformer which can accommodate several line voltages, and be sure it is wired for your mains voltage as described later in this manual before you plug in the o^plifirr.
Input
Conventional shielded cables, such as those supplied with your preamplifier, provide the input signal to the sockets on the back panel of the DH-220. Be sure that the outer shield connec- tion is secure, to avoid hum. The length of these cables (so as to permit remote location of the amplifier, if desired) is limited only by the output impedance of the preamplifier. If it is 600 ohms or less, as with the DH-l0l and DH-l10 Hafler preamps, for in- stance, cable lengths up to 50 feet are premissible without loss of
