Practical Electronics No 9 2025

Read in the issue 9 Practical Electronics 2025

Compact Hi-Fi Headphone Amplifier, part one by Nicholas Vinen.
This Headphone Amplifier is easy to build, sounds great, is inexpensive and fits into a
compact case. It’s ideal for beginners or those who want to get the best out of a set of
traditional wired headphones. It’s plugpack-powered, so no mains wiring is required.

Two Discrete Ideal Bridge Rectifiers by Phil Prosser & Ian Ashford.
This simple circuit uses just a handful of transistors, diodes and resistors. But it still
provides a very useful function: active rectification of the output of a centre-tapped
transformer or combining two DC supplies with low losses.

Automatic LQ Meter by Charles Kosina.
A Q Meter is an indispensable tool for anyone contemplating RF design. This new
design features two instruments in one, measuring inductance from 0.1 to 999pH and
Q from 10 to 300 with a test frequency from 100kHz to 90MHz!

Dual-Rail Load Protector by Stefan Keller-Tuberg.
It disconnects a load from its power supply if the voltage is reversed or too high. It
also disconnects the load if it draws current above the adjustable trip level. Its dual-rail
support means it can work with devices like audio amplifiers with a split supply.

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