Vacuum Tubes and Preparation for Use
Your HD220 amplifier is shipped with the vacuum tubes
packed in a foam block. These must be unpacked and
installed before you attempt to operate the amplifier
Included are two 6922 dual triodes, and two 6H30 dual
triodes used in the input/ driver stage. Proceed according to
the following instructions.
Carefully remove each vacuum tube from the protective
foam and match its location “V” number (written on the
base of the tube) to the “V” number printed next to each
socket. Firmly seat each tube in its matching socket, taking
care to “key” the tube pins to the socket holes. Retain the
foam blocks with other packing materials for possible
future use. Refasten top cover on amplifier.
Life expectancy of the vacuum tubes in the HD220 is up to
4000 hours.
Panel Controls
The front panel has:
1 – Switch:
1 - Power line On-Off
1 – Indicator:
1 - Power "on" LED (Green)
1 – Indicator:
1 - Warmup "standby" LED (Yellow)
Use of Controls
POWER-ON SWITCH
:
Initiates/terminates AC line power
to the amplifier. For first 40 seconds at turn on, yellow
“standby” LED illuminates until unit is warmed up, then green
“on” LED illuminates.
N o t e :
Audio Research does
n o t
recommend leaving your
HD220 “on” 24 hours a day as is the custom of some audio-
philes to achieve maximum sonic performance on demand.
While this is often recommended for solid-state equipment,
Audio Research does not recommend this procedure for
hybrid or vacuum tube power amplifiers. (2,000 hours of
tube life will elapse in 84 days!)
Installation
To insure normal component life and safe operation this
unit
must be operated only in an upright position
.
Adequate air flow and proper cooling can occur only if
there is no restriction above and behind the unit and on
either side. Be sure that airflow to the 12V D. C. cooling
fans located on the rear panel is not blocked.
The special non-marring elastomer feet provide adequate
spacing and stability only on a smooth, hard surface.
F o r
upright stability, never operate the unit while it is sitting
on a soft surface such as a thick rug or carpet.
Due to its weight, this amplifier must be supported on a
surface specifically rated for such a load. Check with the
manufacturer 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.
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 the HD220 power amplifier to run moder-
ately warm to the touch. All components within are operat-
ed at safe, conservative levels and will not be improperly
affected, providing the requirements outlined above are
adhered to. (Also see “Cooling Fans” section, page 4.)
Connections
The rear panel has:
2
– RCA input connectors, for single-ended connections,
L & R
2
– XLR input connectors, for balanced connection, L & R
4
– Output binding posts, (+) and (-), L & R
1
– Power line fuseholder
1
– Power line cord IEC connector for removable power
cord (supplied)
2 – 12V remote start in and out jacks
2 – Switches for XLR or RCA input operation, L & R
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 con-
nected so that the audio signal arriving at the speakers has
correct absolute polarity or phase (i.e. is
n o t
i n v e r t e d ) .
Connect the black or (-) speaker terminal to the wire that
connects to the appropriate-channel (-) gold binding post
on the amplifier. Connect the red or (+) speaker terminal to
the wire that connects to the appropriate-channel (+) bind-
ing post on the HD220. Tighten the binding posts firmly to
assure good contact for best sonic results.
For “b i - w i r ed” loudspeaker systems (i.e. running separate
wires to bass and treble speaker terminals), simply repeat
the above instructions, taking care that all connections
have the same (+) or (-) polarity.
Model HD220
2
