Studio Stereo Headphone Amplifier Circuit Diagram

Description

Here’s a premium headphone amplifier capable of delivering full power to both high and low impedance headphones, with minimal noise and distortion. For optimal performance, it can be combined with the Stereo Preamplifier detailed last month. Alternatively, it can be utilized as a standalone unit, requiring only a power supply and a volume control potentiometer for operation with any line-level signal source, such as a CD/MP3 player. It incorporates dual outputs, allowing for shared listening with a companion.

Picture of the circuit:

Many of our high-power audio amplifier designs already incorporate an output for headphones. The supplementary circuitry necessary for headphone support is quite straightforward, consisting of just two resistors in series with the speaker outputs to restrict the drive current and safeguard the headphones in the event of amplifier failure.

Considering its simplicity, this resistive limiting scheme proves effective, though it can introduce distortion if the load exhibits non-linear characteristics—a common scenario with most headphones. Beyond mitigating this potential source of distortion, there are several reasons to consider a separate headphone amplifier.

To begin with, not everyone possesses a top-rated pair of headphones or a high-performance power amplifier. After all, an amplifier that equals or surpasses the performance of this new headphone amplifier would represent a considerable financial investment!

Parts layout:

Another factor to consider is compatibility with modern “high-tech” audio electronics. The headphone outputs in much of this gear are often unable to drive low-impedance headphones—or at least not to satisfactory listening levels. Furthermore, available output power in portable devices is deliberately restricted to conserve battery energy. This can result in significant distortion at higher listening volumes, even when utilizing sensitive headphones.

One solution is to feed the line-level outputs of this equipment into a power amplifier and then connect your low-impedance headphones to that. However, this approach creates a fixed connection. Besides, the power required to drive headphones is approximately one-thousandth of that demanded by loudspeakers, making a large power amplifier somewhat oversized for the job!

Circuit diagram:

Main Features:

Measured Performance:

Note:

All tests were performed with the amplifier driven from a low source impedance. For crosstalk measurements, the non-driven input was back-terminated into 600?.

CAUTION!

Prolonged exposure to extreme noise levels, including high volumes of music, can result in hearing loss and tinnitus. Hearing loss is a cumulative, gradual, and often symptomless condition!