Hafler DH-200 User Manual download pdf (Page 3)

INSTALLATION

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-110. 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

after

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

ventilation

for the amplifier.

Unobstructed

air circulation

around the finned heat sinks and

above

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.

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 unlikely event that the amplifier ceases to function, and the

amp 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 DH-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, a 2 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

fuses of that value and install them in the back panel.

Loudspeaker 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

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 pIug in the amplifier.

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-101 and DH-110 Hafler preamps, for in-

stance, cable lengths up to 50 feet are premissible without loss of

DH-101

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Hafler DH-200 User Manual Page 3

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