Whether tube or solid-state, power amplifier designs from Audio Research have always emphasised 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 REF110, 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 REF3 preamp). This vacuum-tube input/driver arrangement sets the stage for superbly musical performance and lifelike, nuanced 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, 410 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 loads, and power supply energy storage is an amazing 200,000 mF capacitance for explosive dynamics and rock-solid bass impact control. One look under the cover tells you that the HD220 is all about performance.But the HD220 offers livability as well, with the dual-triode front-end tubes all running conservatively within their operating range for longer life. We've 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 detachable 20-amp IEC connector power cord.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 previous hybrid design. Its musicality is superb, with a degree of transparency and grainless purity that is nothing short of eery, thanks 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 that tube amps are famous for, 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.
