Audio Research HD220 Hybrid stereo power amplifier

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Power output 220 watts per channel into 8 ohms from 20Hz to 20kHz. 380 watts per channel into 4 ohms.
Power bandwidth  
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 taps  
Output regulation Approximately 0.07dB 8 ohm load to open circuit
Overall negative feedback None
Damping factor Approximately 130
Slew rate  
Rise time  
Hum & noise Less than 0.1mV RMS -112dB below rated output (IHF weighted, input shorted).
Power supply energy storage 200,000 µF
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 "idle."
Tube complement (2) 6H30 driver, (2) 6922 voltage amp.
Other Output polarity: Non-inverting. Balanced input pin 2+ (IEC-268).
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

This item cannot be ordered online. If you are interested please click on the Ask a Question button below.

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 about performance.

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 Reference 110.

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® story.


We endeavour to despatch same day for orders placed up to 2pm on available stock items (items with stock message "Usually dispatched within 24 hours"). Please remember to check with us first for a physical stock check if next day delivery is important to you. Any items with stock message "Usually dispatched within 72 hours" are items that we do not hold in stock but order in from the importer or manufacturer as soon as a customer order is recieved. Occasionally these may be delayed beyond 72 hours due to importer/manufacturer stock levels but we will inform you as soon as we can if this is the case.

UK ORDERS:  We despatch the bulk of our UK mainland items on a 24 hour service – Free of Charge.  Non Mainland locations - Isle of Man, Isle of Wight, the Scilly Isles, the Scottish highlands and Islands, the Channel Islands and Northern Ireland may take a day or so longer and are not Free of Charge. Smaller items are delivered using Royal Mail recorded delivery or special delivery. Larger items are delivered using a courier service such as Interlink Express, DPD, UPS or DHL. 

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COLLECT IN STORE OR HOME INSTALL:At the request of the manufacturer some items cannot be supplied by mail order but you can click and buy them and then elect to collect them from our store or arrange a home install (if applicable). Applicable items clearly state that they are Collect in store or home install. Once ordered you will receive a message prompting you to contact us by phone or email to arrange for us to deliver and install or to reserve and collect from our store at your convenience, you will also be advised of the delivery time / stock availability as not all Home install / collect in store items are held in stock. 

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