Hafler Stereo Amplifier DH 500 User Manual

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

Please refer to this serial

number in all communications

regarding this equipment.

$3.00

THE DAVID HAFLER COMPANY

5910 Crescent Boulevard, Pennsauken, New Jersey 08109

DH-500

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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:

kHz-0.002%; 10 kHz-0.007%

Frequency Response into 8 ohms: -3 dB, 0.5 Hz to 120 kHz at 1 watt

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

Rise Time: 10 kHz, 80 volts p/p square wave, 10% to 90%: 2.5 us.

Slew Rate: kHz, 120 volts p/p square wave: 45 V/us.

kHz into 8 ohms; 60 to 10 kHz into 8 ohms

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.

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INTRODUCTION

The Hafler DH-500 is a two channel audio power

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

ient overload.

amplifier designed to the very highest performance stan-

dards. 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 impe-

dances 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 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 re-

lated 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 re-

markable 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 over-

sized power transformer, the conservative operating levels

of the MOSFETs, the computer-grade electrolytics total-

ling 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!

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 con-

ditions at such high powers. This is one of the direct ben-

efits of the power MOSFET’s ability to current limit under

abnormal 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 get

even hotter, the MOSFET self-corrects to reduce the cur-

rent, 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 com-

plex protective circuits.

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 ele-

ments. You can look forward to just a few hours of con-

struction fun, to hear the finest audio amplifier yet pro-

duced.

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 re-

quired less compensation to stabilize the circuit, with the

result that it was faster overall. With the built in bandwidth

CONTENTS

installation

Operation

Connections

.........................

...............................

.Page 4

Schematic Diagram

Component Values

.....................

......................17

AC Line Connectionsfor Overseas Use

... .I8

.16

............................

....................

Kit Parts List

.............................I9

Assembly Instructions

If Problems Arise

.......................

Service and Warranty

...................

.20

.I4

......................

Pictorial Diagram

Circuit Description

.I5

....................

.Insert

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INSTALLATION

The DH-500 may be installed out of sight in many appli-

A power transformer of this size puts out a noticeable

hum field, even though the special design of this trans-

former 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 re-

quire more separation from the amplifier. Check at a rela-

tively high volume setting, while swinging the tone arm

throughout its arc. A few inches additional space will usu-

ally solve any problem.

cations, 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 cur-

rent, so you should make sure your preamplifier has the

switching capacity for the amplifier’s needs, as well as any

other equipment which it also switches. inadequate switch

current capacity may eventually render the switch in-

operative

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 DH-

500. 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 sub-

stantial additional current for other equipment, or if your

control unit does not have the 15 ampere switching capac-

ity, 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 pos-

sible loudspeaker damage from turn-on transients gener-

ated by source equipment.

Ventilation is most important! Unobstructed air circula-

tion 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 instal-

led w h e n the unit is supported by the front panel

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.

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 osciIla-

tion). 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 con-

sumption is likely around 250 watts. The unit’s efficiency

is about 5O%, so some full power tests may exceed the ca-

pacity of a 15 amp circuit. When performing tests, voltage

losses due to long lines should be taken into consideration,

or compensated for.

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 longer

delay to avoid their internally generated turn-on pulses.

Information on extending this turn-on delay is available

from the company on request.

Loudspeaker Fuse Selection

A standard 2-wire power cord was chosen in preference

to 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, a

ground lug may be attached to the chassis adjacent to the

AC line fuse holder.

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 can-

not 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 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.

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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.

appropriate size for your speakers.

Loudspeaker Power Ratings

There are no U.S. standards for rating the power han-

dling capabilities of loudspeakers. As a result the manufac-

turers’ usual “ music power” ratings, or suggested

amplifier limits, are of only minimal help in determining

safe operating levels with amplifiers which can deliver

enormous amounts of power. On the other hand, some

speakers, particularly tweeters, can also be damaged

through the use of too small an amplifier if it is driven into

sustained 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), so

you may wish to separately protect the tweeters with fuses

of lower rating. You must take into consideration the type

of music, and the levels you like, to provide long term

trouble-free operation of your speaker choice, when you

have a very powerful amplifier like the DH-500.

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 SUBSTAN-

TIALLY MORE POWER THAN MOST SPEAKERS

CAN SAFELY TOLERATE. Therefore the Hafler Com-

pany cannot assume any responsibility for damage to the

load (loudspeaker) because the choice o f fuse six is in

If more than one pair of speakers will be connected to

the amplifier, proper protection would dictate that each

speaker be separately fused, since when they are operated

in parallel, the combination of lower impedance and the

higher power handling capacity would suggest a much

larger fuse at the amplifier than would provide individual

protection.

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

amps passes 50 watts; 3 amps, 72 watts; 5 amps, 200 watts.

We have included a pair of 5 amp fuses as alternates, for

temporary use as spares; for testing the amplifier at very

high power levels; and for operation into very low load im-

pedances, 5 amps will pass 80 watts into a 4 ohm load. We

suggest that you obtain additional type 3AG fuses of the

If full power tests are to be performed, particularly at

low load impedances, fuse ratings above 10 amps may be

required for the duration of the test.

CONNECTIONS

For professional applications the phono inputjacks may

be easily replaced with l/4” phone jacks. Be sure, in that

case, that they are grounded to the adjacent ground lug.

The 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.

Output

If your line voltage is other than that provided in the

United States, be sure you have the alternate multi-voltage

power transformer, and be sure it is wired for your mains

voltage before you plug in the amplifier. The connections

for other line voltages will be found in the back of this

manual.

The 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 you

can connect stranded wire through the vertical hole in the

shaft which is visible when the cap is unscrewed. To be cer-

tain that no strands of wire are unsecured, a tinned end, or

a spade lug soldered to the wire is recommended.

Input

Standard phono jacks are installed to accept conven-

tional shielded cables, such as those supplied with your

preamplifier. Be sure that the outer shield connection is

secure, to avoid hum. The length of these cables (so as to

permit remote location of the amplifier, if desired) is lim-

ited only by the output impedance of the preamplifier. If it

is 1000 ohms or less, as with Hafler preamplifiers, cable

lengths of up to 100 feet are permissible without loss of per-

formance. Special low capacitance cables enable even

greater distance between preamp and power amplifier. It is

desirable to keep the left and right input cables close to-

gether throughout their length to minimize the likelihood

of hum pickup. They should cross AC cords at right

Be sure to maintain correct speaker phasing by watching

the 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. If

the speakers are out of phase, you will find that the sonic

image has a “hole in the middle”, and there will be a loss of

bass. 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 high

damping factor of the DH-500, Standard 18 gauge lamp

cord is the minimum suggested, and is suitable for short

distances. The next larger wire is #16. There are also a

angles

never running parallel to AC lines at close range.

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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.

It is important that the red terminals never be connected

together when operating in stereo. Thus it is important that

you carefully observe the proper connections when using a

common ground device, to be sure there is no reversal.

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, to

utilize headphone junction boxes, or other accessories

employing a common ground system.

In the special case where the amplifier has been inter-

nally modified to convert it to monophonic bridged opera-

DH-502

tion, with the addition of the DH-502, then only one input

jack is connected, and the output is taken only from the

two red terminals. Such a “floating” connection must be

maintained, with no connection to the black terminals.

ASSEMBLY INSTRUCTIONS

There are three basic rules for success in electronic kit

building:

4. A wire stripping tool for removing insulation. This can

be a single-edge razor blade, but inexpensive stripping

tools are safer, faster and easier.

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

der.

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

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

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

8. Diagonal or side-cutting small pliers.

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

2. Make secure solder connections which are bright and

smooth.

3. Check your work carefully after each step.

The DH-500 amplifier is a versatile component with

sophisticated circuitry which has been made remarkably

easy to build by individuals with many years ofexperience

in the design and engineering of the finest performing

audio kits, and in the preparation of their manuals.

10. A 1/4" “Spin-tite” nut driver may be helpful, but is not

necessary.

A soldering “gun” is not recommended. The unfamiliar

user is more likely to damage the etched circuit boards

with 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 solder

connections are more likely. Pencil irons are much lighter

and easier to use, and there is no waiting time when solder

connections follow in sequence, as in kit building. Make

sure you have a holder for it, though, and always unplug it

when you take a break.

Kit building should be fun, and we are certain you will

find this to be so. Assembly will be faster, easier, and more

enjoyable if you have someone help you by reading the

steps aloud, selecting the required parts, and preparing the

necessary wire lengths in advance as you proceed. Fatigue

increases the risk of error, so take a break rather than push

to early completion. There are relatively few separate

components in this design, to make it easy to pack every-

thing away, if need be.

Your work area should have good lighting, the proper

tools, and a place where the large pictorial diagram can be

tacked to the wall within easy reach for checking. The

tools 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 in

position while heat and solder is applied.

40 to 60 watt pencil soldering iron with a 306” or

2. Heat thejunction of the wire and lug, or eyelet, with the

smaller tip which reaches 700°F.

bright, shiny tip of the iron.

2. 60/40 (60% tin) ROSIN CORE solder

or smaller.

l/16” diameter

3. After heating for a couple seconds, apply solder to the

iunction. It should melt immediately and flow smoothly

around both surfaces.

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

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4. Allow the connection to cool undisturbed.

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 the

iron. When properly done, the wire is uniformly bright,

and no larger than before. The hookup wire supplied with

this kit does not normally need tinning, for it is pre-tinned.

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 in

place, but some prefer to just place it through the hole and

rely on the stiffness of the wire to hold it while soldering.

Eyelet connections, of course, are handled this way.

Wiring the Kit

Good solder connections are essential for trouble-free,

noise-free operation. A good solder joint does not require

much solder around the conductors. Never “butter” par-

tially melted solder on the joint, as it is useless. A good

connection looks smooth and bright because the solder

flows 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 be

used frequently to wipe the tip, and occasionally you must

add a small amount of solder to the tip, too. If a connection

is difficult to heat, “wet” the tip with a small blob of solder

to provide a bigger contact surface to the joint. Once the

solder flows around the conductors, any movement must

be avoided for a few seconds to allow a good bond. When

cool, check the connection by wiggling the wire. If in

doubt, 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 is

then wiped on the sponge.

If any components are unfamiliar to you, checking the

pictorial diagram should quickly identify them. Or, the

quantities, and the process of elimination as you check the

parts list, will help. The pictorial diagram is necessarily

distorted to some extent for clarity, so that you can trace

every wire in a single overall view for verification as you

work. You may wish to check off on the diagram as you

solder each location.

To “prepare” a wire means to cut the designated length

from the coil of that color, and strip about l/4” of insulation

from each end. The wire supplied in the kit is #18 and #22,

so you can set adjustable wire-strippers accordingly. The

transformer leads are #18, and the line cord is #16. Be

careful that you do not nick the wire when you strip it (that

can happen more easily if you do not use wire strippers) for

that weakens it. The wire supplied in this kit is “bonded

stranded,” which provides exceptional flexibility with re-

sistance to breakage for easier use.

ALL SOLDER USED MUST BE ROSIN CORE

Whenever a connection is to be soldered, the instruc-

tions will so state, or indicate by the symbol (S). If more

than one wire is to be soldered to the same point, they will

be indicated by (S-2), (S-4), etc. If soldering is not called

for, 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, it

is best to clip off any excess lead length to minimize the

possibility of a short circuit (as on switch lugs, where ter-

minals are very close together), and for neatness.

Never use acid core solder or any separate flux in elec-

tronic work. Silver solder is also not suitable. If in doubt

about unmarked solder, always obtain a fresh supply of

rosin core solder. We recommend 60/40 for easiest use. Do

not confuse it with 40160, which is harder to melt.

The general procedure is to use a hot iron for a short time

to heat a connection, then add solder with the iron still in

contact. Remove the solder once it flows, and then remove

the iron. A cooler iron applied for a longer time is more

likely to damage components, or lift the copper circuit pat-

tern from the boards. A break in the etched circuit can be

mended by simply soldering a small piece of wire across it.

nnot

touch adjacent

Be sure that uninsulated wires ca

terminals or the chassis metalwork.

not allow much build-up of solder on the tip of the iron,

The symbol (#) indicates a connection is to be made to

that point. When a lug number is specified without (#), it is

simply a locating reference.

or it may fall into adjacent circuitry.

When soldering to an eyelet or hole on the board, insert

the wire from the components side, and apply the iron to

the bottom, leaving some bare wire exposed so that you

can see that the eyelet is then filled with solder for a secure

bond. A round wooden toothpick is suggested so that you

can heat and clear an eyelet of solder if it hinders your in-

serting the wire. Some builders prefer to clear every eyelet

first with a touch of the iron and toothpick. Others connect

the lead by bringing it up to the center of the eyelet on top

of the board, applying the iron from the bottom of the

board, and pushing the lead in as the solder in the eyelet

melts. If the wire has first been “tinned,” usually no addi-

tional solder is necessary, but it is a good practice to push

the wire through, and then back it up a bit, to be sure solder

fills the eyelet. On the bottom of the board, make certain a

bright, shiny flow is evident from the wire onto the circuit

pattern on the board.

When the instructions call for twisting two or three

wires together, the length of wire indicated anticipates a

fairly tight, uniform twist by hand, of three full turns every

two inches. If you find the wires too short, loosening the

twist will gain some needed length.

Handle the circuit boards carefully. They represent a

major part of the kit cost. Stand-up components, such as

transistors, should be checked when you install the mod-

ule, to be sure all leads are separated, and that the large

electrolytic capacitors have not broken loose from the

board.

Take the time to be accurate and neat, and you can be

sure that your completed amplifier will meet the per-

formance of a factory assembled unit, and can continue to

perform properly for years to come. Check your work, and

make sure the entire step has been completed before plac-

ing a check mark in the space provided, and continuing on

to the next step.

"Tinning”

refers to the process of applying a light coat-

ing of solde r to the bared wire end. This k eeps all the

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Select the two input sockets and 4 sets of hardware.

Install the sockets at LS and RS inside the chassis

so that the short lug is nearest the hole in the chas-

sis between the two sockets.

MECHANICAL ASSEMBLY

For security in shipping, the power transformer

and the amplifier module have been fastened to the

chassis. Remove the chassis cover, the inner front

panel and the larger front plate, and set these aside.

Be particularly careful in handling the amplifier

module. to see that the leads of the upright compo-

nents on the circuit boards are not stressed. This

module accounts for more than half the kit cost,

and has already been thoroughly tested for

specified performance before it was packed.

Select the single ground lug (with lockwasher

teeth) and one set of hardware. Install it between

the input sockets. Point it toward the bottom, and

bend it out for access. Be certain this lug is tight.

The locking teeth must cut through the chassis

paint for a good ground connection.

Turn the chassis upside down, and rest it on the

module and transformer to remove these parts. In-

clude all of the hardware you have removed with

the rest when you check off the components

against the parts list in the back of this manual. We

recommend 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 pictorial

diagram. Although the perspective of the diagram

has sometimes been distorted to show connections

more clearly, it should enable you to recognize any

unfamiliar component. An egg carton is ideal for

keeping small items like hardware at hand.

Select the two round fuse holders with caps, and

their l/2” hardware: rubber washers, metal

lockwashers, and nuts. First install the rubber

washer on each holder, so it will be outside the

chassis, and then fasten them at locations LF and

RE The holes have flats which mate with the fuse

holder to keep it from turning. Point the tip lugs to-

wards each other. Be sure all of this hardware is

tight, as it will not be accessible once the amplifier

is completed.

Select the two red output terminals and their

hardware: the red washers, 4 nuts without

lockwashers, and two plain connecting lugs. Note

that each part of the terminal has a flat which mates

with the flat top of the chassis hole. Install the ter-

minals in the two center holes LR and RR so that

the washer flat is engaged, tighten one nut securely,

add the lug pointing up, and tighten the second nut.

It will simplify matters if you first separate the #4 nuts

from the #6 nuts, which have the same outside dimen-

sions. A #4 screw will pass through a #6 nut, aiding iden-

tification.

“set” of hardware includes one screw and one KEP nut

(with its attached lockwasher). Always install the

lockwasher side of the nut first. If the size of the hardware

Select the two black output terminals, their hard-

ware, and two plain connecting lugs. Install them at

LB and RB as in the previous step.

is not specified, use the

size, which is the smallest. #10

is the largest. Always insert the screw from the outside of

the chassis.

With the chassis upside down, select the 4 rubber

feet and 4 sheet metal screws. The screw head re-

cesses fully into the foot. Install these in the holes

which are about I” in from each corner.

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. Twist

the bare strands tightly, and tin each lead. 13” from

the ends make a sharp “V” in the cord by bending it

sharply back on itself. Install the strain relief as

shown, with the small end of the strain relief

nearest the stripped end of the line cord. Crimp the

two halves of the strain relief around the wire at the

V with heavy pliers, to partially form it before in-

sertion into the back panel. Considerable squeez-

ing is necessary, because the thick insulation “pops

back” quickly. Then grip the larger diameter of the

strain relief with the tips of heavy pliers, squeeze it

tightly, and insert the end of the cord through the

back panel AC hole from the outside. Note that the

hole has two flat sides, and the relief is shaped ac-

cordingly. This is a very tight fit-you will have to

pull on the cord to help-but it snaps into position

when fully inserted.

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Select the plastic encased relay, the longer

L-shaped mounting bracket, and 2 sets of hard-

ware. Insert the screws through the bracket with

the bracket foot pointing away from the lugs at the

opposite end of the relay. ‘lighten this hardware se-

curely, but do not risk breaking the plastic.

Select the two 2 amp fuses and install them in the

round fuse holdders on the back of the chassis. This

will keep the caps from being loosened and lost.

This completes the basic mechanical assembly of the

chassis. Set it aside for the present.

Select 2 sets of hardware and mount the relay near the 2

red terminals, with the bracket facing front. Install the

screws from below the chassis.

Select the large front plate, the smaller front panel

with the edges turned back, the two handles, and

four #lO screws. With the power switch cutouts

aligned, place the screws through the panel from

the rear, through the front plate, and secure the

handles. Set this assembly aside.

Select the 2 shorter L brackets, 4 sets of hardware,

and the circuit board

C-9-9. Mount the brackets on

the circuit side of the board, with the feet pointing

away from the board.

Select the amplifier module. Handle it with care!

The fan is mounted on the front of the module, with

a foam gasket on the rear. On the bottom, two

thermal sensors for the fan, and two safety thermal

breakers are already mounted on the heat sinks.

With the module upside down, and the fan away

from you (to keep the left channel on the left, for

consistency) cut the right fan lead to 5-3/4”, strip it

l/4”, and connect it to TS2 lug #6.

Select 2 sets of hardware and install the circuit

board between the line cord and terminal RB, with

the components facing to the rear.

Select the 7-lug terminal strip and 2 sets of

hardware. Install it at the two inner holes in front of

PC-9. The hole near the right chassis edge is not

used. The mounting feet face forward.

Cut the left fan lead to 4”, strip it l/4”, and connect it

to TBl lug #l.

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 the

clip from turning too far.

A soldering iron will be used regularly from now on. Be

sure you wipe its tip frequently with a damp cloth or

sponge, as a bright tip will make connections easier with

less likelihood of overheating components. If it is difficult

to heat a connection in a couple of seconds, apply a small

amount of fresh solder to the tip so it can flow around the

connection and provide good heat transfer.

Select the 2 dual fuse clips and 4 sets of hardware.

Install one of these in the pair of holes nearest the

center of the chassis, and the other in the pair of

holes aligned with it near the left edge.

Select the 3/4” long #6 screw and a nut, and the rec-

tifier diode block which has four lugs. Install the

rectifier DB in the front center hole nearest the fuse

holders. Note the lug positioning in the diagram,

and check the marked location of the + lug.

Select the two round capacitor brackets, the two

large capacitors, and 8 sets of #6 hardware. Place a

bracket around the bottom of each capacitor and

fasten it with one set of hardware through each

clamp. Note the direction of insertion of the screw

for easy servicing access in the future. The clamp

should be snug, but not tight. Place each assembly

so the clamping screws are accessible from the

front at locations CL and CR, and secure each with

3 sets of hardware. Then loosen the clamps and ro-

tate the capacitors so that each + terminal is

positioned as in the diagram. Make sure the

capacitors are seated against the chassis and

tighten both clamps.

Select the 4 plain connecting lugs and four l/4” long

large screws with lockwashers attached. Install

these on top of the capacitors with the lugs pointing

as in the diagram.

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There are two gauges of wire supplied with the kit. For

connections which pass substantial current, the heavier

wire is used. Other connections need only the lighter gauge

wire. Connect the wires to the bottom of the module from

the right side,

While excessive heat or careless “scrubbing” with the iron

can lift the circuit foil from the board, more people tend to

use insufficient heat, making it difficult for the solder to

flow smoothly around the connection. A smooth, bright

connection is important.

Prepare a 9-1/2“r ed wire and connect one end to TS2

lug #6. (S-2).

Prepare an 8” black wire and an 8” red wire. Start

with the red wire 1/2" longer at one end, and twist

these wires together throughout their length. Con-

nect the longer end of the red wire to eyelet #l of

the board which is to your left as you face the rear

of the module. Eyelet #l is the upper eyelet. Con-

nect the black wire to eyelet #2. Be sure both

eyelets are securely soldered. Place these wires

down under the module.

Prepare a 71/2” green wire and connect one end to

TBl lug #l. (S-2).

Select the ‘inrush limiter’, which is a disc about the

size of a quarter. Trim the leads to 1/2" and connect

it between TBl lug #2 and TB2 lug #3. Solder both

lugs.

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 wire

connects to the upper eyelet #2 of the circuit board

to your right. (S). Connect the yellow wire to eyelet

#l. (S). Place this pair under the module. Now turn

the module around so the fan is toward you.

Prepare a 7-1/2"” white wire and connect one end to

TB2 lug #4. (S).

Prepare a l-1/4” black wire. Connect one end to TSl

lug #7. (S). Connect the other end to TS2 lug #8.

Prepare a 9” black wire. Connect one end to TS2 lug

#8. (S-2).

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 on

the underside of the board.

Prepare a 10-1/2” yellow wire. Connect one end to

TSl lug #5. (S).

Twist the red, yellow and black wires from TSl and

TS2 together. Also twist together the green and

white wires from TBl and TB2. Place both of these

wire groups off to the right of the module. Then turn

the module right side up, with the fan away from

you, and the wires extending off to the left.

Prepare two 7” white wires. Connect one to the

right circuit board eyelet #8, towards the bottom.

(S). Connect the other wire to eyelet #6. (S). You

may find it easier to work if the module is laid flat

on its back foam gasket. Bend these wires toward

the bottom of the fan bracket, and twist them to-

gether throughout their length.

When soldering to eyelets (holes) on the circuit boards, the

wires will be connected to the outside (top) of the board,

but they must be soldered securely to the circuitry on the

underside. It is best to heat the eyelet on the inner surface

while the wire is inserted from the outside. This requires an

iron with a small tip (preferably chisel shaped) and some

care on your part. It is easiest to melt a small blob of solder

on the tip, and position it at the eyelet so that the solder

blob, more than the tip itself, is heating the eyelet. If the

eyelet is first filled with solder, and the wire end is pushed

all the way through the heated eyelet first, then withdrawn

part way to expose a bit of the bare end outside the board

before the solder cools, you should have a firmly soldered

connection if it cools undisturbed.

Prepare a 13”green wire. Connect it to eyelet #7 of

the right board. (S).

Prepare an 1l”white wire. Connect it to eyelet #5 of

the right board. (S). Bend this wire toward the bot-

tom of the bracket.

Prepare a 3”green wire and connect it to eyelet #lO

of the right board. (S).

Prepare a 6-1/2” white wire and connect it to eyelet

#3 of the right board. (S).

Always tin a wire that is to connect to an eyelet. After

soldering, go back and check by twisting each wire, to

make sure nothing moves on the other side of the board. It

is wise to check any existing wire connected to an adjacent

eyelet, to make sure your work has not loosened it. When

connecting heavy gauge wire to the eyelets, if you get too

much solder on in the tinning process, it will be hard for the

wire to penetrate the eyelet.

Prepare a 13” green wire and connect it to eyelet #7

of the left board. (S).

Prepare a 13” white wire and connect it to eyelet #5

of the left board. Bend this wire toward the bottom.

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Select the spade lug and connect it to the free end of

the white wire from LT lug 6. Place this wire to the

left, and twist it lightly together with the green wire

from LT lug 3.

40 Prepare two 9” white wires. Connect one to eyelet

#8 of the left board. (S). Connect the other to

eyelet #6. (S). Bend these toward the bottom, and

twist them together.

41 Prepare a 3” white wire and connect it to eyelet #3.

(S).

When connecting wires to the PC-9 circuit board note that

the eyelets on this board are numbered in the reverse direc-

tion from the lug numbers on the terminal strip.

Prepare a 6” green wire and connect it to eyelet #10

(S). Set the module aside temporarily.

Prepare a 23/4" red wire. Connect one end to PC-9

eyelet #8. (S). Connect the other end to relay RY

lug #7.

CHASSIS WIRING

43 Select the chassis and the .39 mfd capacitor. Trim

each lead to 1/2". Connect one lead of the capacitor

to L T lug #3. Connect the other lead to lug #4.

54 Prepare a 2” yellow wire. Connect one end to PC-9

eyelet #7. (S). Connect the other end to RY lug #9.

Select the silicon diode. Note that one end has a

stripe for identification. Connect the striped end to

LT lug #3. Connect the other lead to lug #2.

55 Strip a 1-1/2“length of heavy wire bare. Connect one

end to large capacitor CL lug X2. (S). Connect the

other end to CR lug #3. (S). Be very sure that these

connections are well soldered because they will

carry considerable current.

45 Select the 1/2 watt 1 megohm (brown-black-green)

resistor. Trim each lead to l/2” and connect one lead

to LT lug #2. (S-2). Connect the other lead to LT lug

#l.

56 Prepare an 8-1/2” red wire. Connect one end to PC-9

eyelet #6. (S).

46 Prepare a 7-1/2” white wire. Connect one end to LT

lug #1. (S-2). Connect the other end to fuse clip FC

lug #l. (S).

57 Prepare a 19’ black wire. Connect one end to PC-9

eyelet #5. (S).

47 Prepare a 12”green wire. Connect one end to LT lug

#3. (S-3).

Prepare a 9” yellow wire. Connect one end to PC-9

eyelet #4. (S).

48 Select one of the spade lugs. Connect it to the other

end of the green wire just attached to lug #3. (S).

Place the red, black and yellow wires toward the

left and twist them lightly together. Keep these

against the chassis and connect the red wire to dual

fuse clip FR lug #5. Connect the yellow wire to FR

lug #6. Connect the black wire to the center of the

bare wire between the two capacitors CL and CR.

(S). Six other wires will be connected to the center

of this bare wire. The amplifier will have the lowest

hum if the last wire to be connected (from the

The proper way to connect one of the spade lugs to

the wire is to bend the shorter, wider set of tabs

tightly around the bare wire, and bend the outer,

longer set of tabs around the insulation. Then flow

solder into the joint around the bare wire.

Check both conductors of the power cord to see

that they are tinned to secure every strand. Con-

nect one lead of the power cord to FC lug #2. (S).

-a heavy wire) is placed in the exact

transformer

center of this link between the two capacitors, so

leave a small space for it. However, all 7 wires

should be connected as near to the center point as

possible.

50 Select another spade lug and connect it to the free

end of the power cord. (S).

Prepare a 41/2” red wire and connect one end to

PC-9 eyelet #3. (S).

Prepare a 13” white wire. Connect one end to the

lower hole of LT lug #6. (S). Using the lower hole

will make it easier for other wires to be connected

to the same lug.

61 Prepare a 5-3/4” yellow wire and connect one end to

PC-9 eyelet #2. (S). Place this wire and the red wire

from eyelet 3 to the left. Twist them lightly together

and connect the red wire to RY lug #B. (S). Con-

nect the yellow wire to RY lug #A. (S).

NOTE FOR MULTIVOLTAGE OPTION: This wire may need

to be 1” longer, and may connect to another termi-

nal for some line voltages.

1 1

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62 Prepare a 3” white wire. Connect one end to RY lug

#4. (S). Connect the other end to red output termi-

nal LR. (S).

Select the yellow and black twisted pair from the

left side of the module. Connect the black wire to

the short ground lug of input socket LS. (S-2).

Connect the yellow wire to the long lug of LS. (S).

63 Prepare another 3” white wire. Connect one end to

RY lug #6. (S). Connect the other end to output

terminal RR. (S).

Select the red and black pair from the right side,

and connect the black wire to the short lug of input

socket RS. (S-2). Connect the red wire to the long

lug of RS. (S).

64 Prepare a 16”green wire. Connect one end to black

output terminal LB. (S). Connect the other end

close to the center of the bare wire between the two

capacitors. (S).

Select the twisted white pair from the left side.

Connect the longer wire to the side lug of the fuse

holder LE (S). Connect the other wire to the tip lug

of LF. (S).

65 Prepare an 18” green wire. Connect one end to out-

put terminal RB. (S). Connect the other end to the

bare wire between the two capacitors. (S).

Prepare an 11-E” green wire. Connect one end to

dual fuse clip FL lug #4. (S). Connect the other end

to CR lug #4.

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).

67 Prepare a 7” white wire. Connect one end to FL lug

#3. (S). Connect the other end to CL lug #l.

Make sure that all of the unconnected long wires (except

for the green wires to eyelet 7 on each board) are placed off

to the right so that when the module is installed on the

chassis these wires will protrude between the feet below

the right circuit board. The wires to the #7 eyelets, as well

as those to eyelets 3 and 10, connect towards the front of

the amplifier. Carefully lift the module without touching

the components on the circuit boards. Swing it into posi-

tion on the chassis, and check to make sure that no wires

are trapped under the mounting feet. Make sure that the

input socket long lugs have not been bent so that any

shorts are possible there-or to the chassis. Keep all wires

away from the ‘inrush limiter’ disc-against the chassis.

68 Prepare a 12”white wire. Connect one end to FR lug

#7. (S). Place this against the chassis and connect

it to CL lug #l.

69 Prepare a 13” white wire. Connect one end to CL lug

#l. (S-3). Connect the other end to the rectfier

block DB lug #2. (S). This is the lug marked + on

the rectifier.

70 Prepare a 7 1/2’ green wire. Connect one end to FR

lug #8. (S). Connect the other end to CR lug #4.

71 Prepare another 8”green wire. Connect one end to

CR lug #4. (S-3), Connect the other end to DB lug

#3. (S).

It is a good idea at this time to check the fan by hand, to

make sure it rotates freely. Shipping sometimes may cause

a misalignment. If it rubs, bending a strut will correct the

problem.

72 Strip a 3/4" piece of light wire bare. Connect it be-

tween the short ground lug of input socket LS and

the separate ground lug between the 2 input soc-

kets.

78 Select 4 sheet metal screws and secure the module

to the chassis. The easiest procedure may be to tilt

the whole assembly backwards so that the module

is again lying on the gasket, giving you access to the

bottom of the chassis. Start the screws, and then

check again to make sure no wires are trapped be-

fore tightening the screws fully.

73 Prepare a 14” black wire, but strip 3/4" of insulation

from one end. Thread the longer bared end through

the separate ground lug, and connect it to the short

ground lug of input socket RS. Solder only the two

wires at the center ground lug at this time. Place the

wire against the chassis, and connect the other end

to the bare wire between the two large capacitors.

(S). This is the 4th of 7 wires connected at this

point. Remember to leave space in the exact center

for the last wire, but keep all of these close to-

gether.

Select the green and white twisted pair from the

bottom of the module. Connect the green wire to

the terminal strip LT lug #l. Connect this wire to

the lower hole in that lug, and solder it separately

from the two wires which are soldered to the upper

part of the lug, Make sure all 3 wires are soldered.

Connect the white wire to LT lug #4. Use the lower

hole for this wire, and solder it separately now. Do

not solder the capacitor lead to the upper part of the

lug at this time.

Now place the wired amplifier module behind the chassis

in line with the input sockets, so that it is resting on the

foam gasket, with the mounting feet against the chassis. Its

wires will protrude toward the chassis, or to the right.

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The wiring of the amplifier is now to be completed with the

installation of the power transformer and two disc

capacitors. The following instructions refer to the 120 volt

transformer supplied for the USA. If your kit is supplied

with the optional multivoltage transformer for overseas

use, separate instructions in this manual will diagram,

both in pictorial form, and schematically, the connection

for each line voltage.

Select the triad of black, red and yellow wires from

under the module. These will be connected to the

right end of the terminal strip, and to prevent the

heat from the large resistors from melting the insu-

lation on the wires, connect the wires from behind

the terminal strip and keep them against the chas-

sis, so the resistors will be above them. Connect

the black wire to LT lug #5. Connect the yellow

wire to LT lug #6. Connect the red wire to LT lug

#7.

NOTE FOR MULTIVOLTAGE OPTION: The following steps which

describe the installation of the capacitors, and the connec-

tion of the two red leads, and the red/yellow lead of the

transformer 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, may

differ. You should follow all the other steps to the comple-

tion of your amplifier.

Select one of the 300* ohm 7 watt resistors. Trim each

lead to 3/4’

’

Strip two 1/Z” lengths of insulation from a

piece of heavy wire, and place one piece over each

resistor lead as insulation. Connect one lead to LT lug

#5 on the front side of the strip. Connect the other lead

to lug #6. Because lug #6 will eventually have several

wires, it is important that each wire be placed as low as

possible in the opening, and crimped so as to maintain

the largest possible opening for the last wire.

Select the 4 sets of #10 hardware and the 4 washers,

and the power transformer. Carefully place the

transformer in position, making sure no wires are

trapped, with the transformer leads protruding to-

ward the large capacitors. You may if you choose

shorten any lead for neatness, but be sure you do

not cut any lead too short, as leads which are cut

too 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 possible

alternative voltage applications.

In these two steps, use the 600 ohm resistors instead, if the

overseas 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.

Select the remaining 300” ohm resistor. Trim each lead

to 3/4" and place this resistor on the back side of the

terminal strip and connect one lead to LT lug #5. (S-3).

Connect the other lead to LT lug #7. (S-2).

Select the white wire from the left circuit board,

protruding from underneath the module. Connect it

to RY lug #7. (S-2).

The washers are to be placed on the screws on top

of the transformer feet for stiffening. Install the

bolts near the edge of the chassis first. That will

determine which of the inner sets of holes are to be

used. It may be easiest for you to tilt the assembly

up on its right side, so the transformer weight is

supported by the work surface, or you can turn it

upside down. Be careful the transformer does not

swing into the circuit board on the module! Before

you tighten any of the mounting bolts, check to be

sure the line cord and other wires are clear of the

transformer feet.

Select the long white wire from eyelet 5 on the right

circuit board. Place it under the relay and connect it

to RY lug #9. (S-2).

Connect the short white wire from the left side of

the module to fuse clip FL lug #l. (S).

Connect the longer green wire from eyelet 7 on the

left side to the bare wire between the 2 large

capacitors. (S). Place it down against the chassis.

Connect the black lead to LT lug #4. (S-3). One of

these wires has most likely already been soldered

to the lower hole of this lug.

Connect the green wire from eyelet 10 on the left

side to FL lug #2. (S).

Connect the short green wire from eyelet 10 on the

right side to FR lug #6. (S-2).

Connect the black/white lead to LT lug #6. (S-4).

One wire has most likely been soldered to the lower

hole of this lug.

Connect the long green wire from eyelet 7 on the

right board to the bare wire between CL and CR.

(S). Place this wire down against the chassis. One

more connection will be made at the center of this

bare wire.

Connect the red/yellow lead to the center of the

bare wire between CL and CR. Be sure all 7 wires

are well soldered.

Connect one red lead to DB lug #l. Connect the

other red lead to DB lug #4.

Connect the white wire from eyelet 3 on the same

board to FR lug #5. (S-2).

Prepare a 13-1/2”r ed wire. Connect one end to PC-9

eyelet #l. (S). Place this wire down against the

chassis and connect it to DB lug #l.

Now is the best time to turn the amplifier upside down and

shake out any loose bits of solder, wire clippings, etc.

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102

Select the remaining sheet metal screws and the

cover. Before closing up the unit, plug it in and

check to see that the fan turns. Because it normally

operates at low voltage for low speed, a new fan

may 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 the

power switch is turned on, secure the cover.

97 Select the .Ol mfd disc capacitor and trim each lead

to 3/4". Strip two lengths of insulation from a

1/2"

piece of heavy wire, and install these on the

capacitor leads. Connect one lead to DB lug #l.

(S-3). Connect the other lead to DB lug #4. (S-2).

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 way

onto the left switch lug. Slide the line cord’s spade lug

part way onto the middle switch lug. This simply makes

it easier to attach the capacitor to these two spade lugs.

Cut each capacitor lead to one inch (some freedom of

movement is desirable), wrap one lead around the shaft

of each spade lug, and solder each. Then carefully

disconnect the wires from the switch.

103

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.

Install the fuses. The 15 amp slo-blo fuse goes in the

single fuse clip near the power switch. The four 10

ampere fuses, with the thicker elements, go into the

two dual fuse clips on the chassis. If you have not

already placed fuses in the speaker fuse holders on

the back panel, install the 2 ampere size, for these

will give good protection to most speakers. A pair

of 5 ampere fuses are also included for the speaker

holders, in the event your needs require very high

powers. However, for steady state test signals at

the full amplifier capabilities, even larger fuse sizes

will be needed in the speaker fuse holders.

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 is

blinking at about 3 times a second, this indicates that the

thermal safety breaker on one channel has shut down the

amplifier 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 of

an excessive (and possibly inaudible) input signal.

Now you should make a last check of all the solder connec-

tions. Look closely for possible bare wire shorts, Check

If the lamp is not lighted at all, the main fuse in the single

fuse clip inside the chassis at the front is probably open. If

a replacement 15 ampere, slo-blo fuse also blows, the

amplifier needs service, and there is a power supply prob-

lem. If the relay will not close (no signal at the output, with

an input signal) check for excessive DC offset (over 1.8

volts) from either channel at locations 7 or 8 on PC-9-the

small relay circuit board. This indicates a defective

amplifier channel, requiring competent service. If there is

no indication of excessive offset, the fault is in the relay or

on the PC-9 circuit board.

for secure hardware

-especially that on the output termi-

nals. Check that wires are not lying on top of the power

resistors on the 7-lug terminal strip. Remove all pieces of

solder and wire clippings from the chassis.

Three wire ties have been included in the kit which you

may wish to install around groups of wires to make your

finished amplifier look neat. Because it is desirable that

the ground wires which connect between CL and CR be

kept close together, we suggest using one tie at the base of

the capacitors.

On rare occasions with some arm/cartridge combina-

tions, very high signal levels at subaudible frequencies

may cause the relay to cut off the output briefly, because

the 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 are

located above the IC on the small circuit board PC-9A. We

suggest 4700 ohms as the next step. At the other extreme,

it is possible to increase the sensitivity so that the relay

would protect the speaker if a stylus were dropped on the

record, but then it might be activated by powerful low fre-

quency transients.

100

Select the front panel assembly and the power switch,

and make sure that the power switch is oriented with the

red window (#3 lug, or separate lug) to the right, or

nearest edge. The switch is a press snap fit from the

outside of the panel.

101

Select 4 sheet metal screws, and bring the front

panel to its approximate position. Carefully attach

the 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 THE

HANDLES IF THE COVER IS NOT SCREWED

IN PLACE.

If the fan does not turn, or makes a ticking noise, make

sure it is properly centered in its supports, and that ship-

ping abuse has not twisted it so the blades are rubbing the

housing. Moderate pressure on the struts will recenter it.

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CIRCUIT DESCRIPTION

potentiometer PI. Thus the signal sees the bases of transistors

The DH-500 amplifier components have been selected to pro-

tect against failure, and all parts are operated conservatively to

assure unaltered performance and proper operation for many

years. The semiconductors have been thoroughly researched and

selected for minimum noise and distortion in sustained use, and

the printed circuit board associated with the audio signals has

been pretested in the circuit to insure that each kit amplifier will

meet or exceed all specifications.

Q12 and Q13 tied together. Pl adjusts the voltage to bias the

amplifier for Class AB operation, and therefore determines the

quiescent (idle) current in the driver and output stages. Complete

circuit stability is assured by the positive temperature coefficient

of 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 channel

MOSFETs in parallel for the positive half of the signal, and Q17,

Q18 and Q19 are P channel MOSFETs for the negative signal half.

The amplifier stages are fully DC coupled, with a dual differ-

ential pair for the input, and a fully complementary MOSFET

output stage. Its power supply is a full wave bridge with 20,000

mfd capacitors on both the plus “+” and minus “-” supplies to

provide excellent filtering and dynamic load stability. Protection

circuitry includes two separate power supply fuses for each

channel, individual thermal sensing devices for each channel to

turn the amplifier off if the heat sinks should reach excessive

temperature, a relay to disengage the output if excessive DC

offset is detected, and output fuses to protect the speakers, in ad-

dition to an AC line fuse.

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 being

overdriven 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 interrupt

the output of the amplifier. If the heat sink temperature rises to

the amplifier is turned off until it cools.

The relay circuit has a 3 section low pass filter which prevents

signals above 10 Hz from opening the relay. This circuit allows

DC to pass to IClOlA and IClOlB, which sense any offset above

1.8 volts, opening the relay to protect the speakers. DlOl, RlO6

and R107 form the reference for the positive offset detector

IClOlA. D102, R109 and RllO form the reference for the negative

offset detector IClOlB. C104’s charging time is the time delay at

turn on, and after any relay actuation.

Transistors Q3, Q4, Q5 and Q6, the input differential pairs,

are matched to control the DC offset of the amplifier. T o

optimize the input pair parameters, they are driven from

constant current sources

Ql and Q2.

An adjustable voltage reference is formed by transistor Q9 and

FUNCTIONAL

BLOCK DIAGRAM

AMPLIFIER CIRCUIT

CLASS AB

BIAS

REGULATOR

DIFFERENTIAL

AMPLIFIER

PASSIVE

OUTPUT

SIGNAL

INPUT

FEEDBACK

NETWORK

. .

AMPLIFIER

NEGATIVE

OUT PUT

NEGATIVE

D R I V E R

CURRENT

SOURCE

B -

RELAY CIRCUIT

F I L T E R

NEGATIVE

RELAY

DRIVER

SPEAKER

DELAY

O F F S E T

ETECTOR

T I M E R

R E L A Y

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COMPONENT VALUES

All resistors are watt 5% carbon film unless otherwise noted.

All capacitors are 100 volt minimum unless otherwise noted

Part No.

470,000 ohms

1,800 ohms

ohms

RC044

RC023

RC043

RC045

RC043

RC045

RC023

RC029

RC039

2 mfd,

330

.Ol mfd, Film

mfd, Film

Film

c 4

CC124

CP136

CC125

47,000 ohms

560 ohms

47,000 ohms

560 ohms

.OOl mfd, Film

mfd, Film

c 7

c 9

Cl0

Cl 1

Cl2

Cl3

.I mfd, Film

470 mfd,

150

330

mfd, Film

100 mfd,

mfd, Film

non-polar Electrolytic

CNI

560 ohms

Film

1,800 ohms

270 ohms

47 ohms

1,800 ohms

270 ohms

1,800 ohms

82 ohms

560 ohms

470 ohms

10 ohms

33,000 ohms

3,300 ohms, lw, metal film

1,000 ohms,

150 ohms,

1,800 ohms

82 ohms

47 ohms, carbon

CC124

CL122

CC124

CL122

CC124

Electrolytic

100 mfd,

.Ol mfd, Film

R16

R20

Cl6

mfd, Film

150

Film

CC124

CC125

CP136

CEl17

CEI 17

CNl14

CL125

RC023

RC029

RC023

RC053

RC045

.Ol mfd, Film

mfd, Film

.l mfd, Film

.OOl mfd,

mfd, Film

1 mfd,

22 mfd,

.Ol mfd,

680

mfd, Film

20,000 mfd,

mfd,

mfd, Film

mfd,

1 N4 148 Diode

FDH400 Diode

Diode

Cl8

Cl9

c21

c22

C23

Cl01

Cl02

Cl03

R22

R23

R24

R25

R26

R27

R28

R29

R30

R31

R32

R33

R34

RC04

Film

RC036

RM02

w. metal film

w, metal film

Non-polar Electrolytic

Electrolytic

RC023

Disc

CM121

CC125

CL123

Mica

220 ohms,

2,200 ohms,

10 ohms

RDI 14

RDl15

RC013

RWO12

RWO13

RM053

Electrolytic

Disc

R36

R37

R38

ohm, 10 w

ohms, 5 w

C E l 1 7

Disc

ohms,

100,000 ohms

120,000 ohms

150,000 ohms

27,000 ohms,

22,000 ohms

3,900 ohms

w, metal film

Q D 1 1 6

Q D l 2 1

R102

R104

RC019

RC02 I

Q D l 1 6

Q D l l l

Dll

D12

D13

D14

D15

D16

RC02

Zener Diode

RD122

RC026

RC037

RC026

RD122

R106

R107

Diode

3,900 ohms

22,000 ohms

27,000 ohms,

10 megohms

4,700 ohms

10 megohms

1 megohms

10,000 ohms

100,000 ohms

150,000 ohms

10 megohms

22,000 ohms

1,500 ohms, 2 w, metal film

470 ohms,

220 ohms,

1 megohms,

300 ohms, 7 w

600 ohms, 7 w

Zener Diode

Q D l l l

QDlll

R l l l

D102

D103

D104

lN4148 Diode

Diode

RC042

RC018

RC047

RC016

QDl15

QDlll

Diode

1 OV Zener Diode

D106

D108

Rl15

Rl17

Zener Diode

RC02 I

RC026

RDI 17

D40

Diode

QP122

QN128

RI20

R401

R402

R403

QP122

QP123

QN124

QN128

RDl17

RDl14

R405

R406

R408

R409

RDl13

QN125

QP123

QN128

QNl13

RW024

Diode Bridge

176

F40

F402

Fuse,

3AG (value optional)

GLH

SF01

SF013

SF014

SF021

QNI

4403

Slo-Blo MDA

QPl13

Q405

Q406

Fuse, 7A Slo-Blo MDA

Power switch

Inductor,

1000 ohms

Power Transformer

Power Transformer, multi-voltage

DPDT relay

TAl12

Thermal breaker

Inrush limiter

Thermal sensor

SF024

TB40 1

TB402

TR40 1

TS40 I

TS402

TAl16

TAl17

T40 1

T402

RY40 1

SF025

Fan,

volt

Fan, 200-240 volt alternate

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AC LINE CONNECTIONS FOR OVERSEAS USE

multi-voltage transformer is installed. This, the 600 ohm

resistors, the mounting hardware, and the alternate line fuse are

supplied in kits which include this transformer.

The power transformer supplied in DH-500 amplifiers sold in

the USA is intended for 120 volt, 60 Hz operation only. For use

in other countries, a multi-voltage transformer is supplied in

Export versions, available at higher cost. It has dual tapped

primary windings which can be connected in series or parallel

combinations for 100, 120, 200, 220 or 240 volt, 50 or 60 Hz

power sources. The connections which are different from the

standard 120 volt connections described in the kit assembly

instructions are all related to the transformer lead terminations,

and to the large resistors on the 7-lug terminal strip. An

The diagrams below show pictorially and schematically the

alternative wiring. Only the pertinent wire connections are

shown. There are other wires connected to the 7-lug terminal

strip which are unchanged. If the amplifier is to be operated with

line voltages between 200 and 240 volts, a different fan, part

#AA128, is required, the 600 ohm resistors must replace the

300 ohm values, and the 7 ampere slo-blo fuse must replace the

15 ampere line fuse.

3-lug terminal strip is required when the

additional

1402

100v.

TO PWR SW

240

240V.

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SMALL PARTS ENVELOPE

KIT PARTS LIST

Part No.

MS153

MS154

CZ113

cz112

CE117

QDll5

RZ016

RD113

RWOl5

xzo14

Minor variations may sometimes be encountered in value or appear-

ance. These will not affect performance. Some of the hardware listed

here has been used to secure parts for shipping the kit.

Bracket, L-shape, 2”

Bracket, L-shape, 3”

Capacitor, 0.005 mfd Disc

Capacitor, 0.01 mfd Disc

Capacitor, 0.39 mfd Film

Diode, IN4003

Part No.

Chassis

Cover

MS127

MS126

MS161

Inrush Limiter

Front plate (rack mount)

Front panel (inside)

Resistor, 1 megohm, Mwatt

Resistor, 300 ohm, 7 watt

Spade lug terminal

MS128

HZ167

Handle

Amplifier module with fan #AA1 13

Power transformer

AH324*

TA116

AC line cord with plug, 16 Ga.

Bracket, capacitor, round

Capacitor, 20,000 mfd, 100 volt

Circuit board, PC-9C, assembled

Label, serial number

Relay, enclosed

WA016

HZ124

CL123

AC009

LR015

sz113

LARGE PARTS ENVELOPE

Diode block, silicon rectifier

Foot, rubber

Fuse clip, single

Fuse clip, dual

Fuse holder, round, panel mount

Input socket

Power switch

Strain relief, plastic

Terminal post, black, complete

w/black washer and 2 nuts

Terminal post, red, complete

w/red washer and 2 nuts

Terminal Strip, 7 lug

QD117

HR146

XA012

XA014

XA013

XPO14

SLlll

HR144

Manual

Warranty card

Wire, white #18

Wire, green #18

Wire, Yellow #18

Wire, Black #22

Wire, Red #22

XK013

XK014

XK019

HARDWARE ENVELOPE

Part No.

FUSE ENVELOPE

2 ampere

5 ampere

10 ampere

15 ampere, slo-blo

Lug, ground, internal tooth, #6

Lug, plain connecting, #lO

Nut, #4-40 KEP

Nut, #6-32 KEP

Nut, #l0-32 KEP

HZ115

SF011

SF012

SF013

SF014

HZ1 16

HKlll

HK112

HK113

HK118

HA1 13

HA116

HA119

HA118

HP1 17

HA1 15

HW114

HW116

HR117

HR138

Nut, 1/2"

Screw, machine, #4-40

Screw, machine, #6-32

5/16”

1/2"

For Alternate Multi-Voltage Transformer Only

TA117

Power Tmnsformer

Terminal strip, 3 lug

Screw, machine, #4-40 x 5/16"

Nut, #4-40 KEP

Fuse, 7 ampere, slo-blo

Resistor, 600 ohm, 7 watt

Screw, machine, #l0-32 x M”

Screw, SEMS, #l0-32 x 1/4"

Screw, sheet metal, #6 x 3/8"

XK017

HA1 13

HKlll

SF021

Screw, machine, #6-32

Washer, flat, #lO 7/8"

3/4"

RW024

Washer, internal tooth, 1/2"

Washer, rubber, M”

* For use with 200-240 volts AC, a different fan, part#AA128,

must be fitted to the amplifier module.

Wire ties, nylon, 4”

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DH-502 INSTALLATION INSTRUCTIONS

Disconnect AC power from the DH-500 and remove all connect-

10. Remove the rear rop screw securing the right channel amplifier

ing cables.

circuit board to the hear sink just above where the twisted pair was

disconnected. Do nor lose the fiber spacing washer which is

between the circuit board and the heat sink. This washer is not

used on later production DH-500s. Select one of the screws from

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.

the bridging kit, and the mounting bracket. The bracket

anchored at this location, flat surface up, with the screw inserted

fust through the single tab from inside the bracket. then through

the circuit board. the fiber spacing washer, (optional) and into the

heat sink.

Turn the amplifier over, or stand it on the nansformer end.

Loosen, but do not remove the two front screws which secure the

amplifier module near the front (center) of the chassis. Remove

the two screws at the rear which secure the module. Return the

amplifier t o its upright position.

11. Select the two screws and nuts and the circuit board PC-7A. With

the components facing out, secure the board t o the outer surface

of the bracket tabs.

Prepare one each red and green wires each 16” long. Twist them

together throughout their length.

Select the short twisted pair of wires connected to eyelets 4 and

6. Connect the red wire to the upper eyelet #l of the right circuit

board at the center rear. (S) Connect the green wire

Select the PC-7A circuit board. Note that the eyelets arcnumbered

on the circuit side of the board, with eyelet #l to the left when the

row of eyelets is nearest you, and the board is upside down to

make soldering easier. Connect the wires from the components

side of he board, and be sure each is securely soldered to the

circuitry.

t o

the lower

eyelet #2. (S)

13. Place the long pair of wires from eyelets 1 and 3 down between

the amplifier module mounting bracket and the back of the

chassis. The module can be tilted forward t o facilitate this.

Connect the red wiret o the lower ey elet #l on the left circuit

Connect the red wire of the twisted pair to eyelet

Connect the green wire to eyelet #3. (S)

1 of PC-7A. (S)

board. (S) The easiest way is to wrap it in a tight loop around

Prepare a 3-l/2” green wire and a 4” red wire. With one pair of

ends even, twist these together. At the uneven ends, connect the

green wire to cyelet #4 of PC-7A. (S). Place the pair off toward

eyelet #l, and connect the red wire to eyelet #6. (S)

bare stub of the wire presently connected to this eyelet. Be sure

both wires are soldered securely to he board. Connect the green

wire

t o

the upper eyelet #2 in the same fashion. (S)

Making sure that no wires are trapped by the mounting bracket,

reinstall the. two screws securing the rear of the module to the

chassis. Tighten all 4 screws.

Prepare a 5” red wire and a 6” green wire. Twist these together

with one pair of ends even. At the even ends connect the red wire

to eyelet #2. (S) Connect the green wire to eyelet #5. (S)

Connect the red wire of the remaining twisted pair from PC-7A

to 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 existing

wire 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.

Unsolder the twistcd pair of leads from eyelets 1 and2 of the right

amplifier module at the center rear of the amplifier. This pair of

leads which connects to the right inputsocket, will no longer be

used while the amplifier is funtioning monophonically. These

leads must be taped securely so that there is no possibility for the

bare wire to contact any portion of the circuit. Masking tape is

sufficient, but electrical tape is preferred. These leads may be

removed if desired.

16.0 Reinstall the amplifier cover.

PC-7A PARTS LIST

LIST

PC-7A PARTS

RMP/4-2212

RC/4-222

RC/4 -222

RC/4-470

RC/2-822

RC/4-770

RC/4-222

RMP/4-2212

RC/4-101

RC/4-770

RM l-332

RMl-332

22.1K, l%, metal film

2.2K. 1/4w, 5% carbon film

2.2K, 1/4w, 5% carbon film

47 ohms, 1/4w. 5% carbon film

8.2K, 1/4w, 5%, carbon film

8.2K, 1/4w, 5 % , carbon film

47 ohms, 1/4w, 5% carbon film

2.2K, 1/4w, 5% carbon film

RlO

C OMPONENT SIDE

0 5

0 6

Rll 2.2K, 1/4w, 5% carbon film

R12 22.1K, l%, metal film

IO0 ohms, 1/4w, 5% carbon film

100 ohms, 1/4w, 5% carbon film

R15 47 ohms, 1/4w, 5% carbon film

R16 3.3K, lw, 5% metal film

R17 3.3K, lw, 5%. metal film

R13

R14

0 4

0 2

R15

CERNP-106

CM -068

CER-226AA

OmF, 16V. non-polarized

0 3

6.8pF.

00V, dipped mica

22mF. 25V, electrolyte

SSH-650

SSH-65 1

SSH-695

SSH-645

BC55OC NPN nansistor

BC55OC NPN transistor

BC56OC PNP transistor

MPSA63 PNP transistor

MPSA13 NPN transistor

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INSTRUCTIONS FOR

THE HAFLER DH-502 AMPLIFIER BRIDGING KIT

FOR THE DH-500

The DH-502 Amplifier Bridging Kit for the DH-500 consists

indication be made as to the appropriate connections, and that be

attched to the back panel. Because of this floating output, neither

of a PC-7A circuit board comprising a 6 transistor phase inverting

amplifler, a mounting bracket, necessary hardwareandconnecting

wire. Installation may take about an hour. All changes to the

side of the output signal may be grounded; such as thru

speaker

switching box or head phone adapter that has a common ground

between the left and right channels.

amplifier wiring are performed on the right channel the side

nearest the power switch. Only the left channel input will be utilized

after conversion so an additional pair of input wires will be

connected to that jack to enabie it to feed the complete amplifier.

When converted to monophonic operation, the loudspeaker

For equivalent load impedances, the speaker fuses provide the

same power output protection as in stereo operation, but because

of individual fuse variations, only one fuse may blow at these

levels. It is best to replace both fuses if one blows, as the other

may have been weakened.

load is

t o

be connected to the t w o centerred (+) outputs only. The

right (+) will act as the common and should be attached to the

speaker (-)_ This is what is known as a floating output, for no

connection is made to either black ground terminal. It is sug-

gested that once the amplifier has been converted, some clear

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 soldcrcd

connection),

KIT PARTS LIST

PC-7 Board

WP-PC7

SM-BRT202*

HWH-145

HWH-105

3.0’

ounting bracket

Screw, Machine, 4-40 x 5/16”

Nut. 4-40 KEP

Wire Red #20 GA

Wire, Green #20 GA

Warranty Card

T O

3.0’

LIT-WAR

LIMITE D WAR R ANTY

The 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 board

or in the kit, simply return the individual part, or if the problem is unknown, retumthedefcctive board to the factory, prepaid, together with the serial number

and 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 bridging

module only. Hafler is not responsible for consequential damages. This warranty gives you specific legal rights. You may also have other rights which

vary from state lo state.

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

A Division Of Rockford Corporation

613 S. Rockford Drive, Tempe, Arizona 85281 (602) 967-3565

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The weight of a DH-500 (unless it includes the special

multi-voltage power transformer), when packed exactly as

it came from the factory, should be just under 50 pounds,

and may be shipped by UPS. However, be certain it is fully

protected, and insure it for the full value.

The DH-500 Power Amplifier has been carefully en-

gineered to provide many years of use without requiring

any maintenance or servicing.

Factory assembled units are subjected to many physical

and electrical tests before shipment. The amplifier module

assemblies 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 assembled

properly, or human error interferes, so service may be

needed. The David Hafler Company provides complete

service 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, and

the performance of the unit is likely to be compromised

with “similar type” substitutions, we strongly recommend

factory service, or obtaining the requisite parts from the

factory.

If you choose, it is possible to return only a portion of

the amplifier for factory service, with some disassembly

on your part. This assumes that you are certain the prob-

lem lies only in the returned portion, and that you assume

full responsibility for reinstalling it correctly, since a ser-

vice warranty cannot be extended for other than the actual

portion serviced. Because the transformer is so heavy, and

a problem there is most unlikely, its removal by unsolder-

ing a few leads is a logical choice. The balance of the

amplifier should be insured for at least $700. It is also pos-

sible to unsolder the module, and return it, if that is where

the only problem lies. However, it requires much more

care in packing, to protect the delicate components on the

circuit boards, and many more connections must be unsol-

dered, so there is more risk for reinstallation error. It

should be insured for $400. The service fee for the module

is $50. If you return an amplifier for service or checkout,

and it is functioning correctly, a charge will be made for the

testing time required, as well as for packing and shipping.

It is the owner’s responsibility to return or ship the unit

freight prepaid to the factory service department. Units

shipped freight collect will not be accepted. For units to be

repaired under warranty, a copy of the dated bill of sale

must 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:

WARRANTY FOR KIT-BUILT UNITS

The parts in a DH-500 kit are warranted for a full year

from the purchase date. If a defective component is found

on a circuit board or in a kit, simply return the individual

part to the factory prepaid together with the serial number

and the date of purchase, and it will be replaced at no

charge.

Complete shipping address (Post Office box numbers

are not acceptable, except for correspondence).

2. The serial number, if it is not on the unit.

If you cannot locate what is wrong with your DH-500,

return it to the factory along with a copy of the dated bill of

sale, and a check for $75. If the cause of the problem is a

defective part, the unit will be repaired and returned to you

transportatiion prepaid, and your $75 less the shipping

charges will be returned to you. If the problem is found to

be an error in your assembly of the amplifier, the amplifier

will be put in proper working order, tested to be sure it is

3. Copy of dated bill of sale if repairs are to be made under

warranty.

Description of the malfunction. If intermittent, be sure

to so indicate.

5. You may also wish to attach your address directly to the

unit, or to the line cord.

and returned to you (freight

meeting specifications,

All service work is guaranteed for 90 days.

prepaid within the continental U.S.). Excess shipping

charges for expedited service, or overseas delivery are

your responsibility. At the sole discretion of the factory

service department, if the time required for diagnosis,

repair and testing, and the nature of the malfunction

warrants it, a portion of the submitted repair fee may be

rebated.

This warranty is void if the kit has not been completely

assembled or if other than rosin core solder has been used.

Units assembled with acid core solder or paste flux will be

returned unserviced.

Warranties apply to the original purchaser only. The

warranty is void if the amplifier has been modified without

factory authorization; or if parts have been substituted

which, in the factory’s judgment, are not suitable; or if the

amplifier has been either physically or electrically abused,

or used for some purpose for which it was not designed or

intended.

The warranty on the transformer is void if the leads have

been cut too short for re-use. If you think the transformer

is defective, unsolder, do not cut the leads for its return.

WARRANTY FOR FACTORY ASSEMBLED UNITS

The 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 unit

to the factory and must submit a copy of the dated bill of

sale.

Technical assistance to help you locate the source of a

problem may be obtained by calling the Technical Services

Department 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 of

any tests you have performed. However, we do not rec-

ommend that you attempt your own servicing unless you

are knowledgeable in this regard.

This warranty gives you specific legal rights. You may

also have other rights which vary from state to state.

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