DH-220_amp_man.pdf

THE

POWERAMPLIFIER

INSTRUCTIONS

for OPERATION

and KIT ASSEMBLY

CAUTION:

IF THE SPEAKER FUSES BLOW,

SOME DISTORTED SOUND CAN BE

HEARD. THEREFORE IF AMPLIFIER

MALFUNCTIONS, ALWAYS CHECK

FOR BLOWN FUSES FIRST.

serial number in all communications

THE DAVID HAFLER COMPANY

5910 Crescent Boulevard, Pennsauken, New Jersey 08109

INTRODUCTION

The Hafler DH-220 is a two channel audio power amplifier

designed to the very highest performance standards. It is

available either as a kit, or fully assembled. Its 115 watt per

channel power rating is sufficient for driving all loudspeakers in

home applications, and its design assures extremely low distor-

tion of all types. A combination of high performance, depend-

ability, reliability, and moderate price is in the Hafler tradition of

using the very latest technology to provide outstanding value.

The oversized power transformer and bridge rectifier; the

massive heat sinks; the conservative operating levels of the

MOSFET output devices - all are evidence of the design efforts

to achieve exceptional reliability simultaneously with state of

the art sonics and specifications. And this circuit is convertible to

a high power monophonic amplifier with comparable stability

and specifications.

The fully complementary, symmetrical push-pull circuit,

which is direct coupled throughout (except at the input), incor-

porates all silicon devices in a format which is directly related to

the highly acclaimed DH-110 preamplifier. Its unique self-

protecting output stage prevents the thermal runaway which is

a common threat to solid state amplifiers. The ruggedness and

conservative operation of the output stage allows the DH-220 to

avoid the need for special protective circuits which could com-

promise audio performance. Basic protective systems provide

maximum security against malfunction damage to the amplifier

or the speaker: the AC line fuse, B + fuses, thermal breakers,

and loudspeaker fuses. Nothing hinders the essential purity of

the audio signal.

The DH-220 circuit is a refinement of the DH-200 design, a

Hafler landmark which has achieved worldwide recognition,

and has elicited glowing reviews since its 1979 introduction. As

in the DH-110 preamplifier, particular attention has been paid to

component quality, using polypropylene or film capacitors

wherever feasible, for example, for superior sound.

Combining the latest power MOSFET technology with uni-

quely simple and effective circuit topology reduces distortion of

all types, and at all power levels, over the full audio frequency

spectrum, to the vanishing point. In addition to its pace-setting

performance achievements, the conservative mode of opera-

tion accomplishes a new high in long term reliability and excep-

tional resistance to abusive operating conditions. This is one of

the direct benefits of MOSFET utilization in overcoming a

serious limitation of conventional transistors - their tendency

to self-destruct under other than normal operating conditions.

So rugged is the DH-220 that it can deliver more than ten

amperes into a short circuit!

Those who use these instructions to assemble the DH-220 kit

will find that the left and right audio modules (printed circuit and

heat sink assemblies) are preassembled and pretested. This

greatly simplifies the kit assembly so that it can be done in only a

few hours without special skills or know-how. Because of the

modular arrangement, it is possible to operate on one channel if

the other requires service, and avoids the need to return the en-

tire amplifier in cases where only one channel is at fault.

The speed - measured as the slew rate - of this design

delivers unmatched transient linearity, revealing the most

delicate shadings, textures and nuances of the music, surpassing

the capabilities of the most revealing loudspeakers and cart-

ridges by a wide margin. Coupled with its unconditional stabili-

ty, and ability to deliver adequate power into any loudspeaker

load, the result is absolute freedom from listening fatigue. The

longer you listen to this phenomenal amplifier, the more certain

you will be that you could not have made a better choice.

Accessories for special applications include provision for

monophonic use; a panel for standard 19” rack mounting; and

an alternative power transformer for international AC line

voltages.

Through advanced engineering geared to the audio perfec-

tionist, and an efficient no-frills approach, Hafler is making high

technology high fidelity affordable.

CONTENTS

Operation........................Page 3

Assembly Instructions..................4

Wiring the Kit......................6

If Problems Arise......................10

Service and Warranty..................11

AC Line Connections for Overseas Use....12

Kit Parts List.........................13

Schematic Diagram................... 14

Component Value Listing...............15

Pictorial Diagram...................Insert

INSTALLATION

The DH-220 is most likely to be installed out of sight in most

applications, since its power may be controlled by the AC

switching of most audio preamplifiers, like the Hafler DH-110. If

your control unit does not provide switching capacity sufficient

for the amplifier’s 7 amp needs (plus other equipment it is also

switching), you should use the amplifier’s own power switch. In

that case, turn on the preamplifier first; then turn the amplifier

on a few seconds after the preamp has been turned on, to avoid

any unnecessary turn-on transients from some preamplifiers.

Likewise, switch the power amplifier off first.

than others, and require separation from the amplifier. Check at

a comparatively high volume setting, and while swinging the

tone arm throughout its arc. Often a few inches additional spac-

ing will eliminate the problem.

Be sure to provide sufficient ventilation for the amplifier.

Unobstructed air circulation around the finned heat sinks and

above the amplifier is important for long, trouble-free life. Never

put anything on top of the cover perforations. It is normal for the

top and the heat sinks to become warm in use.

If the amplifier is to be installed close to a record player, you

should first check its position for freedom from hum pickup by

the cartridge from the field radiated by the power transformer

of the DH-220. Although the design of the transformer

minimizes such radiation, certain cartridges are more sensitive

It is expected that the amplifier will always be resting on its

feet, which should be on a hard enough surface that air flow

underneath is not obstructed. If it is mounted in a rack, or

through a panel, the feet may be removed so long as adequate

ventilation is provided through the bottom openings.

OPERATION

The red pilot lamp which is integral with the power switch

glows whenever the amplifier is turned on. A blown AC line fuse

is the most likely cause if it is not illuminated when the amplifier

is switched on.

Loudspeaker Power Ratings

There are no U.S. standards for rating the power handling of

loudspeakers. As a result, the manufacturers’ usual “music

power”ratings, or suggested amplifier limits, are of only

minimal help in determining safe operating levels with

amplifiers which can deliver substantial amounts of power. You

must take into consideration the type of music, and the levels

you like, to provide long term trouble-free operation of your

speaker choice, when you have a sizeable amplifier like the

DH-220.

The pilot lamp also provides a high temperature indication. In

the unlikely event that the amplifier ceases to function, and the

amp blinks on and off steadily, it indicates that one of the ther-

mal breakers has shut down the amplifier because of excessive

temperature rise in a heat sink. When the heat has dissipated in

a few minutes, the amplifier should return to normal operation.

If the lamp again blinks, check for insufficient ventilation, or an

excessive input signal, or an input which may have dangerous

signal content (such as oscillation). Failing evidence of this, the

amplifier may have malfunctioned. Because of the very large

heat sinks, it is highly unlikely that any normal signal will cause

the amplifier to overheat.

Connections

The AC power cord should be plugged into 120 volts, 60 Hz,

on the switched outlet of a preamplifier which can provide at

least 7 amps, or 840 watts. Then the amplifier power switch may

be left on, and it will be controlled by the rest of the system. Or. it

may be plugged into a 120 volt wall outlet, and switched on and

off independently.

Loudspeaker Fuse Selection

The DH-220 power amplifier is supplied with 2 amp fuses in

the speaker lines. Experience has shown that since an overload

must exist for a few seconds for a fuse to blow, a 2 amp fuse will

protect most speaker systems, and only blow when overload oc-

curs. Smaller fuses tend to blow too easily, and larger fuses do

not adequately protect most speaker systems.

If your line (mains) voltage is different, be sure you have the

alternate power transformer which can accommodate several

line voltages, and be sure it is wired for your mains voltage as

described later in this manual before you pIug in the amplifier.

A pair of 5 amp fuses are also supplied as alternatives for the

speaker fuse holders. These should be substituted if the power

output of the amplifier is to be tested, and these or intermediate

values may be used if the amplifier is to be operated at very high

power levels into 4 ohm loads.

Input

Conventional shielded cables, such as those supplied with

your preamplifier, provide the input signal to the sockets on the

back panel of the DH-220. Be sure that the outer shield connec-

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

permit remote location of the amplifier, if desired) is limited only

by the output impedance of the preamplifier. If it is 600 ohms or

less, as with the DH-101 and DH-110 Hafler preamps, for in-

stance, cable lengths up to 50 feet are premissible without loss of

If the manufacturer of your speakers recommends a specific

value of fuse for their protection, we suggest that you obtain

AC fuses of that value and install them in the back panel.

performance. Special low capacitance cables enable even

greater distance between preamp and amplifier. It is desirable

to keep the left and right input cables close together throughout

their length to minimize the likelihood of hum pickup. Also, you

should avoid running them parallel to AC cords - these should

be crossed at right angles.

plugs are used, be suretheyare color coded, or that you follow

the indexing mark ononeside of the double connectors.

Select speaker wire of sufficient size to preserve the high

damping factor (and excellent speaker control) of your

amplifier. Standard 18 gauge lamp cord (“zipcord”) is satisfac-

tory for distances up to 30 feet for an 8 ohm speaker. As the

distance increases, larger wire sizes are recommended. The

next larger wire size is#16, and it is often preferred by perfec-

tionists. If you have 4 ohm speakers, the maximum cable length

for best results is halved.

Output

The loudspeakers (or headphones) connect to the red and

black terminals on the back panel. These binding posts provide

several convenient alternative connecting methods. The screw

cap may clamp the bared wire end, or a “spade lug” attached to

it, but a better connection will be made by locating the hole drill-

ed through the shaft of the terminal when the cap is unscrewed.

Insert the twisted end of the bared wire so that the cap will

clamp it in place. Always be sure that no strands of wire are

unsecured, and that the bared end is not too long to risk contac-

ting other elements. A soldered end or fitting is the safest solu-

tion.

The black output terminals are electrically connected to the

chassis internally. Be certain that when the amplifier is operated

in its normal stereo mode that the red output terminals are never

connected together. In the special case when the amplifier has

been internally modified for monophonic bridged operation,

the output is taken from the two red terminals only. Then, the

black terminals are left unconnected.

These terminals also accept standard plug-in “banana pin con-

nectors,” including the double ones with standard 3/4” spacing,

available from electronic supply houses. These are the most

convenient, especially if you may wish to interchange speakers

occasionally.

Headphones are normally operated from the loudspeaker

outputs, but are usually connected through a junction box

which provides switching from phones to speakers. Such a box

usually provides some added resistance to reduce the sensitivity

of the phones, and thus minimize the likelihood of hearing com-

ponent noise, because of the low setting required at the volume

control. Some headphone boxes utilize a “common ground”

system which makes it particularly important that you carefully

observe the proper connections. While the black ground ter-

minals can be connected together, the red ones must not be.

It is important to maintain correct phasing of the speakers

when making their connections. Some speaker terminals are

coded red and black, or + and -, etc. It is important that the

“sense” of one speaker’s connections match the others. If one is

reversed, you will find that the sonic image has a “hole in the

middle,” and that it is deficient in bass. Speaker wire always

identifies one conductor to make this easy. There may be a

molded ridge in one lead, or the color of the insulation on one

wire is different, or the wire itself may be color coded. If pin

Some headphones, such as electrostatic types, are less sen-

sitive and may need little or no resistance in series for normal

operation. These could be easily interchanged with the

speakers through the use of double banana plugs.

KIT ASSEMBLY INSTRUCTIONS

There are three basic rules for success in electronic kit

building:

Your work area should have good lighting, the proper tools,

and a place where the large pictorial diagram can be positioned

within easy reach for checking. The tools should include:

1. Read the instructions carefully, and follow them in order.

2. Make secure solder connections which are bright and

smooth.

3. Check your work carefully after each step.

A 40 to 100 watt soldering iron with a 1/4" or smaller tip which

reaches at least 600°F.

60/40 (60% tin) ROSIN CORE solder, 1/16" diameter or

smaller. (Smaller diameters are easier to work with.)

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

A wire stripping tool for removing insulation. This can be a

single-edge razor blade, but inexpensive stripping tools are

safer, faster and easier.

A medium-blade screwdriver (about 1/4" wide).

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

Diagonal or side-cutting small pliers.

Large “gas” or “slip-joint” pliers.

The DH-220 amplifier is a versatile component with

sophisticated circuitry which has been made remarkably easy

to build by individuals with many years of experience in the

design and engineering of the finest performing audio kits, and

in the preparation of their manuals.

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, selec-

ting 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 everything away, if need be.

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 operating 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.

few seconds to allow a good bond. When cool, check the con-

nection 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 heating it and allowing the solder to flow onto

the iron, which is then wiped on the sponge.

ALL SOLDER USED MUST BE ROSIN CORE.

Never use acid core solder or any separate flux in electronic

work. Silver solder is also not suitable. If in doubt about unmark-

ed solder, always obtain a fresh supply of rosin core solder. We

recommend 60/40 for easiest use. Do not confuse it with 40/60,

which is harder to melt.

Proper Soldering

There are four steps to making a good solder connection:

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 pattern from the boards. A

break in the etched circuit can be mended 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.

Make a good mechanical connection to hold the wire in posi-

tion while heat and solder is applied.

Heat thejunction of the wire and lug, or hole, with the bright,

shiny top of the iron.

After heating for a couple seconds, apply solder to the junc-

tion. It should melt immediately and flow smoothly around

both surfaces.

Allow the connection to cool undisturbed.

When soldering to a numbered hole on the board, insert the

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

some bare wire exposed so that you can see that the hole is then

filled with solder for a secure bond. A round wooden toothpick

is suggested so that you can heat and clear the hole of solder if it

hinders your inserting the wire. Some builders prefer to clear

every hole first with a touch of the iron and toothpick. If the wire

has first been “tinned,” no additional solder may be necessary if

solder fills the hole, but it is good practice to push the wire

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

from both sides. Make certain a bright, shiny flow is evident

from the wire, across the hole, onto the circuit pattern on the

board.

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. Connections to numbered

holes on the circuit board are handled this way.

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” partially 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 easily 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 pro-

vide a bigger contact surface to the joint. Once the solder flows

around the conductors, any movement must be avoided for a

“Tinning” refers to the process of applying a light coating of

solder to the bared wire end. This keeps all the strands secured,

and also makes a good connection easier. Simply touch the wire

with the iron for a couple of 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.

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