September 2025

Compact Hi Fi Headphone Amplifier (Part 1)

This compact headphone amplifier is easy to construct and sounds great. The project is ideal for beginners or for any audio enthusiast wanting to get the best out of a pair of traditional wired headphones. It features two stereo inputs that are mixed with independent volume controls. Discrete through-hole circuit board simplifies construction. The circuit description is outlined this month with full constructional and setting up procedures following in Part 2 next month.

Low-cost electronic modules –
0.91” Monochrome OLED screen

This feature investigates the application of a small, low-cost mono OLED display that sports a 128 x 32 pixel screen, available in white or blue. It has an I²C interface so it can easily be driven by a microcontroller for example.

The Fox Report

Exploring the promising A2D2 analog to digital converter and applications in digitising and streaming analog audio.

Techno Talk

Recounting the story of breadboard systems and easy-to-connect electronic kits (such as the classic Radio Shack Science Fair etc.), with quick-connect wire terminals suggested more than 100 years ago.

Discrete ‘Ideal’ Bridge Rectifier

This ‘electronic’ bridge rectifier will provide active rectification of a centre-tapped transformer, or combine two DC supplies with low losses. It can generate split rails (positive or negative) and its high efficiency reduces power dissipation compared with standard rectifier designs. Both through-hole and surface mount designs are provided.

Max’s Cool Beans
Weird & Wonderful Arduino Projects
Part 9: a crash course in logic

Max muses over the finer points of switch bounce and renders a thorough briefing of the basics and truth tables of logic gates, in readiness for more work on the retro games console.

Automatic LQ Meter

This sophisticated test gear will surely find a place on the RF enthusiast’s workbench. It measures two parameters in one instrument, inductance (L) from 0.1 to 999µH and Quality (Q) from 10 to 300. It also has a built-in signal generator. Based on an Arduino Nano, it utilises a 16 x 2 LCD display.

Net Work

The welcome return of occasional articles continues on the theme of smart meters and the enforced replacement of out-of-date meters, plus there’s more on BYD’s quest to conquer the EV world and we look at some surprise bargains that Chinese vendor Temu has to offer.  See this month’s Net Work blog for more details and ready-made links to click on.

Circuit Surgery

Explanations and insights into the advanced topic of digital signal processing continue with the implementation of a finite impulse filter (FIR), specifically a windowed sine digital filter.

EDA Software Review
Altium Designer 2025

This is the latest iteration of the electronics design automation (EDA) software that we have used for 25 years. We share our thoughts of this sophisticated PCB design suite in this special review feature.

Dual-Rail Load Protector

This circuit will safeguard loads against reverse or excess supply rail voltages or over-currents. Its dual-rail support means it can operate with eg audio circuits having split supplies. Rated 4-36V or ±4-18V, current rating 7A or more. Typical insertion loss <300mV. Built on a single PCB using mostly through-hole components.

Audio Out

Our expert in analog audio continues with the theme of a cascode-input power amplifier, showing us the design and prototyping steps taken in the pursuit of optimum performance.

Next month

Seaside Sound Simulator; 3D printer Filament Dryer; Custom electric guitar (and bass) pickguards.