The DH-110 achieves all these objectives with great versatility, providing for two record players with magnetic cartridges, two tape recorders, a tuner, and an additional stereo input for a compact (digital audio) disc player or video audio. It also includes inputs and outputs for an external signal processor such as a graphic equalizer, time delay device, or noise reduction unit. The performance of the DH-110 is exemplary, and its assembly from an array of discrete components of exceptional quality should ensure reliability and longevity of its capabilities.
Precise interchannel balance at all frequencies is maintained with close tolerance components, and RIAA phono equalization is engineered to very narrow limits, maintaining accurate phase relationships and correct spatial perspectives, as well as exceptional unit-to-unit consistency. The tone controls, which can provide contouring of response for individual needs when switched in, are normally isolated from the circuit for ruler-flat response. The components in the DH-110 have been selected for their superb audio performance as well as for their reliability. They have been incorporated in the unique Hafler fully complementary symmetry push-pull circuit in a carefully designed circuit board layout which reduces crosstalk and maintains separation for a synergistic audio result that defies comparison, regardless of cost. Those who have chosen to build the kit will find that its step by step instructions will ensure a properly working unit even for the novice builder. A substantial amount of preassembly has enabled us to check out each kit in nearly every aspect of performance, and makes the DH-110 a particularly fast, easy and enjoyable construction project, which you will likely complete in one evening. We suggest that you read the installation and operation sections of this manual carefully, even though much may be familiar to you. There are some subtle and significant points which may be new, and their proper appreciation will enable maximum satisfaction with your DH-110. We wish you to have the very best in sound.
Exceedingly low noise and distortion is a hallmark of the DH-110. Noise is essentially inaudible in the absence of a signal, and distortion of all types, both steady state and transient, is at or below the threshold of the finest measurement capabilities. These excellent characteristics are maintained far outside the customary 20 Hz to 20 kHz band, and signals well beyond that are handled without the need to restrict bandwidth.

INPUTS-Magnetic Phono

There are two pairs of phono inputs, identified as Phono 1 and Phono 2. These are independent, and thus they may have different capacitive termination for differing cartridge requirements. As assembled, Phono 1 is provided with a compensation capacitor of 120 picofarads, and Phono 2 is provided with 220 picofarads. One of these values will accommodate most Moving magnet cartridges. These have output levels intended for normal phono inputs (0.5 millivolts per centimeter or higher) and are the most popular. Some high output moving coil design cartridges are not sensitive to capacitive loading, so they may be used with either input. Though some phono cartridges are comparatively free of loading sensitivity, if the cartridge manufacturer specifies the proper load capacitance (which is the sum of the preamps internal capacitance, and the cables you use, as well as the above described capacitor), the most accurate sound will be obtained by following that recommendation. If you have chosen the DH-110 for its sonic attributes, you will be more likely than most to be aware of these differences, and will want proper cartridge termination.
These are high level (line-50 millivolts or more) signals from FM, AM or TV tuners, or compact digital audio disc, video disc, or VCR players. These inputs are grounded at the selector switch when they are not chosen for listening. The input impedance is approximately 33K ohms.

INPUTS-Tape 1, Tape 2

These are at line level and impedance. They connect to Tape Play outputs on the tape deck. They are not grounded when unused, since they can be connected by either the main selector switch or the Tape Monitor switch. They are terminated with 1 megohm resistors to avoid a possible switching transient.

RECORDING OUTPUTS

These connect to the Line Inputs of tape decks. The two pairs of outputs are wired in parallel. Thus two tape recorders receive identical signals. These outputs are buffered with a series resistor, and have an output impedance of 1.5K ohms. To provide full specification performance, the total tape recorder load should not be lower than 10K ohms (i.e. two 20k ohm recorder inputs on each channel). Because it is possible that a preamplifiers overall performance may be adversely affected by rectification ef-
fects that can result from unpowered electronic circuits in the tape decks when they are connected to the Recording Outputs, it is recommended that tape recorders be switched on when the preamplifier is in use. This is a commonly overlooked cause of less-than-ideal preamplifier performance. Signals at these outputs are at line input level (phono signals are first amplified and equalized). These outputs are unaffected by external processing circuits, or by the DH-110s Mono, Filter, Tone or Volume controls. Only signals indicated by the Selector switch are available, including the other tape input, so tape copying is provided using either recorder as a source.

LINE OUTPUTS

which is otherwise a possibility. We recommend that you turn off power amplifiers before connecting headphones, or that they be plugged in before the system is switched on, as a precaution. The Direct outputs provide conventional signal levels independent of the headphone circuit. If headphones are plugged in, the level of the Direct output will be greatly reduced. These outputs should not be used when headphone use is anticipated. The performance specifications will be met so long as the input impedance of the power amplifier is 10K ohms or higher, and the cable capacitance is less than 1Onf. This is no problem with typical interconnecting cables up to 10 feet. If you are planning to use very long cables between preamp and power amplifier, special low capacitance cable can be obtained.

EXTERNAL PROCESSING LOOP

Two pairs of outputs are provided for your power amplifier connection. The set labelled Via Phones is suggested for those who regularly listen through headphones as an alternative. These are wired so that when headphones are plugged in, the signal is disconnected from the power amplifier. Two purposes are thus served. Since many headphones require fairly high volume control settings, you avoid inadvertent high signal levels to your speakers. And a power amplifier which is turned off cannot degrade the quality of signal to the headphones-
Send is an output at line level for the purpose of driving an external signal processor such as an equalizer, time delay, or noise reduction unit. Like the recording outputs, the load impedance should not be less than 10K ohms. The EPL Return input impedance is 33K ohms, and should also be at line level. The EPL Return can also function as an additional high level input, switched from the front panel.
OPERATION When you turn on the DH-110, power is also applied to duplicated by selecting the playback tape recorder on the the switched AC outlets on the back panel. One of the red Selector switch, and recording on the second machine. LEDs on the front panel will light, indicating that the PHONO AMPLIFIER preamp is functioning. Typically, it will be the left-most The button in the lower left of the front panel selects LED, indicating that the Selector switch is determining either Phono 1 (in the OUT position) or Phono 2. The the signal source. At turn-off, it is normal for the LED to switch may be operated to compare two cartridges while fade slowly as the operating voltages decline. music is playing, but if them is no cartridge connected to one input, noise or RF interference may cause a small auDELAYED TURN-ON dible transient. The phono signal is accurately RIAA An internal muting circuit prevents the voltage tranequalized and amplified 34dB (at 1kHz), then passed to the sients which may occur at turn-on or turn-off from causing Selector switch at line level. annoying noises, blown fuses or damaged loudspeakers. At turn-on, the Line Outputs (but not the Recording Outputs or EPL Send output) will be held near ground potential for a few seconds until the internal voltages have stabilized, and the unit is ready for operation. Only a faint output can be heard during this time. At turn-off, whether by operating the preamps power switch, or as a result of external AC failure (a brown-out, pulled plug, or blown house fuse), the line output will be instantaneously lowered. Following power interruption, the muting circuit will initiate a few seconds delay before allowing full signal at the line outputs.

SIGNAL SELECTION MONITOR SWITCH
To facilitate tape recording with tape decks which provide an independent monitoring facility, the DH-110 provides this second selection function. When it is OFF, the regular Selector switch determines what signals are heard. When the Monitor switch is turned to either Tape 1 or Tape 2, the line amplifier is quietly disconnected from the signal being recorded, and is connected to the tape playback instead. This enables direct comparison of the signal source with the taped replica, without affecting the recording process. Tape decks which do not provide separate record and playback heads are not able to utilize this comparison. Note: Do not turn the Monitor switch to Tape 1 if the Selector is also set to Tape 1. Likewise avoid simultaneous Tape 2 settings on both switches. Feedback will occur, and there is a possibility of damage. When the Monitor switch is not in the OFF position, the LED at the Monitor switch will light, in place of the Selector LED, reminding you that tape playback has been selected.
Your choice of signal sources is usually indicated by the Selector Switch, identified by the adjacent lighted LED. This switch passes line level signals direct to the Recording Outputs and to the EPL Send output as well as to the Mono switch and subsequent line amp controls. Either or both tape recorders may record this source. Tapes may be
The following controls affect all signals which are heard through speakers or headphones. They have no effect on the signals to the recording outputs. MONO SWITCH When this button is IN, left and right channel information is combined, and the composite signal is fed to both left and right outputs. In this mode the sound image should appear to be centrally located between the loudspeakers. Critical listeners sometimes choose the mono mode for system evaluation, for it enables you to isolate system response from the complexity of stereo effects. This switch is also useful when listening to monophonic program material. It cancels the unwanted vertical phonograph modulations which are heard as noise from monaural records. FILTER SWITCH This is a low frequency cutoff to remove much of the signal below 25 Hz, such as noise, turntable rumble, or loudspeaker-turntable feedback. Even in cases where the speakers may have little response at these frequencies, this filter can be useful. Very low frequencies can modulate audible midband signals, so eliminating this interference can improve overall clarity. Note: The Filter button should be OUT when the DH-110 is turned ON to avoid a switching transient during the first minute of operation. If it is IN at turn-on, wait one minute before releasing it. EPL SWITCH This is the External Processor Loop. Engaging this switch enables a signal processing device to be inserted in the preamplifier signal path. Such devices include equalizers, time delays or ambience simulators, expanders, compressors, and noise reduction systems. Since the switch permits bypassing the processor loop, an unpowered device in the EPL circuit will not deteriorate the DH-110 performance, as might be the case with switched-off tape decks in the Record Outputs. The EPL switch can also function as an additional input selection. TONE SWITCH Until this button is depressed, all tone control circuitry is completely removed from the signal path. Activating this button may cause a slight change in the tonal balance even when both Bass and Treble controls are in their median (detent) position. Potentiometer tolerances preclude coincident mechanical and electrical centering. The tone control circuitry limits, to an extent, the total bandpass of the DH-110. Operation of the Tone button will be silent if it is depressed in a natural, deliberate manner. Rapid switching may generate small transient pulses. BALANCE CONTROL This adjusts the proportion of left and right channel signals to the Line outputs. In its detented center position the channels will be matched to 0.1 dB. Only the Left signal

will be heard with the control fully counterclockwise, and only the Right signal at the other extreme. The ideal situation would find symmetry in room acoustics and in the electronics, but this realization is rare. Stereo reproduction is, at best, a splendid illusion, and the function of the Balance control is to optimize this illusion in the listening space. Sound wave reflections from walls, furniture and people can unbalance the stereo stage. With judicious application of the balance control, much of the attendant distortion of stereo imaging can be overcome. With the preamplifier in the Mono mode, it will be easier to use the Balance control to centrally position the apparent sound source. This mono setting can then serve as a useful reference point, though the appropriate balance setting may vary from recording to recording in the stereo mode. Our point is that Balance and Tone controls are intended to facilitate the most satisfying sound to the listener; it is appropriate that they be used to this end. BASS and TREBLE CONTROLS The Tone Switch must be IN for these controls to be effective. At full rotation, each control provides about 17 dB of boost (clockwise), or cut (counterclockwise) at the frequency extremes from the center flat (detent) position. The Bass control has a variable inflection, or hinge point so that only the very low frequencies are affected by small amounts of rotation either side of center. This facilitates low frequency corrections without noticeably altering the musical balance, but speakers with diminished low frequency response will not reflect small angular movements from the detent. As the control is turned further, frequencies closer to 500 Hz are affected, so the effect is more apparent. The Treble control has a fixed hinge point at 1kHz and has a shelving action above 5kHz. This affords proper correction without irritation from excessive boost at the extreme. VOLUME CONTROL This step action control was selected for its very accurate tracking between channels, and for its low contact distortion. Clockwise from the 12 oclock position it increases in increments of roughly 1 dB. From 12 oclock counterclockwise it progresses in increasing increments to full attenuation. HEADPHONE JACK A 3-circuit shorting jack is connected so that the tip is the left channel, in series with one set of line outputs, so that the power amplifier is automatically disconnected when the headphones are plugged in. We recommend that you turn off the power amplifier before you connect headphones, or that they be plugged in before the preamplifier is turned on, to guard against needless transients. Be sure the volume is turned down before headphones are disconnected.

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 unmarked 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. 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 solderonce 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 onto adjacent circuitry and cause a short circuit. 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 inserting 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 additional 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. 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 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.

Wiring the Kit

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. To prepare a wire means to cut the designated length from the length 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 resistance to breakage for easier use. Whenever a connection is to be soldered, the instructions 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-3), etc. If soldering is not called for, other connections have yet to be made to that terminal. They would be more difficult if the connection was already soldered. Every connection in the kit will be soldered 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, and for neatness. Be sure that uninsulated wires cannot touch adjacent terminals or the chassis metalwork. 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. Take the time to be accurate and neat, and you can be sure that your completed preamplifier will meet the performance 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 placing a check mark in the space provided, and continuing on to the next step.

cable interconnecting assemblies. Plug one end of each cable onto the pin connectors at the top of the board so the cables extend past the back of the board. The marked edge of the cable is not significant. Now check socket J1 to make sure it does not contact the stub of wire at hole A.
23 [7 Select the 6 black 5/8" screws, the 6 spacers, and 6 small nuts. Insert the screws from the outside of the back panel at the locations nearer the center of the panel (not in the end holes marked Grounds). Install a spacer on each screw and tighten them. Place the PC-12 assembly in position so that its two screws pass through the end holes. Install the nuts on the black screws, and tighten them. Select the 2 small nuts and the 2 knurled thumb nuts. Install a nut on each of the Ground screws, making sure the lockwasher surface is tight against the panel. It must cut through the painted surface to make a chassis ground connection. Then add the thumb nuts. With a pair of pliers, carefully twist the 8 lugs on the AC outlets counter-clockwise l/6 turn, or about 60. This will enable a wire to be passed horizontally through these lugs. Cut a 2 piece of the bare buss wire. Slide it through lug #2 of AC outlet B and connect it to lug #l and to lug #3. Solder lugs 1 and 2. Cut a 3% length of bare wire. Slide it through AC outlet lugs #6 and #7, and connect it to lug #5 and to lug #8. Solder lugs 5,6 and 7. Prepare a 13 length of white wire. Connect one end to AC outlet C, lug #3. (S-2). Place this wire over the top of the transformer. Prepare a 13 blue wire. Connect one end to outlet D lug #4. Place this and the following wire over the transformer. Prepare a 12 length of yellow wire. Connect one end to outlet D lug #8. Select the two side pieces, the rubber grommet, and 4 sets of #6 hardware. Install the grommet in the side piece location adjacent to the power transformer when the flanges bend towards the outside of the unit. Before bolting this piece in position, pass the line cord through the grommet from the outside, and under the transformer. From the inside thread the 3 wires which come from the AC outlets and over the top of the transformer out through the grommet. Fasten both side pieces to the back panel. Connect the shorter line cord conductor to outlet D lug #8. (S-3). Connect the other conductor to lug #4. (S-2). Join the front and rear halves of the preamp so that the tabs on the main board rear bracket ate outside the side pieces. Select 2 sheet metal screws and fasten the bracket tabs to the side pieces.
Plug the two flat wire assemblies onto the pin connectors on PC-14. 35 IJ Prepare a 1% piece of white wire. Connect one end to the rear lug of the power switch. (S). Connect the other end to eyelet Y of PC-14, nearest the fuse. (S). All eyelet connections should be soldered on the bottom of the board for secure connections. 36

Select the white wire from the tear grommet. Connect it to eyelet W on PC-14. (S).
Select the blue wire from the grommet. Connect it to the side lug of the power switch. (S). Select the yellow wire. Connect it to eyelet T on PC-14. (S). The transformer leads may be shortened as desired for neatness, but if there is any possibility that the transformer may be connected for a different line voltage for use outside the USA, be sure to leave each lead long enough for any alternative connection. We suggest that these leads be made just long enough that they can be twisted together for neatness, and placed outside the end piece where they can be later secured with a wire tie. Connect the Red-Yellow lead to eyelet A in the tear comer of PC-14. (S). Connect the two Red leads to eyelets B and C along the rear edge of the board. Solder both. For 120 volt wiring as in the USA, the following lead connections are to be used. Refer to the alternative line voltage diagrams in the manual for other line voltages. Connect each lead as follows and solder: Brown/White to eyelet D Black/White to eyelet E Brown/Red to eyelet F Black/Red to eyelet M Brown to eyelet R Black to eyelet S Connect the short black wire from the forward lug of the phone jack to eyelet G2. (S). There are two groups of wires connected to the phone jack under PC-14. The red and green wires which connect to lugs 2 and 3 (these ate the lower lugs, adjacent to the circuit board edge) are to be connected to the upper (left channel) holes P and Q on the back panel circuit board PC-12, adjacent to the line outputs. Make certain you have the correct group. The black wire is not connected to the board. Instead, keep it twisted with the other wires until it is close to the board, then wrapped tightly around the red and green pair. Make sure no bare wine protrudes from the black insulation. Connect the red

LEFT PHON 0

i 1.IN 02 ,1 I13 I!

15-1 04

SELECTOR

MONITOR

PHONO M

K FLAT D13 D14

HT LINEaa ;T

No 0109

- LEFT LINE Fl v 0

co 0 0

527 (0 Do

-r 0107 (J

Q-&xo

-D5k -D7k - M l +D6-

8 Ic38) --R57-

--R66-R658 -R62-

--R56-

iD12--R59-

VOLUME
--R45QlizJ 141--R144-R44-
wire to hole Q, which is between the center lugs of Jll and 512. (S). The wire should not protrude significantly beyond the front surface of the board to avoid coming in contact with a connector. To assure a good solder connection, bare wire should be visible on the circuit side of the board. Connect the green wire to hole P in like manner. (S). At the rear of the phone jack, connect the black wire from the first group (lugs 2 and 3) to PC14 eyelet G3. (S). 45 [7 Select the other group of three wires, and connect the black wire to PC- 12 hole T. (S). Connect the red wire to

hole S between Jl 11 and J112. (S). Connect the green wire to hole R. (S). Make sure the wires do not protrude
cap into the slots of the front panel. Select the 4 cap screws and nuts, and secure the end caps with the large Allen wrench. Install the appropriate loading capacitors at the pairs of holes identified E, F, G and H below the phono input sockets on the back panel board. The correct choice is discussed in the Additional Information section of this manual. In lieu of more specific information, we suggest the 120 pF values at E and G for Phono 1, and the 220 pF values at F and H for Phono 2. Bend one lead around the capacitor so it is parallel with the lead at the opposite end. The leads should extend more than 1% from the body, but must not be longer than %, or they might touch the metal back panel. Plug each into adjacent pairs of holes.
Now check to make sure that there are no strands of power transformer leads, or the line cord, that are unsoldered. Where the line cord passes under the transformer, make sure it is clear of the screw hole in the back panel flange. Check that a 11 ampere (lOOmA) fuse is installed in the PC-14 clips, and /0 that the Red/Yellow transformer lead connects to the corner eyelet A.
significantly beyond the outside surface of the board. Connect the black wire of the second group to PC14 eyelet G1. (S). Select the 2 red LEDs. To install these with correct
polarity, observe the tiny flat on the LED flange which
marks the cathode lead. This must he towards the near end of the PC- 14 board, or Phono switch S 1, when the
LED is attached to the front, near the edge. When the nipple of the LED is pointed toward you, with the flat on the left, bend the leads (together, with long-nosed pliers) upward at a right angle, so the bend will be 7/10 from the back surface of the LED (about ). Solder the LEDs to the front holes on the under side of PC-14 with the bent
q A wire tie can secure the transformer leads to the
side piece through the slot behind the PC-14 bracket. These ties can be used only once, and lock securely when the tail is pushed through the head end from the flat side. Cut off the excess after pulling it tight.
portion of the leads emerging on the top side. Each LED protrudes through the front sub-panel hole. Solder both

As supplied, the phono load resistance of the DH-110 is 46.55K ohms, which is accurate loading for most cartridges. This value may be changed if need be, by replacing Rl and RlOl on the main circuit board. See the board diagram in the center of the manual. The input resistance is determined by the parallel combination of Rl (101) and R2 (201), each of which is 93.1K ohms (white, orange, brown, red). A different value of Rl (101) will change the desired load to the value RT in accordance with the formula:
Rl = 1 - 93.1/RT To simplify, the following standard 1% values of Rl will provide desired loads RT as shown (all in Kohms): Rl Value Kohms 11.3 17.8

24.9 34.8 44.2 56.2

Desired Load Kohms 10 15
Metal film type resistors are recommended for lowest noise.

=110 pF

This is close enough to the 120pF supplied that Phono 1 can be used without change.
MINIMIZING NOISE IN THE SYSTEM
Your choice of separate components is the right way to secure the best performance from a music system, but the wide-band characteristics and complexity of the best systems may also not conceal the introduction of ground loops and noise pickup-especially RFI (radio frequency interference). With exceedingly high quality equipment we may become conscious of distractions that would be ignored on a lesser level. Careful interwiring practice will greatly reduce the likelihood of such problems. The DH-110 is a very quiet preformer. There can be occasions where even the finest equipment exhibits hum or noise due to irregularities in its interconnection. The simple expedient of reversing line cord plugs will often reduce hum. Listen to the hum level after each change, reversing only one cord at a time. Do not indiscriminately disconnect and reconnect a power amplifier when other components are turned ON. Use the DH-110 muting circuit for protection against loud noises. With the power amp connected to a switched convenience outlet on the DH-110, turn the preamp OFF, reverse the amplifier line cord, and then turn the preamp ON.

CAUTION:

Use connecting cables of high quality, and treat them with care. Unplug cables by grasping the connector-not the cord-to maintain good connections. We have no evidence that special connector platings are required, but the surfaces should be free from grease, fingerprints, or any contaminate that may prevent a firm and complete connection. Some audiophiles are convinced that a good contact cleaner is an important adjunct to a high quality music system. It does not usually reduce noise to connect each component to an earth ground. This may even aggravate a ground loop problem, for good earth grounds are hard to find, and unsatisfactory grounds are likely carriers of RFI. The previous suggestions may also help reduce RFI. In difficult cases, RFI filters can be purchased for insertion between the line cord plug and the wall outlet, or a device called a ferrite bead may be installed in the phono stage by a competent technician. If you use a pre-preamplifier and find that it is RF1 sensitive, increasing the cartridge compensation capacitor may help (moving coil cartridges do not require a specific value), or try connecting a 0.01 mfd capacitor across the phono input jack that feeds the prepreamplifier. Even for experienced engineers, RFI presents problems which often demand that they simply try and try again.

Tape 2 TONE

CD/Video

FILTER

Phono 1 Phono 2
Tuner Record Out EPL Send EPL Roturn

C 2 C R

PHONO 1
Treble Bass SAL V O L v v,
LINE OUTPUTI To Right Channel

Switched E Direct

FUNCTIONAL BLOCK DIAGRAM

COMPONENT VALUES

All resistors are 1/4 watt I% Metal Film unless otherwise noted. RI R2 R3 R4 R.5 R6 R7 R8 R9 RIO RI1 RI2 RI3 RI4 Rl5 R16 RI7 RI8 RI9 R20 R2l R22 R23 R24 R25 R26 R27 E R30 R3l R32 R33 R34 R35 R36 R37 R38 R39 R40 R41 R42 R43 R44 R45 R46 R47 R48 R49 R50 R5l R52 R53 R54 R55 R56 E8 R59 R60 R6l R62 R63 R64 R65 ii: R68 R69 :: s3 s4 S5 s6 93,lOOohms 93,1OO ohms 1,100 ohms 22,100 ohms 22,100 ohms 147.000 ohms 147,000 ohms 22,100 ohms 22,100 ohms 47,500 ohms 47,500 ohms 100 ohms, 1/2 w, 5% carbon film 100 ohms, 1/2 w, 5% carbon film 11,000 ohms 301 ohms 100 ohms 147,800 ohms II,000 ohms 499 ohms I megohm 1,100 ohms 1megohm I megohm 1,100 ohms 100,000 ohms linear taper potentiometer (Balance) 50,000 ohms log taper potentiometer (Volume) 147.000 ohms 17,400 ohms 17,400 ohms 82,500 ohms 82,500 ohms 47,500 ohms 47,500 ohms 100 ohms, 1/2 w, 5 % carbon film 100 ohms, 1/2 w, 5% carbon film 316 ohms 100 ohms ll,O00 ohms 100,000 ohms inverse log taper potentiometer (Treble) 4990hms 1,100 ohms 11,000 0hms 100,000 ohms inverse log taper potentiometer (bass) 316 ohms 1.100 Ohms 11,000ohms 11,000 ohms 1,lOOohms I megohm 22,100 ohms 270 ohms, w, 5% carbon film 1,800 ohms, w. 5% carbon film 270 ohms, w, 5% carbon film 1,800 ohms, w. 5% carbon film 4,708 ohms, 4c1 w, 5% carbon film 4XWOOohms, w. 5% carbon film 470,OW Ohms, w. 5% carbon film 39,OoOohms, w, 5% carbon film 10,000 ohms, w, 5% carbon film 2.2 megOhms, w, 5% carbon film 680,000 ohms, w, 5% carbon film 27Oohms. w, 5% carbon film 100,000 ohms, w, 5% carbon film 47,008 ohms, w. 5% carbon film 10,000 ohms. w. 5% carbon film 1,800 ohms; w; 5% carbon film 1,000 Ohms, w, 5% carbon film 1,000 ohms, w, 5% carbon film 4,640 ohms, w, 5% metal film Phono Input Selector, DPDT Source Selector Monitor Sckctor EPL switch, 4PDT Mono switch, 4PDT (assembly) Tone switch, 4PDT Filter switch, 4PDT (assembly) Power switch
Rii channel corresponding values have designations above 100. Cl :: :: :5 ET0 ClmF, polypropykne, 5Ov 120 pF, polypropylene, 50v 220 pF, polypropykne. 50v 10nF polypropylene, 5Ov 22 mfd, NP ekctmlytic, 5Ov 220 mfd, NP ekctmlytic, IOv 220 mfd, NP ekctrolytic, 10v I5 nF, polycarbonate, 5Ov I5 nF, polycarbonatc, 5Ov 25 nF I%, poiypropykne, 50v 6.8 nF, 1%. polypropylene, 5Ov 1000 mfd, NP ekctrolytic, 6v 1.5 nF, polypropykne, 50v IO nF, polypropylene, 50v 22 mfd, NP ekctrolytic, 50v 470 mfd, low ESR electrolytic, 470 mfd, low ESR electrolytic, 470 nF, polypropylene, 50v 68 pF, polypropylene, 50v 10 nF, polypropylene, 50v 22 mfd, NP electrolytic, 5Ov 470 mfd, low ESR electrolytic, 470 mfd, low ESR electrolytic, I.5 nF, polypropylene, 50v I5 nF, polycarbonate, 50v 47 nF, polycarbonate, 5Ov 470 nF, polycarbonate, 5Ov 4.7 mfd, NP ekctrolytic, 25v 47 mfd, NP ekctrolytic. l6v 100 nF, polycarbonate. 50v 1000 mfd, electrolytic, 50v 1000 mfd, electrolytic, 50v 22 mfd, ekctmlytic, 50v 100 nF, polycarbonate, 50v 22 mfd, ekctrolytic, 50 v 100 nF. polycarbonate, 50v 47nF, polycarbonate, 50v 4.7 mfd, NP ekctmlytic, 25v 4.7 mfd, NP ekctrolytic. 25v 22 mfd, electrolytic, 50v IN4003 IN4003 lN4003 IN4003 IN4003 IN4003 IN525lF 22v Zener, 1% IN4003 IN4003 IN525IF 22v Zener, I% IN4003 IN524OB 10v Zener, 5% LED LED LM3l7T Positive Regulator LM337T Negative Regulator LM393 Dual Comparator 414C Transistor 416C Transistor 416C Transistor 55OB Transistor 556B Transistor 546B Transistor 550C Transistor 560C Transistor 550C Transistor 560C Transistor 560B Transistor 55OB Transistor 56OB Transistor 550B Transistor Jll2 FET Fl CP111 CPll2 CPl16 CP11 CNll6 CNll2 CN112 CC123 CC123 CZ1 I4 CZll5 CN111 CPll4 CPII I CNI I6 CL111 CL111 CPl18 CP144 CPlll CN116 CL111 CL111 CPCC123 CC114 CC115 CN118 CNll9 CC125 CL124 CL124 CL117 CC125 CL117 CC125 CC114 CNl18 CN118 CL117 QD115 QD115 QD115 QDQD115 QD115 QD113 QD1 I5 QDll5 QDll3 QDII5 QDlll QD119 QDI 19 QBll3 QBll4 QBll6 QNll7 QPIl7 QP117 QNl18 QP124 QNl26 i$;:9 i$l% QPII8 QNll8 QPII8 QNII8 QNl3l TAII8

Audio cable pair

NON-COMPONENT (BACK) SIDE
MS138 MS137 MEMS132 MS136 MS135 TA118 KB037 KF319 KF346 WA011 WA016 HRl27
CP111 CP112 CPI16 HW121 HKI 14 XM019 RM025 RM035 RM044 HP122 XM012 HWlll QD119 HR135 HK111 HKl12 HK113 HK115 HKHW118 HA113 HP112 HAHPHPI 14 HP116 HZ112 HKl22 HW113 XA015 MS133 HR134 HR128 HK117 XZ015 HD121 XP0l I HR144 SL112 HR138 H W I 19 MCI11 HDll8 HDl17 WA017 MC112 SF022 HZ138 HZ139

f 4 : 1 I 1

End Caps, rack mount Fuse, 1/10 ampere Slo-Blo Wrench, Allen, 5/32 cap screw Wrench, Allen, +8 set screw
SERVICE POLICY AND LIMITED WARRANTY Your DH-110 Preamplifier has been carefully engineered to provide many years of use without maintenance or service. Factory assembled units undergo many physical and electrical tests before shipment. The circuit board in kits is similarly tested to meet all primary specifications before it is packed. Nevertheless, shipping damage can occur, or human error may intervene to make service necessary. Because many of the components in this refined design are not readily available, and because substitution of apparently similar parts can easily compromise its performance, we strongly recommend that you make use of our complete factory service facilities, or order exact replacement parts from the factory. It is the owners responsibility to return the unit, freight prepaid, to the factory service facility. Units shipped freight collect will not be accepted. Shipment should be made via United Parcel Service whenever possible. We will not be responsible for damage caused by parcel post shipment; repairs in this case will be made solely at the owners expense. Be sure you insure for the full value of an assembled unit. Use the original carton and packing materials, and enclose all of the following: 1. Complete shipping address (Post Office Box numbers are not acceptable for UPS return) 2. Serial number (if not on the unit). 3. Copy of dated bill of sale (for service under warranty) 4. Description of malfunction. If it is intermittent, please indicate this. 5. You may also wish to attach your address directly to the unit, or to the line cord. All service work is guaranteed for 90 days. Warranties apply only to the original purchaser, and are void if the Preamplifier has been modified without factory authorization, or if parts have been substituted which, in the factorys opinion, are not suitable, or if the Preamplifier has been physically or electrically abused or used for some purpose for which it was not designed or intended. Technical assistance to help you locate the source of a problem may be obtained by calling the Hafler Company Technical Service Department at 609-662-6084 between 8 am and 4:30 pm, eastern time. It will be helpful to know the serial number, and the results of any tests you have performed. However we do not recommend that you attempt your own servicing unless you are knowledgeable in this regard. If you return a properly functioning Preamplifier for service or a checkout, a charge will be made for the checkout time required, as well as for packing and shipping. WARRANTY FOR FACTORY ASSEMBLED UNITS The assembled DH-110 is warranted for three years from the purchase date, including parts, labor and normal return shipping costs from the factory to the owner within the continental United States. The owner is responsible for shipment to the factory and must submit a copy of the dated bill of sale.

WARRANTY FOR KIT-BUILT UNITS The parts in a DH-110 kit are warranted for a full year from the purchase date. If a defective component is found on a circuit board or in the kit, simply return the individual part to the factory prepaid, together with the serial number and the date of purchase. It will be replaced at no charge. If you cannot locate the cause of a problem in your DH110, return it to the factory along with a copy of the dated bill of sale, and a check for $30. If the difficulty is solely a defective part, the unit will be returned to you prepaid, and your $30 less shipping and packing charges will be returned to you. If the problem is found to be an error in your assembly of the kit, the unit will be put in proper working order and returned to you prepaid. 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 or silver solder, or paste flux, will be returned unserviced. This warranty gives you certain rights. You may also have other rights which vary from state to state. PC13

Q) 0 Ba c130 Ko 6 10

?tlON?

Printed in USA

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. Component Value Listing. 15 Pictorial Diagram. Insert
Copyright 1984, All rights reserved.

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 7 amp needs (plus other equipment it is also s switching), you should use the amplifier own power switch. In s 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. 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 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 spacing 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. 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. 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 thermal 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.

KIT ASSEMBLY INSTRUCTIONS
There are three basic rules for success in electronic kit building: 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. 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, 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 everything away, if need be. 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, A 40 to 100 watt soldering iron with a 1/4" or smaller tip which reaches at least 600F. 2. 60/40 (60% tin) ROSIN CORE solder, 1/16" diameter or smaller. (Smaller diameters are easier to work with.) 3. A damp sponge or cloth to wipe the hot top of the iron. 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. 5. A medium-blade screwdriver (about 1/4" wide). 6. Needle-nose pliers (a long, narrow tip). 7. Diagonal or side-cutting small pliers. 8. Large gas or slip-joint pliers. 9. 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 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 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 unmarked 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. 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. 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. 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.

Proper Soldering

There are four steps to making a good solder connection: Make a good mechanical connection to hold the wire in position 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 junction. It should melt immediately and flow smoothly around both surfaces. Allow the connection to cool undisturbed. Remember that the connection is made by the solder, not by mechanically attaching the wire to the terminal. Usually the wire is looped through the lug and crimped 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 noisefree 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 why the damp sponge s 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

Wiring the Kit

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 1/4" of insulation from each end. The wire supplied in the kit is #18, so you can set adjustable wire-strippers accordingly. The transformer leads are #16 or #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 resistance to breakage for easier use, and it is pre-tinned. Whenever a connection is to be soldered, the instructions will so state, or indicate by the symbol (S). If more than one wire is to be soldered to the same terminal, they will be indicated by (S-2), (S3), etc. If soldering is not called for, other connections have yet to be made to that terminal. They would be more difficult if the connection was already soldered. Every connection in the kit will be soldered 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 terminals are very close together), and for a neat appearance. Be sure that uninsulated wires cannot touch adjacent terminals or the chassis metalwork. 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. 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 module, to be sure all leads are separated. All of the active circuitry is contained on the PC-19 board, which has been carefully tested to assure that it meets every specification. Only the interconnection of power supply elements is left to the builder. Take the time to be accurate and neat, and you can be sure that your completed amplifier will meet the performance 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 placing a check mark in the space provided, and continuing on to the next step. KEP nuts have been supplied as a convenience. These have lockwashers attached, and the lockwasher always goes onto the screw first. If the sheet metal screws have hex heads, you may 6

find it easier to first start them with a regular screwdriver, to set the thread, and then use the more convenient nut driver, if one is available.

Mechanical Assembly

1 r When you unpack your kit, you will find that the transformer, large capacitors, and the output assemblies have been temporarily fastened to the chassis for safe shipment. Disengage these, and include this hardware with the rest when you check off the components against the parts list in the back of the manual. We recommend this check-off to be sure you have everything, and to enable you to identify any unfamiliar items by comparing them with the pictorial diagram. An egg carton is ideal for keeping hardware items separated. A 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 is not specified, use the #6 size. The smallest size is #4 and #lO the largest. Always insert the screw from the outside of the chassis. It will simplify matters if you first separate the #4 nuts from the #6 nuts, which have the same outside dimensions. A #4 screw will pass through a #6 nut, aiding identification. 2 L Select the four rubber feet, four sets of # 6 hardware, and the chassis. Insert each screw through a foot so that the head is recessed, and install the feet on the outside at each corner hole. Select th e two red output terminals. Install them in the sequence shown below, in the two center holes LR and RR marked ' +at the rear of the chassis. Before you fully tighten the first nut, unscrew the cap to expose the hole drilled through the threaded shaft. Connection of loudspeaker wires will be easier if these holes are positioned vertically. A nail through the hole will keep it positioned while the hardware is tightened. Each connecting lug should point downward before the last nut is secured. Be sure both nuts on each terminal are tight, as they are difficult to reach when the amplifier is completed.

170 Prepare two more 7 white wires. Start as before with one wire 3/4" longer, and twist them together. Connect the longer end to LF lug #2 (S). Connect the other wire to LF lug #l. (S). Place these wires off to the left. Prepare an 8 green wire and a 10 white wire. Start with the white wire 3/4 longer than the green wire, and twist them uniformly together. Connect one end of the green wire to the lug on black output terminal LB. Connect the corresponding end of the white wire to red terminal LR. (S). Place these wires off to the left.
Select the power switch. Install it with the red window to your right as viewed from the front. The switch snaps into chassis hole PS from the outside. 13 q Select the AC line cord and the plastic strain relief. Separate the two conductors for 2. Cut 1 off one of the two leads, and strip 1/4" of insulation from each lead. Twist the strands tightly, and tin each end. Make a sharp 'V' in the cord 8 1/2" from the longest cut end by bending it back on itself. Install the relief with the small end nearest the cut end of the cord. Crimp the two halves of the relief around the wire at the 'V' with heavy pliers, to partially form it before insertion into back panel hole AC. Then grip the larger diameter with the plier tips, squeeze it tightly, and insert the cord and the relief from the outside. A flat side of the relief mates with the hole shape, and it snaps into position when fully inserted.
19 c3 Prepare a 7 green wire. Connect one end to terminal LB. (S-2). Place this wire towards the center of the chassis. 20 Ll Prepare a 10 white wire and a 10 green wire. Starting with the white wire 3/4" longer, twist them together. Connect the projecting white wire to red terminal RR. (S). Connect the green wire to terminal RB. Place these wires off to the right. C Prepare a 51/2" green wire. Connect one end to terminal RB. (S-2). Place this wire towards the center of the chassis. Prepare a 16 green wire, but strip 1 1/4" of insulation from one end. Prepare a 15 white wire. Start with the normally stripped (l/4) ends even, and twist these wires uniformly together. Thread the longer bared end of the green wire through LS short lug #2 from the top left, then through GLlug #3, and connect it to RSshort lug #4. Solder only LS lug #2. Connect the corresponding end of the white wire to LS lug #l. (S). Place this wire up under the chassis rear lip, above the output terminals, and off to the left. 23 L! Prepare a 6 1/2" green wire. Connect one end to CL lug #3. (S2). Place this wire over the rear of the chassis. 24 C Prepare a 10 green wire and a 10 white wire. Twist these together with the ends even. Connect the green wire from the right to RS short lug #4. (S-2). Connect the white wire to RS lug #5. (S). Place these wires off to the right. Prepare two 22 white wires, and twist them together throughout their length. 8 in from one end of the pair, cut one of the wires, and unwind it about 11/2" in each direction from the cut. Strip 1/4" of insulation from each of these cut ends. Place the longer portion of the wire along the lower front edge of the chassis, with the break at the terminal strip TS. Connect the cut end from the left to TS lug #2. Connect the other end to the lower hole of TS lug #5. (S). Place this pair along the front edge of the chassis, under the power switch, with the ends projecting from the front corners of the chassis. 26 il Select a 1 megohm resistor (brown-black-green) and trim the leads to 1/2. Connect one lead to TS lug #2. (S3). One of these 3 leads has already been soldered to the lower lug hole. Connect the other lead to TS lug #3. 27 n Select the diode and trim its leads to 1/2. Note that one end of the diode is marked with a stripe (or an arrow head will point to that end). Connect the marked end to TS lug #4. Connect the other lead to TS lug #3. (S2). Prepare a 4 green wire. Connect one end to TS lug #4. Select a spade connecting lug, and solder it to the other end. Place this wire down against the chassis, and connect it to the PS lug on the right, near the edge of the chassis. The proper way to attach a spade lug to a wire is to first cut the bared wire end to the right length (no more than 1/4" so that the insulation will be securely gripped by the longer, outer tabs, while the wire does not protrude into the spade clamp area. Tin the bare wire end. Bend the 8 29

Select the green and white pair of wires from input socket RS. Connect the white wire from the left to the top (rear) hole #l. (S). Connect the green wire to hole #2. (S). These wires should be soldered to the circuitry on the underside of the board, although they are connected from the top side of the board, assuring a good connection. These wires will be specifically positioned later, though they now seem long.
55 I Select the white pair of wires at the front of the chassis. Tuck the excess-wire into the corner and connect one wire to each of the lugs on the thermal breaker. Solder each. [ Select the left output module, check it as before to see that underside connections near the holes are secure, and that the holes are visible. Place it against the left side of the chassis with the breaker at the front, board up. Prepare a 6 green wire. Connect one end to hole #lo. (S). Be sure it cannot touch the transistor mounting screw! Connect the other end to FL lug #2. (S). Select the green and white pair from output terminals LB and LR. Connect the green wire to hole #7. (S). Connect the white wire to hole #5. (S).
green ground leads from the black output terminals and the ground lug should be brought together through most of their length. Check all your soldered connections - especially those on the fuse clip lugs, which are sometines difficult to solder to. Clip off any excess bare wire which could short to adjacent lugs or the chassis. Pay particular attention to the stranded wires from the transformer and line cord, and check the power switch connections. Now turn the amplifier upside down and shake out any bits of wire or solder. Slide the cover in place, and install it with the eight sheet metal screws.
59 I Select the white pair from LF. Connect the shorter wire to hole #8 (S). connect the other wire to hole #6 (S). 60 : Prepare a 5 1/2 white wire. Connect one end to hole 3. (S). Connect the other end to FL lug #4. (S). Select 4 sheet metal screws and fasten the module to the chassis, making sure no wires are trapped.
Remove the backing from the serial number label, and apply it to the bottom at the center rear. (This may have already been done at the factory.)

IF PROBLEMS ARISE

Each circuit module, which comprises all the active amplifier circuitry, has been incircuit tested to standards identical to factory built amplifiers, prior to being packed in a kit. Thus, with careful assembly, the likelihood of a circuit fault is near zero. If you are certain the problem lies in the power amplifier, check the pilot lamp. If it is blinking, excessive temperature has shut down the amplifier. After a few minutes to cool, it will turn on automatically. If it soon shuts down again, and the amplifier has sufficient ventilation, the malfunction is either internal, or the result of an excessive (and very likely inaudible) input signal. In that case, the source must be investigated. If the pilot lamp is not lighted, the main fuse in the single fuse clip near the power switch is probably open. If a replacement 7 ampere Slo-Blo fuse (do not use a larger value) also blows, the amplifier has a power supply problem, and requires professional service. If there is a problem in only one channel of the amplifier, that channel may be isolated by removing the power supply fuses in the adjacent dual fuse clip, and the other channel may be used monophonically. We do not encourage local service of this amplifier because some components may not be available locally, and substitutions are not recommended at all. You may return a defective module for factory service. This reduces shipping weight and the likelihood of damage. To remove the module (leave the heat sink attached to the circuit board) tag each wire with the circuit board hole number as you unsolder it from the board, and insulate each bare wire end. It is safer to also remove the power supply fuses from that channel. The wires to the thermal breaker must be temporarily soldered together, and insulated.

62 ! Select the green and white pair from input socket LS. Connect the green wire to the top rear hole #2. (S). Connect the white wire to hole #l. (S). Solder these on the back of the board. 63 I ! Tuck the excess of the remaining white pair of wires into the front corner, and connect one wire to each lug of the thermal breaker. Solder each. 64 : : Select the 7 ampere slo-bid fuse (a slo-bid fuse has distinctive internal construction) and install it in the single fuse clip FC. 65 C Select four 5 amp regular fuses, and install them in the dual fuse clips FL and FR. Select the two 2 amp fuses, and install them in the twist type fuse holders on the back panel. These fuses will provide reasonable protection for most speakers. See the Operation section of this manual for more detailed information. The remaining 5 amp fuses are alternates for the back panel holders for high power test purposes. For lowest distortion performance and lowest noise, correct placement of some wires is important. The wires from the output terminals and the back panel fuse holders should be kept against the chassis. The input socket pairs should be about an inch above the chassis, (the left pair can be tucked under the rear chassis lip), and should turn upwards at the bottom center of the circuit board, about 1/2" to 1 off the board, in the plane defined by the edges of the finned heat sinks. The wires to the dual fuse clips should be kept away from the board and against the chassis, bringing the excess length forward of the fuses. The leads to the power supply capacitors should be kept away from the boards. The 10
Adjustments for Bias and DC Offset
These two potentiometers on each circuit board have been set at the factory and should not normally require adjustment for the life of the amplifier. In the event of repairs such as transistor replacement, the following is the procedure, after removing all input and output connections to the amplifier.
Bias Remove the B + fuse F2. This fuse is in the line from the + c a p a c i t o r terminal to hole #3 on the board. Connect an ammeter ' + ' !ead to the fuse clip nearest the large filter s capacitors. Connect the - lead to the other side of the fuse clip. Avoid intermittent connections, and do not short the leads together. Turn the amplifier on, and if possible adjust the line voltage to 120 volts. Adjust P2, near the middle of the board, to 275 mA. Turn the amplifier off, and when the current drops to zero, then remove the ammeter and replace the fuse. Offset A DC voltmeter capable of resolving 10 mV variations is needed. Connect it to the output terminals of the selected channel, and adjust Pl, near the top of the board, to zero volts, + 10 mV. A small correction of the control will produce a large initial change, which will settle down in a second. Repeat these small changes to achieve zero volts.

The transformer warranty is void if the leads have been cut too short for reuse. If you think a transformer is defective the leads must be unsoldered, not cut, for its return. Technical assistance to help you locate the source of a problem may be obtained by calling the Technical Services Department at 609-662-6084, 8 a.m.-4:30 p.m. E.T. It is helpful to know the serial number of the unit and the results of any tests you have performed. SERVICING AN AMPLIFIER MODULE If you are certain that the problem is confined to one of the amplifier modules (comprising the circuit board, heat sink, and output transistors), you may remove and return only the module for service. Be sure that the components on the circuit board are well protected - as by a surrounding sleeve of corrugated cardboard which rests against the heat sink, and projects beyond the components. Properly packed and insured for $150, this assembly can be sent by parcel post, as well as UPS, if necessary. A service fee of $20 must be sent with every module, since the fault may have been caused by a wiring error elsewhere. For this reason, too, and because we have no control over its proper reinstallation, the service warranty on a separate module is limited to assurance of its proper functioning when it leaves the service facility. All modules are tested before being returned to you. If you believe the fault is the factory warranty s responsibility, include the serial number and the bill of sale. If in our judgement the fault is entirely a manufacturing defect, a portion of the service fee will be refunded. Only a complete amplifier can be fully checked and given a service warranty. WARRANTY FOR KIT-BUILT UNITS The parts in a DH-220 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. If you cannot locate what is wrong with your DH-220, return it to the factory with a copy of the dated bill of sale, and a check for $40. If the sole cause of the problem is a defective part, the unit will be repaired and returned to you transportation prepaid, and your $40 less a charge for repackaging and shipping 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 meeting specifications, and returned to you (freight 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. WARRANTY FOR FACTORY ASSEMBLED UNITS The DH-220 is warranted for three years from the purchase date including parts and labor and normal shipping costs from the factory to the owner within the continental U.S. The owner is responsible for returning the unit to the factory and must submit a copy of the dated bill of sale. This warranty gives you specific legal rights. You may also have other rights which vary from state to state. 11

SERVICE POLICY AND LIMITED WARRANTY
The DH-220 Power Amplifier has been carefully engineered to provide many years of use without requiring any maintenance or servicing. Factory assembled units are subjected to several physical and electrical tests before shipment. The output circuit board assemblies of kit units are similarly tested prior to shipment. In spite of all this testing,shipping damage does occur, kits are not assembled properly or someone goofs and service and/or maintenance will be required. The David Hafler Co. provides complete service facilities at the factory to make any necessary repairs. It is the owner responsibility to return or ship the unit freight s 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. Shipment should be via UNITED PARCEL SERVICE. Parcel Post is not a safe way to ship electronic equipment. The factory will not be responsible for damage caused by parcel post shipment and repairs will be made at the owner expense. When s shipping your DH-220 be sure to insure it for the full value of an assembled amplifier. Use the original carton and packing material to ship your amplifier. Enclose with the unit the following information: 1. Complete shipping address (Post Office Box numbers are often n o t acceptable.) 2. The serial number. 3. Copy of dated bill of sale if repairs are to be made under warranty. 4. Description of the malfunction. If intermittent, please note. 5. We also suggest further identifying the unit as yours by putting a label on the bottom or tieing a label with your name and address on the line cord. All service work is guaranteed for 90 days. Warranties apply to the original purchaser only. Warranties are void if: a) the amplifier has been either physically or electrically abused or used for some purpose for which it was not designed, or b) the amplifier has been modified without factory authorization.
The power transformer supplied in DH-220 amplifiers sold in the lJSA is intended for 120 volt, 60 Hz operation only. For use in other countries, a multi-voltage transformer is available at higher cost. It has dual tapped primary windings which can be arranged in various series-parallel combinations for 100, 110, 120, 200, 220 and 240 volt 50 or 60 cycle AC mains. The schematic diagram details the wiring combinations which are represented pictorially here. Note that a separate 2-lug terminal strip is required when the multi-voltage transformer is used. This is supplied in kits which include the special transformer. If the amplifier is operated with 200 to 240 volt tines, the 7 amp line fuse which is supplied should be replaced with a 4 amp Slo-Blo type fuse.

VOLTAGE CHART measured with 120 volt line, no signal. with respect to the ground buss between the two capacitors in the power supply. E 62.6 -62.6 B 62.1) -62.0 c 0.88 -0.37 61.8 61.8 -62.0 -62.0 E 63.0 -1.27 -63.0 -63.0 1.0 -0.8 B 62.0 -0.6 -62.0 -62.0 1.54 -1.35 c 1.54 1.-1.35 65.0 -65.0 s G 1.0 1.0 -0.8 -0.8 D 65.4 65.4 -65.4 -65.4

-0.32 0.8 0.8

0.22 0.22 0.22

Q4 Q5 Q6

QlO Q11

Ql2 Q13

Q401 Q402 Q403 Q404
KIT PARTS LIST KIT PARTS LIST
Minor variations may sometimes be encountered in value or appearance. These will not affect performance.
Fuse Envelope 6 Fuse, 5 ampere 2 Fuse, 2 ampere 1 Fuse, 7 ampere, Slo-Blo 1 Additional fuse, 4 ampere, Slo-Blo (International use only) Hardware Envelope 1 Lug, solder type, internal tooth, #Lug, solder type, #lO 3 Lug, spade, l/Nut, #4-40 KEP 11 Nut, #6-32 KEP 4 Nut, #l0-32 KEP 2 Nut, l/2, for fuse holder 12 Screw, machine, #4 x 5/ Screw, machine, #6 x l/Screw, machine, #l0 x l/Screw, #l0 x l/4, SEMS 16 Screw, sheet metal, #6 x l/Screw, machine, #6 x 3/Washer, flat, 7/Washer, locking, internal tooth, l/2 for fuse holder 2 Washer, rubber, l/2, for fuse holder Small Parts Envelope 1 Capacitor,.0l mfd, disc (103M) 1 Capacitor,.005 mfd, disc (502M) 1 Capacitor,.39 mfd 1 Diode 1 Label, serial number 1 Resistor, 1 megohm
Part No. SF012 SFSFSF026 Part No. HZHZxzo14 HKlll HK112 HK113 HK118 HAHAHAHAHPHAHW114 HW116 HRll7 Part No. CZ112 CZ113 CEl l7 QD115 LR015 RDl13
Part No. 1 Chassis MS149 Cover MS152 CL121 Capacitor. 10,000 mfd, 75V Bracket, round, for capacitor HZ125 Diode rectifier block QDll1 Feet, rubber HR149 Fuse holder, round XA013 Fuse clip, single XA012 Fuse clip, dual XA014 Input socket XPO14 Line cord, with plug WA016 Output module assembly (1 each, left & right) AH326 Output terminal, black, with hardware XKOll Output terminal, red, with hardware XK012 Power switch SLlll Strain relief, plastic HR144 Terminal strip, 5 lug XK018 Additional 2 lug terminal strip (International use only) XK016 Power transformer TA123 Alternate transformer (International use only) TA124 Wire, white, #18 WS024 wso22 Wire, green, #18 LM016 Registration card

- - o , * +d2-D3+t -Rg-

-R4_R 2-C2__cs-
VIEWED FROM COMPONENT SIDE
COMPONENT VALUES COMPONENT VALUES
All resistors are l/4 w carbon film unless specified otherwise
Rl R2 R3 R4 R5 R6 R7 R8 R9 RIO Rll R12 R13 R14 R15 R16 R17 R18 R19 R20 R21 R22 R23 R24 R25 R26 R27 R28 R29 R30 R31 R32 R33 R34 R35 R36 R37 R38 RR402 R403 R404 R405 Cl C2 C3 C4 C5 C6 C7 C8 C9 Cl0 Cl1 Cl2 Cl3 Cl4 Cl5 Cl6 Cl7 Cl8 Cl9 C20
470,000 ohms 1,800 ohms 47,000 ohms 47,000 ohms 1,000 ohms 1,000 ohms 47,000 ohms 560 ohms 560 ohms 1,800 ohms 1,800 ohms 270 ohms 47 ohms 47 ohms 47 ohms 47 ohms 1,800 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, 1/4W, metal film 150 ohms, 1/4W, metal film 1,800 ohms 82 ohms 47 ohms, 1/4W, carbon comp. 47 ohms, 1/4W, carbon camp. 220 ohms, 1/2W 2,200 ohms, 1/2W 10 ohms 1 ohm, 1OW 10 ohms, 5W 28,000 ohms, 1/4W, metal film 470 ohms, 1/2W 470 ohms, 1/2W 220 ohms, 1/2W 220 ohms, 1/2W 1 meg ohms, 1/2W 2 mfd, 5OV, Film 330 pF, 63OV, Film.Ol mfd, 25OV, Film.OOl mfd, 25OV, Film.OOl mfd, 25OV, Film 0.1 mfd, lOOV, Film 0.1 mfd, lOOV, Film 470 mfd, 1 OV, Non-polar Electrolytic 150 pF, 63OV, Film 330 pF, 63OV, Film.Ol mfd, 25OV, Film 100 mfd, lOOV, Electrolytic.Ol mfd, 25OV, Film 100 mfd, lOOV, Electrolytic.Ol mfd, 25OV, Film.Ol mfd, 25OV, Film 150 pF, 63OV, Film.Ol mfd, 25OV, Film.Ol mfd, 25OV, Film 0.1 mfd, lOOV, Film

Part No. RC044 RC023 RC043 RC043 RC015 RC015 RC043 RC045 RC045 RC023 RC023 RC029 RC039 RC039 RC039 RC039 RC023 RC023 RC029 RC023 RC053 RC045 RCRC013 RC036 RZo13 RMo21 RM013 RC023 RC053 RZOll RZOll RD114 RDl15 RC013 RW012 RW013 RM053 RDll7 RDI 17 RDll4 RDl14 RDI 13 CP115 CP134 CP135 CP136 CP136 CC125 CC125 CN113 CP133 CP134 CP135 CL122 CP135 CL122 CP135 CP135 CP133 CP135 CP135 CC125 15
C21 C22 C23 CC402 C403 C404 C405 C406 C407 C408 Dl D2 D3 D4 D5 D6 D7 D8 D9 DlO Dll D12 D13 D14 D15 D16 D40 1
0.1 mfd, lOOV, Film 0.1 mfd, lOOV, Film.OOl mfd, 25OV, Film 680 pF, 5OOV, Mica 0.1 mfd, lOOV, Film 10,000 mfd, 75V, Electrolytic 10,000 mfd, 75V, Electrolytic.Ol mfd, lOOOV, Disc.39 mfd, lOOV, Polyester.005 mfd, lOOOV, Disc 0.1 mfd, IOOV, Film INDiode INDiode INDiode INDiode INDiode INDiode INDiode INDiode FDH-400 Diode FDH-400 Diode INDiode lN5240B 1OV Zener Diode IN5240B 1OV Zener Diode INDiode IN4003 Diode IN4003 Diode IN4003 Diode
CC125 CC125 CP136 CM121 CE115 CL121 CL121 CZI 12 CEl17 cz113 CEl15 QDll6 QD116 QD116 QD116 QDll6 QD116 QD116 QDl16 QD121 QDl21 QD116 QDlll QDlll QD116 QD115 QD115 QD115 QD117 RPOll RPOll SFSF012 SF012 SFSF026 TA123 TA124 QP122 QNl28 QN128 QN128 QP122 QP122 QP122 QP123 QN124 QNl28 QN125 QN125 QP123 QNl12 QNl12 QPl12 QP112 SF024 SF024 TA112
DBDiode Bridge, 25A Pl P2 1,000 ohms trimpot 1,000 ohms trimpot
F4O1 7A, Slo-Blo MDX F402 5A, 3 A G F403 5A, 3AG F404 2A, 3AG (size optional) F405 4A, Slo-Blo MDX TPower Transformer, Domestic T402 Power Transformer, International
:: QlO Qll Q12 Q13 Q401 Q402 Q403 Q404
2N5401 2N5550 2N5550 2N5550 2N5401 2N5415 NP2222 2N5550 2N3440 2N3440 2N5415 2SK134 2SK134 2SJ49 2SJ49
TB40 I Thermal Breaker TB402 Thermal Breaker Ll Output Inductor

SPECIFICATIONS

Power Rating: Less than 0.02% total harmonic distortion at Input Impedance: 47,OOO ohms. Input Sensitivity: 1.55 volts rms for watts into 8 ohms. Damping Factor: 300 to 1 kHz into 8 ohms z
any power level up to 115 watts continuous average power per channel into 8 ohms at any frequency between 20 Hz and 20 kHz with both channels driven.
IM Distortion ( S M P T E:) Less than O.OOS%, from 1 watt to 1 15

watts into 8 ohms.

Typical THD at 115 watts into 8 ohms:
60 to 10 kHz into 8 ohms z
Rise Time: 10 kHz. 60 volts peak to peak square wave, %
I kHz - 0 0025% __ IO kHz - 0. 7 % 20 kHz - 0.012/
Frequency Response into 8 ohms:

to % 2.5 us.

Slew Rate: 10 kHz. 60 volts peak to peak square wave: 30 VI,~ s. Semiconductor Complement: 26 transistors. 8 power Mosfets, 29 diodes, 4 zener diodes. 1 diode bridge.
- 3 dB. 2 Hz to 160 kHz at 1 watt +O, -0.5 dB, 6 Hz to 60 kHz at watts
Typical Channel Separation: 20 Hz:> 75 dB
Power Consumption: watts into 8 ohms: 840 VA;
1 kHz:>85 dB 20 kHz: >6S dB
Signal to Noise Ratio, unweighted: Better than 100 dB at 115
Quiescent: 125 VA. Size: 5-1/8 high. 16 wide, 10-l/2 deep.

Net Weight: 26 Ibs.

Shipping Weight: 30 Ibs.
All Specifications are subject to change without notice.

Printed in USA

INSTRUCTIONS FOR THE HAFLER DH-222 AMPLIFIER BRIDGING KIT DH-222 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 channels 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 BED ( +) 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 channels. The speaker fuses may be replaced with higher values than the 2-5 ampere range suggested for stereo operation, if desired, 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 user risk. s Both speaker fuses should be the same value. If one speaker 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 (ability 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 construction 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 operation, with the possibility of damage to the amplifier.