Welcome (back) to Linear Audio, your tech audio resource! Volume 3 is already our fourth issue! At 188 pages, Vol 3 packs another smorgasbord of stimulating, interesting and thought-provoking articles. Why 'tweaks that cannot work' can still sound different, digital interpolation, class-A thermal case design, mic preamps. Headphone preamps with in-ear equalization, correcting cartridge (and speaker) resonances, passive I/V conversion, active subwoofer design, a simulated inductor and a low noise preamp for your test bench. Then an essay on the state of analog and digital audio, and closing with two book reviews. Another issue you'll want to have at your side so you can grab it again and again. Enjoy!

Articles in this Volume:

Design Considerations for a Class-A Amplifier Enclosure
EUVL

Many class-A amplifiers are placed in a largish enclosure with heatsinks that ‘look about right’. But, just as with the electronics involved, you can calculate the requirements for such an enclosure and specifically the heat sink size and geometry. Patrick K goes to the whole process with an example project. He shows that with some simple calculations you can quickly home in on a good solution to make sure that the amp is not overheating and that you don’t spend more than necessary on the hardware. As a bonus, he provides many tips and tricks for enclosure design and construction to ensure that the final amplifier not only performs well but also has a very professional look-and-feel.

 

Correcting Transducer Response with an Inverse Resonance Filter
Steven van Raalte

altSteven van Raalte set out to combat the resonance in phono cartridges. Manufacturers often rely on this resonance to compensate for the hf roll off caused by cartridge induction and load impedance. Although the frequency response can be made to look quite flat, the result is often severe phase shifts and resultant time smearing. Steven develops a Sallen-Key based topology that ‘undoes’ the time smearing, and shows how it makes the square wave response of the combination cartridge- filter impeccable. He even shows how to dimension the filter such that the RIAA 2120 Hz turnover point can be deleted and become part of the filter! At the end of the article he also shows how to use the technique to compensate for the resonance at the low frequency side of a speaker.

 

Audio design is moving forward – or is it?
Stan Curtis

altWith all our focus on individual designs and equipment and trying to improve our amps and speakers, it is easy to lose sight of the big picture. Stan Curtis, who has literally designed 100’s of audio components but also founded several well-regarded audio companies, steps back and looks at that big picture. He concludes that for analog audio, we’re pretty much at the point where possible improvements are small and incremental, but that with digital audio there’s still a lot of work to be done.
 

 

Audible tweaks that cannot work
Burwen
 
In his Guest Editorial, Richard Burwen confronts that age-old question: how is it that tweaks that ‘cannot work’ can still lead to audible differences? He has a surprising answer, which can easily be verified with a sound level meter and a signal generator.
 
 

 

How Discrete Signal Interpolation Improves Digital-to-Analog Conversion
Rick Lyons
 
Digital Interpolation is a way to reduce complexity and requirements for post-DAC analog filtering. Richard Lyons shows not only how it is done, but also discusses the D-A conversion process itself, what aliasing is and how to handle it, the Nyquist criterion and of course analog filtering. Truly a Tutorial for anyone who wants a clearly to follow explanation of the issues involved.
 
 
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