Analog DIY Audio Generator - Page 1
Forum section: electronics / projects

author: electroagenda
author_rank: Newbie
timestamp: July 24, 2022, 09:35:02 pm
content: This project consisted of designing an audio generator based on a balanced Wien-Bride oscillator, which provides low harmonic distortion.The home made boards were included in a modded box (that originally was a professional audio generator).All the building process and performance measurements are reported here:https://electroagenda.com/en/low-distortion-audio-oscillator-build/During the project, a notch filter was also designed to suppress the fundamental allowing to measure harmonic distortion in a spectrum analyzer. That notch filter is reported here:https://electroagenda.com/en/bainter-notch-filter-design-and-tuning/

author: jonpaul
author_rank: Super Contributor
timestamp: July 25, 2022, 01:05:45 pm
content: Very old work, See 1980s papers and notes by the late and great engineer Jim Williams at Linear Technology, starting with restoration of original HP 200 oscillator 1930s, to state of the art.00001% THD designs.after a bit of research your work will be better definedj

author: electroagenda
author_rank: Newbie
timestamp: July 25, 2022, 01:47:14 pm
content: Quote from: jonpaul on July 25, 2022, 01:05:45 pmI was totally aware that are better figures out there. For sure Jim Williams at Linear Technologies and many others at many companies with way more resources than a homemade work.I´d never intend to create a homemade project that achieves state of the art figures....I hope the shared report can be helpful for electronics and audio hobbyists.Thank you for pointing it out so that others can improve their figures in their projects.

author: eugene
author_rank: Frequent Contributor
timestamp: July 25, 2022, 02:57:55 pm
content: Quote from: jonpaul on July 25, 2022, 01:05:45 pmI could have sworn that Jim Williams' adventure with that HP 200 was one of the chapters inThe Art and Science of Analog Circuit Design, but for some reason I can't find it. Must have read it somewhere.In any case, the whole book is a must-read for anyone serious about analog electronics. More to the topic, the article where Jim Williams takes us step by step as he wrings every available microliter of performance out of a (then) 50 year old Wein bridge oscillator is an absolutely must read for anyone that wants to make a high performance sine wave oscillator. One doesn't need to start with an HP 200 from the 1930's like he did.Wish I could find that article.

author: andy3055
author_rank: Super Contributor
timestamp: July 25, 2022, 04:08:47 pm
content: During the project, a notch filter was also designed to suppress the fundamental allowing to measure harmonic distortion in a spectrum analyzer. That notch filter is reported here:https://electroagenda.com/en/bainter-notch-filter-design-and-tuning/That is a neat job! Great details. I agree that it is old but the OP is correct in that the design is based on parts available at the time. I love to see old and simple designs like this.I have not come across the Jim Williams stuff, hence can't comment. A link will be helpful.

author: RoGeorge
author_rank: Super Contributor
timestamp: July 25, 2022, 04:40:50 pm
content: Quote from: andy3055 on July 25, 2022, 04:08:47 pmSee chapter "7. Max Wien, Mr. Hewlett, and a Rainy Sunday Afternoon"http://www.introni.it/pdf/Williams%2007%20-%20Book%20Chapters.pdf

author: Gyro
author_rank: Super Contributor
timestamp: July 25, 2022, 04:56:10 pm
content: Quote from: jonpaul on July 25, 2022, 01:05:45 pmI wouldn't say that what Jim Williams did was a restoration the HP200. He spent his Sunday afternoon working from the basis of a Wien-Bridge oscillator, departing from the filament PTC stabilisation, briefly experimenting with JFET before settling on a vactrol.He then experimented with notching out specific harmonics using yet more opamps.Yes, what he did was clever (of course!) and he had fun, but it was hardly a standard Wein bridge oscillator by the time he had finished.EDIT: Sorry, I must have been thinking about another design (maybe John Linsley Hood) regarding the notching out of harmonics, maybe using a state variable design.

author: jonpaul
author_rank: Super Contributor
timestamp: July 25, 2022, 10:09:48 pm
content: Jim Williams was friend, and a genius circuit and IC engineer, his hobby was working with vintage equipment, I recall Jim at an AES convention présentation of the HP200, and Silicon Valley AARL ham radio flea markets, alongside Bob Pease. His books and articles are worth finding.A very sad day in 2011 when Jim died of stroke. Bob Pease was returning from the funeral and crashed on the way home. A catastrophic loss to the Analog world.ultra low distortion audio oscillators are fascinating, the Tektronix SG505 was a modern design.Just a walk down memory lane.....Jon

author: andy3055
author_rank: Super Contributor
timestamp: July 25, 2022, 11:45:22 pm
content: Thanks

author: moffy
author_rank: Super Contributor
timestamp: July 26, 2022, 12:18:54 am
content: Quote from: jonpaul on July 25, 2022, 01:05:45 pmJim Williams got his best performance, THD, out of a fixed frequency wein bridge oscillator by optimizing the gain and making the control range of the gain control element very small. It is a different matter to try the same for a wide band wein bridge oscillator as the gain needed varies with frequency, and the gain control element, a bulb and ldr, needs much greater range hence more distortion. These are very decent results and kudos to electroagenda.