Hafler 2 Series User manual

PREAMPLIFIER
Qpripc 9
DH-100 PREAMPLIFIER
OWNERS MANUAL
LM163
THE DAVID HAFLER COMPANY
Division of Rockford Corp.
5910 Crescent Boulevard, Pennsauken, New Jersey 08109
613 South Rockford Drive • Tempe, AZ 85281
Please refer to this serial
number in all communications
regarding this equipment.
A 3838601

SPECIFICATIONS
(Specifications stated with load of 27K ohms in parallel with
1.5 nanofarads, and for the band between 20Hz and 20KHz
unless noted.)
PHONO PREAMP SECTION:
Rated Output: 3 Vrms
Maximum Output: 8 Vrms
Harmonic Distortion: Less than 0.005%
RIAA Frequency Response: ± 0.25 dB, 20-20 KHz
±0.1 dB, 40-20 KHz
Sensitivity: 10 mV for V 2 volt @ Record Out
Maximum Input: 180 mV @ 1 KHz
Gain: 34 dB @ 1 KHz
Input Impedance: 47.5 K ohms in parallel
with 130 pF.
Signal/Noise Ratio: greater than 100 dB,
‘A’ weighted.
LINE AMPLIFIER SECTION:
Rated Output: 3 Vrms
Maximum Output: 8 Vrms
Harmonic Distortion: less than 0.005%
Frequency Response: ± 0.25 dB, 20-20 KHz
Gain: 20 dB
Input Impedance: greater than 35 K ohms
Signal/Noise Ratio: greater than 100 dB,
‘A’ weighted
Crosstalk: down 80 dB
Separation: greater than 70 dB @ 1 KHz,
55 dB @ 10 KHz
Bass Control: ± 10 dB @ 20 Hz, moving
inflection type
Treble Control: ± 10 dB @ 20 KHz,
shelving type
GENERAL SPECIFICATIONS:
Semiconductors: 7 integrated circuits,
5 diodes, 1 LED
Inputs: Phono, Tuner, Aux, Tape
Outputs: Record, Line
Controls: Volume, Balance, Treble,
Bass, Input select by push
button, Tape Monitor, Power
AC Supply Voltage: 95-130 or 190-260 VAC,
50-60 Hz.
Power Consumption: less than 5 watts
AC Convenience Outlets: 2 switched
Size: 13-9/16 x 3 x 10 inches
Shipping Weight: 9 lbs.
Net Weight: 7 lbs.
DH100 FUNCTIONAL DIAGRAM
WARNING: To prevent fire or shock hazard, do not expose this equipment to rain or moisture.
© Copyright 1988. All rights reserved.
CONTENTS
Specifications.2
Functional Diagram.2
Installation .3
Component List.4
Parts Placement Diagram.4
Schematic Diagram.5
Additional Parts List.5
Operation.6
Notes on the Circuitry.6
Additional Information .7j
Warranty and Service Policy.8

INTRODUCTION
The DH100 Preamplifier must surely represent the highest
quality per dollar of any audio product manufactured in this
decade. Initial response to the performance of this unit, during
development and testing, has been unusually enthusiastic. The
Puality arises from the meticulous application of good
engineering practice — respect for the fragility of the audio
signal; simple, straightforward circuitry; careful component
selection and testing; generous circuit card topology, and use
of precision tolerances where they contribute significantly to
performance.
The design philosophy of the DH100 exemplifies simplicity
and economy. To achieve this we have provided only those func¬
tions that are primary to a good audio system, and we have been
most careful to see that the integrity of the electronics con¬
forms to a high standard.
Although it might be thought that a low-cost preamplifier
would not find its place among higher-priced components, the
DH100 may change such thinking, for its ability to preserve the
detail rendered by expensive cartridges, power amplifiers and
loudspeakers is most impressive. We invite you to compare its
performance with the highest-rated preamplifiers, and to tell us
of your findings.
INSTALLATION
1.0 MOUNTING
The DH100 Preamplifier is intended for table top or shelf
mounting. No rack mount provision is made. It is important
that the Preamplifier not be placed directly on top of power
amplifiers or other high-current devices; otherwise hum fields
may be intercepted by the Preamplifier and heard in the loud¬
speakers. It is not necessary to provide much ventilation to the
DH100, however it is a good rule to allow air circulation around
any electrical device.
2.0 POWER CONNECTIONS
Preamplifiers are supplied with transformers for standard
United States line voltage. Wide variations are tolerated, be¬
tween 100 volts and 130 volts. For overseas use, an Interna¬
tional transformer is available which accommodates line
voltages between 200 and 260 volts (Hafler Part Number
TA127). It is recommended that the Preamplifier be connected
directly to a wall or floor outlet, and not to an extension cord,
k articularly if the Preamplifier is being used to switch a power
mplifier.
2.1 A C C E S SORY OUTLETS
Two outlets are provided, both controlled by the Preampli¬
fier POWER switch, and adequate to operate a DH-120, XL-280
or DH-500 power amplifier and a tuner or tape transport. In
some countries the AC convenience outlets are not provided.
3.0 OUTPUT CONNECTIONS
Output jacks are labeled ‘L’ for left channel and ‘R’ for right
channel.
3.1 LINE OUTPUT
These jacks connect to the power amplifier input jacks of
your system. The signals at the Line Outputs are affected by
the BALANCE, VOLUM E, BASS, and TREBLE Controls and the
MUTING circuit. Note that the DH100 is not meant to drive
audio cables longer than six feet.
3.2 RECORD OUTPUT CONNECTIONS
These are signal outputs to a tape recorder, for making re¬
cordings from PHONO, TUNER, and AUX inputs. You will use a
‘line’ input on your tape recorder (not a microphone input!) and
adjust the tape input level controls for a good meter reading.
Note that a tape recorder or other signal source connected to
the TAPE input of the DH100 may not be recorded. The
MUTING circuitry does not protect the RECORD outputs.
4.0 LINE INPUTS
I I A LINE LEVEL input is a general purpose input (as opposed
o an equalized input, like PHONO) which expects a standard
nominal voltage for proper operation. Most equipment for use
with a preamplifier — tuners, tape decks, etc. — have an out¬
put that more or less conforms to this standard voltage.
All the line level inputs, TUNER, AUX (Auxiliary), and TAPE,
in the DH100 have the same signal capability and may be used
for other than their labelled purpose. For instance, a tape
recorder or video sound source may be connected to any of
these inputs. The ‘sound’ output from most home computers
may be connected to these inputs as well (see ADDITIONAL
INFORMATION.)
You must observe Left and Right Channel symmetry (ie:
connect Left to Left and Right to Right) between the DH100
and any signal source connected to it.
The PHONO, TUNER, and AUX switches are self-cancelling;
that is, the last button pushed releases the previous button.
Note, however, that the TAPE switch is not part of this self¬
cancelling group and that it supersedes any other input you
may have selected. Be certain to check the position of this
switch if your preamplifier sometimes seems inoperative.
Whilethenominal signal level foralineinput is50millivolts,
higher level signals may be accommodated because they
pass through the VOLUME control before being amplified. The
input impedance is approximately 35000 ohms. When a tape
recorder is connected to the RECORD outputs, this im¬
pedance will drop slightly.
Input jacks are labelled ‘L’ (for Left) and ‘R’ (for Right) Chan¬
nel signals.
5.0 PHONO INPUT
The PHONO input is meant to accommodate standard mov¬
ing magnet cartridges with signal outputs in the 5 millivolt
range. Some ‘high output’ moving coil cartridges will operate
satisfactorily with the DH100 as well, although VOLUME set¬
tings will be in the upper third of the range of that control. Nor¬
mally, use of a moving coil cartridge will require a pre-pream¬
plifier (‘head amp’) or step-up transformer. (Your dealer will be
glad to tell you about suitable products for this purpose.) A
grounding lug is provided on the back panel, under the Right
PHONO input, normally used to connect the ground wire from
the turntable to the Preamplifier chassis. (Sometimes the user
encounters unpredicted behaviorintheturntable-preamplifier
connection. In case of difficulty, see the section on PHONO in¬
stallation, ADDITIONAL INFORMATION, later in this Manual.)
5.1 CARTRIDGE LOADING
The input impedance is 47,500 ohms in parallel with 130
picofarads. This resistance value is standard for most car¬
tridges. The capacitance (130 pf) when added to customary
cable capacitances in the leads between turntable and
preamplifier, will bring the total capacitance value within the
range recommended by most cartridge manufacturers. (To
‘customize’ these input specifications, see ADDITIONAL IN¬
FORMATION.) The PHONO input is ‘guarded’ by a 1 micro¬
farad blocking capacitor (Cl) to protect both the Preamplifier
and the cartridge. THE DAVID HAFLER COMPANY will not
assume responsibility for equipment damage, of any kind, if
this capacitor is removed or defeated. (See ADDITIONAL IN¬
FORMATION.)
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PREAMPLIFIER
DH100
SCHEMATIC
DIAGRAM
PC23B
SERIES
2

OPERATION
6.0 POWER CIRCUITRY
When the DH100 is turned ON, the red LED will illuminate at
the left center of the panel. At the same time, an internal muting
circuit will limit the signal passing from the Preamplifiertoyour
power amplifier for about 1.5 seconds, until the Preamplifier cir¬
cuits have stabilized. During this 1.5 seconds you may hear the
tuner or phonograph or other selected signal at greatly reduced
level. When the DH100 is turned OFF, the muting circuit
engages to protect the power amplifier against turn-off tran¬
sients. If you turn OFF the Preamplifier and turn it ON again im¬
mediately, the muting circuit will still allow only reduced output
for 1.5 seconds. During muting time, what signal you hear may
sound distorted. Such distortion is normal and does not in¬
dicate a Preamplifier problem; it will disappear when muting is
completed.
6.1 SIGNAL SELECTION PUSHBUTTONS
The function of these controls has been discussed in Section
4.0. The Line level inputs, TUNER, AUX, and TAPE, all have the
same input circuitry. When any switch is NOT selected, its input
is left ‘floating’ (not grounded, as in most preamplifiers) but an
isolating ground is imposed between the incoming signal and
the Preamplifier to eliminate inter-source feedthrough. The
reason for providing this kind of input is to accommodate signal
sources that will not tolerate a short circuit to ground at any
time, such as some tape recorder and computer outputs.
6.2 VOLUME CONTROL
This control has a smooth continuous rotation. The ‘unity
gain’ position (where Line input and output voltages are the
same) is at about the 11 o’clock setting of the VOLUME control.
6.3 TONE CONTROLS
The tone circuit in the DH100 is unusual in three respects; it is
not switched IN or OUT, it has an amplifier dedicated to tone
operations only, and it uses a unique balanced circuit to obtain
boost and cut.
The reason many preamplifiers provide tone switching is that
tone circuits tend to interfere with the bandwidth, or overall fre¬
quency response, of the preamplifier. This is not the case in the
DH100. Neither response nor distortion are deteriorated by the
tone circuitry, and when the controls are in their center
(detented) position, response is flat within 0.1 dB.
A ‘balanced’ circuit is obtained by using an operational
amplifier in a differential configuration. This type of control per¬
mits a simple, economical parts symmetry, with adequate feed¬
back for low distortion. Precision tolerances are used in this cir¬
cuit to provide a flat response at detent position and to provide
similar characteristics from unit to unit. The controls are
tapered so that small changes will occur in the area of the de¬
tent, with boost or cut becoming more evident as the control is
moved away from center. As a general rule, extreme settings of
the tone controls indicate a frequency response limitation in
some part of the system, usually the signal source or the
loudspeaker. When high settings are used, it is most likely you
are listening to large amounts of hiss and rumble, and not too
much music. The minimum amount of boost and cut necessary
for enjoyment is the best.
6.4 BALANCE CONTROL
The BALANCE control adjusts the relative amount of Left
and Right loudspeaker volume. We find that customers have a
hesitation in using this control, and it should not be so. The pur¬
pose of balancing the sound is to make the image of the music
seem centered in your listening area. The placement of the
speakers and furnishings in the room, your listening position in
the room — all affect the position of the stereo image. It is
legitimate to use the BALANCE control to make this image
comfortable for you. Not all phonograph recordings and broad¬
casts are balanced at their source, so you may want to correct
for this with the BALANCE control. Usually, experiment will dic¬
tate a normal setting in your room.
When the control is fully clockwise only the Right Channel in¬
formation will be heard, from the right loudspeaker. If it’s com¬
ing from the left, check the connection of your cables. Some¬
thing is reversed. A fully counter-clockwise setting produces
only Left Channel information, from the left loudspeaker. The
center detent provides equal level to both loudspeakers with an
accuracy of 0.1 dB.
Careful interconnection is the best way to insure that Left in¬
formation will be on the left and Right information on the right.
An additional check can be made if you own recordings of a
symphony orchestra, for virtually every orchestra of this type
places violins on the left and cellos on the right of the stage.
Careful listening will confirm this location for these in¬
struments if Left and Right signals are correct.
NOTES ON THE CIRCUITRY
7.0 PHONO STAGES
Two operational amplifiers make up the phono section of the
DH100. The RIAA equalization is passive in this preamplifier,
which means that feedback is not used to determine the
necessary response curve for playing phonograph records. All
the passive components in the PHONO circuit carry 1%
tolerances. The use of passive circuitry offers considerable
design freedom when using integrated circuits, and permits
these ‘chips’ to function adequately in a quality preamplifier by
not asking a single chip to “do too much.” Two stages also pro¬
vide exceptional input-output isolation and a slightly better in¬
put overload characteristic. The gains of the two stages have
been selected to provide, in our opinion, the most practical divi¬
sion for gain, noise, and overload specifications. DC coupling
has been preserved to eliminate both the cost and compromise
of yet another coupling capacitor. Special care has been taken
to insure close tolerances to the RIAA characteristic in the
critical mid-band region.
7.1 POWER SUPPLY
We are mindful of the beneficial influence of a clean power
supply, with good dynamic regulation and the accompanying
low impedance at all audio frequencies. The dual-tracking
regulator in the DH100 tolerates a wide range of line voltage
variations. To maintain a low impedance at high frequencies we
have employed low ESR electrolytic capacitors and bypassed
the power carrying traces at frequent intervals with polypropy¬
lene capacitors. The ground traces have been drawn at five
times their required size, to ensure very low ground path im¬
pedances.
7.2 SWITCHING
A deliberate effort was made to keep the number of switch
contacts in the signal path to a minimum; this meant, eventu¬
ally, only two switches for each signal to pass through, except
the TAPE input, which manages with only one.
7.3 CAPACITOR SELECTION
Capacitors with polypropylene and polycarbonate dielec-
tries have been used wherever possible to take advantage of
their low distortion. Such use is very rare in economical audio
components and contributes significantly to the sonic qualities
oftheDHIOO.
6

ADDITIONAL INFORMATION
8.0 The following paragraphs discuss some of the answers to
frequently-asked questions regarding connection of peri¬
pherals to the DH100 amplifier. If you have a problem, read this
section carefully before contacting the Factory.
8.1 PHONO INPUT CAPACITOR
Coupling Capacitors, Cl (Left) and C101 (Right), are placed at
the input to the Phono stage to provide DC isolation between
the cartridge and the input amplifier. The value is 1.0 mfd. When
this capacitor is jumpered, thus removing it from the circuit,
several problems may arise. Some turntables ‘short’ the car¬
tridge leads to ground when the tone arm is in the rest position.
With the capacitor removed, this grounding may upset the
‘balance’ of the Phono amplifier and produce a dangerous tran¬
sient to the power amplifier, enough to damage a loudspeaker.
Other times, this grounding may produce an unpleasant hum.
There is a small and usually harmless direct current flowing
from the input stage through your cartridge without this
capacitor, but unless you have engineering knowledge of the
parameters involved, you cannot rely on the safe value of this
current. PLEASE NOTE THAT THIS MODIFICATION (eliminat¬
ing these capacitors) MAY INVALIDATE YOUR WARRANTY.
8.2 PHONO GROUNDING
Nearly all turntables have three cables connecting them to
the preamplifier; one each for Left and Right Channels, and a
third single wire for grounding. The single wire is meant to be
secured under the thumb screw below the Right PHONO input
jack. A bad connection at this point will surely be a source of
hum and must be corrected.
Hum will also be heard if the Left and Right Channel plugs are
not firmly seated on the PHONO jacks.
After checking all the conditions stated above, if your system
hums on PHONO but not on any Line input, turn OFF the
Preamplifier and reverse the line plug to your turntable. Often
this will cure the problem.
As a rule, it does not help hum, anywhere in the system, to
ground the Preamplifier to an ‘earth’ ground, such as a water
pipe. Good grounds like this are hard to find, and such a connec¬
tion often makes the situation worse, particularly in the case
where there is Radio Frequency Interference (RFI).
8.3 PHONO INPUT PARAMETERS
The value of PHONO input resistance (R1, R101) may be
changed if necessary. If the value is decreased (less than 47.5 K)
then C1-C101 will have to be increased to preserve the frequency
response. If R1-R101 are increased, the input capacitors will not
have to be changed, and the low frequency response will im¬
prove slightly. Seethe Parts Placement Diagram for the position
of these resistors.
The input loading capacitors, C2,C102 may also be changed
if necessary. The total load capacitance on a cartridge is the
algebraic sum of three separate capacitances; a) the
capacitance of the cable between the turntable and the
Preamplifier, b) the value of C2 or C102, and the input
capacitance of the DH100 phono stage without C2.
Typical cable value is 150 pf.
a)
150
Present value is 120 picofarads.
+ b)
120
Input value without C2 is 10 pf.
+ c)
10
Total capacitance = 280 pf.
Required values for proper cartridge loading can lie between
100 and 470 picofarads. While it is desirable to have the value
close to the manufacturer’s recommendation, this value is not
critical.
When replacing these components, use a good
polypropylene capacitor for Cl and C2, and a metal film resistor
for R1.
8.4 M O N O OPERATION
A preamplifier in MONO mode usually combines the Left and
Right Channel information and delivers this summed signal to
both outputs. Its use is limited to older phonograph recordings
and to a few inputs which are available in MONO only, such as a
monaural tape deck, video sound signal, and computer sound
outputs.
There are two options open to the user if a MONO source is to
be used. The easiest option is to connect the signal to the Left
input jack and listen to the source with the BALANCE control
fully counterclockwise. Or the BALANCE control may be set at
center and a grounding plug inserted in the Right input jack. In
either case, only the Left loudspeakerwill be active. If one mono
signal is applied to AUX left, and one to AUX right jacks, then
the BALANCE control will select one, the other, or a mixture of
the two — two inputs for one.
A more satisfactory input configuration is through the use of
a ‘Y’ interface cable. This device accepts a mono input plug and
branches out to two plugs, one each for the Left and Right
Preamplifier jacks on a Line input. The advantage is that both
loudspeakers will reproduce the mono signal source. In this
case, only one device may be connected per Line input.
Home computers with sound output may be connected to the
DH100. Such outputs vary widely from one computer to another,
so you will have to consult a dealer or the computer schematic
diagram to see what the signal parameters are. We have
eliminated one potential problem for you by seeing to it that the
input signal is never grounded when not in use. Keep in mind
that the computer output level may be much higher than typical
for audio components. In this case a resistive voltage divider
may be used to reduce the signal level. FIG 8.4 shows a typical
connection. Ry should be kept at 10000 ohms, and Rx varied for
a good signal level. It would be possible to adjust Rx so that
computer level is the same as the TUNER or PHONO at similar
VOLUME control settings. FIG 8.4 also shows Rx and Ry com¬
bined in a level control potentiometer which must be mounted
exterior to the Preamplifier, perhaps in a junction box of some
kind. +v c
8.5
FIG 8.4 COMPUTER INTERFACE
c
t Rx
_ .
0
M
-Ml—-1 —
C Ry J
r- 3
C = 1-5 mF
R = 4.7 K
R *1 V c = 5 - 12 V
«- if * > To AUX
i—J
HEADPHONE CONNECTION
The DH100 has no output jack for headphones. The Line out¬
puts will, however, drive high impedance headphones (200 to
2000 ohms) to a level satisfactory for normal listening. It is
assumed that if you use the DH100 for headphone listening, you
are not also using it with a power amplifier. The DH100 controls
make it a very good preamplifier for headphone use. There are
conversion ‘boxes’ available from your dealer for connecting
headphones to the power amplifier and these will prove to be a
satisfactory way to use both loudspeakers and headphones on
the same system, including standard low impedance phones (4
ohms).
8.6 PREAMPLIFIER OUTPUT CAPACITOR
In this day of higher and higher audio power, protection cir¬
cuitry is a most important feature of HAFLER equipment. The
protection circuitry in our preamplifiers and power amplifiers is
meant for the benefit of both these units and your valuable
loudspeakers. For this reason you should never defeat the
coupling capacitors in a HAFLER preamplifier or power
amplifier. The DH100 Muting circuitry requires the coupling
capacitor to prevent DC output to the power amplifier.
REMOVAL OF THIS CAPACITOR MAY INVALIDATE YOUR
WARRANTY.
7

SERVICE POLICY AND LIMITED WARRANTY
The DH100 Preamplifier has been carefully designed to pro¬
vide many years of use without maintenance or service. Factory
assembled units undergo rigorous testing before they are ship¬
ped. However, damage in transit and human error can intervene
to make service necessary.
It is the owner’s responsibility to return the unit, freight
prepaid and insured, to the factory, or to the nearest factory
authorized service facility. Units shipped freight collect will not
be accepted. Shipment should be made by United Parcel Ser¬
vice (UPS) wherever possible. We will not be responsible for
damage incurred in shipments by Parcel Post; repairs, in this
case, will be made solely at the owner’s expense. All shipments
should be insured for the full value of the unit.
Use the original carton and packing material, and enclose all
of the following:
a) Complete shipping address (PO Box numbers are not ac¬
ceptable),
b) Serial number (if not on unit)
c) Copy of dated Bill of Sale, for Warranty service.
d) Description of malfunction. If it is intermittent, indicate
this!
Warranty service is guaranteed for 90 days. Warranties apply
to the original purchaser only and are void if the Preamplifier
has been modified without factory consent, or if parts have
been substituted which the factory considers unsuitable, or if
the Preamplifier has been physically or electrically abused or
used for some purpose for which it was neither designed nor
intended.
WARRANTY FOR FACTORY-ASSEMBLED UNITS:
A factory assembled DH100 is warranted for 3 full years from
purchase date, including parts, labor and normal return ship¬
ping costs to the owner within the continental United States.
The owner is responsible for shipment to the factory or authoriz¬
ed service facility, and must submit a copy of the dated bill of
sale when warranty service is requested.
WARRANTY FOR KIT-BUILT UNITS:
The parts supplied in a DH100 kit are warranted for one full
year from the purchase date. If a defective component is found
on a circuit board or in the kit, simply return the i ndividual 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 DH-100K,
return it to the factory (with a copy of the dated bill of sale if in
warranty) and a money order for $35. Personal checks must first
clear. VISA and Mastercharge can be processed by phone with
your daytime phone number. If the difficulty is solely a defective
part, the unit will be repaired and returned to you prepaid
together with the amount of your payment less a charge for
packing and shipping. If the problem is found to be an error in kit
assembly, the unit will be put in proper working order and re¬
turned to you, prepaid within the continental USA.
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 core, or paste flux, will
be returned unserviced.
This warranty gives you certain rights. You may also have
other rights, the extent of which may vary from state to state.
5910 CRESCENT BOULEVARD, PENNSAUKEN, NJ 08109 • 609/662-6355
Division of Rockford Corp. • 613 South Rockford Drive • Tempe, AZ 85281

THE HAFLER DH-100 PREAMPLIFIER
KIT BUILDER’S MANUAL
LM164
ASSEMBLY INSTRUCTIONS
There are three basic rules for success in electronic kit
building:
1. Read the instructions carefully, and follow them in or¬
der.
2. Make secure solder connections which are bright and
smooth.
3. Check your work carefully after each step.
The DH-100 preamplifier is a versatile component with
sophisticated circuitry which has been made remarkably
easy to build by individuals with many years of experi¬
ence in the design and engineering of the finest perform¬
ing 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. 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 and the pro¬
per tools. The tools should include:
1. A 40 to 60 watt pencil soldering iron with a 3/16" or
smaller tip which reaches 700°F.
. 60/40 (60% tin) ROSIN CORE solder, 1/16" diameter or
smaller.
3. A damp sponge or cloth to wipe the hot tip 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.
Proper Soldering
There are four steps to make a good solder connection:
1. Make a good mechanical connection to hold the wire
in position while heat and solder is applied.
2. Heat the junction of the wire and lug, or circuitry on the
board, with the bright, shiny tip of the iron.
3. After heating for a couple of seconds, apply solder to
the junction. It should melt immediately and flow
smoothly around both surfaces.
4. Allow the connection to cool undisturbed.
Remember that the connection is made by the solder,
not by mechanically attaching the wire to the terminal.
Usually the wire is looped through the lug and crimped in
place, but some prefer to just place it through the hole
and rely on the stiffness of the wire to hold it while solder¬
ing. Connections to the circuit board, of course, 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” par¬
tially melted solder on the joint, as it is useless. A good
connection looks smooth and bright because the solder
flows into every crevice when the parts are hot enough.
Continued on back page.

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 occasion¬
ally you must add a small amount of solder to the tip, too.
If a connection is difficult to heat, “wet” the tip with a
small blob of solder to provide a bigger contact surface to
the joint. Once the solder flows around the conductors,
any movement must be avoided for a few seconds to
allow a good bond. When cool, check the connection by
wiggling the wire. If in doubt, or if the connection is not
shiny, re-heat the joint. Excess solder may be removed
from a connection by 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 elec¬
tronic work. Silver solder is 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 cir¬
cuit pattern from the board. 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.
Assembly Tips
A ‘set’ of hardware includes a screw and a KEP nut
(which has a lockwasher attached). Always install the
lockwasher side first. Screws are always inserted from
the outside of the chassis unless otherwise specified in
the instructions. #4 hardware is smaller than #6, and in
this kit, the #6 screws are finished in black, to match the
cover.
To ‘prepare’ a wire means that you are to cut the desig¬
nated length from that color supplied, and strip about 1/4"
of insulation from each end. The wire supplied in the kit is
#18 white, and #22 red and green, so you can set adjust¬
able wire strippers accordingly. The line cord is #16. Be
careful that you do not nick the wire when you strip it (that
can happen more easily when you do not use wire strip-
pers), for that weakens it. The wire supplied in the kit is
‘bonded stranded,’ which provides greater flexibility with
resistance to breakage for easier use.
Whenever a connection is to be soldered, the instruc¬
tions will so state, or will indicate by the symbol (S). If
more than one wire is to be soldered at the same point,
the indication will be (S-2) or (S-3). 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, but some builders prefer to solder
each connection as they go. Every connection in the kit
will be soldered when it is complete. Every lead which
connects to a hole on the circuit board is to be soldered.
After soldering a connection, clip off any excess lead
length for neatness, and to minimize the possibility of a
short circuit.
‘Tinning’ refers to the process of applying a light coat¬
ing of solder to a bared wire end. On the line cord, for
example, it 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, as it is pre-tinned.
It is a good idea to check off all the parts before you (
begin, to make sure that nothing has been overlooked,
and to help you identify any unfamiliar items by compar¬
ing them with the list for each parts bag, and with the
pictorial diagram. If a part is missing, a postcard, or a
phone call to Customer Service at [phone] will
bring a prompt response.
KIT PARTS LIST
This list is in addition to the individual lists included in each of the parts bags, #1 through #4.
Part No.
Part No.
1
Circuit board assembly, PC-23
KF343
1
Fuse, spare, 1/16 amp slo-blo
SF019
1
Cover
MS174
2
End cap, front panel
MC111
1 Back panel
MS199
4
Knob, metal
HD117
1
Bottom plate
MS173
1
Line cord with plug
WA043
1
Front panel
ME118
1
Transformer, power, 120 volt
TA126
1 Front sub-panel
MS169
or alternate 240 volt
TA127
2 Side pieces
MS171
1
Label, serial number
LR015
1
Allen wrench, L-shape, 5/32"
HZ138
1
Registration card
LM016
1
Allen wrench, L-shape, #8 set screw
HZ139
1
Owner’s Manual
1 Cable pair, audio
WA017
n °n
THE
i ra
U /company
5910 Crescent Boulevard • Pennsauken, New Jersey 08109 • 609/662-6355
Division of Rockford Corp. • 613 South Rockford Drive • Tempe, AZ 85281

BUILDING THE DH-100 KIT
Because many of the circuit components are already
installed on the etched circuit board, the essential per¬
formance of your preamplifier has already been con¬
formed to meet specifications before it was packed in the
*it. Most of the remaining assembly is simply mechanical,
but good solder connections are essential. Read the pre¬
ceding section carefuly if electronic kit construction is
not familiar to you.
2 □ Select the two right angle brackets and 3 sets of #6
hardware (1/2" black screws). Fasten the long leg
of each bracket to the inside of the back panel at
either end of the long central cutout. The third bolt
simply fills the holes between the two rectangular
openings for the AC outlets. This hole has no pur¬
pose in your kit.
The pictorial diagram shows every connection, and the
parts that you will install on the circuit board. The top of
the board is marked with each component designation
next to the mounting holes. Separate lists for each parts
‘bag’ will help you identify unfamiliar parts as you un¬
pack them, and these, together with the pictorial diag¬
ram (which is sometimes distorted for clarity of connec¬
tions) should leave no question as to where each part
goes. In some cases, a specific orientation of a part is
called for, and the circuit board will identify the + lead,
or marked end. However, some part manufacturers will
instead identify the opposite, or (-) lead on the compo¬
nent, so be sure you install these parts correctly.
Mechanical connections in a preamplifier must be
tight, because many of them conduct electrical signals,
even through the chassis. The exception will be the nylon
screws and nuts used in special cases, where they should
be tightened only until they resist your tools slightly, to
^void stripping their threads. It will be easier if you first
Separate the hardware by size and type in an egg carton,
verifying the count on the parts list as a check on how
they are identified. #4 and #6 nuts look almost alike, but
the larger #6 size can be selected by sliding jt over the
single long #4 screw.
1 □ We’ll tackle the most difficult step in this kit right
away—installing the AC line cord and its strain re¬
lief. This requires heavy ‘gas’ or slip-joint pliers be¬
cause of the stiffness of the line cord. Select the
back panel, the AC line cord, and the plastic strain
relief. 9" from the cut end of the cord, make a sharp
‘V’ in the line cord by bending it back on itself with
the ribbed conductor positioned as shown. Install
the strain relief with the smaller diameter nearest
the cut end of the cord. Crimp the two halves of the
strain relief around the cord at the ‘V’ to partially
form it before insertion into the back panel. Then
grip the larger diameter section with the tips of the
pliers and squeeze tightly. Avoid scratching the
back panel when you insert the cord end and the
smaller part of the strain relief through the hole AC
from the outside. Note that the hole has ‘flats’
which keep the relief from twisting. It snaps into
position when fully inserted.
Separate the two conductors of the line cord. Cut
the ribbed conductor so that 2" projects from the
strain relief, and strip 1/4" of insulation from the
end. Strip 1/4" from the longer end as well. Twist
the strands of each conductor tightly, and ‘tin’ each
end with solder to secure the strands.
3 □ Select the two AC outlets. Note that one plug slot
on each outlet is wider. The wider slot goes at the
bottom of the back panel when you snap them in
from the outside. Connect the ribbed end of the
line cord to AC outlet lug #3 (wide).
4 □ Prepare a 2" length of white wire, but strip 1" of in¬
sulation from one end. Connect the shorter bared
end to AC outlet lug #3. (S-2). Pass the longer bared
end all the way through AC outlet lug #4, and 3/8"
beyond that lug, bend the wire downward at a right
angle. Solder lug #4.
5 □ Prepare a 1-3/4" white wire. Connect one end to AC
outlet lug #2, pointing the wire toward the angle
bracket.
6 □ Prepare a 1-1/4" white wire. Connect one end to AC
outlet lug #2. (S-2). Connect the other end to AC
outlet lug #1.
7 □ Prepare a 9" white wire. Connect one end to AC
outlet lug #1. (S-2).
LM164

8 EH Select the ground lug, the longer bright screw, a #4
KEP nut, and the knurled thumb nut. Fasten the
ground lug on the inside of the back panel with the
screw head on the inside, secured with the KEP
nut on the outside, at the lower hole labeled ‘GND.’
The ground lug should point toward the strain re¬
lief. Be sure this connection is tight. Then place
the knurled thumb nut on the screw.
9 EH Prepare a 1-1/4" white wire. Connect one end to the
ground lug so that the wire projects towards the
strain relief. (S). Set the back panel aside temporar¬
ily.
10 EH Select the bright finished front sub-panel, and one
of the rubber grommets. Orient the panel so that
the two single holes are in the upper left corner,
and install the grommet in the larger of the two
holes.
11 □ Select the two lug terminal strip, and one set of #4
hardware. Mount the terminal strip next to the
grommet on the outside (facing you with the
grommet in the upper left) of the panel, below its
mounting hole.
12 □ Select the power switch and two #4 screws. Mount
it on the inside of the panel, below the terminal
strip, so that its two connecting lugs are upper¬
most behind the terminal strip. Set the front panel
aside temporarily.
When installing components on the etched circuit
board, be sure you are using the correct holes, then make
sure the part is oriented correctly if that is specified,
place the part flat against the board, solder the leads on
the underside of the board, and cut off the excess lead.
This board has ‘plated through’ holes, which means that
the hole is coated with metal on the inside. Solder will be
drawn into the hole when it is heated along with the lead,
so you do not have to leave a large mound of solder on the
outside. Just be sure the connection is smooth and
bright. It is expected that you will solder every component
lead which passes through the board, so individual
instructions will not repeat that point.
13 □ Select the circuit board and the 4 diodes, which are
marked with a stripe on one end. The stripe must
be on the end which is nearest the center of the
board when these are installed in the locations
marked D1, D2, D3 and D4, below the transformer
location in the upper left corner. Solder every lead.
14 □ Select the disc capacitor C30 (502M), and install it
between the diodes.
15 □ Select the 2700 ohm resistor, which has color
bands red/violet/red, and install it at R39 near the
left front corner of the circuit board.
16 EH Select the two .033 mfd capacitors, and install
them at C20 and C21.
17 □ Select the two 470 mfd capacitors. Note that the
negative lead may be marked, and/or the positive
lead is longer. The hole for the positive lead is
marked by an arrow on the board at locations C18
and C19. Be sure these are oriented correctly.
18 □ Select the four 1 mfd capacitors (1.0K) and install
them in the lower right corner of the board, in the 2
locations marked C8 and in the 2 locations marked
C11.
19 E H The 12 phono jacks will now be installed at loca¬
tions J1 through J12, along the back of the board. It
is important that these be mounted flat against the
board, and it is also important that a phono plug be
inserted in the jack while the center conductor is
soldered to the board. Because the outside mount¬
ing lugs of adjacent jacks share a common hole in
the circuit board, we suggest the following proce¬
dure as the simplest way to make sure all of the
jacks are properly aligned.
Install the jacks in pairs, starting at J1, but tem¬
porarily ‘tack solder’ only the two mounting lugs in
the one hole at the center of each pair. This will
hold the jacks in position for checking and resol¬
dering as necessary, until they are all in a straight,
flush row. The go back and solder the remaining
mounting lugs securely. After a final alignment
check, go down the line and permanently solder
those lugs which were just tacked in place at first.
Now insert a phono plug (one end of the audio ca¬
bles supplied in the kit) fully into each jack as you.
solder the center conductor of each. (
(g
2P
f <-
V- TACK SOLDER
20 □ Select the four gang pushbutton switch, and note
that the flat metal mounting bar will be tight
against the top surface of the circuit board when
the switch assembly is installed correctly.
Initially tack solder two opposite corner switch
lugs, and check to make sure the switch assembly
is flush against the board, and that all lugs project
through the board. When you are certain that it is
correct, solder every switch lug securely.
21 □ The 4 potentiometers, or controls, may look alike,
but only two are identical. The balance control will
be marked ‘50K’ as a part of the printed numbers
on the control, but otherwise it looks like the 25K^^
bass and treble pots. The volume control is also^J
50K, but it does not have the metal disc on the
back. Install the volume control in the right corner
of the board first. Because control position is
critical for proper mounting to the front panel, and

it is very difficult to make any change after multi¬
ple lugs are soldered, we suggest that you solder
only one lug on each control as you install them at
this time. Even so, take care to position each so
that it is flush against the board, and so that the
control shaft is parallel to the surface of the board.
Select the 50K balance control, and install it in the
center location. Then install the two 25K pots in
the bass and treble positions.
22 □ Select the two large 1000 mfd capacitors, and not¬
ing the + lead arrows on the board, install these at
C16 and C17, just below the diodes.
23 □ Select one of the side pieces, and two sets of #4
hardware. Position the side piece on top of the left
edge of the board, with the flanges pointing out¬
ward, and with the rectangular cutout above the
designation for ‘Regulators IC6 and IC7’. Bolt the
side piece to the board.
24 □ Select the two rubber grommets and install them
in the holes in the side piece.
25 □ Select the two regulators, IC6 and IC7, their 2 flat
plastic insulators, 2 insulating shoulder washers,
and 2 sets of #4 hardware. Install IC7, designated
#7815, on the inside at the rear of the cutout in the
side piece. The flat side of the regulator is towards
the side piece, when the leads are inserted in the
correct holes on the board. Install a shoulder
washer on a screw with the larger diameter next to
the screw head. Hold a flat insulator between the
1C and the side piece, and insert the screw from
the inside, through the 1C, the insulator, and the
metal side. Fasten snugly with a nut, but don’t
overtighten. Solder each lead on the bottom of the
board. Install IC6, #7915, in the same manner in the
adjacent front location.
26 D Select the other side piece, and two sets of #4
hardware. Mount it on the board with the rectangu¬
lar cutout toward the front of the board, at the top.
27 □ Select the front sub-panel assembly, and the 4
large Allen socket-head black screws. Mount the
sub-panel to the board, just sliding the screws into
their corner holes. They need not be secured with
nuts at this time.
28 D Select the 4 nuts and 4 washers for the controls,
and secure the controls to the panel.
29 □ Solder all of the remaining lugs of the 4 front panel
controls to the underside of the circuit board.
30 □ Select the power transformer and the two long
nylon screws and two nylon nuts. Note the lug
numbers on the transformer. Position the trans¬
former so that these match the numbers on the cir¬
cuit board, and solder each transformer lead after
making sure that the transformer is flat against the
board. In the 100-120 volt version used in the USA,
there are no lugs at positions 2 and 3. Install the
nylon screws from the bottom of the board, and
secure with the nylon nuts, but do not overtighten
these.
NOTE: If the transformer supplied with your kit has
lugs at positions 2 and 3, it operates only from
200-260 volt AC mains.
31 □ Select the back panel assembly, and 4 sets of #6
hardware. Feed the end of the AC line cord and the
white wire through the rear grommet in the side
piece from the inside, making sure the angle
brackets are on top of the board, and secure the
back panel to both side pieces.
32 □ Select the two sets of #4 hardware, and fasten the
back panel angle brackets to the top of the circuit
board.
33 □ Connect the short bare wire from AC outlet lug #4
to hole ‘D’ on the circuit board. (S). Connect the
white wire from AC outlet lug #2 to hole ‘F.’ (S).
34 □ On the bottom of the board, connect the white wire
from the ground lug to hole ‘H.’ Solder this on the
bottom of the board. Check to make sure that the
bare wire cannot protrude above the top of the
board so far as to risk contacting a phono plug in¬
serted in that socket.
35 D Thread the line cord and white wire through the
front grommet in the side piece. Connect the white
wire to the rear lug of the power switch. (S). Con¬
nect the line cord to the top lug of the switch. (S).
36 □ Select the plastic wire tie and thread it through the
two slots in the center of the left side piece, to sec¬
ure the line cord and the white wire. This tie can be
used only once, and it locks securely when the tail
is pushed through the head end from the flat side.
Cut off the excess after pulling it tight.
37 □ Prepare a 4" red wire, and a 3-1/2" green wire. Start¬
ing with one pair of ends even, twist these wires
together throughout their length. At the even ends,
connect the red wire to hole ‘A’ on the board, near
the power switch. (S). Connect the green wire to
hole ‘B.’ (S). Thread these wires through the rubber
grommet in the front sub-panel, and connect the
red wire to the farther lug #1 of the terminal strip.
Connect the green wire to lug #2.

38 □ Select the red LED, and note that adjacent to one
lead the red flange has a tiny flat which marks the
cathode lead. This lead will be connected to the
green wire, and thus to hole ‘B’ on the board. To
position the LED properly, so that it will engage the
hole in the front panel, hold the LED pointing to¬
ward you with the flat on the right side. Bend the
lead upwards at a right angle, 1/8" behind the red
base flange. Then bend the leads into an open ‘V,’
so that they may be pushed up through the holes in
the lug terminal strip. When the tip of the LED is
1/2" above the top surface of the square plastic
switch shaft, bend the LED leads sharply outward
to support the LED while it is soldered. This should
position it so that the rear surface of the red flange
is in a vertical line with the front of the switch
handle when it is out (released). Solder the red and
green wires to the lugs, as well as the two LED
leads. Before you cut off the excess LED lead
length, it is best to check by temporarily putting
the front panel in position, after placing the black
plastic switch pushbuttons on the switches for
alignment.
over the LED so that it touches the upturned leads
at the rear. Hold a lighted match below it, and it will
shrink to fit, and thus prevent extraneous glow
from the rear of the LED.
40 □ Reinstall the round plastic pushbutton on the
switch shaft, and select the 4 knobs, the 4 set
screws, and the small L-shaped Allen wrench.
Place a screw on the end of the wrench, and thread
it into a knob. Install each of the knobs so that the
set screw engages the flat on the control shaft.
41 □ Select the front panel, the two end caps, and the
four large nuts. Remove the long cap screws which
were temporarily holding the front sub-panel in
place, slip the end caps into the ends of the front
panel, and install the assembly on the chassis. Be
sure the LED protrudes through the front panel
hole properly. Fasten the assembly to the chassis
with the four cap screws and their nuts, using the
large Allen wrench.
42 □ Install the long U-shaped piece of plastic grommet
over the top lip of the front sub-panel.
Make a visual inspection of the diode orientation,
capacitor orientation, the green wire which is connected
to the ‘B’ hole, and the nomenclature on the controls, as
well as the general quality of solder connections on the
bottom of the board. Make sure the wire to hole ‘H’ does
not protrude too far. Check that the fuse is in place.
43 □ With 6 of the black sheet metal screws, install the
bottom so that the edges turn inward, toward the
top of the unit. The narrow edge is to the rear.
Select the 4 rubber feet, remove their backing, and
install them in the corners of the bottom plate,
about 1" in.
44 □ Slide the cover on from the rear, and secure it with
4 sheet metal screws on the bottom, and one at the
center rear. Affix the self adhesive serial number
label to the center rear of the bottom.
39 □ Remove the round pushbutton from the power You may wish to secure the small Allen wrench (for the
switch shaft, and select the piece of black plastic knobs) to the bottom of the unit with tape, for future con-
shrink tubing. Cut a 1/4" length of tubing, and slip it venience.
CONGRATULATIONS!
Enjoy this truly outstanding preamplifier.
5910 Crescent Boulevard • Pennsauken, New Jersey 08109 • 609/662-6355
Division of Rockford Corp. • 613 South Rockford Drive • Tempe, AZ 85281