The "0-Ohm" Headphone Amplifier

December 01, 2001

The

The Sonic Advantages of Low-Impedance Headphone Amplifiers

- An introduction to "The 0-Ohm Headphone Amplifier" White Paper

The circuits used to drive headphones are often added to a product without careful consideration of the difficult loads presented by high-quality headphones. The most common circuit is an opamp driver followed by a 30-Ohm series resistor. The series resistor provides short-circuit and overload protection while isolating the opamp from the inductance and capacitance of the headphones. The series resistor protects the opamp while keeping it stable. In contrast, today's state-of-the-art headphone amplifiers eliminate the series resistor, and use a high current driver. This change reduces distortion and flattens the frequency response when a headphone is driven. These new high-end designs are often called "0-Ohm" headphone amplifiers, and are essentially miniature power amplifiers.

This paper provides measurements which demonstrate the significant advantages of headphone amplifiers with very low (near 0-Ohm) output impedances. A low output impedance increases the damping factor of the amplifier-headphone system. This paper will show that a high damping factor reduces distortion at the headphone input, improves the phase response, and flattens the frequency response.

Download the White Paper:

The "0"-Ohm Headphone Amplifier - John Siau 

Additional reading:

More information on headphones and headphone amplifiers can be found here.



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