Dynaco PAT-4
1803] 033
This number must be men-
STEREO PREAMPLIFIER Concerning this equipment
voi UME
Price $1.00
patents pending 929518
| A Ud LO I nN LC = 3060 Jefferson St., Philadelphia, Pa. 19121 U.S.A.
Operating Instructions ....................
3 Assembly Instructions .................... 7
Technical Information .................... 6 Schematic Diagram ...................... 12
Circuit Description ................... 6 Voltage Chart ....................... Lo... 14
Center Channel System ............... 6 In Case of Difficulty ............... т. x 21
Optional Connections .......... eee 7 Factory Service and Warranty ............. 22
240 Volt Connections ..... TEE ah 7 Parts List ....... aa aa a a a ee a ee 23
Frequency Response:
Distortion at rated
2 volt output:
Hum and Noise:
Tone Control Range:
Maximum Output:
Semiconductor Complement:
Shipping Weight:
Power Consumption:
20 50 100 Hz 1000
High Level inputs: +0.5 db from 10 Hz to 100 KHz
Low Level inputs: +1 db from 20 Hz to 20 KHz (equalized)
THD less than 0.05% 20 Hz to 20 KHz
IM less than 0.05% with any combination of test frequencies
Magnetic Phono: 70 db below a 10 mv input signal
High Level: 85 db below a 0.5 volt input signal
Magnetic Phono: 54 db at 1000 Hz
High Level: 20 db
+16 db @ 50 Hz
+12 db @ 10 KHz
10 volts into high impedance
5 volts into 600 ohms
Magnetic Phono: 47,000 ohms
Tape Head: 100,000 ohms
High Level: 100,000 ohms
Audio Output: 600 ohms |
To Tape: from low level inputs, 600 ohms
from high level inputs, same as source
Amplifier Input: Nominal load 10,000 ohms or higher
Low level or high level RIAA magnetic phono or ceramic phono; NAB
7%2" tape head; Special (normally microphone); Tape amplifier;
Tuner; Spare high level for TV, etc.; Front panel high level
Tape output ahead of controls; 2 Audio outputs (one switched by
front panel jack); Front panel output
Selector switch; Volume control; Balance control; 2 Bass controls;
2 Treble controls; High Filter switch @ 15 KHz, 10 KHz and 7 KHz;
Loudness compensation switch; Tape Monitor switch; Low Filter
switch; paired Stereo-Mono switches to provide A or B channels inde-
pendently or combined (A +B) with 6 db blend for 3rd channel output,
or stereo; illuminated power switch
8 transistors; 2 diodes
131” wide by 4%” high by 9” deep
10 lbs.
5 watts
5000 20000 20 50 100 Hz 1000 5000
100 Hz Square Wave
10 KHz Square Wave
2 cycle 100 Hz Tone Burst
2 cycle 10 KHz Tone Burst
Tone bursts are indistinguishable at out-
put of PAT-4 (top) from generator out-
put (bottom).
100 Hz 1000 5000 20000
The Dynaco PAT-4 is an all silicon solid state control
center and preamplifier which must be used in conjunction
with a basic power amplifier, such as the Dynaco Stereo 70
or Stereo 120, and a pair of loudspeakers. In addition, the
PAT-4 provides sufficient power for a pair of 600 ohm
headphones. When headphones only are to be used, a
power amplifier is not required.
All input signal sources, such as a phonograph, radio
tuner, tape recorder, etc., are connected to the inputs of
the PAT-4 and this preamplifier is the control center for
all mono and stereo signals. Thoughtful planning has pro-
vided exceptional flexibility to accommodate future re-
quirements for such sources as a second phonograph or a
microphone, television sound, musical instruments requir-
ing electronic amplification, etc. A standard phone jack
input and output on the front panel enables convenient
connection of a tape recorder or headphones, even when
the preamplifier is installed in a cabinet.
The components in the PAT-4 are of the highest quality
to protect against failure, and all parts are operated con-
servatively with close tolerances to assure continued proper
operation. The transistors have been specially selected for
Connection to Power Amplifiers
On the back panel of the PAT-4 there are two pairs of
audio outputs which may be connected to a power amplifier,
and one pair for connection to a tape recorder. The upper
row of sockets is for the Left or “A” channel, and the lower
row is for the Right or “B” channel of a stereo system. A
monophonic connection may be made to either channel, but
the left one is most commonly used. The PAT-4 may also
be used on either channel as a monophonic preamplifier
without difficulty and without termination of the second
Output 1 provides a low impedance (600 ohms) output at
all times for normal connection to the amplifier through
shielded single conductor cable of any length up to 50 feet.
Two 6 foot audio cables are supplied with the unit for this
Output 2 is identical to Output 1 with the exception that
it is interlocked with the front panel Output jack, so that
Output 2 is automatically disconnected when a phone plug
1s inserted into the front panel jack. Thus, if headphones
were connected, the loudspeakers would be silenced.
If Output 1 is used, and headphones are also connected,
it will be necessary to advance the volume control farther
because of the power requirements. of the headphones to
obtain the same level of sound from the loudspeakers.
minimum noise and distortion in sustained use and the
etched circuit modules have been pretested in the circuit
to ensure that every unit, after assembly, will meet the
specifications normally associated only with laboratory
The specifications of the PAT-4 speak for themselves,
The distortion and noise, up to levels well beyond those
required to drive any conventional amplifier, are comparable
to the finest tube designs and below the levels which can be
accurately measured with commercial grade test equipment.
Specifications cannot define all the facets of superior audio
performance, however. In use with varying program mate-
rial, the PAT-4 achieves its design goals of sonic ease and
naturalness always sought but rarely achieved in solid state
designs. There is remarkable clarity and an impression of
direct contact with the original without the extra brightness
or stridency which, unfortunately, is sometimes attributed
to high fidelity sound.
Like any precision equipment, the superior capabilities
of the PAT-4 will best be realized when it is properly con-
nected and operated. Please read the Operating Instruc-
tions below before attempting to use this preamplifier.
Connection from Phonograph
There are three pairs of input sockets marked “Phono.”
The type and output level of the cartridge used determines
which pair (only one at a time) should be used. One pair
is for a ceramic cartridge, marked Cer, and the other two
pairs provide RIAA equalization for magnetic cartridges.
The Low input is used with all normal magnetic cartridges
(maximum inputs up to 80 mv). If higher output car-
tridges become available, these can be used instead on the
High input with a simple modification to each circuit
board. Information and parts for this change will be sup-
plied on request by Dynaco.
Ground Connection
Sometimes the phonograph or tape machine will have an
extra wire which is to be attached to the preamplifier chassis.
A grounding screw Gnd is provided for this purpose. Under
some unusual conditions of use, where it is advisable to
ground the system to a water pipe or similar earth connec-
tion, this screw can serve as the connection point.
In general, it is advisable to use the minimum number of
separate ground leads necessary to achieve lowest hum.
Some experimentation may be necessary, but extra leads
often cause an increase in the hum level of a good music
Connection from Tape Playback
Two pairs of inputs are provided for playback from a tape.
If the machine has no electronic playback circuitry, but the
output is directly from the playback head, the Tape Head
inputs provide NAB 714” equalization. Use the shortest
possible shielded cables to this input because of the require-
ments of the playback head. This input is selected by turn-
ing the front panel selector switch to Tape Head. A separate
ground wire should be connected from the tape deck’s rec-
ommended grounding point to the Gnd screw on the PAT-4
to avoid hum.
When the Tape Head inputs are not used, the two shorting
plugs supplied should be inserted in those input sockets.
This will reduce noise which would otherwise be heard when
switching through this position with the selector switch.
Most tape machines available today include playback
preamplifiers. For these, audio cables should be connected
from their “preamp output” or “line output” sockets to
the Tape Amp inputs, and the selector switch turned to
Tape position on the PAT-4.
Connection to Tape Recorder
If your tape machine has recording facilities, then audio
cables should be connected from the To Tape output
sockets on the PAT-4 to the “radio”, “high level” or “line”
inputs on the recorder. The recorder inputs should require
signal levels nominally between 100 millivolts and one volt
for full recording level. The microphone inputs on the
recorder are not suitable, because their sensitivity is too
To Tape output connections are made in the PAT-4
ahead of the volume, balance, filter and tone control cir-
cuits so that these controls may be operated to adjust the
amplifier signal to the speakers during the recording
process without affecting the signal going to the tape re-
corder. This is the normal connection for recording.
To Tape outputs are ahead of the stereo-mono switches,
however, so each output is independent and should not be
externally connected together for monophonic recording
from a stereo sound source.
If you wish to use all the controls in the preamplifier to
correct the recording signal, the amplifier Output 1 may
be used. Remember that the volume control of the PAT-4
will then control not only the speaker and/or headphone
level, but also the signal level going onto the tape. The
filter, stereo-mono switches and tone controls may be help-
ful when transferring older 78 rpm discs to tape, for
example. A higher signal level can be obtained from
Output 1 by advancing the volume control than from
To Tape because of added gain in the output stages of the
preamplifier, enabling the transfer of weak input signals
(such as Tape Head playback) with less noise. You may
wish to disconnect the power amplifier and use headphones
in this case, however.
The PAT-4 does not provide the equalization and bias
requirements of a complete tape recording preamplifier. It
therefore cannot be used as such.
Connection from Radio Tuner and other
High Level Sources
The Tuner and Spare inputs are identical and receive
flat high level signals from AM/FM/Multiplex radio
tuners, additional tape recorders, audio signals from a TV
set, etc., via regular shielded cables.
Connection from Microphone and other
Special Sources
The pair of inputs marked Special are normally con-
nected for a flat high gain input such as a high impedance
(50,000 ohms) microphone using single conductor shielded
cable. Alternatively, by internal change described in the
Technical Section of this manual, the Special input can be
used as an additional phono input or other high gain
equalized input.
Selector Switch
The selector switch connects your choice of program
source, selecting both channels simultaneously, together
with the proper equalization for phono or tape head. This
switch also enables you to select a tape recorder’s output,
differing from the conventional switching arrangement in
which the tape had been selected separately by the Monitor
switch. In the PAT-4 there is a Monitor switch as well
(described later), but selection of the recorder for routine
playback is made in the same way as all other inputs to
avoid confusion.
Volume Control
The output of both channels is controlled simultaneously
by this control, with close tracking of the two stereo chan-
nels so that the program material will remain in balance
over most of its range. The taper rate of this control has
been chosen to provide a slow increase in volume over the
first half of rotation and a more rapid volume increase
above 12 o’clock. This enables most satisfactory operation
with both low and high efficiency speakers.
Balance Control
The balance control is normally centered, giving equal
signal strength to both channels. Rotation to the right
shifts the apparent sound source to the right by reducing
the left channel level, and conversely to the left. This
control has a very gradual action in the first 90° of rota-
tion either side of center, so that delicate adjustments in
balance can easily be made, but its action increases rapidly
to the extremes of rotation, where one channel or the
other is silenced.
A balance control is required because some program
sources are not accurately balanced, and it is possible that
the speakers used may have different efficiencies, or some
rooms may absorb more sound energy from one speaker
than from the other. A certain amount of balancing adjust-
ment is thus semi-permanent, while the rest varies with the
source. If you find that your balance control gives best
results in the normal listening location when it is con-
sistently offset from center, you may wish to loosen the
set screw and reposition the control knob so that it points
straight up for most listening.
Tone Controls
There are individual bass and treble controls for each
channel, but to make normal operation easier, the two sets
of controls utilize split knobs. This enables you to make
routine adjustments on both channels simultaneously, yet
vary them independently when special occasions call for it.
The forward knob controls the left channel, and the one
nearest the panel adjusts the right channel.
The normal or “flat” position is centered, with increasing
effect to the right, and a decrease to the left. Tone con-
trols alter the original signal to suit the user; but these
alterations are deviations from truly accurate reproduction.
The reference point should always be the center, which
gives no frequency discrimination. The tone controls also
help to correct for record compensation characteristics of
older discs which do not follow the present RIAA standard
playback curve.
The special tone control design in the PAT-4 is a
patented Dynaco design which assures that the tone con-
trols are “out of the circuit” when they are centered. This
provides the convenience of continuously variable correc-
tion without the complication of extra disabling switches.
High Frequency Filter
The Hi Filter rotary switch gives sharp reduction of the
frequencies above the points which are marked (in KHz)
on the front panel. The first step away from “flat” is
barely detectable, being at the extreme of the audio range.
Further steps have an increasing but still subtle effect.
The 15 KHz position may be useful in filtering out super-
sonic disturbances when recording from some stereo radio
programs. Successive steps will assist in reducing high
frequency distortion in poorer program sources.
Monitor Switch
The spring-return Monitor switch enables direct com-
parison of the source signal as indicated by the selector
switch, with the same signal played back from the playback
amplifier of a tape recorder. This feature is applicable
when recording through the PAT-4 to a tape recorder
Which has separate preamps and 3 or more heads designed
for simultaneous playback while recording. For example,
while recording from a radio tuner, the selector switch is
on “Tuner,” and “To Tape” is connected to the recorder
input. 'The playback output of the recorder is connected
to “Tape Amp.” You will hear the tuner directly until
you depress the Monitor switch against the spring. Then,
you will hear the program just recorded as it is played back
from the tape.
Loudness Switch
The Loudness switch is normally left “Off,” but it may
be used at lower settings of the volume control to provide
an Increase in bass to compensate for the ear’s lack of
sensitivity to low frequencies at low sound levels. The
high fidelity purist usually avoids any such compensation;
but many listeners will find this switch, used in modera-
tion, adds listening enjoyment at low levels. This sonic
correction does not add boom or muddiness to the
Low Filter Switch
When “On” the Low Filter reduces the level of signals
below 100 Hz, and thus minimizes rumble and similar low
frequency disturbances.
Stereo-Mono Mode Switches
The pair of switches marked Stereo-Mono is normally
left in the stereo position, with the bottom of each switch
depressed. They provide three additional choices: 1) The
left input channel “A” is switched through both outputs by
depressing the top of the “A” switch alone; 2) conversely,
the right input channel “B” is available at both outputs
when “B” top is depressed, and the bottom of “A” is de-
pressed; 3) a partially blended mono signal is obtained at
both outputs by depressing the tops of both switches.
When the tops of both switches are depressed this is a
blended position to be used for combined channel mono
signals. This gives 6 db of separation and is desirable for
reducing the apparent separation between stereo speakers,
or for establishing the proper spatial effect for more
natural sound in stereo headphones. This is the normal
position for playing mono records with a stereo cartridge.
It can also be used when operating a center speaker in the
Dynaco derived center channel system. This 3rd channel
system is described in the Technical Section of this
manual. The Technical Section also describes the minor
wiring change to obtain a fully blended (A+B) mono
signal if desired.
Since the stereo-mono switching system enables you to
play a mono program through both output channels, it is
possible to have extra mono inputs by using the Spare or
Special positions for different signal sources in the left and
right inputs. For example, a TV input could be selected
for the Spare “A” input, and a mono tape machine for the
Spare “B” input. Then selection between these would be
made with the stereo-mono switches.
Front Panel “Input”
The front panel Input jack will override the selector
switch and cut out the signal from all other inputs when
a phone plug is inserted. 'This is a normal high level input,
identical to the Tuner and Spare inputs. You may wish
to connect a tape recorder here, but remember that the
Monitor function is not operable on this input. Another
possibility is to insert the output plug from a musical
instrument requiring amplification, such as an electronic
guitar. If the plug from a mono source is only partially
inserted (to the first detent, or notch) then only the right
channel is activated by the front panel input, and you can
mix a guitar, for example, on the right channel, with a
record (selector switch on phono) heard on the left chan-
nel. You can adjust relative levels with the balance con-
trol. If desired, you can mix the two signals (if they are
already properly balanced) by depressing the tops of both
mode switches. Thus you can accompany a musical instru-
ment with a record, tape, radio, or a microphone.
If a mono phone plug is fully inserted, it will provide
signal to the left “A” channel only; then depressing the
top “A” button will switch it through both output channels.
Front Panel “Output”
The front panel Output jack provides a normal 600 ohm
output in parallel with amplifier Output 1 on the back
panel. Connecting to the front panel output mutes Out-
put 2 on the rear, enabling the use of headphones, for
example, to automatically cut out the speakers.
If an amplifier is connected to Output 1, which is not
muted by the front panel jack, the introduction of head-
phones will cut the amplifier signal approximately in half.
Headphones should be of medium impedance (nominally
600 ohms) or higher. If only low impedance (4 to 16
ohms) headphones are available, such as are normally con-
nected to amplifier outputs, then a matching transformer
should be used.
Because of the load imposed when headphones are con-
nected, the high filter switch operation is altered, and in
effect, only the 15 KHz position has any marked effect,
albeit at a lower frequency.
AC Line Connections
There are two black AC outlets which are switched on
and off with the PAT-4 power switch, and two red outlets
which are always connected to the AC line. The power
amplifier and radio tuner are usually connected to the
switched outlets, and a phonograph and tape recorder are
usually connected to unswitched outlets so that their drive
mechanisms cannot be damaged if the preamp power is
turned off without disengaging the machine.
Each channel of the PAT-4 uses two pairs of npn tran-
sistors In similar configurations. One pair provides the
low level amplification and equalization for phono car-
tridges, tape heads, microphones, and similar low level
sources. The input transistors are selected low noise
types. The low level phono input can handle signals up
to 100 millivolts without overload, and the high level
phono input will accept up to 800 millivolts.
The other pair of transistors comprises the tone control
and filter stages, and operates at the higher signal levels
of tuners, tape recorders, etc., as well as from the output
of the phono preamplifier stage. Each pair has a DC feed-
back loop to stabilize operating conditions, as well as an
AC feedback loop to provide optimum audio performance.
The operating parameters of each stage have been criti-
cally adjusted to achieve the lowest possible distortion
levels —below that which can be measured with commercial
test equipment.
The special feedback tone control system of the PAT-4
is an exclusive Dynaco development which provides con-
tinuous independent adjustment of the frequency extremes,
while providing a specific “center-flat” setting. When the
controls are set to the normal mid-point of rotation, they
are effectively out of the circuit and have no effect whatso-
ever on performance. This is accomplished through the
use of special Dynaco-designed potentiometers. The treble
controls have a discontinuous taper, and the bass controls
utilize a dual wiper design. When the tone controls are
operated away from the “flat” center point, the frequency
response 1s varied by changes in the amount of feedback
at the frequency extremes.
The output impedance of the PAT-4 is 600 ohms, en-
abling it to be used with long output cables, and to be
relatively noncritical of load impedance. Its specifications
are based on a load of 10,000 ohms or higher, encompass-
ing virtually every tube or transistorized amplifier. If a
lower impedance load is applied, there is some reduction
in the maximum output level which can be obtained with
low distortion. The high frequency filter, which is at the
output of the preamplifier, is also altered in effect with
lower load impedances, as is the bass cut curve.
While it is possible to obtain moderate levels with even
low impedance (4 to 16 ohms) headphones connected
directly to the output jack of the PAT-4, the frequency
response and distortion at the output will be significantly
affected, and a 600 ohm matching transformer should be
used to preserve high fidelity results.
Installing your PAT-4
Your PAT-4 generates very little heat; so it is unnec-
essary to provide ventilation, even with continuous duty
operation. If it is stacked with the Dynatuner, the tuner
should always be placed on top, since it does require some
ventilation. The PAT-4 may be mounted in any position
in a cabinet, and for panel mounting an accessory PBK
bracket kit is available from Dynaco for $2 postpaid. No
CODs please. À single rectangular cutout 13” by 3-13/16”
is required in any panel up to one inch thick. Or, you can
simply provide a shelf flush with the bottom of the open-
ing. The rubber feet are not used in such mounting. In a
cabinet which provides for “face up” mounting, the PAT-4
can simply be supported in the cutout by its front panel.
This method of deriving the center (third) channel of a
stereo system is an exclusive Dynaco development which
utilizes special circultry in the PAT-4 preamplifier to pro-
vide the proper in-phase (A+B) signal without loss of
stereo separation and without the need for an additional
amplifier. It is useful where the left and right speakers must
be widely separated, and it also enables the use of the
third channel speaker as a monophonic system in another
It should be recognized, however, that a two channel
system will have a wider apparent sound source than any
system utilizing a center speaker in a derived third channel
arrangement, if the spacing between the left and right chan-
nel speakers remains the same. In order to maintain equiv-
alent spread of sound, somewhat greater spacing between
the outside speakers is required in any 3 speaker system.
The connection of the 3 speakers is diagrammed below.
The use of 3 identical speakers is essential to achieve the
most natural sound throughout their range. In any event,
all speakers must have the same efficiency, and the left and
right speakers should be identical. Connection of dissimilar
speakers will reduce separation and adversely affect spatial
orientation. The use of individual level controls in series
with any of the speakers will also reduce separation. They
are neither necessary nor desirable when matched speakers
are used. If the speaker systems provide controls for the
adjustment of relative tweeter or midrange levels, these
should be set before the system is adjusted as described
below. Be sure all speakers are correctly phased.
— + — + — +
Po ET ]
| GND |
| I
Adjusting the system is easy. Set the tone controls in
their “flat” centered positions, switch off the loudness com-
pensation and both filters, and adjust the volume control for
normal listening level. Depress the top of both A and B
mode switches for partially blended channels. Now use a
monophonic source so that identical signals will be fed to
both channels, and temporarily remove one of the wires to
the center speaker. Either wire gives the same result. Adjust
the balance control for minimum sound output. If neces-
sary, the balance control knob can be recentered so that the
upright pointer indicates the position of precise balance.
Then reconnect the speaker wire.
Now all program material, both stereo and mono, can be
played with the mode switches in the blended position, and
generally without any need to readjust the balance control.
Monophonic programs will appear predominantly in the
center speaker. Stereo programs will retain their separation,
and when the listener changes position, the apparent distri-
bution of sound will not shift, so that the stereo perspective
will be less dependent on the listening position. If you wish
to turn off the center channel speaker, normal two channel
stereo 1s obtained by shorting across the terminals of the
center speaker.
If the third channel is to be used as a remote monophonic
speaker, it is advisable to first install it as a center channel
of the stereo system for proper balance adjustment as indi-
cated above. It then may be moved to another area.
The design of the PAT-4 makes it easy to “customize”
in several ways to suit individual needs. A few of these
are described here.
Monitor Switch
If frequent use of the Monitor switch makes it desirable
that it operate with a normal detent action, instead of a
spring-return, you can obtain the same switch as is used
in the other function positions for $1.00 postpaid by re-
questing Dynaco part #334002. It is possible but not
simple to remove the spring in the present switch.
A+B Full Blending
If you wish the (A+B) position of the mode switches
to provide complete blending with the tops of both
switches depressed, rather than the normal 6 db separa-
tion, connect a short piece of wire across the 7,500 ohm
(violet-green-red) resistor between lugs #2 and #5 of switch
AS. You need not remove the resistor.
Special Phono Input
If, instead of a microphone input, you wish to use the
Special position for a second low level phonograph input
with RIAA equalization (so that you might use a separate
changer and turntable, for example) change each channel
for stereo as follows: Remove the wire from eyelet #8 on
the circuit board. Do not disconnect the other end from
rear lug #2 of the selector switch wafer, but shorten the
wire and solder the free end to lug #4 of the same wafer.
Provision for Other Equalization
There is a separate group of equalization components
for each low level input on each circuit board. Other
values can be substituted to provide special variations if
desired. R7, R8, C5 and C6 are in the Phono channel.
R10, R11 and C8 affect the Tape Head input. R9 and C7,
together with the wire jumper on the board at that point,
control the Special input as used for microphone.
It 1s necessary to connect to separate input sockets,
rather than simply bridging from one position to the next,
when changing from one equalization position to another,
because of the automatic shorting of the unselected low
level inputs incorporated in the selector switch to elim-
inate feedthrough from unused inputs. Such shorting
action can be removed only by deforming the selector
switch contacts on the back of each switch wafer.
Driving a Third Channel Amplifier
A simple arrangement to power a center channel speaker
without the need for an additional amplifier has been
given earlier. This is an alternate approach to a three
channel system.
You can obtain a combined channel signal to drive a
third channel separate amplifier by connecting one pair of
outputs together through isolating resistors, and taking the
signal from their junction. For example, a 47,000 ohm
1% watt resistor in series with each output will maintain
adequate separation between the main channels, provide
a medium impedance output, and will be only about 6 db
lower in signal level than the main channels. A 100,000
ohm or higher value potentiometer could be used as a
center channel level control from this junction.
The power transformer supplied in the PAT-4 may be
connected for a 240 volt AC line as well as for the stan-
dard 120 volt AC line, which is how the transformer is
connected unless this manual is stamped “240 volt”. The
transformer has dual primary windings. They are con-
nected in parallel for 120 volts, and in series for 240 volts.
The notes to Steps 37, 40 and 41 on page 18 and the dia-
gram on page 23 detail the 240 volt connections.
The 1/10 ampere (100 ma) slo-blo fuse supplied with
120 volt wiring should be replaced with a 1/20 ampere
(50 ma) slo-blo fuse when the preamplifier is wired for
240 volt use.
The PAT-4 is designed for use with either 50 Hz or 60
Hz current. Variations of line voltage up to 1097 from
nominal value will not affect performance.
Assembly of the PAT-4 is exceptionally simple when
compared to other kits. The preassembled etched circuit
boards have saved you much of the work, and the assembly
that remains is arranged in an open, uncluttered layout
that makes wiring quick and easy. The construction time
will be several hours. It is better to work slowly and care-
fully rather than worry about the time.
When you unpack your kit, check off the components
against the parts list at the back of the manual. You can
identify unfamiliar parts by matching them to the pictorial
diagram or photograph.
Have the proper tools at hand before starting assembly.
You will need a pencil-type soldering iron of 30- to 60-watt
rating with a small tip, long nosed pliers, diagonal cutting
pliers, a medium-sized screwdriver, and 60/40 rosin core
solder not larger than %6” diameter. You will also find a
damp sponge or cloth helpful to wipe the tip of the iron
clean periodically. An inexpensive wire stripping tool is
helpful, but some people prefer a single-edged razor blade
for removing the insulation.
Although your PAT-4 has been designed to be as free
from trouble as possible, there is always the chance that
a defective component or improper assembly will cause dif-
ficulty. However, because the circuit is essentially simple,
and the layout accessible, it should not be difficult to locate
and correct the source of trouble.
Because 90% of the difficulties which are encountered in
kit-built units can be attributed to incorrect wiring or to
poor solder connections, it is strongly recommended that
you ask someone else to check your wiring against the pic-
torial diagram, as frequently one person will overlook the
same error repeatedly. Unless a wiring error has been
made which would cause the breakdown of one or more
parts, it is highly unlikely that inoperation upon comple-
tion will be caused by a faulty component on either of the
circuit boards, since these have been in-circuit tested prior
to shipment.
There are certain general precautions to be observed in
servicing any transistorized equipment:
1. Never make circuit changes (connections or disconnec-
tions) of any kind when the preamplifier is turned on.
2. Be particularly careful not to short any transistor leads
to each other or to the chassis when the power is on.
3. When using test equipment, you must avoid transient
voltage peaks and excessive test voltages.
4. Exercise caution when soldering and unsoldering tran-
sistor and diode leads to avoid excessive heat.
The average kit-builder should confine his servicing to
the basic suggestions given here, after first checking to
make sure the fuse is intact. Audio transistors, unlike
tubes, cannot be easily checked locally for any other than
gross defects, and even this should be left to the qualified
First, construction problems should be eliminated by
close inspection and rechecking. Trace the wiring, and
examine solder connections closely. Look for small flecks
of solder, especially on the back (etched circuit side) of
the boards, which may be causing improper connections.
Sometimes a connection which appears solid between an
eyelet and the wire will not have a smooth flow of solder
from the wire to the eyelet and also from the eyelet to the
board. The positions of the wires should be essentially as
shown in the photograph, since the pictorial diagram must
necessarily be distorted for clarity.
Second, a systematic procedure should be followed to
trace the source of the trouble, once you understand the
basic circuit configuration of the PAT-4.
Power Supply
The power supply section includes the line cord, power
switch, power transformer, the rectifier diodes on the 5-lug
terminal strip, and the large electrolytic capacitor (C-29).
If the voltages at the lugs of this capacitor, measured with
a VTVM, are reasonably close to those indicated on the
voltage chart, then the power supply must be operating
satisfactorily. However, if they measure more than 25%
low, detach the wires which connect each PC-16 board to
the capacitor at eyelets #4 and #12 to see if the voltages
go to normal or above. If they do, some fault in connection
with one or the other circuit board is imposing an exces-
sive load on the supply, and the fault is not in the supply.
Try connecting only one or the other board to the capacitor
to localize the trouble area.
Preamplifier—Tone Controls
All four pairs of transistors are used in essentially similar
configurations. On each circuit board, the first pair is the
low level preamplifier for the Phono, Tape Head and
Special inputs. The second pair is the tone control and
output section. High level inputs, such as for Tuner, Tape
Amp, and Spare connect directly to this section. Most of
the other controls and switches are located after the low
level circuitry with the exception of the Hi Filter which is
placed at the output of the tone control section. The two
pairs of transistors which comprise each channel are inter-
connected by the selector switch. A problem can thus be
localized to one or the other channel, and then to the
preamp or tone control sections.
For example, if there should be insufficient output on the
left channel with the phonograph playing, see if this chan-
nel is operating properly with a tuner input. If it is, then
the trouble is in the low level section of the left channel.
Again, if there is no output on the right channel from any
input, then the low level section can be tested by exercis-
ing some ingenuity. If you realize that the “To Tape”
output signal is available before the volume and tone con-
trols, you can connect the right channel tape output directly
to the power amplifier, or into the identical input on the
left channel as the program source you are switched to on
the right channel. If you then have suitable signal level,
you have determined that the trouble lies in the right
channel tone control and output section.
An additional aid is to compare voltages measured with
a VI'VM with the chart in this manual. A higher than
normal voltage at the collector of one of the transistors, for
example, is possibly indicative that it is open and requires
If the problem is one of little or no signal, then simple
signal tracing, following the signal path carefully and in-
jecting some hum by touching each connection in turn, is
advisable. If there is a point after which hum occurs, and
before which there is silence, you have localized the trouble.
Check especially the double (front and rear) lugs #2,
*5 and *9 on each wafer of the selector switch (and par-
ticularly #5 if you get no phono signal) to make sure they
have not been twisted in their insulated mountings on the
rear of each wafer.
As another example, if you have signal on both channels
with the hi-filter in the flat position, but the left channel
signal drops sharply when you switch to one of the high
frequency cut positions, remember that this switch is at the
output of the preamp, so everything prior to it must be
working properly. Examining the circuit shows that the
choke coil L-71 is in series with the output signal, but is
shunted out when the switch is in the flat position. There-
fore, a break in its coil would prevent signal from passing
until the switch is “off,” when the shunt permits the signal
to pass. Replacing L-7 1 would correct the trouble.
Hum and Noise
The PAT-4 is inherently hum-free, and if any hum is
detected the inputs should be unplugged to see if the hum
disappears. If there is no hum with the cables removed,
at the same volume setting which produced hum when
cables were attached, the problem must be corrected in
the associated equipment. Frequently hum which is in-
jected via the phonograph cables can be eliminated by con-
necting a ground wire between the record player chassis
and the preamp. Some phono cartridges are more hum
susceptible than others, and may not be suitable in certain
installations where they are close to power transformers,
AC power lines, etc.
Hum traced to the PAT-4 may indicate power supply
problems. If it is common to both channels, it is almost
certainly in the supply, which should be checked carefully,
including bridging additional capacity across the large
electrolytic filter capacitor to determine if any of the three
sections are ineffective. Hum tests should be made with
the cover in place, however, for external hum fields will
affect the results.
When there are no cables connected to the low level
inputs, it is normal to have a high hiss level at higher
volume settings on Phono, Tape Head and Special. With the
usual sources connected, the hiss should be inaudible at the
settings used in normal listening, though at much higher
settings, some hiss may be evident.
Objectionable hiss at normal listening levels may be
caused by a faulty input transistor Q1, unless it occurs on
both channels. If there is hiss on all low level inputs of one
channel, you can interchange transistor Q1 between chan-
nels to determine if one is defective. The transistors in the
tone control stages will not be a source of objection-
able hiss.
Checking Transistors
An ohmmeter is all that is required to locate a transistor
which has failed. Transistors must be removed from the
circuit board for test. All transistors can be considered (for
this test procedure) to be two diodes connected in series
with common elements tied together. The junction point
represents the base of the transistor. Observed from the
bottom, the collector, base and emitter are arranged coun-
terclockwise, with the collector attached directly to the case.
With one ohmmeter probe connected to the base, the
other probe should be touched to the collector and emitter
in turn. Readings from the base to the collector, and from
the base to the emitter should be similar. With one orien-
tation of the probes, there should be a high resistance read-
ing (almost an open circuit). When the polarity of the
probes is reversed, there should be a relatively low reading.
Then the ohmmeter should be connected from collector to
emitter, and a high resistance (almost open circuit) should
be read, regardless of the orientation of the probes. If all of
these qualifications are met, the transistor does not exhibit
any gross defects. Determination of more subtle defects
than “opens” or “shorts” requires specialized transistor
testers and/or curve tracers.
In similar fashion, diodes can be checked by verifying
that they have a high resistance in one direction, and low
resistance in the other.
When replacing transistors, the larger ones with the
finned radiators should have the radiators transferred to
the replacement. The silicon grease between transistor and
radiator should be transferred to the new transistor. Be
careful to insert the leads into the proper eyelets. Do not
use excessive heat on the leads—let the heat go to the eye-
let instead.
When making replacements, standard types can be used
provided they are screened beyond the manufacturer's rou-
tine specifications. This is necessary because transistors of
a given type vary far more widely than do tubes. The
requirements for each transistor are given in the parts list
with the schematic diagram. No screening will be neces-
sary for transistors obtained from Dynaco if the application
(Q-number) or the Dynaco part number is specified.
While the parts list does not show all of the possible
transistor options, Q1, Q2 and Q3 are selected for low
noise, low leakage and high Beta. Q4 is a high Beta selec-
tion from the 2N3053 type. While almost any low power
npn transistor can be temporarily substituted for Ql, Q2
or Q3, optimum performance will not be assured unless all
specifications are met.
The PAT-4 has been designed to provide reliable, trouble-
free operation for a long period of time when it has been
properly assembled and installed. So conservative is its
design that it will deliver unchanging performance with the
maximum variations in AC line voltage (110 to 130) per-
mitted in normal use.
Despite these precautions, service may sometimes be
needed, and you should be sure to return the Guarantee
Card promptly to validate your warranty. Dynaco main-
tains a complete factory test and repair facility for which
no return authorization is required. Unless specifically
authorized in advance by the factory, Dynaco cannot assume
any responsibility for local service charges.
A factory assembled PAT-4/A is warranted to be free
of defects in materials and workmanship for a period of one
year from the date of purchase. During the warranty pe-
riod, no charge will be made for testing or servicing any de-
fective factory assembled preamplifier returned to Dynaco.
All parts used in a PAT-4 kit are warranted to be free
of manufacturing defects for one year from the date of pur-
chase. Defective parts will be replaced promptly at no
charge upon receipt for inspection at the factory. After the
warranty period has passed, Dynaco will supply any non-
standard parts at net prices. Standard parts can generally
be obtained from a local electronics supply store.
The guarantee does not apply to other than the original
purchaser, nor to units which have been subjected to ne-
glect, abuse, misuse or accident.
If you suspect a defect in the power transformer, the
leads must be unsoldered, not cut for its return. The war-
ranty on the transformer is void if the leads have been cut
too short for re-use.
If the kit has been completely assembled, yet does not
function properly, or if difficulty develops after some use,
Dynaco will service the PAT-4 for a maximum charge of
$10.00. After one year, assembled units and kits are subject
to the same charge, plus the cost of parts.
Once a completed PAT-4 has been serviced by Dynaco for
which a regular service fee was charged, a 90 day service
warranty is given.
Factory service is not available for kits which are incom-
pletely wired, or kits wired with other than rosin core
solder, or units physically or electrically modified or used
contrary to the Operating Instructions, without prior fac-
tory authorization.
Technical assistance which may facilitate local diagnosis
or service is available at no charge. Such assistance de-
pends entirely on your description of the difficulty and any
tests performed. Be as complete as possible.
The serial number of the PAT-4 which is on the cover
of this manual should be mentioned in all correspondence,
and whenever a part or the unit is returned to the factory.
When shipping the preamp to Dynaco Inc. for service,
include a note listing the symptoms, the name and address
of the sender, and the serial number of the unit. Pack the
unit securely to withstand the abuses of handling in transit.
The complete original packing, if properly used, and in
good condition, will be sufficient for Express or U.P.S.
alternative is available, the unit must be double-packed
with substantial packing between the cartons, and it must
be insured.
Shipments should be made by insured prepaid Express,
Motor Freight, or United Parcel Service. Serviced units
will be returned by Express or United Parcel Service, col-
lect for all transportation and service charges, unless these
charges have been prepaid.
Dynaco reserves the right to limit the service facility or
the established service fees to one year from the date of
purchase. Dynaco assumes no liability or responsibility for
damages or injuries sustained in assembly or operation of
this equipment.
Parts of similar type which do not change performance
will sometimes be included as a matter of expediency.
This will account for slight variations in value and appear-
1 Chassis 711024
1 Back panel 711025
1 Cover 711023
1 Front plate, gold 769018
2 Circuit board assembly, PC-16 556016
1 Selector switch - 334602
1 Filter switch 334603
1 Power transformer 10415 464018
1 Line Cord | 322092
2 Shielded audio cable 321072
1 Wire, hookup, black
1 Wire, hookup, green
1 Wire, hookup, red
1 Capacitor, electrolytic, C-29 294228
1 Bracket, 134” diameter 717001
2 Bracket, “U” shape 717010
2 Knob, large with set screw 764186
2 Knob, small solid with set screw 764185
2 Knob, small dual with 2 set screws
front 764234
rear 764235
2 Socket strip, 5 inputs 355005
4 Socket strip, 3 inputs 355003
1 Terminal strip, 5 lugs 375002
1 Terminal strip, 2 lugs 372001
1 250 K dual volume control 177254
1 220 K dual balance control 167224
1 40 K dual treble control 161403
1 50 K dual bass control 161503
1 Switch, power, lighted rocker 334001
1 Switch, rocker, spring return 334003
4 Switch, rocker, DPDT 334002
2 Circuit module, PEC, 5 leads 555005
2 Jacks, phone 355014
1 Fuse holder with hardware 341001
2 AC outlet, black 351001
2 AC outlet, red
NNNNNN N == DN HS = юн N
N >
Foot, rubber
Fuse, 1/10 amp, slo-blo
Lockwasher, #4
Lockwasher, #6
Lockwasher, 34”
Lug, ground
Nut, hexagonal, #4-40
Nut, hexagonal, #6-32
Nut, hexagonal, 34”
Plug, phono
Screw, machine, 44-40 x 14”
Screw, machine, #6-32 x 145”
Screw, sheet metal, #6 brass
Strain relief, plastic
Washer, flat 34”
Rectifier diode, 200 ma, 200 prv
.01 mfd mylar
.02 míd disc
.022 mfd mylar
1.0 mfd tubular electrolytic
3,300 ohm (orange-orange-red)
10,000 ohm (brown-black-orange)
18,000 ohm (brown-gray-orange)
7,500 ohm (violet-green-red)
220 ohm, 3 watt
Choke coil, L-71
.0033 mfd mylar
.0047 mfd mylar
.0082 mfd mylar
.01 mfd mylar
.015 mfd mylar
027 mfd mylar
15,000 ohm (brown-green-orange)
18,000 ohm (brown-gray-orange)
QF fe
5 lug terminal strip
printed in U.S.A.
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