Audio Research Reference 250, Руководство пользователя

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V1 SET hole in the front panel so the meter
reading is in the center of the labeled bias
range. Press BIAS switch again to check V3
tube bias level which should be within the
bias range arc. Press the BIAS switch again
and check the V5 tube bias level in the
same way. Note that the V3 and V5 tube
bias levels are controlled by the V1 bias
setting.
Press the BIAS switch once more to read and
adjust V2 tube bias level with the bias tol in
the V2 SET hole in the front panel in same
way the V1 tube bias level is adjusted. Press
BIAS switch again to check V4 tube bias
level, and once again to check the V6 tube
bias level.
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 250 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 250 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 250 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 250 puts out the same
amount of power whether the 4, 8 or 16-
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 250. Connect
the red or “+” speaker terminal to the wire
that connects to the “4” or “8” terminal on
the Reference 250 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
250 input to the preamplifier or electronic
crossover, using only the highest grade of