Owner`s manual

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6!
The ‘ambient’ operating temperature
should never exceed 120 F or 49 C.
Improper installation will cause premature
tube failure and will affect your warranty,
as well as the service life of the unit.
It is normal for a vacuum tube power
amplifier to run quite warm, and if used for
prolonged periods, hot to the touch. All
components within are, however,
operated at safe, conservative levels and
will not be improperly affected thereby,
providing the requirements outlined above
are adhered to.
Connections
Input Connector: The Reference 75 uses a
fully balanced circuit topology and has a
pair of balanced XLR input connectors 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 75 before turning on the
amplifier.
Output Connectors: Proprietary, heavy-
duty output terminals are provided on the
rear panel for 4 or 8-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 75 puts out the same
amount of power whether the 4 or 8-ohm
terminals are used.
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 75. Connect the
red or ‘+’ speaker terminal to the wire that
connects to the ‘4’ or ‘8’ terminal on the
Reference 75 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 75 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 75 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 75 for On/Off
control of the amplifier, or the 12V start-up
trigger for remote installations.
The AC power source for the Reference75
amplifier should be capable of supplying
10 amperes for 100 or 120 volt units, or 5
amperes for 220 or 240 volt units.
For the very best performance on
domestic 100 or 120 volt circuits, the
Reference 75 should be connected to its
own AC power circuit branch, protected
by a 15 amp breaker. The preamplifier and
other audio equipment should be
connected to a different power circuit
and breaker.
The Reference 75 should be turned on
after the other components of your system.
If the Reference 75 is turned on before
other components, the amplifier will
amplify any extraneous turn-on noises
those components might generate, which
could potentially damage the
loudspeakers. Good operating practice
dictates that the amplifier should be
turned on last, and turned off first in an
audio system.