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.
Build Accurate LC Meter and start making your own coils and inductors. This LC Meter allows to measure incredibly small inductances making it perfect tool for making all types of RF coils. LC Meter can measure inductances starting from 10nH - 1000nH, 1uH - 1000uH, 1mH - 100mH and capacitances from 0.1pF up to 900nF. The circuit includes an auto ranging and reset function to make sure the readings are as accurate as possible ... [more]