6
of your support system to be sure it is rated to
handle this weight.
If the unit is to be operated in an enclosure such as
an equipment rack, make certain that adequate
air flow above and to each side of the unit is
provided. The “ambient” operating temperature
should never exceed 120º F or 49º C. Additional
ventilation can be provided by fan-cooled,
perforated tube covers available for purchase
through your Audio Research dealer. If these
covers are used, do not place paper, wood, or any
other objects on top of the cover that could
obstruct cooling or create a fire hazard. Improper
installation will cause premature tube failure and
will affect your warranty, as well as the service life of
the unit. Keep children and pets away from
exposed tubes at all times to prevent possible burns
or injury.
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.
Warnings
1.
To prevent fire or shock hazard, do
not expose this product to rain or
moisture.
2.
This unit operates on voltages which can cause
serious injury or death. Do not operate with top
cover or side panels removed. Any necessary
servicing should be carried out by your authorized
Audio Research dealer or other qualified
electronics technician.
3
. Use only the plastic insulated screwdriver
included with this unit when making front panel
bias adjustments.
4.
The power cord on this unit is safety-tested and is
equipped with a proper grounding plug. If used
normally, it will provide a safe earth ground
connection of the chassis. Defeat of the
grounding plug, or any unauthorized modification
of the active circuitry or controls of this unit,
automatically voids warranty coverage,
5.
For safe operation and protection against fire
hazard, replace fuses only with those of the same
type and rating as those supplied with this unit.
6.
At 170 lbs. (77.2 Kg) net weight per chassis, the
Reference 750 amplifier is too heavy for one
person to lift. To avoid injury, do not attempt to
unpack, lift or move the unit without the help of at
least one other person.
7.
Always mute the preamplifier when cueing a
phono cartridge stylus up or down.
Due to the immense power supply reserves, high
power output, and wide bandwidth of the
Reference 750, added emphasis must be placed
on use of your preamplifier's mute switch from a
safety standpoint. A transient signal burst or “pop”
such as caused by tonearm cueing, accidental
dropping or brushing of the phono cartridge stylus–
even at a normal listening level–could cause an
instantaneous peak power demand on the
amplifier of up to 1000 watts (which the Reference
750 will try to deliver). The importance of lowering
the preamplifier volume level to a minimum setting
and activating the mute switch whenever cueing
the tonearm or making contact with the phono
cartridge stylus cannot be overemphasized.
Adhering to this precautionary muting procedure is
equally important when turning your system on or
off, and when connecting or disconnecting any
cables in the system. Carefully following this
recommendation will minimize the chance of
causing undue stress and potential damage to your
amplifiers and loudspeakers. (See your preamplifier
Owner's Manual for more detailed instructions on
use of muting provisions.)
Description of Controls
POWER:
Press the POWER switch to turn the unit on,
indicated by a lit green LED directly above the
switch. When turned on, there is an automatic
warm-up sequence which lasts for approximately
45 seconds before the unit is operational.
FAN:
Press the FAN switch to select low (dim Power
LED) or high (bright Power LED) for fan speed
setting.
Only applicable to installed optional top
cover with ventilation fans.
LIGHT:
Press the LIGHT switch to select high, low, or
no meter illumination.
BIAS
(Adjustment Procedure):
NOTE: Amplifier should be turned on and operating
for at least 30 minutes prior to adjusting bias of the
output tubes.
Press BIAS switch once and the V1 output tube LED
is illuminated with its bias level indicated on the
front panel meter. Adjust V1 tube bias level with
the plastic flat-bladed bias tool (provided), inserted
in the 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 repeatedly and check the V5, V7,
V9, V11, V13 and V15 tube bias levels in the same
way. Note that each of the odd V number the
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 tool in the V2 SET
