{"id":872,"date":"2015-12-20T17:15:20","date_gmt":"2015-12-20T17:15:20","guid":{"rendered":"http:\/\/stompville.co.uk\/?p=872"},"modified":"2020-10-11T12:29:14","modified_gmt":"2020-10-11T12:29:14","slug":"wien-bridge-oscillator","status":"publish","type":"post","link":"https:\/\/stompville.co.uk\/?p=872","title":{"rendered":"Wien Bridge Oscillator"},"content":{"rendered":"<p>You may have gathered from my last-but-one post on <a title=\"Bit-banging the AD9833 DDS module\" href=\"https:\/\/stompville.co.uk\/?p=853\" target=\"_blank\" rel=\"noopener noreferrer\">bit-banging the AD9833 DDS module<\/a> that I have been playing with audio oscillator designs. As part of this process, I have tried a few Wien bridge oscillator designs that purport to not require a proper non-linear device (such as a miniature lamp or an RA53 thermistor). I could not get any of these designs to work in a stable, predictable and reliable fashion. Eventually, I turned to the classic Bill Hewlett-inspired miniature lamp with op-amp design. Here&#8217;s the basic schematic from a Linear Technology App. Note:<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\" wp-image-873 aligncenter\" src=\"http:\/\/stompville.co.uk\/wp-content\/uploads\/2015\/12\/P163SV.jpg\" alt=\"P163SV\" width=\"387\" height=\"272\" srcset=\"https:\/\/stompville.co.uk\/wp-content\/uploads\/2015\/12\/P163SV.jpg 450w, https:\/\/stompville.co.uk\/wp-content\/uploads\/2015\/12\/P163SV-300x211.jpg 300w\" sizes=\"(max-width: 387px) 100vw, 387px\" \/><\/p>\n<p>Why the above equation identifies the frequency as 1.000kHz (to three decimal places!), when the math clearly results in a frequency of 995Hz is anybody&#8217;s guess.<\/p>\n<p>One of the things about this design is that the current consumption is much lower than you might imagine. The #327 lamp is rated at 28V 1.12W giving a nominal current of 40mA. But the above circuit runs at just a few mA &#8211; the lamp is most certainly not being used as a lamp and is by no means glowing.<\/p>\n<p>I wanted a battery-powered oscillator, so I came up with the following design (click for a larger version):<\/p>\n<p><a href=\"http:\/\/stompville.co.uk\/wp-content\/uploads\/2015\/12\/197SV.png\" target=\"_blank\" rel=\"noopener noreferrer\"><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-874 \" src=\"http:\/\/stompville.co.uk\/wp-content\/uploads\/2015\/12\/197SV-1024x448.png\" alt=\"197SV\" width=\"720\" height=\"315\" srcset=\"https:\/\/stompville.co.uk\/wp-content\/uploads\/2015\/12\/197SV-1024x448.png 1024w, https:\/\/stompville.co.uk\/wp-content\/uploads\/2015\/12\/197SV-300x131.png 300w, https:\/\/stompville.co.uk\/wp-content\/uploads\/2015\/12\/197SV.png 1400w\" sizes=\"(max-width: 720px) 100vw, 720px\" \/><\/a>The TLE2426 splits the 9V from the battery into +\/- 4.5V and theMCP111 provides a low-battery-voltage indication. PR1 should be adjusted to ensure that the output is stable (it also adjusts the headline output voltage). You can try almost any jelly-bean op-amp (e.g. TL072, RC4558) in place of the LM833, but bear in mind that many op-amp outputs don&#8217;t go anywhere near the rails so you shouldn&#8217;t be shooting for more than about 1V r.m.s. output voltage. D1,D2 and R8 protect the op-amp output and C9\/R9 make an attempt to isolate the circuit from noisy grounds. The circuit as shown with PR1 adjusted for a nominal 1V r.m.s. output at pin 1 of the LM833 consumes about 7mA of current. \u00a0<img loading=\"lazy\" decoding=\"async\" src=\"http:\/\/stompville.co.uk\/wp-content\/uploads\/2012\/02\/svfavicon.png\" alt=\"svfavicon.png\" width=\"16\" height=\"16\" \/><\/p>\n","protected":false},"excerpt":{"rendered":"<p>You may have gathered from my last-but-one post on bit-banging the AD9833 DDS module that I have been playing with audio oscillator designs. As part of this process, I have tried a few Wien bridge oscillator designs that purport to not require a proper non-linear device (such as a miniature lamp or an RA53 thermistor).\u2026 <span class=\"read-more\"><a href=\"https:\/\/stompville.co.uk\/?p=872\">Read More &raquo;<\/a><\/span><\/p>\n","protected":false},"author":3,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[5],"tags":[],"_links":{"self":[{"href":"https:\/\/stompville.co.uk\/index.php?rest_route=\/wp\/v2\/posts\/872"}],"collection":[{"href":"https:\/\/stompville.co.uk\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/stompville.co.uk\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/stompville.co.uk\/index.php?rest_route=\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/stompville.co.uk\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=872"}],"version-history":[{"count":5,"href":"https:\/\/stompville.co.uk\/index.php?rest_route=\/wp\/v2\/posts\/872\/revisions"}],"predecessor-version":[{"id":1392,"href":"https:\/\/stompville.co.uk\/index.php?rest_route=\/wp\/v2\/posts\/872\/revisions\/1392"}],"wp:attachment":[{"href":"https:\/\/stompville.co.uk\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=872"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/stompville.co.uk\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=872"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/stompville.co.uk\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=872"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}