Designing a good, balanced-input audio pre-amplifier  
Wednesday 01 September 2021, 19:15 - 22:00

The St George Amateur Radio Society is continuing to hold their monthly gatherings on line; the next is on Wednesday evening 1st September 2021.

Several months ago, Brian VK2GCE gave a presentation entitled "An Introduction to Operational amplifiers." Now Brian is back with a sequel.

Brian has been designing op amp circuits since 1968, when he wanted to multi-track record his playing in bands and orchestras. His designs were kicked off by chance comments from a fellow Masters degree student and an air-conditioning engineer. The pathway was strewn with hurdles, not least because op amp ICs back then weren't all that wonderful.

He started with Jim Rowe's 1969 Electronics Australia circuit, using the Fairchild 709. He then moved through more and more sophisticated ICs. In 1974 he started working for De Lane Lea, one of the big-name recoding firms in Soho, London. Here he designed IC-based pre-amplifiers and audio amplifiers for dubbing studios when audio equipment was valve-based and massive. One of Brian's early IC-based mixers caught the eye of De Lane Lea's chief electronics designer - you'll see pix of this mixer. Brian's apotheosis was designing the microphone mixer for the London recordings of Pink Floyd's 'The Wall'; this recording had been kicked of by the band members' reactions to deaths at the Berlin Wall in 1964. The London tracks of the 'The Wall' were laid in about 1978.

Brian will take us through the iterative process of designing a very good, balanced-input audio pre-amplifier. He will then take us on the next stage of the journey to design a mixer using several of these pre-amps. Major concerns and the workarounds include noise, EMI, headroom, frequency response - and compromise

September's presentation will begin at 7.30pm, Wednesday evening 1st September 2021, on your computer or smart device screen. To join the on line gathering, use a web browser (preferably Google Chrome) and copy the following link;

Only if prompted, enter your name & callsign, otherwise just click "Ask to Join". Help on how to join can be found at:

If the browser / computer asks for permission to use your camera and microphone please "allow" this if you want to participate in the meeting and have others be able to see and hear you, or, join by phone (for audio only): Dial 02 9051 7153  - when prompted, enter the following PIN followed by the "#" key on your phone: 513 688 905#

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