Source: Official website, Last Accessed: 2015/07/24

The Hafler HA75 is a vintage inspired headphone amplifier that has been meticulously designed to produce Hafler’s legendary sound quality while adding excitement and character of a real tube circuit to optimize the listening experience.
The design begins with a 14 gauge steel casing to shield the internal workings from external magnetic fields and RF contamination. This is complimented with a black anodized aluminum front panel for clean, aesthetic appeal. A choice of either unbalanced RCA or balanced XLR inputs are available. These are gold-plated to eliminate tarnishing over time while optimizing signal flow.
Inside, a 100% discrete class-A head-amp combines with a 12AX7 tube drive to power the headphones. This employs a unique non-radiating charge pump that applies 140 volts to the tube to maximize headroom as it delivers the character and warmth that so many listeners prefer over solid state counterparts, the company says. Unique to the HA75 is a negative feedback control. This enables the user to increase or decrease the negative feedback to produce either a more clinical (solid state) or a warmer (tube) response, further enhancing the signal path for the type of program material that is at play.
To simulate the response of listening to loudspeakers in an acoustic space, a "Focus" control may be engaged that brings the stereo image to the center via a potentiometer. This active control features a matrix that delivers exciting results without collapsing the stereo image. A "Deep" function warms the tone akin to an old-school loudness control, addressing the Fletcher-Munson curves to deliver equal loudness when listening at low levels. The same control can also can be used and create a boom-box effect for those that enjoy a more exaggerated response.
According to Hafler, the HA75’s amplifier stage is able to handle all types of headphone impedance from 8 Ohms to 400 Ohms without choking as it quietly delivers plenty of warmth and character to truly enhance the listening experience.

For more information: http://www.hafler.com/

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