7
hole in the front panel in same way the V1 tube
bias level is adjusted. Again, press the BIAS switch
repeatedly to check V4, V6, V8, V10, V12, V14 and
V16 tube bias levels, which should all be within the
bias range arc. Note that each of the even V
number tube bias levels are controlled by the V2
bias setting.
Note that the corresponding V number LED is
illuminated for each output tube as you proceed
through the bias adjustment and monitoring
sequence. Press BIAS switch a final time to exit the
bias status function and return the meter to the
power level monitoring function.
The Reference 750 is shipped from the factory with
all tubes properly biased and ready to use. It is not
necessary to check bias each time the amplifier is
turned on.
Under typical circumstances, most owners will find
that checking the bias level once a month or so will
insure proper operation and good service life of the
output tubes. Audio Research-supplied output
tubes are warranted for 90 days, and under normal
conditions should provide up to 2000 hours of
service life. This expected life will vary depending
on conditions of use–ventilation, speaker loads,
average playing level and A. C. voltage and line
condition.
Complete sets of replacement tubes or individual
tubes are available from Audio Research, and are
strongly recommended for best sonic performance
and reliability. These tubes are burned in,
measured, matched and specifically selected for
your Audio Research amplifier. Contact your
authorized dealer for suggested retail prices.
METER:
Press METER button to turn on or of the
power level monitoring meter function.
NOTE: The FAN, LIGHT and METER settings at turn off
are retained each time the amplifier is turned on.
Connections
INPUT CONNECTOR:
The Reference 750 uses a fully
balanced circuit topology and thus has one
balanced XLR input connector on the rear panel. It
therefore requires a balanced preamplifier output,
as provided by most Audio Research preamplifiers.
Connect your preamplifier's output to the
Reference 750 before turning on the amplifier.
OUTPUT CONNECTORS:
Proprietary, heavy-duty
output terminals are provided on the rear panel for
4, 8,or 16-ohm speaker impedance loads. Using
high-quality speaker cables, securely fasten the (-)
speaker lead to the appropriate (-) terminal, then
the (+) lead to the matching (+) terminal, following
your
speaker
manufacturer's
impedance
specification. The Reference 750 puts out the same
amount of power whether the 4, 8 or 16-ohm
terminals are used, provided the speaker and
amplifier terminal impedances are matched.
IMPORTANT:
Use the best available speaker wires
and interconnects. Audio Research cannot
emphasize this enough. As better components and
systems are developed, it becomes increasingly
important to avoid the limitations of inferior system
interconnections. It is important sonically that your
entire system be connected so that the audio
signal arriving at the speakers has correct, or
“absolute” polarity (i.e., non-inverted). Connect
the black or “-” speaker terminal to the wire that
connects to the “0” terminal on the Reference 750.
Connect the red or “+” speaker terminal to the wire
that connects to the “4” or “8” terminal on the
Reference 750 and tighten the speaker terminals
securely to ensure best sonic results.
MATCHING
: It is important to use as close as
possible an impedance match between the
amplifier and speaker for optimum transfer of
power to the speaker with minimum distortion. In
the case of speaker systems with significant
variations in impedance throughout the frequency
spectrum, such as most electrostatic types,
determine the best impedance match empirically
for best overall sonic results. Connect the
Reference 750 input to the preamplifier or
electronic crossover, using only the highest grade of
audio interconnect cables. To avoid sonic
degradation use the shortest practical length of
cables.
A.C. POWER CONNECTIONS:
It is important that the
Reference 750 be connected via its supplied 20
amp IEC 12-gauge power cord to a secure,
dedicated A.C. power receptacle. Never connect
to convenience power receptacles on other
equipment. Only use the power switch on the front
of the Reference 750 for On/Off control of the
amplifier, or the 12V start-up trigger for remote
installations.
The A.C. power source for the Reference 750 should
be capable of supplying 20 amperes for 120V units,
or 10 amperes for 220/240V units. Preferably, the
amplifier should be connected to its own A. C.
power circuit branch, protected by a 20-30 amp
circuit breaker. The preamplifier and other related
equipment should be connected to a separate
power circuit and breaker. If the power receptacle
is more than 25 feet from the building's power
entrance and breaker box, circuit wiring capable
of 30 amperes should be installed to minimize
voltage drop using a 20-amp breaker. Avoid the
use of extension cords. If they must be used on a
temporary basis, use 12-gauge cords or heavier.
The Reference 750 should be turned on
after
the
other components of your system. If the Reference
750 is turned on before other components, the
