Audio Research HD220 Hybrid Drive Amplifier

Audio Research HD220 in very good condition.

Note: There was an issue with the original Thermal Trak bipolar output devices in which caused the many units to go into thermal shutdown after being on for a while. Audio Research re-placed the Thermal Trak bipolar output devices in this unit with the latest versions and it solved the problem.

New tubes installed with Electro-Harmonix 6H30Pi gold pins and JJ 6922 tubes. This is an excellent sounding amplifier. It has the power of a high wattage solid state amp and a 3D dimensional soundstage of a good tube amp. The HD220 will drive high current or low impedance speakers with ease. I have the original box and manual.

From Audio Research:

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.

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 grain less 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.