For a better sine wave - Page 1
Forum section: electronics / beginners

author: Md Mubdiul Hasan
author_rank: Regular Contributor
timestamp: December 20, 2017, 05:33:34 am
content: Hello sir,This post might be a silly one, but my stupid brain does not find it well.I am looking for a signal generator circuit to fed different frequencies in other circuit.I have found one, take a look(first attachment)But, the person who posted this did wrong on inverting and non inverting sign.Anyway, I simulate this simulation circuit, but noticed that the peak of sinewave is not much sharp rather than it flat.Take a look this circuit (second attachment), I found measurable change while screwing the POT R3.Kindly discuss this design again.1. Feedback path.2. Inverting and non inverting inputs with filter.3. Contribution of the potentiometers here.4. Reason of using follower op amp.5. Further improvement.

author: hamster_nz
author_rank: Super Contributor
timestamp: December 20, 2017, 07:51:54 am
content: That doesn't have the look of 'correctness' about it.The two resistors that control the frequency should usually be of the same value. Also it is usual for the oscillator to have a light bulb on some other part that changes resistance in response to signal level to balance the gain in the feedback loop.Not saying it won't work, but it doesn't look like the classic Wein Bridge Oscillator with a buffered output.

author: danadak
author_rank: Super Contributor
timestamp: December 20, 2017, 11:01:50 am
content: As mentioned oprior you need a method to stabilize amplitude, otheriwseoscillation grows into clipping.Classic is using incandescent bulb -https://en.wikipedia.org/wiki/Wien_bridge_oscillatorhttp://www.zen22142.zen.co.uk/Design/wien_osc/Wien-Bridge%20Oscillator.htmThe original paper on this topic -https://ia801604.us.archive.org/21/items/bstj17-4-574/bstj17-4-574.pdfRegards, Dana.

author: HoracioDos
author_rank: Frequent Contributor
timestamp: December 20, 2017, 12:13:46 pm
content: Hello!Perhaps you may find this thread useful. Here you can find 5 different circuits.https://www.eevblog.com/forum/beginners/best-way-to-amplify-a-sine-wave-without-distorsion/msg1150871/#msg1150871PD: Hero 999 & AudioGuru helped me a lot to build a Wien oscillator. (I'm still grateful to them). FrankBuss also offered a very interesting approach.

author: Md Mubdiul Hasan
author_rank: Regular Contributor
timestamp: December 26, 2017, 02:00:01 am
content: QuoteWhat you will do if you need to vary the frequency?

author: Md Mubdiul Hasan
author_rank: Regular Contributor
timestamp: December 26, 2017, 02:01:22 am
content: QuoteAn expart says, "The main problem with your Wein Bridge oscillator is that there is no Automatic Gain Control. Minimum gain required for oscillation is 3.000+?. If gain is just slightly more, then the amplitude builds up, and the sine wave becomes a clipped sine."

author: Md Mubdiul Hasan
author_rank: Regular Contributor
timestamp: December 26, 2017, 02:21:56 am
content: Quote from: HoracioDos on December 20, 2017, 12:13:46 pmYes, AudioGuru is really very helpful.This thread is helpful indeed.

author: rhb
author_rank: Super Contributor
timestamp: December 26, 2017, 03:00:32 pm
content: Do a search for "Max Wien, Mr. Hewlett and a Rainy Sunday Afternoon" and read that article by Jim Williams.Then join this thread:https://www.eevblog.com/forum/testgear/understanding-what-to-read-on-this-fft-plot/msg1369079/#msg1369079Start with your current circuit, measure the harmonic distortion and iterate the way Jim Williams did. Just make sure you don't over drive the input to the soundcard.Have Fun!Reg

author: Old Printer
author_rank: Frequent Contributor
timestamp: December 27, 2017, 03:17:07 am
content: Quote from: rhb on December 26, 2017, 03:00:32 pmReg, thanks for putting the Jim Williams collection to my attention. Just spent the last two hours immersed in it, a great read. Still have plenty to go and 90% of it is over my head, but you gotta love the guy. !

author: rhb
author_rank: Super Contributor
timestamp: December 27, 2017, 04:44:12 am
content: Can't possibly be over your head. Jim Williams only went to college for a couple of semesters. But he *did* work in the electronics repair shop at MIT ;-)It *is* so much the "right attitude". Check into Bob Pease and Bob Widlar. Both are just as amazing, though perhaps, not a warm and fuzzy as Williams.I *really* want to build Jim's Wien bridge oscillator and see if I can do just a tiny bit better.

author: schmitt trigger
author_rank: Super Contributor
timestamp: December 27, 2017, 02:43:24 pm
content: Besides being extremely bright, these three giants of analog IC design, had some some very unique personalities.With Widlar being the wild one, Pease the eccentric and Williams the fuzziest.Sadly, all died while they were still in their prime.

author: Audioguru
author_rank: Super Contributor
timestamp: December 27, 2017, 03:03:13 pm
content: Quote from: Md Mubdiul Hasan on December 26, 2017, 02:00:01 amSimply use a dual potentiometer. My Wien Bridge oscillator uses opamps with very high impedance Jfet inputs and the dual variable capacitor from an AM radio to change the frequency. The variable capacitor has trimmer capacitors on it to adjust the two tuning capacitors to be exactly the same.

author: Md Mubdiul Hasan
author_rank: Regular Contributor
timestamp: December 28, 2017, 04:05:41 am
content: Thank you to all of you to write in this post.QuoteKindly share some part of your circuit here.QuoteSorry that I have not get what exactly you are suggesting to do. D you suggest any tool for measuring harmonic distortion?

author: rhb
author_rank: Super Contributor
timestamp: December 28, 2017, 04:18:12 pm
content: Read my mesg #7 in this thread and read the thread referenced there.All you need is a sound card and Gnu Octave. Store a .WAV file, read it in Octave, computer the FFT, measure the amplitudes of all the harmonics, sum and divide by the amplitude of the fundamental. Multiply by 100 and you have THD in percent.

author: chris_leyson
author_rank: Super Contributor
timestamp: December 28, 2017, 05:07:52 pm
content: The dual potentiometer arrangement is shown in Fig. 1.http://www.zen22142.zen.co.uk/Design/wien_osc/Wien-Bridge%20Oscillator.htm, link already posted by danadak.There is a similar arrangement using a dual potentiometer but using transistors instead of a op-amp in Fig.2 herehttp://sound.whsites.net/project22.htm.An op-amp version using a smaller light bulb as a thermistor, CML1869 bulb is rated 14mA at 10V and available from Mouser.http://www.jensign.com/oscillators/index.htmlSome useful links to very low distortion oscillators using either led/photocell or voltage controlled amplifiershttp://www.proaudiodesignforum.com/forum/php/viewtopic.php?t=887

author: Md Mubdiul Hasan
author_rank: Regular Contributor
timestamp: December 29, 2017, 12:39:15 am
content: QuoteUnfortunately, I dont have SDD signal generator.

author: Md Mubdiul Hasan
author_rank: Regular Contributor
timestamp: December 29, 2017, 12:53:14 am
content: Dear Sir Chris,Thank you very much to those link.Looking at your reference, this might useful at this moment.QuoteLets study for the seek of 1.amplitude stabilization 2. Source of distortion in low frequency 3. Minimize the THD 4. Automatic gain control 5. Using of FET/JFET

author: rhb
author_rank: Super Contributor
timestamp: December 29, 2017, 12:58:00 am
content: Something is getting lost in translation. The OP in the other thread has built a Wien bridge oscillator and was asking for help in evaluating the THD. You seem to be engaged in a similar project, but haven't yet got as far. I have *no* idea what an SDD signal generator is. I do know what a DDS generator is, but my understanding is you wanted to build a clean analog sine wave oscillator. Within its frequency limitations the Wien bridge is *the* classic design.The Hewlett-Packard company was started in a garage building the Wien bridge oscillator that Bill Hewlett built for his MS at Stanford under Professor Terman.The article by Jim Williams, "Max Wien, Mr. Hewlett and a Rainy Afternoon" is an exercise in building a Wien bridge oscillator whose THD was lower than the best HP distortion analyzer to which Jim Williams had access at work. I explained in the other thread a good bit about how to measure the THD using a soundcard.