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Two-Way Stereo Headphone Adaptor

Do you have a stereo amplifier without a headphone socket but want to listen to your music via headphones? If so, this versatile Stereo Headphone Adaptor will do the job. It connects between your amplifier and loudspeakers, has several operating modes and features two output sockets with individual volume controls.

By Mauro Grassi

If you built our 20W Class-A Stereo Amplifier described last year, you will be aware that it lacks a headphone socket. Similarly, many hifi valve amplifiers also lack a headphone socket, the assumption being that a true hifi enthusiast will want to listen via good-quality loudspeakers.

A headphone output was not included in the Class-A Stereo Amplifier because it would degrade its superb audio performance. Both the wiring paths and the general circuit layout are critical factors in the design and any changes, however slight, can cause big changes in the signal-to-noise ratio and harmonic distortion figures of the amplifier.

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Fig.1: the Stereo Headphone Adaptor connects between your stereo amplifier and the loud-speakers and can drive two pairs of headphones.

If you do want to listen via headphones, a far better option is to build the simple Stereo Headphone Adaptor presented here. It connects directly to the amplifier’s speaker terminals and switches the loudspeakers and stereo headphone sockets using two DPDT (double-pole, double-throw) relays, so there’s no chance of it degrading the audio performance.

As mentioned in the introduction, you can connect up to two sets of stereo headphones. These can be switched on or off at the touch of a button and the volume of each can be individually controlled. In addition, the loudspeakers can be switched on or off and there’s also a Mute switch which turns everything off.

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