- POWER OUTPUT: 220 watts per channel into 8 ohms from 20Hz to
20kHz. 380 watts per channel into 4 ohms.
- FREQUENCY RESPONSE: (-3dB points at 1 watt) 0.5Hz to 200 kHz.
- INPUT SENSITIVITY: 4.0V RMS BAL for rated output. (20.8 dB Bal
gain into 8 ohms.)
- INPUT IMPEDANCE: 300K ohms Balanced, 150k ohms SE.
- OUTPUT POLARITY: Non-inverting. Balanced input pin 2+ (IEC-268).
- OUTPUT REGULATION: Approximately 0.07dB 8 ohm load to open
circuit (Damping factor approximately 130).
- OUTPUT NEGATIVE FEEDBACK: None.
- HUM & NOISE: Less than 0.1mV RMS -112dB below rated output (IHF
weighted, input shorted).
- POWER SUPPLY CAPACITANCE: 200,000 uF.
- POWER REQUIREMENTS: 105-125VAC 60Hz (210-250VAC 50 Hz) 750 watts
at rated output (220 WPC 8 ohms) 1200 watts max (380 WPC 4 ohms) 250 watts at
- TUBES REQUIRED: 2 - 6H30 Driver, 2 - 6922 Voltage amp.
- DIMENSIONS: 19" (48.3 cm) W x 8.75" (22.2 cm) H x 19.5" (49.5
cm) D. Handles extend 1.5" (3.8 cm) forward.
- WEIGHT: 58.9 lbs. (26.8 kg) Net; 73.8 lbs. (33.6 kg) Shipping.
Specifications subject to change without notice.
Whether tube or solid-state, power amplifier designs from Audio Research have
always emphasized the key criteria of musicality, lifelike dynamics and
realistic soundstaging. Whichever technology was used was intended to serve
these priorities in the music reproduction chain.
Recent advances in solid-state output devices and other components have opened
up design possibilities as never before, allowing Audio Research engineers to
combine the strengths of two different technologies in a completely new power
amplifier: the new Hybrid Drive HD220 stereo power amplifier.
We call it "Hybrid Drive" because that's how it works. As in the Reference 110,
a JFET input (for low noise) feeds a 6922 dual triode gain stage, which in turn
feeds a 6H30 dual triode cathode follower which drives the outputs through our
proprietary coupling capacitors (first used in our Reference 3 preamp). This
vacuum-tube input / driver arrangement sets the stage for superbly musical
performance and a nuanced, lifelike character at the front end of the amplifier.
The output stage is comprised of twelve Thermal Trak® bipolar output devices per
channel, producing 220 WPC into 8 ohms, and nearly 400 WPC into 4 ohms. These
new devices have the unique ability to automatically adjust their internal bias
in response to operating temperature, thereby assuring extremely consistent
output performance no matter how hard the amplifier is pushed. Low-noise fan
cooling of the output stage keeps the output devices within their operating
range. Power supply regulation is all solid-state to assure stability and
consistency under high-current-demand loads, and power supply energy storage is
a startling 200,000 mF capacitance for explosive dynamics and rock-solid bass
impact and control. One look under the cover tells you that the HD220 is all
But the HD220 offers livability as well, with all of the dual-triode front-end
tubes being run very conservatively within their operating range for longer
life. We have even included an easy-to-read meter to keep track of tube hours.
And, needless to say, there are no output tubes to replace, ever. Both balanced
and single-ended inputs are provided, as well as a detachable 20-amp
IEC-connector power cord. Output connectors are our proprietary gold-over-copper
binding posts. The chassis dimensions of the HD220 are identical to those of the
In performance, as always, your own ears will be the final judge. But we
honestly believe that this unique amplifier represents the highest level of
sonic performance we have yet experienced from any solid-state or hybrid design.
Its musicality is superb, with a degree of transparency and grainless purity
that is nothing short of eerie, thanks in large part to extremely low distortion
and a low noise floor. Dynamics and bass control are thunderous and controlled,
whether driving dynamic or planar-type loudspeakers, thanks to the Thermal Trak®
output stage. In short, the HD220 gives you the finesse and nuance for which
tube amps are famous, with the consistency and speaker control under
high-current-demand conditions that solid-state amps excel at. This HD220 simply
goes and goes and goes.
If you are a demanding music lover who wants ultimate sonic performance without
the periodic burden of replacing amplifier output tubes, you now have a new
choice - one that opens a new chapter in the Audio Research High Definition®