THE POWER AMPLIFIER INSTRUCTIONS for OPERATION and KIT ASSEMBLY CAUTION: IF THE SPEAKER FUSES BLOW, SOME DISTORTED SOUND CAN BE HEARD. THEREFORE IF AMPLIFIER MALFUNCTIONS, ALWAYS CHECK FOR BLOWN FUSES FIRST. THE DAVID HAFLER COMPANY 5910 Crescent Boulevard, Pennsauken, New Jersey 08109 Hafler DH-200 Power Amplifier serial number in all communications 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. Its 115 watt per channel power rating is sufficient for driving all loudspeakers in home applications, and its design assures extremely low distortion of all types. A combination of high performance, dependability, 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-110 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 uniquely 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 operation accomplishes a new high in long term reliability and exceptional resistance to abusive operating conditions. This is one of the direct benefits of MOSFET utilization in overcoming a serious limitation of conventional transistors - their tendency 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 and cartridges by a wide margin. Coupled with its unconditional stability, 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 with 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 at the input), incorporates all silicon devices in a format which is directly related to the highly acclaimed DH-110 preamplifier. Its unique selfDH-110 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 compromise audio performance. Basic protective systems provide maximum security against malfunction damage to the amplifier or the speaker: the AC line fuse, B + fuses, thermal breakers, 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 entire 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 AC line voltages. Through advanced engineering geared to the audio perfectionist, and an efficient no-frills approach, Hafler is making high technology high fidelity affordable. CONTENTS Operation . . . . . . . . . . . . . . . . . . . . . . . . Page 3 Assembly Instructions .................. 4 Wiring the Kit ...................... 6 If Problems Arise. ..................... 10 Service and Warranty .................. 11 AC Line Connections for Overseas Use. ... 12 Kit Parts List ......................... 13 Schematic Diagram ................... 1 4 Component Value Listing. .............. 15 Pictorial Diagram. .................. Insert Copyright 1984, All rights reserved. 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' 7 amp needs (plus other equipment it is also s switching), you should use the amplifier' own power switch. In s 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 spacing 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 thermal 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 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 AC 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 occurs. 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 A C fuses of that value and install them in the back panel. 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 connection 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 inDH-101 stance, cable lengths up to 50 feet are premissible without loss of performance. Special low capacitance cables enable even greater distance between preamp and amplifier. It is desirable to keep the left and right input cables close together throughout their length to minimize the likelihood of hum pickup. Also, you should avoid running them parallel to AC cords - these should be crossed at right angles. Output The loudspeakers (or headphones) connect to the red and black terminals on the back panel. These binding posts provide several convenient alternative connecting methods. The screw cap may clamp the bared wire end, or a "spade lug" attached to it, but a better connection will be made by locating the hole drilled through the shaft of the terminal when the cap is unscrewed. Insert the twisted end of the bared wire so that the cap will clamp it in place. Always be sure that no strands of wire are unsecured, and that the bared end is not too long to risk contacting other elements. A soldered end or fitting is the safest solution. These terminals also accept standard plug-in "banana pin connectors," including the double ones with standard 3/4" spacing, available from electronic supply houses. These are the most convenient, especially if you may wish to interchange speakers occasionally. It is important to maintain correct phasing of the speakers when making their connections. Some speaker terminals are coded red and black, or + and -, etc. It is important that the "sense" of one speaker' connections match the others. If one is s reversed, you will find that the sonic image has a "hole in the middle," and that it is deficient in bass. Speaker wire always identifies one conductor to make this easy. There may be a molded ridge in one lead, or the color of the insulation on one wire is different, or the wire itself may be color coded. If pin plugs are used, be sure they are color coded, or that you follow the indexing mark on one side of the double connectors. Select speaker wire of sufficient size to preserve the high damping factor (and excellent speaker control) of your amplifier. Standard 18 gauge lamp cord ("zipcord") is satisfactory for distances up to 30 feet for an 8 ohm speaker. As the distance increases, larger wire sizes are recommended. The next larger wire size is #16, and it is often preferred by perfectionists. If you have 4 ohm speakers, the maximum cable length for best results is halved. The black output terminals are electrically connected to the chassis internally. Be certain that when the amplifier is operated in its normal stereo mode that the red output terminals are never connected together. In the special case when the amplifier has been internally modified for monophonic bridged operation, the output is taken from the two red terminals only ...