_^.,_.. ._.. ,..-I_ THE POWER AMPLI FIER for ASSEMBLY and OPERATION CAUTION: IF THE FUSES BLOW, SOME DISTORTED SOUND CAN BE HEARD. THEREFORE IF AMPLIFIER MALFUNCTIONS, ALWAYS CHECK FOR BLOWN FUSES FIRST. LM153 $3.00 Please refer to this serial number in all communications regarding this equipment. THE DAVID HAFLER COMPANY 5910 Crescent Boulevard, Pennsauken, New Jersey 08109 DH-500 Power Rating: Less than 0.025% total harmonic distortion at any power level up to 255 watts continuous average power per channel into 8 ohms at any frequency between 20 Hz and 20 kHz with both channels driven. IM Distortion (SMPTE): Less than 0.007% from 1 watt to 255 watts into 8 ohms Typical THD at 255 watts into 8 ohms: 1 kHz-0.002%; 10 kHz-0.007% Frequency Response into 8 ohms: -3 dB, 0.5 Hz to 120 kHz at 1 watt kO.5 dB, 5 Hz to 40 kHz at 255 watts Typical Channel Separation at 1 kHz: 60 dB Signal to Noise Ratio: Exceeds 100 dB referred to 255 watts into 8 ohms, unweighted Exceeds 90 dB referred to 1 watt into 8 ohms, A weighting Input Impedance: 47,000 ohms Input Sensitivity: 2.35 volts for 255 watts into 8 ohms; 0.145 volts for 1 watt Damping Factor: 200 to 1 kHz into 8 ohms; 60 to 10 kHz into 8 ohms Rise Time: 10 kHz, 80 volts p/p square wave, 10% to 90%: 2.5 us. Slew Rate: 1 kHz, 120 volts p/p square wave: 45 V/us. Semiconductor Complement: 27 transistors, 12 power Mosfets, 33 diodes, 8 zener diodes, one integrated circuit, one diode bridge. Power Consumption: 240 VA quiescent; 1200 VA @ rated power into 8 ohms, 2 channels Size: 7-l/4" high, 19" wide, 13" deep including handles Net Weight: 45 lbs. Shipping Weight: 49 lbs. CAUTION: For continued protection, replace the power fuse only with the same type and rating as indicated. WARNING: TO PREVENT FIRE OR SHOCK HAZARD, DO NOT EXPOSE THIS EQUIPMENT TO RAIN OR MOISTURE. 0 Copyright 1987. All rights reserved. INTRODUCTION 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' ability to current limit under s 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. The fully complementary, symmetrical push-pull circuit is direct coupled throughout (except at the input). It uses all silicon discrete devices in a format which is directly related to the acclaimed Hafler preamplifier circuit. With its unconditional stability into virtually any load, and its enormous power capability, the result is complete freedom from listening fatigue. The longer you listen to this remarkable amplifier, the more certain you will be that you could not have made a better choice. While modest in cost, through the elimination of frills and gadgetry, the quality is evident not only in the sound, but in the conservatively rated components. The oversized power transformer, the conservative operating levels of the MOSFETs, the computer-grade electrolytics totalling 40,000 microfarads, the enclosed relay, the use of film capacitors in signal circuits-all are evidence of the design efforts to achieve exceptional reliability simultaneo'usly with state of the art sonics and specifications. So rugged is the DH-500 that it can deliver over 20 amperes into a short circuit! For those with special power needs, the DH-500 can be adapted to monophonic operation, delivering in excess of 800 watts into 8 ohms, by installing the DH-502 input bridging kit. Those who have chosen to build this amplifier from the kit will find the assembly instructions assume no technical ability other than how to make a good solder connection. Even that has been described for those who are new to the fun of kit building. Through pre-assembly and testing of the complete signal module, the performance of the kit has already been assured, for assembly involves little more than interconnection of the power supply and control elements. You can look forward to just a few hours of construction fun, to hear the finest audio amplifier yet produced. CONTENTS installation ..........................Page 4 Operation ................................4 Connections .............................5 Assembly Instructions .................... .6 If Problems Arise ........................I4 Circuit Description .......................I5 Schematic Diagram ..................... .16 Component Values ......................17 AC Line Connections for Overseas Use ... .I8 Kit Parts List .............................I9 Service and Warranty ................... .20 Pictorial Diagram .....................Insert 3 INSTALLATION The DH-500 may be installed out of sight in many applications, where its power can be controlled by the AC switching of a preamplifier control unit. However, any high power amplifier may draw enormous amounts of current, so you should make sure your preamplifier has the switching capacity for the amplifier' needs, as well as any s other equipment which it also switches. inadequate switch current capacity may eventually render the switch inoperative The power switches in Hafler preamplifiers have been chosen for their high ratings, and have been tested and deemed suitable for normal home switching of the DH500. However, if the amplifier is intended for operation at sustained high power levels, or where power switching is very frequent, or where the control unit must switch substantial additional current for other equipment, or if your control unit does not have the 15 ampere switching capacity, you should use the power switch on the DH-500, and connect it directly to the AC line. In such use, turn the amplifier on last, and switch it offfirst. This will avoid possible loudspeaker damage from turn-on transients generated by source equipment. A power transformer of this size puts out a noticeable hum field, even though the special design of this transformer minimizes such radiation. If the amplifier is to be installed close to a record player, you should first check for freedom from hum pickup by the phono cartridge. Some cartridges are much more sensitive than others, and require more separation from the amplifier. Check at a relatively high volume setting, while swinging the tone arm throughout its arc. A few inches additional space will usually solve any problem. Ventilation is most important! Unobstructed air circulation at the sides and back is important for long trouble-free life. A 3 speed fan operates at its lowest speed whenever the amplifier is turned on, and is automatically switched to higher speeds at the power output demands it. Air is drawn in at the sides, and expelled to the rear. With normal home music levels the cooling capacity is sufficient that the fan will rarely operate at other than low speed, where it is so quiet that your ear must be close to a vent to hear it. The front panel is designed to facilitate mounting in a standard 19" rack. Be sure a l l of the cover screws are installed w h e n the unit is supported by the front p a n e l OPERATION The AC power cord should be plugged into a source of 120 volts, 60 Hz, unless the amplifier is specially provided with the multi-voltage optional transformer. Press the power switch to the right to turn the amplifier on. A red pilot lamp in the power switch signifies that it is on. If it is not illuminated, the most likely cause is a blown AC line fuse. That is the single fuse close to the switch inside the chassis. However, since the amplifier uses a 15 ampere slo-blo fuse, and the typical home circuit is also rated at 15 amps, check that as well. To avoid the turn-on transients generated in many control units, there is a 3 second delay before the relay connects the speakers. A few preamps may require a longer delay to avoid their internally generated turn-on pulses. Information on extending this turn-on delay is available from the company on request. A standard 2-wire power cord was chosen in preference to a 3-wire grounded AC cord, because there is no significant current leakage in this design. Where local requirements dictate the need for a 3-wire power connection, a ground lug may be attached to the chassis adjacent to the AC line fuse holder. If the pilot lamp should ever blink (about 2-3 times a second), this signifies that a protective thermal breaker has shut down the amplifier because ofexcessive heat sink temperature. The fan will be operating at its highest speed, and as soon as the heat sink temperature has declined, the amplifier will automatically return to normal operation. Such an occurrence is extremely unlikely, and if the amplifier shuts down again and the lamp flashes, you should check for inadequate ventilation, or an excessive input signal, an extremely low load impedance, or an input which may have dangerous signal content (such as osciIlation). Failing evidence of this, the fan or the amplifier may have malfunctioned, Because of the very effective fan cooling, any normal signal will not cause the amplifier to overheat. At normal home use levels, the average power consumption is likely around 250 watts. The unit' efficiency s is about 5O%, so some full power tests may exceed the capacity of a 15 amp circuit. When performing tests, voltage losses due to long lines should be taken into consideration, or compensated for. Loudspeaker Fuse Selection The DH-500 is supplied with 2 ampere fuses in the speaker lines. This conservative value has been chosen for initial use because most high quality speaker systems cannot safely handle very high power levels, even though a high power amplifier invariably makes them sound their best. Since a substantial overload must continue for a few seconds before a fuse blows, a 2 ampere fuse will allow very high power peaks to pass without hindrance, yet will protect most speaker systems. Smaller fuses tend to blow too easily, and it is unlikely you will be using speakers with low power ratings with the DH-500. Larger fuse sizes may not adequately protect the majority of speakers intended for home listening. If the manufacturer of your speakers recommends a specific fuse value for their protection, you should obtain 3AG type fuses of that value and substitute them for the ones supplied. The speaker fuses are included in the amplifier design solely for speaker protection. They do not protect, or affect, the amplifier's operation. A blown speaker fuse does not indicate malfunction-simply a higher than normal output signal. If the amplifier produces a low level distorted signal, a blown speaker fuse is the most likely cause. We do not recommend the use of a slo-blo type fuse for speaker protection. If your speakers can handle the higher power levels safely, and you wish to install fuses of higher ratings, we suggest- for the sake of the speakers-that you increase fuse size in l/2 ampere increments. THIS AMPLIFIER IS ABLE TO DELIVER SUBSTANTIALLY MORE POWER THAN MOST SPEAKERS CAN SAFELY TOLERATE. Therefore the Hafler Comp a n y cannot assume any responsibility for damage to the load (loudspeaker) because the choice o f f u s e six is in your hands . The 2 amp fuse, with an 8 ohm load, permits continuous power up to 32 watts, with peaks well above that. 2-l/2 am ...