Audio Research SP4 User manual

audio research
H I G H D E F I N I T I O N®
3900 ANNAPOLIS LANE NORTH/ PLYMOUTH, MINNESOTA 55447-5447 / PHONE: 763-577 - 9700 FAX 763-577 - 0323
August 1977
SP4, SP4A MANUAL
SP4, SP4A SCHEMATIC
AND PARTS LIST

INTRODUCTION
Congratulations on your purchase. The SP -4 stereo preamplifier was
conceived and designed for audio perfectionists .
11
Analog Module
11
circuitry provides unequaled performance under actual dynamic listening
conditions.
In addition to the normal complement of features, the SP-4 has:
provisions for an optional (*) low level head amp, alternate compensation
of magnetic (mag 2) phono section, 1600 watt relay controlled power
outlets, main output
11
turn- on
11
delay, high quality anodized aluminum
panels, knobs, and handles, and a scuff-resistant chassis finish.
Conservative design and extensive use of high quality industrial grade
components insure many years of trouble-free performance.
WARRANTY
A limited 90 - Day Warranty (from the date of purchase by the original purchaser)
is provided by Audio Research Corporation. This warranty is subject to the
conditions and limitations stated within the documents attached to the outer
shipping carton.
LIMITED 3- YEAR WARRANTY
A 3-Year Limited Warranty Application is included with the documents attached to
the outer shipping carton.
THIS LIMITED 3-YEAR WARRANTY WILL NOT BE ISSUED OR EFFECTIVE UNLESS WITHIN THIRTY
DAYS AFTER THE DATE OF SALE THE PURCHASER MAILS TO AUDIO RESEARCH A LIMITED
3- YEAR WARRANTY APPLICATION FORM WHICH HAS BEEN COMPLETED, DATED AND SIGNED BY
BOTH THE SELLING DEALER AND THE PURCHASER AND A COPY OF THE BILL OF SALE OR
OTHER PROOF OF PURCHASE OF THE PRODUCT .
WARNING - FAILURE TO COMPLY WITH THE ABOVE CONDITIONS WILL RESULT IN THE
WARRANTY BEING RESTRICTED TO THE LIMITED 90-DAY WARRANTY .
PACKAGING
Save All The Packaging - Your Audio Research component is a precision electronic
instrument and should be properly cartoned any time shipment is made . You may
never have occasion to return it to the factory for service, but if such should
be necessary, or other occasion to ship it occurs, the original packaging may
save your investment from unnecessary damage or delay.
- 1-

ACCESSORIES
The following optional (*) accessories for your SP -4 preamplifier will
be made available through your Audio Research dealer :
* Walnut veneered oiled finish cabinet
* Programable low level head amp electronics
LINE VOLTAGE CONVERSION
This equipment can be operated from either 120 Volts or 240 Volts A. C. ,
50/60 Hz. Check the position of the line voltage selector switch on the
rear panel. If necessary, remove the switch safety cover and set the
switch to the proper voltage as indicated below the switch. Secure the
switch position with the safety cover and screws with the word "fuse"
showing. Install the appropriate fuse as indicated below if the line
voltage is different than that set for at the factory .
WARNING
Voltage
120
240
Fuse
1/4 Amp . Type 3AG or MDL Slo-Blo
1/8 Amp . Type 3AG or MDL Slo- Blo
To prevent fire or shock hazard, do not expose this equipment to rain or
moisture.
This unit contains voltages which may be lethal . Do not operate this unit
with covers removed . Refer servicing to qualified personnel .
CAUTION
For continued protection against fire hazard , replace only with same type
and rating fuse.
-2-

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REAR PANEL LAYOUT
REAR PANEL FUNCTIONS
Refer to the "Rear Panel Layout" diagram above.
Audio Inputs:
Jl - Head Amp* (optional), Right Channel
J2 - Head Amp* (optional ), Left Channel
Provision for "optional " Head Amp electronics have been made within the
SP -4 directly behind the Head Amp input connectors. These input and
associated electronics will be required only for low output moving
coil transducers. Consult your dealer for information and use of this
special input feature. These inputs are not connected internally at
the factory and are not used in systems employing moderate or high
output moving coil magnetic cartridges.
J3 -Magnetic 1, Right Channel
J4 -Magnetic 1, Left Channel
Connect to tone arm/cartridge on record player. Nominal input impedance
is 50 K ohms (200 PF shunt). Use with magnetic type cartridges requiring
RIAA playback compensation. Note: Normally connect grounding wire from
record pl ayer or arm to the "Ground Terminal 11 screw 1ocated ne xt to and
between Jl and J2. With certain systems this may add hum in which case
no ground wire is required.
J5 -Magnetic 2, Right Channel
J6 -Magnetic 2, Left Channel
Same as above . Allows use of a second record player when selected from
the front pane 1.
Note: The input characteristics and gain of the SP -4 have been factory
set to accommodate most of the high quality magnetic phono cartridges on
the market today. However, the SP -4 low level
11
mag
11
sections can be
programmed by a technician for different gain, input resistance and
capacitance. This feature allows
11
matching
11
of various cartridges to the
magnetic preamp section for optimum performance . Consult your dealer for
further information and use of this special input feature .
-3-

J7 -Tuner, Right Channel
J8 -Tuner, Left Channel
High level inputs. Connect to the output of an AM and /or FM tuner
component. Nominal input impedance is 47 Kin the
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stereo
11
or
11
reverse
11
mode, 30 Kin the
11
left
11
or
11
right
11
mode, and 20 Kin the
"mono" mode.
J9 -Spare, Right Channel
JlO -Spare, Left Channel
Provides high level inputs for any auxiliary system component .
Nomi na 1 input impedance is the same as the
II
tuner
11
inputs J7 and
J8 above .
Jll - Tape 1, Right Channel
J12 - Tape 1, Left Channel
High level inputs. Connect to tape recorder line outputs.
input impedance is the same as for the tuner inputs above -
by any load(s) connected to the tape outputs when the front
tape dubbing switch (S4) is in the
11
copy" position.
Jl3 - Tape 2, Right Channel
J14 - Tape 2, Left Channel
Nominal
shunted
panel
Same as above. Allows use of a second tape recorder when s elected
from the front panel .
Audio Outputs:
J15 - Tape 1, Right Channel
J16 - Tape 1, Left Channel
Connect to tape recorder line inputs. Provides a program source for tape
recording. Output signal is independent of " volume
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control setting and
equal to the source input level, i .e. "tuner" ,
11
spare
11
, "tape l" ,
11
tape 2" ,
or magnetic phono preamplifier output. Nominal output impedance is 50 ohms
plus the output impedance of the selected source . In general, the load
impedance should be greater than 20 Kfor optimum performance .
J17 - Tape 2, Right Channel
J18 - Tape 2, Left Channel
Connect to the line inputs of a second tape recorder when used. Function
and characteristics are same as above.
-4-

J19 - Main 1, Right Channel
J20 - Main 1, Left Channel
Connect to power amplifier (or electronic crossover) inputs. Nominal
output impedance is 50 ohms. In general, the load impedance should
be greater than 10 Kfor optimum performance. The outputs are AC
coupled through a 5 MF capacitor.
J21 - Main 2, Right Channel
J22 - Main 2, Left Channel
Same as (in parallel with) outputs above. Us ed to drive a second
power amplifier. Combined load impedance of Main 1 and Main 2 should
be 10 K minimum for optimum performance.
Power Circuits:
OTl -Switched AC Convenience Outlet
OT2 -Switched AC Convenience Outlet
OT3 -Switc hed AC Convenience Outlet
Connect to system components (power amplifier(s) , tuner(s) , electronic
crossover, etc.) that are to be turned on by the front panel power
switch (Sl) . Will accept 2 or 3 prong line plugs . Outlets are
switched by an internal power relay. Cap acity is 1600 watts total
including the unswitched outlet (OT4). The outlets are not fuse
protected.
Note: An internal .01 MF/1600 V capacitor is connected ( for arc
suppression) across the internal power relay contacts. If an Audio
Research RPR-1 (Remote Power Receptacle) is used in the system to
remotely turn on the power amplifier(s), the .01 MF capacitor must be
removed. The small 60 Hz current passed by the capacitor is sufficient
to turn-on the RPR -1 transmitter electronics continuously even with
the SP-4 power switch (Sl) off.
Since relay contact arcing is not a problem when using the RPR-1 (power
amplifiers are instead connected to the RPR -1 outlets), this capacitor
can be safely removed. To accomplish this, remove the SP -4 top cover
and 8 holding screws. CAUTION: UNPLUG SP-4 POWER CORD BEFORE REMOVING
TOP COVER AND CAPACITOR. Locate the .01 MF/1600 V capacitor nested
between the power relay contacts -towards the rear panel next to the
power transformer. Clip the leads off close to the solder joints, remove
the capacitor, and replace the top cover. The SP-4 is now ready for use
with an RPR-1 .
-5-

OT4 -Unswitched AC Convenience Outlet
Connect to record player, turntable, or tape recorder where power should
be controlled by the component on - off switch only. This unsures proper
"cycling" and mechanism disengagement.
Note: The "grounding" type convenience outlets are provided to
accommodate power amplifiers with 3 prong (grounded) line plugs.
avoid "system" ground loops, the ground circuits of the rear panel
are connected to the ground conductor of the SP -4 line cord only.
preamplifier chassis is not connected to the convenience outlet or
cord/plug ground circuTt -. -
Fl - Preamplifier Line Fuse Receptacle
To
outlets
The
1i ne
Provides protection for preamplifier electronics only. Refer to page 2
for fuse replacement information.
SlO -Line Voltage Selector Switch
Selects for 120 or 240 volt input power . Refer to page 2 for "Line
Voltage Conversion" procedure.
SYSTEM CONNECTION
Before connecting the SP -4 into your system, familiarize yourself with the rear
panel functions by referring to the diagram and description of the rear panel in
the previous section.
Use only high quality shielded phono cables when interconnecting the SP -4 with any
signal sources, power amplifiers, or electronic crossovers. Avoid inexpensive
cables which use "weak
11
or soft metal grounding shells as they may introduce hum
and/or noise into the system. Keep audio cables neatly dressed and away from all
power cords for minimum hum and noise interference .
When connecting to the magnetic and tape inputs, use the number
11
l 11 connectors if
a single turntable and/or tape deck is employed. This will result in easier and
more convenient front panel control switching.
It should be noted that the SP -4 line cord grounds the convenience outlet grounds
only. The preamplifier chassis is not connected to the line cord ground in order
to minimize system ground loops.
-6-

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FRONT PANEL LAYOUT
FRONT PANEL FUNCTIONS
Refer to the "Front Panel Layout" diagram above .
Rotary Controls:
Volume (Rl) -Controls preamplifier "main output" level. Power amplifier
or source gain controls (if available) should be set such
that normal listening levels occur at approximately a 1 or
2 o'clock setting. This will provide ideal volume control
"range
11
•
Balance (R2) -Controls the relative volume of each channel . Equal channel
volume occurs when the control is centered at the indicator
mark. Clockwise rotation from center position increases
right channel "main output" level while decreasing left
channel output. Counter-clockwise rotation increases left
channel output and decreases right channel output.
Bass (R3)
- Bass tone control circuitry is activated when switch (S3) is
moved to the
11
tone
11
position. Response is flat when control
is centered at indicator mark. Clockwise rotation increases
bass response while counter-clockwise rotation decreases response.
Treble (R4) -Treble tone control circuitry is activated when switch (S3) is
moved to the
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tone
11
position. Response is flat when control
is centered at indicator mark. Clockwise rotation increases
treble response while counter-clockwise rotation decreases
response .
Rotary Switches :
Mode (SB)
-Switch selects one of five "main output" modes :
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Mono
11
- Combines the left and right input channels internally
to provide a monaural output (common output for both left and
right main outputs).
"Reverse" -Provides stereophonic operation except channels are
reversed, i.e . left input to right output , right input to left
output.
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0
0

11
Stereo
11
-Provides normal stereophonic operation without
channel revers al, i . e. left input to left output, right input
to right output.
11
Left
11
-Left channel input sources are coupled to both the
left and right "main outputs" simultaneously. The
11
balance
11
control functions as normal .
11
Right
11
- Same as above except right channel input sources
are coupled to both the left and right "main outputs"
simultaneously.
Note : The "tape outputs" are unaffected by the position of
the "mode
II
switch.
Source (S9) -Switch selects one of five rear panel inputs (program sources)
as marked. The selected source is also switched to the "tape
outputs" when switch (S4) is in the
11
norm
11
position.
Note: The "Head Amp*" position is not normally used .
Toggle Switches :
Provisions for optional (*) Head Amp electronics have
been made within the SP-4 directly behind the He ad Amp
input connectors. These inputs and associated electronics
will be required only for low output moving coil transducers.
Consult your dealer for information and use of this special
input feature. These inputs are not connected internally
at the factory and are not used in systems employing
moderate or high output moving coil magnetic cartridges.
Power (Sl) -Preamplifier on - off switch. Move handle up for power
11
on
11
• Also
turns on the
11
switched
11
rear panel outlets . Green indicator (LED)
illuminates when preamplifier is on.
Filter (S2) -Active low frequency (subsonic) filter . Enabled when handle is
moved to
11
filter
11
position. Switch is normally left in the full
range
11
out
11
position for optimum response . Use only for removal
of excessive low frequency noise (turntable rumble , etc . ).
Tone (S3) - Moving handle to
11
tone
11
position activates bass and treble tone
control circuitry. Unless needed, switch should be left in the
11
out
11
position for optimum performance and flat response.
-8-

Tape Copy &Monitor Switches (S4, S5, S6, S7)
S4 -Controls output signal to
11
tape output" connectors (Jl5, Jl6 , Jl7 , Jl8).
In the normal
11
norm
11
position, the signal source selected by the source
switch (S9) is also switched to the tape outputs Jl5, Jl6 , Jl7, Jl8.
When two tape recorders are used in the system and tape copying or
dubbing is desired, the switch is moved to the
11
copy
11
position.
This allows you to tape from one deck to another and at the same time
to listen to another program source as selected by (S9). When S4 is in
the
11
copy
11
position, the "tape outputs" are connected to the
11
tape 1
11
or "tape 2
11
inputs as selected by (S5).
S5 - Used in conjunction with (S4) above. Selects either
11
tape 1
11
or
11
tape 2
11
inputs and connects them to the tape outputs Jl5, Jl6 , Jl7, and Jl8 when
(S4) is in the "copy" position . Position (1 4 2) connects the outputs of
tape recorder #1 to the inputs of tape recorder #2 and position (2 • 1)
connects the outputs of tape recorder #2 to the inputs of tape recorder
#1).
S6 - Used in conjunction with monitor switch (S7) described below . Selects
either "tape l II or
II
tape 2
11
inputs for monitoring of tape recordings when
(S7) is in the
11
monitor
11
position. This switch also functions asa program
or tape input selector when using tapes as a program source.
S7 - Allows monitoring of tape recordings or selection of a program (tape) source
when used in conjunction with (S6) above and in the 1'monitor
11
position. In
the "source" position, selector switch (S9) controls the program source
allowing selection of all "magnetic", "tuner", or
11
spare
11
inputs. Source
switch (S9) is bypassed when S7 is in the
11
moni tor
11
position.
Indicator:
LED -Green light emitting diode. Illuminates when preamplifier power
switch, Sl, is
11
on
11
•
-9-