Hafler DH 222 Service Manual

Page 1

INSTRUCTIONS FOR _
THE HAFLER DH-222 AMPLIFIER BRIDGING KIT
FOR THE DH-220

The DH-222 may be installed in a Hafler DH-220 power
amplifier to enable easy conversion to a high power
monophonic amplifier, bridging the two conventional chan-
nels to a single floating output which can deliver in excess of
400 watts into an 8 ohm load. Its rated power output is 350
watts across the audio band.

When switched to monOphonic Operation (UP), signal input
should be provided to the LEFT input jack only, and the output
should be connected only to the two center RED (+) terminals.
No connection of the load is to be made to the black output
terminals. Because of the floating output, neither side of the
load may be grounded. Thus it is unlikely that stereo speaker
switching boxes, or headphone adapters may be used, as these
often have a common ground between the left and right chan-
nels.

The speaker fuses may be replaced with higher values than
the 2-5 ampere range suggested for stereo operation, if de-
sired, depending on the degree of protection for the speaker
which is intended. The graph shows the nominal sustained
power output limit of a 7 ampere standard fuse, which is the
maximum recommended value. Smaller values will provide
more protection for the speakers; larger ratings are at the
users risk.

Both Speaker fuses should be the same value. If one speaker

KIT PARTS LIST
1 Switch, DPDT 82114
1 Mounting bracket M8183
1 Indexing washer HW123
1 Lockwasher HW122
2 Nut, switch mounting HK125
2 Nut, 6-32 KEP HK112
2 Screw, machine, 6-32 HA116
1 Resistor, 3000 ohms RZ017

Wire, red, 22 gauge
Wire, green, 22 gauge
Wire, black, 22 gauge

fuse blows in mono operation, both should be replaced, for it is
likely that the second has been weakened. For equivalent load
impedance, each speaker fuse provides the same power output
protection as in stereo operation.

With the internal conversion switch DOWN, the amplifier
functions as a conventional stereo amplifier, with normal
input and output connections. The minimum recommended
load impedance, which is limited only by thermal factors (abil-

ity of the heat sinks to dissipate high energy levels), is 6 ohms
in mono; the usual 3 ohms in stereo. The amplifier circuit can
safely accommodate lower impedance loads, of course.

The conversion, which takes less than an hour, involves
only changes to the input wiring, and installation of the switch
with its mounting bracket and one resistor. These instructions
assume familiarity with the usual kit building descriptions,
and reminders. For more details in this regard, see the con-
struction section of your DH-220 amplifier manual. You must
be certain you have made a good solder connection wherever
one is called for, not only to the wire you have attached, but to
any others already connected to that point. The notation (S)
indicates a soldered connection; (S-2) denotes that there are
two wires to be soldered. Use only 60/40 rosin core solder. Be
careful not to let the soldering iron touch adjacent components
on the circuit board; excessive heat could change their opera-
tion, with the possibility of damage to the amplifier.

450-

AMPLIFIER LIMIT

400--

7-AMP. FUSE LIMIT

350-..

CONTINUOUS POWER - WATTS @ 1KHZ

I
I i 1 I
4 8 12 16

RESISTWE LOAD IMPEDANCE - n.

LIMITED WARRANTY

The parts in the DH-222 are guaranteed against defects for one year from the date of purchase. Installation in a DH-220
amplifier is the owners responsibility. In the event of difficulty with the completed unit, charges for service, if any, will be in
accordance with the warranty provisions for the amplifier, if it was purchased as a kit. If it was purchased as a factory
assembled unit, there is the further stipulation that faults incurred as a result of improper installation of the DH-222 are the
owners responsibility, but in other reSpects the original warranty applies. This warranty gives you specific legal rights. You

may also have other rights which vary from state to state.

davfid half (an--.

5910 CRESCENT BOULEVARD, PENNSAUKEN, NJ 08109 0 609/662-6355

LM056

Page 2

DH-222 INSTALLATION INSTRUCTIONS

Disconnect AC power from the amplifier, and remove all con-
necting cables. Wait 5 minutes to allow capacitors to discharge
before proceeding with disassembly.

Remove all 8 screws between the fins of each amplifier module

so that the cover may be removed, and the modules tilted out-
wards for easier access.

Unsolder the pair of twisted wires connected to holes 1 and 2 at
the top of the right channel PC-19 circuit board. The right
channel is the one nearest the power switch. This pair must
also be unsoldered from the right input socket on the back
panel, because it will be more convenient to use lighter gauge
wiring.

Prepare a 6% red wire, and a 6%" black wire. Start with the
black wire it longer than the red wire, and twist them together
uniformly throughout their length. At the end where the black
wire projects, connect it to the short lug of the right input sock-
et. (8-2). Be sure the existing wire to the adjacent ground lug is
properly connected. Connect the corresponding end of the red
wire to the long lug of the input socket. (S). Place this pair off to
the right edge.

Prepare a 5%" red wire, and a 5% black wire. With the ends
even, twist these together and connectthe red wire to hole #1
at the top of the right channel PC-19 circuit board. (S). Connect
the black wire to hole #2. (S).

Prepare a 20" green wire. Cut a 20" black wire, but remove the
insulation from only one end. Starting with the bare end of the
black wire 17%" longer than the green wire, twist these together.

At the far end, where the black insulation has not been re-
moved, the black wire will not be connected, but instead will be
secured by wrapping it in a tight circle around the green wire a
short distance from the bare green end. It is very important
that no bare wire be visible from the black insulation. The
single green wire is to be connected near the center of the lefi
circuit board to the hole designated "B, located just below the
bias adjustment potentiometer. (S). It must be securely sol-
dered, but be careful that you do not damage adjacent compo~
nents.

Making sure that no wires are pinched between the module
and the chassis in the process, reinstall the left module to the
chassis with 4 sheet metal screws.

Select the switch and its 2 nuts, lockwasher and indexing flat
washer, and the switch mounting bracket. Install one nut all

10

11

the way onto the switch collar, and follow it with the indexing
washer with its lug projecting towards the handle lever. Mount
the switch on the bracket so that the lever points in the direc-
tion of the bracket flange, and the indexing lug engages the
locating hole in the bracket. Secure it with the lockwasher and
the second nut.

Select the two machine screws and nuts, and install the switch
bracket between the two transistors at the rear of the right
module, so that the switch lever points towards the fins.

Select the 3000 ohm resistor and trim its leads to it ". Connect it
between switch lugs #4 and #5. Solder only lug #5.

Select the red and black pair from the right input socket and
connect the black wire to switch lug #3. Do not solder this con-
nection yet. Connect the red wire to switch lug #1. (S).

12 G Select the red and black pair from the right channel circuit

13

14

15

16

board holes 1 and 2. Connect the black wire to switch lug #3.
(8-2). Connect the red wire to lug #2. (S).

Select the green and black pair and separate the wires for
about 1%". Connect the green wire to right circuit board hole
"A. (S). Connect the black wire to hole "E. (S). Hole "A is
located in line with the switch about 1%" from the rear edge of

the board. E is located 1a" below hole 2, near the top of the
board.

Place the green and black pair towards the rear of the module,
and down past the midline of the switch. Where it passes lug
#5, approximately 4%" from the end of the wires, out only the
green wire. Strip each end a ". Connect the short green section
to switch lug #4. (S-2): Connect the longer green wire from the
left board to switch lug #6. (S).

Be careful no wires are pinched as you reinstall the right mod-
ule to the chassis with 4 screws. Place the long green and black
pair under the rear lip of the chassis. The pairs to the top
eyelets on each board, and to the connections in the center of
the board should be kept at least 1/2" off the board, where they
are clear of the components. Make sure the unconnected black

wire end near the left circuit board cannot touch any compo-

nents.

The switch lever should be placed in the upper position for

monophonic operation. In the lower switch position, the
amplifier functions as a conventional stereo amplifier. Rein-
stall the amplifier cover with the remaining 8 screws.

l ll/l/ 4/