September 2015

Opto-Theremin (Part 1)

A 21^st Century update of a classic invention in electronic music making, our latest Opto-Theremin uses light sensors for a manual volume control combined with the original principle of using a vertical radio antenna for pitch control.

By manipulating one’s hands around the sensors, it is possible to produce some very exciting, intriguing and sometimes weird electronic music and sounds.

It has a Line Out as well as an integral speaker.  In Part One this month, principles of operation and PCB assembly are described and assembly details will appear in Part Two.

 Surface mount design needs good soldering skills

Wideband Active Differential Scope Probe

This high-performance, active differential probe for oscilloscopes costs much less than commercially available designs, and is ideal for measuring high speed, high frequency circuits. It has very little circuit loading and a usable bandwidth of more than 80Mhz. Hints and tips for using the probe in various applications are included.

 Surface mount components are used throughout. Very good soldering skills will be necessary to complete this design successfully.

Mini-D Stereo 10W/ Channel Class-D Audio Amplifier

An amazing and deceptively powerful little circuit, this tiny Class-D amplifier module is up to 91% efficient and in stereo mode can deliver more than 10W/ channel, or when paralleled more than 25W into a single speaker. Its main feature is that the dedicated Class-D audio amp i.c. needs no heatsinking, making the design compact and efficient. Included are selectable gain, low-power shutdown mode and over-temperature, over-current, short circuit and speaker protection.

 Surface mount components are used throughout. Very good soldering skills will be necessary to complete this design successfully.

Teach-In 2015 (Part 8): Power Amplifiers

The principles of negative feedback are introduced along with an in-depth tutorial on making audio amplifiers both stable and predictable. Classic circuitry including Darlington transistors, the Sziklai feeback pair and a variety of common output transistor configurations are also described this month. Tina software is also utilised to demonstrate on-screen simulations of circuitry, showing how variations in circuitry can affect the results obtained.

Also in this month’s issue

• Techno Talk – Nanowires from graphene? And DIY store B&Q scores a major own-goal
• Net Work – looking at what the EPE website can offer you
• Audio Out Special Product Review – Peak Analysers
• Circuit Surgery –  Noise (Part 2)
• Practically Speaking – getting to grips (literally) with SMD chips
• Audio Out – RIAA Equalisation (Part 3)
• Max’s Hot Beans  – LittleBits modules for budding builders
• Electronic Building Blocks – using cheap as chips bits ‘n bobs off the web to make a Temperature Controller

Next month:

Digital effects processor for guitars and musical instruments; Opto Theremin (Part 2); Courtesy LED Lights delay for cars; Teach-In 2015 Part 9: working with power amplifiers.