Hafler DH-110 manual As assembled, units are normally wired for 120 VAC

The DH-110 is provided with accessory Rack Mount end caps in addition to the standard end caps installed on the unit. These accessory caps extend the width of the front panel to that of a standard 19” rack, with appropriate mounting holes. Installation instructions are detailed later in this manual under Additional Information.

POWER CONNECTIONS

As assembled, units are normally wired for 120 VAC,

50-60 Hz, as in the USA, unless they are specially iden- tified on the carton. In the Additional Information section you will find diagrams of alternate wiring of the power transformer to conform to other line voltages.

The power regulation of the DH-110 will provide full per- formance with line voltages which may vary substantially from the standard. Units wired for 120 volts, for instance, will work properly with line voltages between 95 and 130 volts.

Accessory AC outlets are provided on the back panel for other equipment. One unswitched outlet is provided for a turntable or tape recorder whose mechanical system may require disengagement through its own power switch. Most units, including power amplifiers, tuners, and many tape recorders and record players, may be connected to the switched outlets for convenient remote switching from the preamp’s front panel. The DH-110 power switch has been tested to provide adequate capacity for any Hafler power amplifier and typical related equipment. You should heed the maximum power rating printed on the back panel of the unit.

INPUTS-Magnetic Phono

There are two pairs of phono inputs, identified as Phono 1 and Phono 2. These are independent, and thus they may have different capacitive termination for differing car- tridge requirements. As assembled, Phono 1 is provided with a compensation capacitor of 120 picofarads, and Phono 2 is provided with 220 picofarads. One of these val- ues will accommodate most ‘Moving magnet’ cartridges. These have output levels intended for normal phono in- puts (0.5 millivolts per centimeter or higher) and are the most popular. Some high output ‘moving coil’ design car- tridges are not sensitive to capacitive loading, so they may be used with either input.

Though some phono cartridges are comparatively free of loading sensitivity, if the cartridge manufacturer specifies the proper load capacitance (which is the sum of the preamp’s internal capacitance, and the cables you use, as well as the above described capacitor), the most accu- rate sound will be obtained by following that recommenda- tion. If you have chosen the DH-110 for its sonic attributes, you will be more likely than most to be aware of these dif- ferences, and will want proper cartridge termination.

The Additional Information section of this manual de- tails the determination of the loading capacitor for a specified cartridge load. It also describes how the resistive load of the phono inputs may be changed, if needed, from the standard 47K ohms.

Moving coil design cartridges often require an auxiliary step-up transformer or pre-preamplifier (head amplifier) because of their low output signal. The DH-110 has provi- sion for internal addition of an accessory Hafler pre- preamplifer which you or your dealer can install at any time. This enables the Phono 1 input to accommodate such cartridges directly. The Additional Information describes its installation.

Adjacent to the Phono 1 input sockets are two Ground terminals on the back panel. These thumbscrews provide for connection of separate ground wires often provided on turntables, or as part of their audio cables. This ‘chassis ground’ may sometimes reduce the hum level of a system when it is connected to an earth ground, such as a cold water pipe, or the ground wire of 3-wire house wiring. However, the need for such connection varies with indi- vidual situations. After the system is operative, using a phono source, experiment with and without an earth ground to determine which provides the lowest hum, and use that.

IMPUTS-Tuner, CD/Video

These are high level (line-50 millivolts or more) signals from FM, AM or TV tuners, or compact digital audio disc, video disc, or VCR players. These inputs are grounded at the selector switch when they are not chosen for listening. The input impedance is approximately 33K ohms.

INPUTS-Tape 1, Tape 2

These are at line level and impedance. They connect to Tape Play outputs on the tape deck. They are not grounded when unused, since they can be connected by either the main selector switch or the Tape Monitor switch. They are terminated with 1 megohm resistors to avoid a possible switching transient.

RECORDING OUTPUTS

These connect to the Line Inputs of tape decks. The two pairs of outputs are wired in parallel. Thus two tape recor- ders receive identical signals. These outputs are buffered with a series resistor, and have an output impedance of 1.5K ohms. To provide full specification performance, the total tape recorder load should not be lower than 10K ohms (i.e. two 20k ohm recorder inputs on each channel).

Because it is possible that a preamplifier’s overall per- formance may be adversely affected by rectification ef-

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