The rotary potentiometer is mechanically connected to the volume control by a 150mm long shaft.

ENGADGET: Sennheiser unveils HDVA 600 analog headphone amp, asks for $1,600

On pin 15 (third up from the bottom right) we connected a potentiometer.

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The first couple-dozen laps saw brake points blown and sand traps dredged as years of potentiometer dependency was weaned away.

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This unusually long potentiometer shaft allows the signal path between the audio source and the potentiometer to be kept very short, thus preventing possible interference of the signal.

ENGADGET: Sennheiser unveils HDVA 600 analog headphone amp, asks for $1,600

Linear potentiometer slider near the bottom of the board.

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Both, the housing and the potentiometer control as well as the rotary switch for selecting the source are made of anodised aluminium, while the front panel of the housing and the controls are milled from solid material.

ENGADGET: Sennheiser unveils HDVA 600 analog headphone amp, asks for $1,600