April 2023

This month’s highlights

500W Power Amplifier (Part 1)

This large power amplifier produces big, clear sound with low noise and low distortion. This very robust design delivers 500W into a 4Ω load and 270W into an 8Ω load – and two of them could produce up to 1,000W of power! It has load line protection and speed-controlled fan cooling. A toroidal power supply produces ±80V from an 800VA transformer. Details of a kit of parts including hard to source components are included.

The circuit is described in Part One this month with construction details following in Part Two next month. Part Three (June issue) will include power supply construction and interwiring.

Capacitor Discharge Welder (Part 2)

This high-performance mini spot welder is ideal for spot-welding battery packs together using just the right amount of weld energy each time. In Part Two the constructional details are described in depth.

This design generates extremely high current pulses and therefore strong magnetic fields. Constructors must follow closely the safety warnings that are clearly printed in the article. Not to be used by those wearing a heart pacemaker or any similar sensitive medical device.

This device generates sparks and heat. Suitable PPE must be worn such as welding glasses that offer UV/ IR and weld spatter protection. Do not rely on using prescription glasses for eye protection.

Amplifier Clipping Indicator

This easy-to-build indicator circuit warns of the risk of audio clipping, to avoid distortion or even damage to driver units. It is a straightforward through-hole design using discrete components.

Three low-noise HF-UHF Amplifiers

Another investigation that uses budget-priced Asian electronic modules. All three of the low-cost wideband HF-UHF amplifiers modules described this month claim to provide 20dB of gain over frequency ranges of 1MHz to 3GHz, 5MHz to 6GHz and finally 50MHz to 4GHz.

Also in this issue

Techno Talk – Our new columnist kicks off this month with Max musing over the use of AI and robots in horticulture and agriculture.
The Fox Report – NASty problems trying a lesser-known NAS drive from China
Net Work – news of the latest Matter protocol for IoT devices, SpaceWatch and the work of British radio astronomer Frank W. Hyde revisited, and the last Boeing 747 and the Columbia orbiter commemorated 20 years on.
Circuit Surgery – electronically-controlled resistance – the conclusion of this very comprehensive topic
Audio Out – universal op.amp board optimised for audio electronics – Part 3 (dual op.amp vversion).
Max’s Cool Beans – join Max in Part 4 of his very popular Arduino primer for beginners