November 2015

Currawong Valve Amplifier (Part 1)

A 21^st Century take of a design for anyone yearning for the yesteryear sound of valve (vacuum tube) audio circuitry and modern assembly techniques, this 10W+10W stereo amplifier combines the best of both worlds, featuring a total of four 12AX7 twin triodes and four 6L6 beam power tetroid vacuum tubes in a class-AB ultra-linear stage.

The Currawong valve amplifier is built on a modern double-sided printed circuit board that’s designed to be satisfying but safe to build, showing off eight valves in all their glowing glory!  Other features include delayed HT, HT soft start and remote IR motorised volume control option. In Part One this month, circuit details are described.

 High voltage design suitable for experienced constructors

What is a Currawong? Here’s a Youtube clip:
https://www.youtube.com/watch?v=-gPCa53J5EM

48V Dual Phantom Power Supply

Lots of audio equipment needs so-called “phantom” power that provides power to equipment via balanced signal leads. As well as condenser microphones, phantom power is also needed for active direct-injection (DI) boxes, pre-amps and effects units.

This project runs from a 24VAC mains adaptor and delivers dual regulated 48V DC supplies via XLR sockets to power two devices.  Our project is built on a compact PCB and housed in a rugged diecast box.

Programmable Mains Timer with remote switching

Remote-control plug-in mains switches are popular gadgets for on-off powering of lighting or electronic entertainment devices from a distance. A single hand-held RF control can often power multi-channel devices allowing several mains-powered units to be controlled conveniently around the home. What if you could add a mains timing feature as well? Now you can, with this constructional project. It can be programmed to switch the power on and off after a delay or to switch the power on and off at set times.

Our Remote Switch Timer in effect lets you add a timer function to a standard remote-control mains switch. It interfaces with the remote’s PCB and provides the extra timing functions using a pair of relays wired across the desired on and off switches on the remote’s PCB. Backlit LCD display. PICmicro powered with free downloadable source code.

Teach-In 2015 Discrete Linear Circuit Design (Part 10)

In the last part of our tutorial series devoted to linear circuit design, power supply design is examined in detail including classic full-wave design analysis, and an in-depth look at methods of measuring an audio amplifier, adjusting and fault-finding with virtual instruments.

Also in this issue:

• PIC n MIX – review of MikroElectronika’s ‘mikromedia for PIC32’ development board and ‘microC’ and ‘Visual TFT’ software.
• Audio Out – the principles behind audio volume controls and associated circuitry
• Techno Talk – copper mountains and tin whiskers
• Net Work – Some alternative email programs; first thoughts on Windows 10
• Practically Speaking – circuit diagrams and symbols
• Max’s Hot Beans – mCookie Monster; Simblee modules
• Electronics Building Blocks – make an electronic stethoscope for machinery

Next month:

High-energy Multi-Spark CDI for Performance Cars (Part 1); Time Domain Reflectometry (TDR) Dongle for Oscilloscopes; The Currawong 10+10W Stereo Valve (Tube) Amplifier (Part 2); Dremel 3D Idea Printer full review.