_^.,_.. ._.. ,..-I_

THE

POWER AMPLI FIER

for ASSEMBLYand OPERATION

CAUTION: IF THE FUSES BLOW,SOME DISTORTED SOUND CAN BEHEARD. THEREFORE IF AMPLIFIERMALFUNCTIONS, ALWAYS CHECKFOR BLOWN FUSES FIRST. LM153

$3.00THE DAVID HAFLER COMPANY

5910 Crescent Boulevard, Pennsauken, New Jersey 08109

Please refer to this serialnumber in all communications

regarding this equipment.

Power Rating: Less than 0.025% total harmonic distortion at any power level up to 255watts continuous average power per channel into 8 ohms at any frequency between20 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 wattkO.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, unweightedExceeds 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 ratingas indicated.

WARNING: TO PREVENT FIRE OR SHOCK HAZARD, DO NOT EXPOSE THIS EQUIPMENTTO RAIN OR MOISTURE.

0 Copyright 1987. All rights reserved.

INTRODUCTION

The Hafler DH-500 is a two channel audio poweramplifier designed to the very highest performance stan-dards. It is available as a kit, or factory assembled. Itspower rating of 255 watts per channel is very conservative,and it can deliver appreciably higher powers into impe-dances below the rated 8 ohms. You must be very cautiousin the application of this amplifier, as its output capabilityis more than most speakers can safely tolerate. We urgeyou to read the “Operation” section of this manual so yourspeakers will be reasonably protected. The best protectionis still common sense in choosing program levels whichyour speakers can tolerate.

The DH-500 combines power MOSFET technologywith a uniquely simple and effective circuit which reducesall types of distortion at all power outputs, over the entireaudio spectrum, to levels where the finest test equipmenthas great difficulty in measuring it. The DH-500 sets a newhigh in reliability and resistance to abusive operating con-ditions at such high powers. This is one of the direct ben-efits of the power MOSFET’s ability to current limit underabnormal conditions.

Where the conventional bipolar transistor must be pro-tected by special circuits from entering “thermal runa-way” when it gets hot due to heavy signals, tending to geteven hotter, the MOSFET self-corrects to reduce the cur-rent, and thus the heat under the same conditions. Youthus gain the dual advantages of simpler circuitry and theelimination of one of the chief causes for distorted signalsimposed on the music-the sound of the actuation of com-plex protective circuits.

The speed-measured as the slew rate-of the DH-500delivers unmatched transient linearity, revealing the mostdelicate nuances of the music. In refining the basic HaflerMOSFET circuit the overall open loop gain was reducedby using more local feedback in the input stage. This re-quired less compensation to stabilize the circuit, with theresult that it was faster overall. With the built in bandwidth

limitation at the input, all other stages are free of any trans-ient overload.

The fully complementary, symmetrical push-pull circuitis direct coupled throughout (except at the input). It usesall silicon discrete devices in a format which is directly re-lated to the acclaimed Hafler preamplifier circuit. With itsunconditional stability into virtually any load, and itsenormous power capability, the result is complete freedomfrom listening fatigue. The longer you listen to this re-markable amplifier, the more certain you will be that youcould not have made a better choice.

While modest in cost, through the elimination of frillsand gadgetry, the quality is evident not only in the sound,but in the conservatively rated components. The over-sized power transformer, the conservative operating levelsof the MOSFETs, the computer-grade electrolytics total-ling 40,000 microfarads, the enclosed relay, the use of filmcapacitors in signal circuits-all are evidence of the designefforts to achieve exceptional reliability simultaneo’uslywith state of the art sonics and specifications. So rugged isthe DH-500 that it can deliver over 20 amperes into a shortcircuit!

For those with special power needs, the DH-500 can beadapted to monophonic operation, delivering in excess of800 watts into 8 ohms, by installing the DH-502 inputbridging kit.

Those who have chosen to build this amplifier from thekit will find the assembly instructions assume no technicalability other than how to make a good solder connection.Even that has been described for those who are new to thefun of kit building. Through pre-assembly and testing ofthe complete signal module, the performance of the kit hasalready been assured, for assembly involves little morethan interconnection of the power supply and control ele-ments. You can look forward to just a few hours of con-struction fun, to hear the finest audio amplifier yet pro-duced.

CONTENTS

installation ..........................Page 4Operation ................................4Connections .............................5Assembly Instructions .................... .6If Problems Arise ........................I4Circuit Description .......................I5

Schematic Diagram ..................... .16Component Values ......................17AC Line Connections for Overseas Use ... .I8Kit Parts List .............................I9Service and Warranty ................... .20Pictorial Diagram .....................Insert

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INSTALLATION

The DH-500 may be installed out of sight in many appli-cations, where its power can be controlled by the ACswitching of a preamplifier control unit. However, anyhigh power amplifier may draw enormous amounts of cur-rent, so you should make sure your preamplifier has theswitching capacity for the amplifier’s needs, as well as anyother equipment which it also switches. inadequate switchcurrent capacity may eventually render the switch in-operative

The power switches in Hafler preamplifiers have beenchosen for their high ratings, and have been tested anddeemed suitable for normal home switching of the DH-500. However, if the amplifier is intended for operation atsustained high power levels, or where power switching isvery frequent, or where the control unit must switch sub-stantial additional current for other equipment, or if yourcontrol unit does not have the 15 ampere switching capac-ity, you should use the power switch on the DH-500, andconnect it directly to the AC line. In such use, turn theamplifier on last, and switch it offfirst. This will avoid pos-sible loudspeaker damage from turn-on transients gener-ated by source equipment.

A power transformer of this size puts out a noticeablehum field, even though the special design of this trans-former minimizes such radiation. If the amplifier is to beinstalled close to a record player, you should first check forfreedom from hum pickup by the phono cartridge. Somecartridges are much more sensitive than others, and re-quire more separation from the amplifier. Check at a rela-tively high volume setting, while swinging the tone armthroughout its arc. A few inches additional space will usu-ally solve any problem.

Ventilation is most important! Unobstructed air circula-tion at the sides and back is important for long trouble-freelife. A 3 speed fan operates at its lowest speed wheneverthe amplifier is turned on, and is automatically switched tohigher speeds at the power output demands it. Air is drawnin at the sides, and expelled to the rear. With normal homemusic levels the cooling capacity is sufficient that the fanwill rarely operate at other than low speed, where it is soquiet that your ear must be close to a vent to hear it.

The front panel is designed to facilitate mounting in astandard 19” rack. Be sure a l l of the cover screws are instal-led 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 of120 volts, 60 Hz, unless the amplifier is specially providedwith the multi-voltage optional transformer. Press thepower switch to the right to turn the amplifier on. A redpilot lamp in the power switch signifies that it is on. If it isnot illuminated, the most likely cause is a blown AC linefuse. That is the single fuse close to the switch inside thechassis. However, since the amplifier uses a 15 ampereslo-blo fuse, and the typical home circuit is also rated at 15amps, check that as well.

To avoid the turn-on transients generated in many con-trol units, there is a 3 second delay before the relay con-nects the speakers. A few preamps may require a longerdelay to avoid their internally generated turn-on pulses.Information on extending this turn-on delay is availablefrom the company on request.

A standard 2-wire power cord was chosen in preferenceto a 3-wire grounded AC cord, because there is no signific-ant current leakage in this design. Where local require-ments dictate the need for a 3-wire power connection, aground lug may be attached to the chassis adjacent to theAC line fuse holder.

If the pilot lamp should ever blink (about 2-3 times asecond), this signifies that a protective thermal breakerhas shut down the amplifier because ofexcessive heat sinktemperature. The fan will be operating at its highest speed,and as soon as the heat sink temperature has declined, theamplifier will automatically return to normal operation.

Such an occurrence is extremely unlikely, and if theamplifier shuts down again and the lamp flashes, youshould check for inadequate ventilation, or an excessiveinput signal, an extremely low load impedance, or an inputwhich may have dangerous signal content (such as osciIla-tion). Failing evidence of this, the fan or the amplifier mayhave malfunctioned, Because of the very effective fancooling, any normal signal will not cause the amplifier tooverheat.

At normal home use levels, the average power con-sumption is likely around 250 watts. The unit’s efficiencyis about 5O%, so some full power tests may exceed the ca-pacity of a 15 amp circuit. When performing tests, voltagelosses due to long lines should be taken into consideration,or compensated for.

Loudspeaker Fuse SelectionThe DH-500 is supplied with 2 ampere fuses in the

speaker lines. This conservative value has been chosen forinitial use because most high quality speaker systems can-not safely handle very high power levels, even though ahigh power amplifier invariably makes them sound theirbest. Since a substantial overload must continue for a fewseconds before a fuse blows, a 2 ampere fuse will allowvery high power peaks to pass without hindrance, yet willprotect most speaker systems. Smaller fuses tend to blowtoo easily, and it is unlikely you will be using speakers withlow power ratings with the DH-500. Larger fuse sizes maynot adequately protect the majority of speakers intendedfor home listening.

If the manufacturer of your speakers recommends aspecific fuse value for their protection, you should obtain3AG type fuses of that value and substitute them for theones supplied. The speaker fuses are included in theamplifier design solely for speaker protection. They do notprotect, or affect, the amplifier’s operation. A blownspeaker fuse does not indicate malfunction-simply ahigher than normal output signal. If the amplifier producesa low level distorted signal, a blown speaker fuse is themost likely cause.

We do not recommend the use of a slo-blo type fuse forspeaker protection. If your speakers can handle the higherpower levels safely, and you wish to install fuses of higherratings, we suggest- for the sake of the speakers-thatyou increase fuse size in l/2 ampere increments. THISAMPLIFIER IS ABLE TO DELIVER SUBSTAN-TIALLY MORE POWER THAN MOST SPEAKERSCAN SAFELY TOLERATE. Therefore the Hafler Com-pany cannot assume any responsibility for damage to theload (loudspeaker) because the choice o f f u s e six is inyour hands .

The 2 amp fuse, with an 8 ohm load, permits continuouspower up to 32 watts, with peaks well above that. 2-l/2amps passes 50 watts; 3 amps, 72 watts; 5 amps, 200 watts.We have included a pair of 5 amp fuses as alternates, fortemporary use as spares; for testing the amplifier at veryhigh power levels; and for operation into very low load im-pedances, 5 amps will pass 80 watts into a 4 ohm load. Wesuggest that you obtain additional type 3AG fuses of the

appropriate size for your speakers.

Loudspeaker Power RatingsThere are no U.S. standards for rating the power han-

dling capabilities of loudspeakers. As a result the manufac-turers’ usual “music power” ra t ings , or suggestedamplifier limits, are of only minimal help in determiningsafe operating levels with amplifiers which can deliverenormous amounts of power. On the other hand, somespeakers, particularly tweeters, can also be damagedthrough the use of too small an amplifier if it is driven intosustained clipping. However, tweeters are also more vul-nerable to high level signals which are not always notice-ably loud to the ear (as from electronic music sources), soyou may wish to separately protect the tweeters with fusesof lower rating. You must take into consideration the typeof music, and the levels you like, to provide long termtrouble-free operation of your speaker choice, when youhave a very powerful amplifier like the DH-500.

If more than one pair of speakers will be connected tothe amplifier, proper protection would dictate that eachspeaker be separately fused, since when they are operatedin parallel, the combination of lower impedance and thehigher power handling capacity would suggest a muchlarger fuse at the amplifier than would provide individualprotection.

If full power tests are to be performed, particularly atlow load impedances, fuse ratings above 10 amps may berequired for the duration of the test.

CONNECTIONS

ACThe standard unit is intended for 120 volt, 60 Hz opera-

tion. If it is controlled by an AC switch on a preamplifier,the DH-500 power switch may be left on.

If your line voltage is other than that provided in theUnited States, be sure you have the alternate multi-voltagepower transformer, and be sure it is wired for your mainsvoltage before you plug in the amplifier. The connectionsfor other line voltages will be found in the back of thismanual.

InputStandard phono jacks are installed to accept conven-

tional shielded cables, such as those supplied with yourpreamplifier. Be sure that the outer shield connection issecure, to avoid hum. The length of these cables (so as topermit remote location of the amplifier, if desired) is lim-ited only by the output impedance of the preamplifier. If itis 1000 ohms or less, as with Hafler preamplifiers, cablelengths of up to 100 feet are permissible without loss of per-formance. Special low capacitance cables enable evengreater distance between preamp and power amplifier. It isdesirable to keep the left and right input cables close to-gether throughout their length to minimize the likelihoodof hum pickup. They should cross AC cords at rightangles- never running parallel to AC lines at close range.

For professional applications the phono inputjacks maybe easily replaced with l/4” phone jacks. Be sure, in thatcase, that they are grounded to the adjacent ground lug.

OutputThe loudspeakers connect to the red and black 4-way

binding posts. These are of a particularly heavy duty con-struction to handle the high currents which may be in-volved. They are spaced for double banana plugs, or youcan connect stranded wire through the vertical hole in theshaft which is visible when the cap is unscrewed. To be cer-tain that no strands of wire are unsecured, a tinned end, ora spade lug soldered to the wire is recommended.

Be sure to maintain correct speaker phasing by watchingthe lead identification in the hookup wire, and the identifi-cation of the speaker terminals. It is important that the“sense” of one speaker’s connections match the others. Ifthe speakers are out of phase, you will find that the sonicimage has a “hole in the middle”, and there will be a loss ofbass. This will be most evident on monophonic material.Correct it by reversing the leads to one speaker.

Select speaker wire of sufficient size to preserve the highdamping factor of the DH-500, Standard 18 gauge lampcord is the minimum suggested, and is suitable for shortdistances. The next larger wire is #16. There are also a

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number of specialty speaker cables preferred by perfec-tionists. If you have 4 ohm speakers, larger wire is recom-mended than for the typical 8 ohm speakers, too.

The black output terminals are connected to ground in-ternally. The black terminals may be connected together(common ground) when in the normal stereo mode, toutilize headphone junction boxes, or other accessoriesemploying a common ground system.

It is important that the red terminals never be connectedtogether when operating in stereo. Thus it is important thatyou carefully observe the proper connections when using acommon ground device, to be sure there is no reversal.

In the special case where the amplifier has been inter-nally modified to convert it to monophonic bridged opera-tion, with the addition of the DH-502, then only one inputjack is connected, and the output is taken only from thetwo red terminals. Such a “floating” connection must bemaintained, with no connection to the black terminals.

ASSEMBLY INSTRUCTIONS

There are three basic rules for success in electronic kitbuilding:

1. Read the instructions carefully, and follow them in or-der.

2. Make secure solder connections which are bright and

4. A wire stripping tool for removing insulation. This canbe a single-edge razor blade, but inexpensive strippingtools are safer, faster and easier.

5. A medium-blade screwdriver (about I/4” wide).

6. A #l or #2 Phillips head screwdriver.smooth.

3. Check your work carefully after each step.

The DH-500 amplifier is a versatile component withsophisticated circuitry which has been made remarkablyeasy to build by individuals with many years ofexperiencein the design and engineering of the finest performingaudio kits, and in the preparation of their manuals.

Kit building should be fun, and we are certain you willfind this to be so. Assembly will be faster, easier, and moreenjoyable if you have someone help you by reading thesteps aloud, selecting the required parts, and preparing thenecessary wire lengths in advance as you proceed. Fatigueincreases the risk of error, so take a break rather than pushto early completion. There are relatively few separatecomponents in this design, to make it easy to pack every-thing away, if need be.

7. Needle-nose pliers (a long, narrow tip).

8. Diagonal or side-cutting small pliers.

9. Large “gas” or “slip-joint” pliers.

10. A 1/4" “Spin-tite” nut driver may be helpful, but is notnecessary.

A soldering “gun” is not recommended. The unfamiliaruser is more likely to damage the etched circuit boardswith its higher heat potential and unbalanced weight. Also,because he may not wait long enough for it to reach operat-ing temperature each time it is switched on, poor solderconnections are more likely. Pencil irons are much lighterand easier to use, and there is no waiting time when solderconnections follow in sequence, as in kit building. Makesure you have a holder for it, though, and always unplug itwhen you take a break.

Your work area should have good lighting, the propertools, and a place where the large pictorial diagram can betacked to the wall within easy reach for checking. Thetools should include:

Proper Soldering

There are four steps to making a good solder connec-tion:

1. Make a good mechanical connection to hold the wire inposition while heat and solder is applied.

1. A 40 to 60 watt pencil soldering iron with a 306” orsmaller tip which reaches 700°F. 2. Heat thejunction of the wire and lug, or eyelet, with the

bright, shiny tip of the iron.2. 60/40 (60% tin) ROSIN CORE solder , l/16” diameter

or smaller. 3. After heating for a couple seconds, apply solder to theiunction. It should melt immediately and flow smoothly

3. A damp sponge or cloth to wipe the hot tip of the iron. around both surfaces.

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4. Allow the connection to cool undisturbed.

Remember that the connection is made by the solder,not by mechanically attaching the wire to the terminal.Usually the wire is looped through the lug and crimped inplace, but some prefer to just place it through the hole andrely on the stiffness of the wire to hold it while soldering.Eyelet connections, of course, are handled this way.

Good solder connections are essential for trouble-free,noise-free operation. A good solder joint does not requiremuch solder around the conductors. Never “butter” par-tially melted solder on the joint, as it is useless. A goodconnection looks smooth and bright because the solderflows into every crevice when the parts are hot enough.The iron must have a bright, shiny tip to transfer heat eas-ily to the junction. That’s why the damp sponge should beused frequently to wipe the tip, and occasionally you mustadd a small amount of solder to the tip, too. If a connectionis difficult to heat, “wet” the tip with a small blob of solderto provide a bigger contact surface to the joint. Once thesolder flows around the conductors, any movement mustbe avoided for a few seconds to allow a good bond. Whencool, check the connection by wiggling the wire. If indoubt, or if the connection is not shiny, re-heat the joint.Excess solder may be removed from a connection by heat-ing it and allowing the solder to flow onto the iron, which isthen wiped on the sponge.

ALL SOLDER USED MUST BE ROSIN CORE

Never use acid core solder or any separate flux in elec-tronic work. Silver solder is also not suitable. If in doubtabout unmarked solder, always obtain a fresh supply ofrosin core solder. We recommend 60/40 for easiest use. Donot confuse it with 40160, which is harder to melt.

The general procedure is to use a hot iron for a short timeto heat a connection, then add solder with the iron still incontact. Remove the solder once it flows, and then removethe iron. A cooler iron applied for a longer time is morelikely to damage components, or lift the copper circuit pat-tern from the boards. A break in the etched circuit can bemended by simply soldering a small piece of wire across it.DO not allow much build-up of solder on the tip of the iron,or it may fall into adjacent circuitry.

When soldering to an eyelet or hole on the board, insertthe wire from the components side, and apply the iron tothe bottom, leaving some bare wire exposed so that youcan see that the eyelet is then filled with solder for a securebond. A round wooden toothpick is suggested so that youcan heat and clear an eyelet of solder if it hinders your in-serting the wire. Some builders prefer to clear every eyeletfirst with a touch of the iron and toothpick. Others connectthe lead by bringing it up to the center of the eyelet on topof the board, applying the iron from the bottom of theboard, and pushing the lead in as the solder in the eyeletmelts. If the wire has first been “tinned,” usually no addi-tional solder is necessary, but it is a good practice to pushthe wire through, and then back it up a bit, to be sure solderfills the eyelet. On the bottom of the board, make certain abright, shiny flow is evident from the wire onto the circuitpattern on the board.

"Tinn ning” refers to the process of applying a light coat-ing of solde r to the bared wire end. This k eeps all the

strands secured, and also makes a good connection easier.Simply touch the wire with the iron for a couple seconds,and apply solder. Allow the excess to flow away onto theiron. When properly done, the wire is uniformly bright,and no larger than before. The hookup wire supplied withthis kit does not normally need tinning, for it is pre-tinned.

Wiring the Kit

If any components are unfamiliar to you, checking thepictorial diagram should quickly identify them. Or, thequantities, and the process of elimination as you check theparts list, will help. The pictorial diagram is necessarilydistorted to some extent for clarity, so that you can traceevery wire in a single overall view for verification as youwork. You may wish to check off on the diagram as yousolder each location.

To “prepare” a wire means to cut the designated lengthfrom the coil of that color, and strip about l/4” of insulationfrom each end. The wire supplied in the kit is #18 and #22,so you can set adjustable wire-strippers accordingly. Thetransformer leads are #18, and the line cord is #16. Becareful that you do not nick the wire when you strip it (thatcan happen more easily if you do not use wire strippers) forthat weakens it. The wire supplied in this kit is “bondedstranded,” which provides exceptional flexibility with re-sistance to breakage for easier use.

Whenever a connection is to be soldered, the instruc-tions will so state, or indicate by the symbol (S). If morethan one wire is to be soldered to the same point, they willbe indicated by (S-2), (S-4), etc. If soldering is not calledfor, other connections have yet to be made to that termi-nal. They would be more difficult if the connection was al-ready soldered. Every connection in the kit will be sol-dered when it is complete. After soldering a connection, itis best to clip off any excess lead length to minimize thepossibility of a short circuit (as on switch lugs, where ter-minals are very close together), and for neatness.

Be sure that uninsulated wires caterminals or the chassis metalwork.

nnott touch adjacent

The symbol (#) indicates a connection is to be made tothat point. When a lug number is specified without (#), it issimply a locating reference.

When the instructions call for twisting two or threewires together, the length of wire indicated anticipates afairly tight, uniform twist by hand, of three full turns everytwo inches. If you find the wires too short, loosening thetwist will gain some needed length.

Handle the circuit boards carefully. They represent amajor part of the kit cost. Stand-up components, such astransistors, should be checked when you install the mod-ule, to be sure all leads are separated, and that the largeelectrolytic capacitors have not broken loose from theboard.

Take the time to be accurate and neat, and you can besure that your completed amplifier will meet the per-formance of a factory assembled unit, and can continue toperform properly for years to come. Check your work, andmake sure the entire step has been completed before plac-ing a check mark in the space provided, and continuing onto the next step.

MECHANICAL ASSEMBLY

1 0 For security in shipping, the power transformerand the amplifier module have been fastened to thechassis. Remove the chassis cover, the inner frontpanel and the larger front plate, and set these aside.Be particularly careful in handling the amplifiermodule. to see that the leads of the upright compo-

nents on the circuit boards are not stressed. Thismodule accounts for more than half the kit cost,and has already been thoroughly tested forspecified performance before it was packed.

Turn the chassis upside down, and rest it on themodule and transformer to remove these parts. In-clude all of the hardware you have removed withthe rest when you check off the componentsagainst the parts list in the back of this manual. Werecommend this check-off to be sure you have ev-erything, and to enable you to identify any unfamil-iar items by comparing them with the pictorialdiagram. Although the perspective of the diagramhas sometimes been distorted to show connectionsmore clearly, it should enable you to recognize anyunfamiliar component. An egg carton is ideal forkeeping small items like hardware at hand.

It will simplify matters if you first separate the #4 nutsfrom the #6 nuts, which have the same outside dimen-sions. A #4 screw will pass through a #6 nut, aiding iden-tification.

A “set” of hardware includes one screw and one KEP nut(with its attached lockwasher). Always install thelockwasher side of the nut first. If the size of the hardwareis not specified, use the # 4 size, which is the smallest. #10is the largest. Always insert the screw from the outside ofthe chassis.

2 0 With the chassis upside down, select the 4 rubberfeet and 4 sheet metal screws. The screw head re-cesses fully into the foot. Install these in the holeswhich are about I” in from each corner.

3 0 Select the AC line cord and the plastic strain relief.Separate the two conductors of the cord for 2 in-ches. Strip l/4” of insulation from each lead. Twistthe bare strands tightly, and tin each lead. 13” fromthe ends make a sharp “V” in the cord by bending itsharply back on itself. Install the strain relief asshown, with the small end of the strain reliefnearest the stripped end of the line cord. Crimp thetwo halves of the strain relief around the wire at theV with heavy pliers, to partially form it before in-sertion into the back panel. Considerable squeez-ing is necessary, because the thick insulation “popsback” quickly. Then grip the larger diameter of thestrain relief with the tips of heavy pliers, squeeze ittightly, and insert the end of the cord through theback panel AC hole from the outside. Note that thehole has two flat sides, and the relief is shaped ac-cordingly. This is a very tight fit-you will have topull on the cord to help-but it snaps into positionwhen fully inserted.

4 0 Select the two input sockets and 4 sets of hardware.Install the sockets at LS and RS inside the chassisso that the short lug is nearest the hole in the chas-sis between the two sockets.

5 0 Select the single ground lug (with lockwasherteeth) and one set of hardware. Install it betweenthe input sockets. Point it toward the bottom, andbend it out for access. Be certain this lug is tight.The locking teeth must cut through the chassispaint for a good ground connection.

6 0 Select the two round fuse holders with caps, andtheir l/2” hardware : rubber washers , meta llockwashers, and nuts. First install the rubberwasher on each holder, so it will be outside thechassis, and then fasten them at locations LF andRE The holes have flats which mate with the fuseholder to keep it from turning. Point the tip lugs to-wards each other. Be sure all of this hardware istight, as it will not be accessible once the amplifieris completed.

7 17 Select the two red output terminals and theirhardware: the red washers , 4 nuts wi thoutlockwashers, and two plain connecting lugs. Notethat each part of the terminal has a flat which mateswith the flat top of the chassis hole. Install the ter-minals in the two center holes LR and RR so thatthe washer flat is engaged, tighten one nut securely,add the lug pointing up, and tighten the second nut.

8 0 Select the two black output terminals, their hard-ware, and two plain connecting lugs. Install them atLB and RB as in the previous step.

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F .I

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Selec t the plastic encased relay, the longerL-shaped mounting bracket, and 2 sets of hard-ware. Insert the screws through the bracket withthe bracket foot pointing away from the lugs at theopposite end of the relay. ‘lighten this hardware se-curely, but do not risk breaking the plastic.

Select 2 sets of hardware and mount the relay near the 2red terminals, with the bracket facing front. Install thescrews from below the chassis.

Select the 2 shorter L brackets, 4 sets of hardware,and the circuit board PC-9. Mount the brackets onthe circuit side of the board, with the feet pointingaway from the board.

Select 2 sets of hardware and install the circuitboard between the line cord and terminal RB, withthe components facing to the rear.

13 0 Select the 7-lug terminal strip and 2 sets ofhardware. Install it at the two inner holes in front ofPC-9. The hole near the right chassis edge is notused. The mounting feet face forward.

14 0 Select the single fuse clip and a set of hardware. In-stall it in the single hole between the two “dimples”at the front of the chassis. The dimples prevent theclip from turning too far.

15 0 Select the 2 dual fuse clips and 4 sets of hardware.Install one of these in the pair of holes nearest thecenter of the chassis, and the other in the pair ofholes aligned with it near the left edge.

16 q Select the 3/4” long #6 screw and a nut, and the rec-tifier diode block which has four lugs. Install therectifier DB in the front center hole nearest the fuseholders. Note the lug positioning in the diagram,and check the marked location of the + lug.

17 I-J Select the two round capacitor brackets, the twolarge capacitors, and 8 sets of #6 hardware. Place abracket around the bottom of each capacitor andfasten it with one set of hardware through eachclamp. Note the direction of insertion of the screwfor easy servicing access in the future. The clampshould be snug, but not tight. Place each assemblyso the clamping screws are accessible from thefront at locations CL and CR, and secure each with3 sets of hardware. Then loosen the clamps and ro-tate the capacitors so that each + terminal ispositioned as in the diagram. Make sure thecapacitors are seated against the chassis andtighten both clamps.

18 0 Select the 4 plain connecting lugs and four l/4” longlarge screws with lockwashers attached. Installthese on top of the capacitors with the lugs pointingas in the diagram.

19 q Select the two 2 amp fuses and install them in theround fuse holdders on the back of the chassis. Thiswill keep the caps from being loosened and lost.

This completes the basic mechanical assembly of thechassis. Set it aside for the present.

20 0 Select the large front plate, the smaller front panelwith the edges turned back, the two handles, andfour #lO screws. With the power switch cutoutsaligned, place the screws through the panel fromthe rear, through the front plate, and secure thehandles. Set this assembly aside.

21 0 Select the amplifier module. Handle it with care!The fan is mounted on the front of the module, witha foam gasket on the rear. On the bottom, twothermal sensors for the fan, and two safety thermalbreakers are already mounted on the heat sinks.With the module upside down, and the fan awayfrom you (to keep the left channel on the left, forconsistency) cut the right fan lead to 5-3/4”, strip itl/4”, and connect it to TS2 lug #6.

22 0 Cut the left fan lead to 4”, strip it l/4”, and connect itto TBl lug #l.

A soldering iron will be used regularly from now on. Besure you wipe its tip frequently with a damp cloth orsponge, as a bright tip will make connections easier withless likelihood of overheating components. If it is difficultto heat a connection in a couple of seconds, apply a smallamount of fresh solder to the tip so it can flow around theconnection and provide good heat transfer.

There are two gauges of wire supplied with the kit. For While excessive heat or careless “scrubbing” with the ironconnections which pass substantial current, the heavier can lift the circuit foil from the board, more people tend towire is used. Other connections need only the lighter gauge use insufficient heat, making it difficult for the solder towire. Connect the wires to the bottom of the module from flow smoothly around the connection. A smooth, brightthe right side, connection is important.

23 0 Prepare a 9-1/2“r ed wire and connect one end to TS2lug #6. (S-2).

24 0 Prepare a 7 1/2” green wire and connect one end toTBl lug #l. (S-2).

25 0 Select the ‘inrush limiter’, which is a disc about thesize of a quarter. Trim the leads to 1/2" and connectit between TBl lug #2 and TB2 lug #3. Solder bothlugs.

31 0 Prepare an 8” black wire and an 8” red wire. Startwith the red wire 1/2" longer at one end, and twistthese wires together throughout their length. Con-nect the longer end of the red wire to eyelet #l ofthe board which is to your left as you face the rearof the module. Eyelet #l is the upper eyelet. Con-nect the black wire to eyelet #2. Be sure botheyelets are securely soldered. Place these wiresdown under the module.

26 0 Prepare a 7-1/2"” white wire and connect one end toTB2 lug #4. (S).

27 0 Prepare a l-1/4” black wire. Connect one end to TSllug #7. (S). Connect the other end to TS2 lug #8.

28 q Prepare a 9” black wire. Connect one end to TS2 lug#8. (S-2).

32 0 Prepare an 8-1/2“black wire, and a 7-1/2‘yellow wire.Allow the black wire to project 1/2” beyond the yel-low wire, and twist these together. The black wireconnects to the upper eyelet #2 of the circuit boardto your right. (S). Connect the yellow wire to eyelet#l. (S). Place this pair under the module. Now turnthe module around so the fan is toward you.

29 0 Prepare a 10-1/2” yellow wire. Connect one end toTSl lug #5. (S).

The eyelets are numbered consecutively, one to each cir-cuit tab visible along the edge of the board, from 3 to 10.The small tab numbers are visible adjacent to each tab onthe underside of the board.

30 0 Twist the red, yellow and black wires from TSl andTS2 together. Also twist together the green andwhite wires from TBl and TB2. Place both of thesewire groups off to the right of the module. Then turnthe module right side up, with the fan away fromyou, and the wires extending off to the left.

When soldering to eyelets (holes) on the circuit boards, thewires will be connected to the outside (top) of the board,but they must be soldered securely to the circuitry on theunderside. It is best to heat the eyelet on the inner surfacewhile the wire is inserted from the outside. This requires aniron with a small tip (preferably chisel shaped) and somecare on your part. It is easiest to melt a small blob of solderon the tip, and position it at the eyelet so that the solderblob, more than the tip itself, is heating the eyelet. If theeyelet is first filled with solder, and the wire end is pushedall the way through the heated eyelet first, then withdrawnpart way to expose a bit of the bare end outside the boardbefore the solder cools, you should have a firmly solderedconnection if it cools undisturbed.

33 0 Prepare two 7” white wires. Connect one to theright circuit board eyelet #8, towards the bottom.(S). Connect the other wire to eyelet #6. (S). Youmay find it easier to work if the module is laid flaton its back foam gasket. Bend these wires towardthe bottom of the fan bracket, and twist them to-gether throughout their length.

34 0 Prepare a 13”green wire. Connect it to eyelet #7 ofthe right board. (S).

35 g Prepare an 1l”white wire. Connect it to eyelet #5 ofthe right board. (S). Bend this wire toward the bot-tom of the bracket.

36 0 Prepare a 3”green wire and connect it to eyelet #lOof the right board. (S).

Always tin a wire that is to connect to an eyelet. Aftersoldering, go back and check by twisting each wire, tomake sure nothing moves on the other side of the board. Itis wise to check any existing wire connected to an adjacenteyelet, to make sure your work has not loosened it. Whenconnecting heavy gauge wire to the eyelets, if you get toomuch solder on in the tinning process, it will be hard for thewire to penetrate the eyelet.

37 q Prepare a 6-1/2” white wire and connect it to eyelet#3 of the right board. (S).

38 q Prepare a 13” green wire and connect it to eyelet #7of the left board. (S).

39 q Prepare a 13” white wire and connect it to eyelet #5of the left board. Bend this wire toward the bottom.

10

40 0 Prepare two 9” white wires. Connect one to eyelet 52 q Select the spade lug and connect it to the free end of#8 of the left board. (S). Connect the other to the white wire from LT lug 6. Place this wire to theeyelet #6. (S). Bend these toward the bottom, and left, and twist it lightly together with the green wiretwist them together. from LT lug 3.

41 0 Prepare a 3” white wire and connect it to eyelet #3.(S).

42 0 Prepare a 6” green wire and connect it to eyelet #10(S). Set the module aside temporarily.

When connecting wires to the PC-9 circuit board note thatthe eyelets on this board are numbered in the reverse direc-tion from the lug numbers on the terminal strip.

CHASSIS WIRING

43 0 Select the chassis and the .39 mfd capacitor. Trimeach lead to 1/2". Connect one lead of the capacitorto L T lug #3. Connect the other lead to lug #4.

44 I-J Select the silicon diode. Note that one end has a

53 q Prepare a 2 3/4" red wire. Connect one end to PC-9eyelet #8. (S). Connect the other end to relay RYlug #7.

54 0 Prepare a 2” yellow wire. Connect one end to PC-9eyelet #7. (S). Connect the other end to RY lug #9.

stripe for identification. Connect the striped end toLT lug #3. Connect the other lead to lug #2.

45 0 Select the 1/2 watt 1 megohm (brown-black-green)resistor. Trim each lead to l/2” and connect one leadto LT lug #2. (S-2). Connect the other lead to LT lug#l.

55 /J Strip a 1-1/2“length of heavy wire bare. Connect oneend to large capacitor CL lug X2. (S). Connect theother end to CR lug #3. (S). Be very sure that theseconnections are well soldered because they willcarry considerable current.

56 0 Prepare an 8-1/2” red wire. Connect one end to PC-9eyelet #6. (S).

46 0 Prepare a 7-1/2” white wire. Connect one end to LTlug #1. (S-2). Connect the other end to fuse clip FClug #l. (S). 57 0 Prepare a 19’ black wire. Connect one end to PC-9

eyelet #5. (S).

47 0 Prepare a 12”green wire. Connect one end to LT lug#3. (S-3). 58 q Prepare a 9” yellow wire. Connect one end to PC-9

eyelet #4. (S).

48 0 Select one of the spade lugs. Connect it to the otherend of the green wire just attached to lug #3. (S).The proper way to connect one of the spade lugs tothe wire is to bend the shorter, wider set of tabstightly around the bare wire, and bend the outer,longer set of tabs around the insulation. Then flowsolder into the joint around the bare wire.

49 q Check both conductors of the power cord to seethat they are tinned to secure every strand. Con-nect one lead of the power cord to FC lug #2. (S).

50 0 Select another spade lug and connect it to the freeend of the power cord. (S).

59 0 Place the red, black and yellow wires toward theleft and twist them lightly together. Keep theseagainst the chassis and connect the red wire to dualfuse clip FR lug #5. Connect the yellow wire to FRlug #6. Connect the black wire to the center of thebare wire between the two capacitors CL and CR.(S). Six other wires will be connected to the centerof this bare wire. The amplifier will have the lowesthum if the last wire to be connected (from thetransformer -a heavy wire) is placed in the exactcenter of this link between the two capacitors, soleave a small space for it. However, all 7 wiresshould be connected as near to the center point aspossible.

51 q Prepare a 13” white wire. Connect one end to thelower hole of LT lug #6. (S). Using the lower holewill make it easier for other wires to be connectedto the same lug.

NOTE FOR MULTIVOLTAGE OPTION: This wire may needto be 1” longer, and may connect to another termi-nal for some line voltages.

60 c] Prepare a 4 1/2” red wire and connect one end toPC-9 eyelet #3. (S).

61 /-J Prepare a 5-3/4” yellow wire and connect one end toPC-9 eyelet #2. (S). Place this wire and the red wirefrom eyelet 3 to the left. Twist them lightly togetherand connect the red wire to RY lug #B. (S). Con-nect the yellow wire to RY lug #A. (S).

11

62 0 Prepare a 3” white wire. Connect one end to RY lug#4. (S). Connect the other end to red output termi-nal LR. (S).

63 [7 Prepare another 3” white wire. Connect one end toRY lug #6. (S). Connect the other end to outputterminal RR. (S).

64 0 Prepare a 16”green wire. Connect one end to blackoutput terminal LB. (S). Connect the other endclose to the center of the bare wire between the twocapacitors. (S).

65 0 Prepare an 18” green wire. Connect one end to out-put terminal RB. (S). Connect the other end to thebare wire between the two capacitors. (S).

66 q Prepare an 11-E” green wire. Connect one end todual fuse clip FL lug #4. (S). Connect the other endto CR lug #4.

67 0 Prepare a 7” white wire. Connect one end to FL lug#3. (S). Connect the other end to CL lug #l.

68 0 Prepare a 12”white wire. Connect one end to FR lug#7. (S). Place this against the chassis and connectit to CL lug #l.

69 0 Prepare a 13” white wire. Connect one end to CL lug#l. (S-3). Connect the other end to the rectfierblock DB lug #2. (S). This is the lug marked + onthe rectifier.

70 0 Prepare a 7 1/2’ green wire. Connect one end to FRlug #8. (S). Connect the other end to CR lug #4.

71 0 Prepare another 8”green wire. Connect one end toCR lug #4. (S-3), Connect the other end to DB lug#3. (S).

72 0 Strip a 3/4" piece of light wire bare. Connect it be-tween the short ground lug of input socket LS andthe separate ground lug between the 2 input soc-kets.

73 0 Prepare a 14” black wire, but strip 3/4" of insulationfrom one end. Thread the longer bared end throughthe separate ground lug, and connect it to the shortground lug of input socket RS. Solder only the twowires at the center ground lug at this time. Place thewire against the chassis, and connect the other endto the bare wire between the two large capacitors.(S). This is the 4th of 7 wires connected at thispoint. Remember to leave space in the exact centerfor the last wire, but keep all of these close to-gether.

Now place the wired amplifier module behind the chassisin line with the input sockets, so that it is resting on thefoam gasket, with the mounting feet against the chassis. Itswires will protrude toward the chassis, or to the right.

74 q Select the yellow and black twisted pair from theleft side of the module. Connect the black wire tothe short ground lug of input socket LS. (S-2).Connect the yellow wire to the long lug of LS. (S).

75 0 Select the red and black pair from the right side,and connect the black wire to the short lug of inputsocket RS. (S-2). Connect the red wire to the longlug of RS. (S).

76 0 Select the twisted white pair from the left side.Connect the longer wire to the side lug of the fuseholder LE (S). Connect the other wire to the tip lugof LF. (S).

77 0 Select the twisted white pair from the right side.Connect the longer wire to the side lug of RF (S).Connect the other wire to the tip lug of RF (S).

Make sure that all of the unconnected long wires (exceptfor the green wires to eyelet 7 on each board) are placed offto the right so that when the module is installed on thechassis these wires will protrude between the feet belowthe right circuit board. The wires to the #7 eyelets, as wellas those to eyelets 3 and 10, connect towards the front ofthe amplifier. Carefully lift the module without touchingthe components on the circuit boards. Swing it into posi-tion on the chassis, and check to make sure that no wiresare trapped under the mounting feet. Make sure that theinput socket long lugs have not been bent so that anyshorts are possible there-or to the chassis. Keep all wiresaway from the ‘inrush limiter’ disc-against the chassis.

It is a good idea at this time to check the fan by hand, tomake sure it rotates freely. Shipping sometimes may causea misalignment. If it rubs, bending a strut will correct theproblem.

78 0 Select 4 sheet metal screws and secure the moduleto the chassis. The easiest procedure may be to tiltthe whole assembly backwards so that the moduleis again lying on the gasket, giving you access to thebottom of the chassis. Start the screws, and thencheck again to make sure no wires are trapped be-fore tightening the screws fully.

79 0 Select the green and white twisted pair from thebottom of the module. Connect the green wire tothe terminal strip LT lug #l. Connect this wire tothe lower hole in that lug, and solder it separatelyfrom the two wires which are soldered to the upperpart of the lug, Make sure all 3 wires are soldered.Connect the white wire to LT lug #4. Use the lowerhole for this wire, and solder it separately now. Donot solder the capacitor lead to the upper part of thelug at this time.

12

80 0 Select the triad of black, red and yellow wires fromunder the module. These will be connected to theright end of the terminal strip, and to prevent theheat from the large resistors from melting the insu-lation on the wires, connect the wires from behindthe terminal strip and keep them against the chas-sis, so the resistors will be above them. Connectthe black wire to LT lug #5. Connect the yellowwire to LT lug #6. Connect the red wire to LT lug#7.

81 0 Select one of the 300* ohm 7 watt resistors. Trim eachlead to 3/4’ ’ . Strip two 1/Z” lengths of insulation from apiece of heavy wire, and place one piece over eachresistor lead as insulation. Connect one lead to LT lug#5 on the front side of the strip. Connect the other leadto lug #6. Because lug #6 will eventually have severalwires, it is important that each wire be placed as low aspossible in the opening, and crimped so as to maintainthe largest possible opening for the last wire.

* In these two steps, use the 600 ohm resistors instead, if theoverseas multivoltage transformer option is wired for 200 -240 volt AC lines. See page 18. A 220 volt fan must be used,part #AAI28, and will have been fitted if specified.

82 0 Select the remaining 300” ohm resistor. Trim each leadto 3/4" and place this resistor on the back side of theterminal strip and connect one lead to LT lug #5. (S-3).Connect the other lead to LT lug #7. (S-2).

83 0 Select the white wire from the left circuit board,protruding from underneath the module. Connect itto RY lug #7. (S-2).

84 0 Select the long white wire from eyelet 5 on the rightcircuit board. Place it under the relay and connect itto RY lug #9. (S-2).

85 0 Connect the short white wire from the left side ofthe module to fuse clip FL lug #l. (S).

86 0 Connect the longer green wire from eyelet 7 on theleft side to the bare wire between the 2 largecapacitors. (S). Place it down against the chassis.

The wiring of the amplifier is now to be completed with theinstallation of the power transformer and two disccapacitors. The following instructions refer to the 120 volttransformer supplied for the USA. If your kit is suppliedwith the optional multivoltage transformer for overseasuse, separate instructions in this manual will diagram,both in pictorial form, and schematically, the connectionfor each line voltage.

NOTE FOR MULTIVOLTAGE OPTION: The following steps whichdescribe the installation of the capacitors, and the connec-tion of the two red leads, and the red/yellow lead of thetransformer are to be followed for all units. Only the con-nections for the black and black/white transformer leads,and the additional leads supplied on your transformer, maydiffer. You should follow all the other steps to the comple-tion of your amplifier.

91 0 Select the 4 sets of #10 hardware and the 4 washers,and the power transformer. Carefully place thetransformer in position, making sure no wires aretrapped, with the transformer leads protruding to-ward the large capacitors. You may if you chooseshorten any lead for neatness, but be sure you donot cut any lead too short, as leads which are cuttoo short for re-use may void the transformer war-ranty. If you are using the multivoltage transformer,be sure you leave leads long enough for possiblealternative voltage applications.

The washers are to be placed on the screws on topof the transformer feet for stiffening. Install thebolts near the edge of the chassis first. That willdetermine which of the inner sets of holes are to beused. It may be easiest for you to tilt the assemblyup on its right side, so the transformer weight issupported by the work surface, or you can turn itupside down. Be careful the transformer does notswing into the circuit board on the module! Beforeyou tighten any of the mounting bolts, check to besure the line cord and other wires are clear of thetransformer feet.

87 0 Connect the green wire from eyelet 10 on the leftside to FL lug #2. (S).

92 q Connect the black lead to LT lug #4. (S-3). One ofthese wires has most likely already been solderedto the lower hole of this lug.

88 0 Connect the short green wire from eyelet 10 on theright side to FR lug #6. (S-2).

93 q Connect the black/white lead to LT lug #6. (S-4).One wire has most likely been soldered to the lowerhole of this lug.

89 q Connect the long green wire from eyelet 7 on theright board to the bare wire between CL and CR.(S). Place this wire down against the chassis. Onemore connection will be made at the center of thisbare wire.

94 0 Connect the red/yellow lead to the center of thebare wire between CL and CR. Be sure all 7 wiresare well soldered.

90 0 Connect the white wire from eyelet 3 on the sameboard to FR lug #5. (S-2).

95 0 Connect one red lead to DB lug #l. Connect theother red lead to DB lug #4.

Now is the best time to turn the amplifier upside down andshake out any loose bits of solder, wire clippings, etc.

96 q Prepare a 13-1/2”r ed wire. Connect one end to PC-9eyelet #l. (S). Place this wire down against thechassis and connect it to DB lug #l.

13

97 0 Select the .Ol mfd disc capacitor and trim each leadto 3/4". Strip two 1/2" lengths of insulation from apiece of heavy wire, and install these on thecapacitor leads. Connect one lead to DB lug #l.(S-3). Connect the other lead to DB lug #4. (S-2).

98 0 Select the power switch and the .OO5 mfd disc capacitor.With the red window (or, on some switches, the #3 lug,or the separate lug) of the switch to your right,temporarily slide the white wire’s spade lug part wayonto the left switch lug. Slide the line cord’s spade lugpart way onto the middle switch lug. This simply makesit easier to attach the capacitor to these two spade lugs.Cut each capacitor lead to one inch (some freedom ofmovement is desirable), wrap one lead around the shaftof each spade lug, and solder each. Then carefullydisconnect the wires from the switch.

99 0 Install the fuses. The 15 amp slo-blo fuse goes in thesingle fuse clip near the power switch. The four 10ampere fuses, with the thicker elements, go into thetwo dual fuse clips on the chassis. If you have notalready placed fuses in the speaker fuse holders onthe back panel, install the 2 ampere size, for thesewill give good protection to most speakers. A pairof 5 ampere fuses are also included for the speakerholders, in the event your needs require very highpowers. However, for steady state test signals atthe full amplifier capabilities, even larger fuse sizeswill be needed in the speaker fuse holders.

Now you should make a last check of all the solder connec-tions. Look closely for possible bare wire shorts, Checkfor secure hardware -especially that on the output termi-nals. Check that wires are not lying on top of the powerresistors on the 7-lug terminal strip. Remove all pieces ofsolder and wire clippings from the chassis.

Three wire ties have been included in the kit which youmay wish to install around groups of wires to make yourfinished amplifier look neat. Because it is desirable thatthe ground wires which connect between CL and CR bekept close together, we suggest using one tie at the base ofthe capacitors.

100 0 Select the front panel assembly and the power switch,and make sure that the power switch is oriented with thered window (#3 lug, or separate lug) to the right, ornearest edge. The switch is a press snap fit from theoutside of the panel.

101 0 Select 4 sheet metal screws, and bring the frontpanel to its approximate position. Carefully attachthe 3 wires to the switch lugs: white to the left;green to the right. Push the lugs fully on, and as-semble the front panel to the chassis. NEVER AT-TEMPT TO PICK UP THE AMPLIFIER BY THEHANDLES IF THE COVER IS NOT SCREWEDIN PLACE.

102 0 Select the remaining sheet metal screws and thecover. Before closing up the unit, plug it in a n dcheck to see that the fan turns. Because it normallyoperates at low voltage for low speed, a new fanmay need a bit of encouragement at first. Any stiff-ness is normally overcome after a few minutes op-eration. Once you are sure it turns on each time thepower switch is turned on, secure the cover.

103 0 Peel off the backing from the serial number label,and affix it to the bottom of the chassis.

CONGRAI’ULATIONS!YOU HAVE COMPLETED ONE OF THE FINEST

AUDIO AMPLIFIERS EVER DESIGNED.ENJOY ITS SUPERB SOUND.

IF PROBLEMS ARISE

If you are certain the problem lies in the power amplifier,check first to see that the red pilot lamp is lighted. If it isblinking at about 3 times a second, this indicates that thethermal safety breaker on one channel has shut down theamplifier because of excessive temperature. In this case,the exhaust air will be warm. After a few minutes of cool-ing, the amplifier will commence operation automatically.If it shuts down again, and the amplifier has sufficient ven-tilation, the malfunction is either internal, or is the result ofan excessive (and possibly inaudible) input signal.

If the lamp is not lighted at all, the main fuse in the singlefuse clip inside the chassis at the front is probably open. Ifa replacement 15 ampere, slo-blo fuse also blows, theamplifier needs service, and there is a power supply prob-lem. If the relay will not close (no signal at the output, withan input signal) check for excessive DC offset (over 1.8volts) from either channel at locations 7 or 8 on PC-9-thesmall relay circuit board. This indicates a defectiveamplifier channel, requiring competent service. If there isno indication of excessive offset, the fault is in the relay oron the PC-9 circuit board.

On rare occasions with some arm/cartridge combina-tions, very high signal levels at subaudible frequenciesmay cause the relay to cut off the output briefly, becausethe sensing circuit sees this as DC offset. If this is annoy-ing, and you are willing to accept a little less relay protec-tion, you you can change R107 and R108 to a higher value.These are now each 39000hms (orange, white, red) and arelocated above the IC on the small circuit board PC-9A. Wesuggest 4700 ohms as the next step. At the other extreme,it is possible to increase the sensitivity so that the relaywould protect the speaker if a stylus were dropped on therecord, but then it might be activated by powerful low fre-quency transients.

If the fan does not turn, or makes a ticking noise, makesure it is properly centered in its supports, and that ship-ping abuse has not twisted it so the blades are rubbing thehousing. Moderate pressure on the struts will recenter it.

14

CIRCUIT DESCRIPTION

The DH-500 amplifier components have been selected to pro-tect against failure, and all parts are operated conservatively toassure unaltered performance and proper operation for manyyears. The semiconductors have been thoroughly researched andselected for minimum noise and distortion in sustained use, andthe printed circuit board associated with the audio signals hasbeen pretested in the circuit to insure that each kit amplifier willmeet or exceed all specifications.

The amplifier stages are fully DC coupled, with a dual differ-ential pair for the input, and a fully complementary MOSFEToutput stage. Its power supply is a full wave bridge with 20,000mfd capacitors on both the plus “+” and minus “-” supplies toprovide excellent filtering and dynamic load stability. Protectioncircuitry includes two separate power supply fuses for eachchannel, individual thermal sensing devices for each channel toturn the amplifier off if the heat sinks should reach excessivetemperature, a relay to disengage the output if excessive DCoffset is detected, and output fuses to protect the speakers, in ad-dition to an AC line fuse.

Transistors Q3, Q4, Q5 and Q6, the input differential pairs,are matched to control the DC offset of the amplifier. T ooptimize the input pair parameters, they are driven fromconstant current sources - Ql and Q2.

An adjustable voltage reference is formed by transistor Q9 and

potentiometer PI. Thus the signal sees the bases of transistorsQ12 and Q13 tied together. Pl adjusts the voltage to bias theamplifier for Class AB operation, and therefore determines thequiescent (idle) current in the driver and output stages. Completecircuit stability is assured by the positive temperature coefficientof the power MOSFETs.

The driver and output stages of the DH-500 are of the full com-plementary configuration. Q14, Ql5 and Q16 are N channelMOSFETs in parallel for the positive half of the signal, and Q17,Q18 and Q19 are P channel MOSFETs for the negative signal half.

There is none of the usual volt amp limiting in the DH-500. D7,D8, D9 and D10 prevent the gates of the MOSFETs from beingoverdriven in the event of abnormally high signal levels. The B +,B- and speaker fuses limit the maximum current in the outputs.The thermal protection, unlike most circuits, does not interruptthe output of the amplifier. If the heat sink temperature rises to7X, the amplifier is turned off until it cools.

The relay circuit has a 3 section low pass filter which preventssignals above 10 Hz from opening the relay. This circuit allowsDC to pass to IClOlA and IClOlB, which sense any offset above1.8 volts, opening the relay to protect the speakers. DlOl, RlO6and R107 form the reference for the positive offset detectorIClOlA. D102, R109 and RllO form the reference for the negativeoffset detector IClOlB. C104’s charging time is the time delay atturn on, and after any relay actuation.

FUNCTIONAL BLOCK DIAGRAM

AMPLIFIER CIRCUIT

INPUT

-zz

rmunlvtn

DIFFERENTIAL CLASS AB0

AMPLIFIERBIAS

REGULATOR93 Q4 = l r . Pig Q9

PASSIVE 4

FEEDBACK OUTPUTc . . a

INETWORK SIGNAL

IDIFFERENTlAL 4

AMPLIFIER ih

Q5vQ6 ’

L 1 I 1NEGATIVE 1

r 11 NEGATIVE 1

? PREDRIVER OUT PUTCURRENT

t ,, LQlO* Qll

L ! + D R I V E R

913 Q171Q11SOURCE Qlq

42 B -& .

R E L A Y C I R C U I T

a F I L T E R ], k , , + ~

I I NEGATIVE1 1 1 DELAY f

t II IRELAY

r 1I ISPEAKER

I O F F S E T 1 +0 ETECTOR T I M E R ’ + DRIVER r D R E L A Y

lC[B ICl D Ql, . l 15

All resistors are ‘1’4 watt 5% carbon film unless otherwise noted. part N,,.RlR2R3R4R5R6R7R8R9RIORI1RI2RI3RI4RI5R16RI7RI8RI9R20R21R22R23R24R25R26R27R28R29R30R31R32R33R34R35R36R37R38RIO1R102RI03R104RI05R106R107RI08RIO9Rl IOR l l lRI 12R113R114Rl15Rl16Rl17RI18RI19RI20R401R402R403R404R405R406R408R409R410R411R412DB401F40 1F402F403F404F405IC40 1LlPIP2T40 1T402RY40 1

470,000 ohms1,800 ohms

47,ooO ohms47,000 ohms

560 ohms560 ohms

47,000 ohms560 ohms560 ohms

1,800 ohms1,800 ohms

270 ohms47 ohms47 ohms47 ohms47 ohms

1,800 ohms1,800 ohms

270 ohms1,800 ohms

82 ohms560 ohms470 ohms

10 ohms33,000 ohms3,300 ohms, lw, metal film1,000 ohms, l/s w. metal film

150 ohms, % w, metal film1,800 ohms

82 ohms47 ohms, carbon camp.47 ohms, carbon camp.

220 ohms, ‘/z w2,200 ohms, l/z w

10 ohmsI ohm, 10 w

10 ohms, 5 w28,ooO ohms, % w, metal film

100,000 ohms120,000 ohms150,000 ohms150,000 ohms27,000 ohms, % w22,000 ohms

3,900 ohms3,900 ohms

22,000 ohms27,000 ohms, % w10 megohms4,700 ohms

10 megohms1 megohms

10,000 ohms100,000 ohms150,000 ohms

10 megohms22,000 ohms

1,500 ohms, 2 w, metal film470 ohms, % w

470 ohms, ‘1’2 w470 ohms, % w220 ohms, % w220 ohms, ‘/z w220 ohms, % w

1 megohms, % w300 ohms, 7 w300 ohms, 7 w600 ohms, 7 w600 ohms, 7 w

Diode BridgeFuse, 2A, 3AG (value optional)Fuse, IOA, GLHFuse, lOA, GLHFuse, 15A Slo-Blo MDAFuse, 7A Slo-Blo MDALM339NInductor, I .4uH1000 ohms trimpot1000 ohms trimpotPower TransformerPower Transformer, multi-voltageDPDT relay

RC044RC023RC043RC043RC045RC045RC043RC045RC045RC023RC023RC029RC039RC039RC039RC039.RCO23RC023RC029RC023RC053RC045RC04 1RC013RC036RZ013

RM02 IRM013RC023RCOS3RZOllRZOl IRDI 14RDl15RC013

RWO12RWO13RM053RC017RC019RC02 IRC02 1RD122RC026RC037RC037RC026RD122RC018RC042RC018RC047RC016RC017RC02 IRC018RC026RZ015RDI 17RD117RDl17RDl14RDl14RD114RDl13

RW015RW015RW024RW024QDI 17SF01 1SF013SF013SF014SF021

QBl15TAl12RPOllRPOl ITAl16TAl17sz113

All capacitors are 100 volt minimum unless otherwise noted

Clc2c3c 4c5C6c 7C8c 9Cl0Cl 1Cl2Cl3Cl4Cl5Cl6Cl7Cl8Cl9c20c21c22C23Cl01Cl02Cl03Cl04Cl05Cl06c401C402c403c404c405C406c407C408Dl-D8D9DlOD l lD12D13D14D15D16DlOlD102D103D104D105D106D107D108D40 1Ql

::

;:

2;Qf3

$0QllQ12413QlOlQ401440244034404Q405Q406s401TB40 1TB402TR40 1TS40 ITS402

2 mfd, 5OV, Film330 pF, Film.Ol mfd, Film.OOl mfd, Film.OOl mfd, Film1 mfd, Film.I mfd, Film470 mfd, 6.3V, non-polar Electrolytic150 pF, Film330 pF, Film.Ol mfd, Film100 mfd, IOOV, Electrolytic.Ol mfd, Film100 mfd, lOOV, Electrolytic.Ol mfd, Film.Ol mfd, Film150 pF, Film.Ol mfd, Film.Ol mfd, Film.l mfd, Film.l mfd, Film.l mfd, Film.OOl mfd, 25OV, Film.39 mfd, Film.39 mfd, Film.39 mfd, Film1 mfd, 25V, Non-polar Electrolytic22 mfd, lOOV, Electrolytic.Ol mfd, lOOOV, Disc680 pF, Mica.l mfd, Film.I mfd, Film20,000 mfd, lOOV, Electrolytic20,000 mfd, lOOV, Electrolytic.Ol mfd, IOOOV, Disc.39 mfd, Film.005 mfd, IOOOV, Disc1 N4 148 DiodeFDH400 DiodeFDH400 DiodelN4148 DiodelN5240B 1OV Zener DiodelN5240B 1OV Zener DiodelN4148 Diode1 N4003 Diode1 N4003 DiodelN5240B 1OV Zener DiodelN5240B 1OV Zener DiodelN4148 DiodelN4148 Diode1 N4003 DiodeI N4003 Diode1 N5240B 1 OV Zener DiodelN5240B 1OV Zener DiodeIN4003 Diode2N540 12N55502N55502N55502N540 12N540 12N540 12N5415NP2222A2N55502N34402N34402N54152N55502% 1762SKl762SKl762SJ562SJ562SJ56Power switchThermal breaker Thermal breakerInrush limiterThermal sensor Thermal sensorFan, I20 voltFan, 200-240 volt alternate

Part No.CPl15CPl34

CP136CP136CC125CC1 25CNI 13CPl33CPl34CC124CL122CC124CL122CC124CC124CPl33CC124CC124CC125CC125CC125CP136CEl17CEl17CEI 17CNl14CL125cz112

CM121CC125CC125CL123CL123cz112 0C E l 1 7 0cz113 3:Q D 1 1 6 3Q D l 2 1 pQDl21Q D l 1 6 2Q D l l l 4Q D l l l <QD116 >

QD115 EQDll5Q D l l l gQ D l l lQDi 16QD116QDl15QDl15Q D l l lQ D l l lQDll5QP122QN128QN128QNl28QP122QP122QP122QP123QN124QN128QN125QN125QP123QN128QNl13QNll3QNI 13QPI 13QPI 13QPl13SLI I1SF024SF024RZ016SF025SF025

AAI i3AA128

CC124

AC LINE CONNECTIONS FOR OVERSEAS USEThe power transformer supplied in DH-500 amplifiers sold in multi-voltage transformer is installed. This, the 600 o h m

the USA is intended for 120 volt, 60 Hz operation only. For use resistors, the mounting hardware, and the alternate line fuse arein other countries, a multi-voltage transformer is supplied in supplied in kits which include this transformer.Export versions, available at higher cost. It has dual tapped The diagrams below show pictorially and schematically theprimary windings which can be connected in series or parallel alternative wiring. Only the pertinent wire connections arecombinations for 100, 120, 200, 220 or 240 volt, 50 or 60 Hz shown. There are other wires connected to the 7-lug terminalpower sources. The connections which are different from the strip which are unchanged. If the amplifier is to be operated withstandard 120 volt connections described in the kit assembly line voltages between 200 and 240 volts, a different fan, partinstructions are all related to the transformer lead terminations, #AA128, is required, the 600 ohm resistors must replace theand to the large resistors on the 7-lug terminal strip. An 300 ohm values, and the 7 ampere slo-blo fuse must replace theadditional 3-lug terminal strip is required when the 15 ampere line fuse.

100v.

240V.

fW

ii.31402

BRfR

BR

BKfW

BKfR

K

TR4Ol

I ,415 7

TO PWR SW

240 V

18

KIT PARTS LIST SMALL PARTS ENVELOPEMinor variations may sometimes be encountered in value or appear-ance. These will not affect performance. Some of the hardware listedhere has been used to secure parts for shipping the kit.

211

Bracket, L-shape, 2”Bracket, L-shape, 3”Capacitor, 0.005 mfd DiscCapacitor, 0.01 mfd DiscCapacitor, 0.39 mfd FilmDiode, IN4003Inrush LimiterResistor, 1 megohm, MwattResistor, 300 ohm, 7 wattSpade lug terminal

1Part No. 1

Chassis MS127 1Cover MS126 1Front plate (rack mount) MS161 1Front panel (inside) MS128HandleAmplifier module with fan #AA1l 13

822942228842914223

Power transformerAC line cord with plug, 16 Ga.Bracket, capacitor, roundCapacitor, 20,000 mfd, 100 voltCircuit board, PC-9C, assembledLabel, serial numberRelay, enclosedManualWarranty cardWire, white #18Wire, green #18Wire, Yellow #18Wire, Black #22Wire, Red #22

HARDWARE ENVELOPE

Lug, ground, internal tooth, #6Lug, plain connecting, #lONut, #4-40 KEPNut, #6-32 KEPNut, #l0-32 KEPNut, 1/2"Screw, machine, #4-40 x 5/16”Screw, machine, #6-32 x 1/2"Screw, machine, #l0-32 x M”Screw, SEMS, #l0-32 x 1/4"Screw, sheet metal, #6 x 3/8"Screw, machine, #6-32 x 3/4"Washer, flat, #lO x 7/8"Washer, internal tooth, 1/2"Washer, rubber, M”Wire ties, nylon, 4”

TA116WA016HZ124CL123AC009LR015sz113 UH- )2U

Part No.HZ115HZ1 16HKlllHK112HK113HK118HA1 13HA116HA119HA118HP1 17HA1 15HW114HW116HR117HR138

PC-%

Part No.MS153MS154CZ113cz112CE117QDll5RZ016RD113RWOl5xzo14

141222112

2

1

LARGE PARTS ENVELOPEDiode block, silicon rectifierFoot, rubberFuse clip, singleFuse clip, dualFuse holder, round, panel mountInput socketPower switchStrain relief, plasticTerminal post, black, completew/black washer and 2 nutsTerminal post, red, completew/red washer and 2 nutsTerminal Strip, 7 lug

QD117HR146XA012XA014XA013XPO14SLlllHR144

XK013

XK014XK019

FUSE ENVELOPE2 ampere5 ampere10 ampere15 ampere, slo-blo

SF011SF012SF013SF014

For Alternate Multi-Voltage Transformer Only1 Power Tmnsformer TA1171 Terminal strip, 3 lug XK0171 Screw, machine, #4-40 x 5/16" HA1 131 Nut, #4-40 KEP HKlll1 Fuse, 7 ampere, slo-blo SF0212 Resistor, 600 ohm, 7 watt RW024

* For use with 200-240 volts AC, a different fan, part #AA128,must be fitted to the amplifier module.

HZ167AH324*

3

DH-502 INSTALLATION INSTRUCTIONS1. 3

2. 3

3. cl

4. El

5.

6. 0

7.

8. c!

9.3

Disconnect AC power from the DH-500 and remove all connect-ing cables.Remove the 17 screws which secure the cover along the top front,sides and rear. Set cover aside. DO NOT GRAB THE AMPLI-FIER PANEL OR HANDLES WHEN THE COVER IS RE-MOVED. You might bend the chassis.Turn the amplifier over, or stand it on the nansformer end.Loosen, but do not remove the two front screws which secure theamplifier module near the front (center) of the chassis. Removethe two screws at the rear which secure the module. Return theamplifier t o its upright position.Prepare one each red and green wires each 16” long. Twist themtogether throughout their length.Select the PC-7A circuit board. Note that the eyelets arcnumberedon the circuit side of the board, with eyelet #l to the left when therow of eyelets is nearest you, and the board is upside down tomake soldering easier. Connect the wires from the componentsside of he board, and be sure each is securely soldered to thecircuitry.Connect the red wire of the twisted pair to eyelet # 1 of PC-7A. (S)Connect the green wire to eyelet #3. (S)Prepare a 3-l/2” green wire and a 4” red wire. With one pair ofends even, twist these together. At the uneven ends, connect thegreen wire to cyelet #4 of PC-7A. (S). Place the pair off towardeyelet #l, and connect the red wire to eyelet #6. (S)Prepare a 5” red wire and a 6” green wire. Twist these togetherwith one pair of ends even. At the even ends connect the red wireto eyelet #2. (S) Connect the green wire to eyelet #5. (S)Unsolder the twistcd pair of leads from eyelets 1 and2 of the rightamplifier module at the center rear of the amplifier. This pair ofleads which connects to the right input socket, will no longer beused while the amplifier is funtioning monophonically. Theseleads must be taped securely so that there is no possibility for thebare wire to contact any portion of the circuit. Masking tape issufficient, but electrical tape is preferred. These leads may beremoved if desired.

COMPONENT SIDE PC-‘IA

c Rl’ 0 6 0 5

v A c R2-0c RID-a c c2-

cR12-0 - R13-

.-- Rll- A - R5--rv

- R3-

c R6-0 0 4 0 2c R9+

- R7-

it-Cl_

)- R6+ i+c4-+ R15 A D--R& Rlv

*C3+

1 0 3 J 01

- R17- - R16--,

. .6 : 1 ; : 1

10. Remove the rear rop screw securing the right channel amplifiercircuit board to the hear sink just above where the twisted pair wasdisconnected. Do nor lose the fiber spacing washer which isbetween the circuit board and the heat sink. This washer is notused on later production DH-500s. Select one of the screws fromthe bridging kit, and the mounting bracket. The bracket i sanchored at this location, flat surface up, with the screw insertedfust through the single tab from inside the bracket. then throughthe circuit board. the fiber spacing washer, (optional) and into theheat sink.

11. Select the two screws and nuts and the circuit board PC-7A. Withthe components facing out, secure the board t o the outer surfaceof the bracket tabs.

12.0 Select the short twisted pair of wires connected t o eyelets 4 and6. Connect the red wire t o the upper eyelet #l of the right circuitboard at the center rear. (S) Connect the green wire t o the lowereyelet #2. (S)

13. Place t h e long pair of wires from eyelets 1 and 3 down betweenthe amplifier module mounting bracket and the back of thechassis. The module can be tilted forward t o facilitate this.Connect the red wire t o the lower ey elet #l on the left circuitboard. (S) The easiest way is to wrap it in a tight loop around t h ebare stub of the wire presently connected to this eyelet. Be sureboth wires are soldered securely t o he board. Connect the greenwire t o the upper eyelet #2 in the same fashion. (S)

14.0 Making sure that no wires are trapped by the mounting bracket,reinstall the. two screws securing the rear of the module t o thechassis. Tighten all 4 screws.

15.0 Connect the red wire of the remaining twisted pair from PC-7Ato eyelet #6 of the PC-9 circuit board behind the power trans-former, (S)This wire may be connecred t o the stub of the existingwire as before. Connect the green wire to eyelet #4 of PC-9. (S)Eyelei #I of PC-9 is nearest the edge of the chassis.

16.0 Reinstall the amplifier cover.

RlR2R3R4R5R6R7R8R9RlORllR12R13R14R15R16R17

PC-7A PARTS22.1K, l%, metal film2.2K. 1/4w, 5% carbon film2.2K, 1/4w, 5% carbon film47 ohms, 1/4w. 5% carbon film47 ohms, 1/4w. 5% carbon film8.2K, 1/4w, 5%, carbon film8.2K, 1/4w, 5 % , carbon film47 ohms, 1/4w, 5% carbon film47 ohms, 1/4w, 5% carbon film2.2K, 1/4w, 5% carbon film2.2K, 1/4w, 5% carbon film22.1K, l%, metal filmIO0 ohms, 1/4w, 5% carbon film100 ohms, 1/4w, 5% carbon film47 ohms, 1/4w, 5% carbon film3.3K, lw, 5% metal film3.3K, lw, 5%. metal film

RMP/4-2212RC/4-222RC/4 -222RC/4-470RC/4-470RC/2-822RC/2-822RC/4-770RC/4-770RC/4-222RC/4-222RMP/4-2212RC/4-101RC/4-101RC/4-770RM l-332RMl-332

Cl 1 OmF, 16V. non-polarized CERNP-106c 2 6.8pF. 1 00V, dipped mica CM -068c3 22mF. 25V, electrolyte CER-226AAc4 22mF. 25V, electrolyte CER-226AA

Ql BC55OC NPN nansistor SSH-650Q2 BC55OC NPN transistor SSH-650Q3 BC56OC PNP transistor SSH-65 1Q4 BC56OC PNP transistor SSH-65 1Q5 MPSA63 PNP transistor SSH-695

Q6 MPSA13 NPN transistor SSH-645

LIST

INSTRUCTIONS FORTHE HAFLER DH-502 AMPLIFIER BRIDGING KIT

FOR THE DH-500

The DH-502 Amplifier Bridging Kit for the DH-500 consistsof a PC-7A circuit board comprising a 6 transistor phase invertingamplifler, a mounting bracket, necessary hardwareandconnectingwire. Installation may take about an hour. All changes to theamplifier wiring are performed on the right channel - the sidenearest the power switch. Only the left channel input will be utilizedafter conversion so an additional pair of input wires will beconnected to that jack to enabie it to feed the complete amplifier.

When converted to monophonic operation, the loudspeakerload is t o be connected to the t w o centerred (+) outputs only. Theright (+) will act as the common and should be attached to thespeaker (-)_ This is what is known as a floating output, for noconnection is made to either black ground terminal. It is sug-gested that once the amplifier has been converted, some clear

indication be made as to the appropriate connections, and that beattched to the back panel. Because of this floating output, neitherside of the output signal may be grounded; such as thru a speakerswitching box or head phone adapter that has a common groundbetween the left and right channels.

For equivalent load impedances, the speaker fuses provide thesame power output protection as in stereo operation, but becauseof individual fuse variations, only one fuse may blow at theselevels. It is best to replace both fuses if one blows, as the othermay have been weakened.

These installation instructions designate connections in ac-cordance with the DH-500 owner’s manual and pictorial diagram,and use the same terminology (i.e. “S” indicates a soldcrcdconnection),

KIT PARTS LIST1 PC-7 Board WP-PC71 M ounting bracket SM-BRT202*2 Screw, Machine, 4-40 x 5/16” HWH-1452 Nut. 4-40 KEP HWH-1051 Wire Red #20 GA 3.0’I Wire, Green #20 GA 3.0’1 Warranty Card LIT-WAR

T O ORIYER CAR0

B-

LIMITED WARRANTYThe parts in the DH-502 are warranteed for a full year from the purchasedateincluding parts and labor. If a defective componcnr is found on a circuit boardor in the kit, simply return the individual part, or if the problem is unknown, retumthedefcctive board to the factory, prepaid, together with the serial numberand a copy of the dated bill of sale, and it wil be repaired or replaced at no charge. This warranty is limited to repair or replacement of the DH-502 bridgingmodule only. Hafler is not responsible for consequential damages. This warranty gives you specific legal rights. You may also have other rights whichvary from state lo state.

This warranty is void if acid core solder or paste flux has been used.

A Division Of Rockford Corporation613 S. Rockford Drive, Tempe, Arizona 85281 l (602) 967-3565

The DH-500 Power Amplifier has been carefully en-gineered to provide many years of use without requiringany maintenance or servicing.

Factory assembled units are subjected to many physicaland electrical tests before shipment. The amplifier moduleassemblies of kit units are similarly tested to meet perfor-mance specifications prior to packing. In spite of this,shipping damage does occur, a kit may not be assembledproperly, or human error interferes, so service may beneeded. The David Hafler Company provides completeservice facilities at the factory to make any necessary re-pairs. Because many of the components in this refined de-sign are not readily available through local sources, andthe performance of the unit is likely to be compromisedwith “similar type” substitutions, we strongly recommendfactory service, or obtaining the requisite parts from thefactory.

It is the owner’s responsibility to return or ship the unitfreight prepaid to the factory service department. Unitsshipped freight collect will not be accepted. For units to berepaired under warranty, a copy of the dated bill of salemust accompany the unit.

Use the complete original carton and all packing mate-rial to ship your amplifier. Enclose with the unit the follow-ing information:

1.

2.3.

4.

5.

Complete shipping address (Post Office box numbersare not acceptable, except for correspondence).The serial number, if it is not on the unit.Copy of dated bill of sale if repairs are to be made underwarranty.Description of the malfunction. If intermittent, be sureto so indicate.You may also wish to attach your address directly to theunit, or to the line cord.

All service work is guaranteed for 90 days.

Warranties apply to the original purchaser only. Thewarranty is void if the amplifier has been modified withoutfactory authorization; or if parts have been substitutedwhich, in the factory’s judgment, are not suitable; or if theamplifier has been either physically or electrically abused,or used for some purpose for which it was not designed orintended.

The warranty on the transformer is void if the leads havebeen cut too short for re-use. If you think the transformeris defective, unsolder, do not cut the leads for its return.

Technical assistance to help you locate the source of aproblem may be obtained by calling the Technical ServicesDepartment at 609-662-6084, 8am-4:30 pm E.T. It is help-ful to know the serial number of the unit, and the results ofany tests you have performed. However, we do not rec-ommend that you attempt your own servicing unless youare knowledgeable in this regard.

The weight of a DH-500 (unless it includes the specialmulti-voltage power transformer), when packed exactly asit came from the factory, should be just under 50 pounds,and may be shipped by UPS. However, be certain it is fullyprotected, and insure it for the full value.

If you choose, it is possible to return only a portion ofthe amplifier for factory service, with some disassemblyon your part. This assumes that you are certain the prob-lem lies only in the returned portion, and that you assumefull responsibility for reinstalling it correctly, since a ser-vice warranty cannot be extended for other than the actualportion serviced. Because the transformer is so heavy, anda problem there is most unlikely, its removal by unsolder-ing a few leads is a logical choice. The balance of theamplifier should be insured for at least $700. It is also pos-sible to unsolder the module, and return it, if that is wherethe only problem lies. However, it requires much morecare in packing, to protect the delicate components on thecircuit boards, and many more connections must be unsol-dered, so there is more risk for reinstallation error. Itshould be insured for $400. The service fee for the moduleis $50. If you return an amplifier for service or checkout,and it is functioning correctly, a charge will be made for thetesting time required, as well as for packing and shipping.

WARRANTY FOR KIT-BUILT UNITSThe parts in a DH-500 kit are warranted for a full year

from the purchase date. If a defective component is foundon a circuit board or in a kit, simply return the individualpart to the factory prepaid together with the serial numberand the date of purchase, and it will be replaced at nocharge.

If you cannot locate what is wrong with your DH-500,return it to the factory along with a copy of the dated bill ofsale, and a check for $75. If the cause of the problem is adefective part, the unit will be repaired and returned to youtransportatiion prepaid, and your $75 less the shippingcharges will be returned to you. If the problem is found tobe an error in your assembly of the amplifier, the amplifierwill be put in proper working order, tested to be sure it ismeeting specifications, and returned to you (freightprepaid within the continental U.S.). Excess shippingcharges for expedited service, or overseas delivery areyour responsibility. At the sole discretion of the factoryservice department, if the time required for diagnosis,repair and testing, and the nature of the malfunctionwarrants it, a portion of the submitted repair fee may berebated.

This warranty is void if the kit has not been completelyassembled or if other than rosin core solder has been used.Units assembled with acid core solder or paste flux will bereturned unserviced.

WARRANTY FOR FACTORY ASSEMBLED UNITSThe DH-500 is warranted for three years from the

purchase date including parts and labor and normal ship-ping costs from the factory to the owner within the conti-nental U.S. The owner is responsible for returning the unitto the factory and must submit a copy of the dated bill ofsale.

This warranty gives you specific legal rights. You mayalso have other rights which vary from state to state.

20