SINE WAVE OSCILLATOR: Twin T RC Filter OSC with LTSpice Simulation and Breadboarded Circuit

Linear oscillator circuits designed with RC filters in the feedback loop of an amplifier can generate sine waves that are usable in audio applications like test tone generators, analog synth sounds etc.
One RC oscillator that can produce these sine waves is the Twin T oscillator configuration. Let's look at the theory of using an amplifier as an oscillator, simulate the Twin T filter network and op amp oscillator in LTSpice, and build the circuit on a breadboard.
Note: in the video I forgot to point out that I didn’t have 16 K resistors so I used 20 K and that will have a big impact on the frequency and that’s how we got from around 1 kHz down to around 650 kHz.
RC Oscillator Info
en.wikipedia.org/wiki/RC_osci...
pdfs.semanticscholar.org/e5cb...
www.electronics-tutorials.ws/...
www.n5dux.com/ham/files/pdf/RC...
Twin T Oscillator and Filter Info
www.eng.auburn.edu/~deanron/Le...
fourier.eng.hmc.edu/e84/lectur...
www.discovercircuits.com/Andy/...
www.nutsvolts.com/magazine/ar...
www.theremin.us/Circuit_Libra...
LTSpice Files
github.com/GadgetReboot/misc_...
Patreon: / gadgetreboot
Pinterest: www.pinterest.ca/GadgetReboot
Twitter: @GadgetReboot / gadgetreboot

[@SuperFredAZ]

Hewlett Packard built an empire based on the twin-tee oscillator 70 years ago!

[@VeryMuchBlessed]

Very good comprehensive video, complete with values makes it easy to follow along on my workbench. Thanks much for making this video.

[@SidneyCritic]

It's still surprising when a SIM hits the mark. We used to SIM HP curves with simplistic engine SIMs, and it always surprised us when we got the dyno figures and it matched the SIM.

[@oscarilmio7148]

That's how,to an electronic like me,like to see the electronic explained. Bravo. BTW,happy n.y.

[@leachim66]

I love the analog videos you've been doing, keep it up!

[@SimpleEnough2k9]

Best wishes to you and your family for the New Year !!! Once again, thank you for the good and well explained material you're having on your channel. Best regards!

[@GadgetReboot]

Happy new year and thanks for watching!

[@pileofstuff]

Building your own synthesizer next?

[@GadgetReboot]

Absolutely! It turns out I had a magazine I think from 1993 that actually had this type of circuit generating drum sounds, I stumbled on a scanned copy of that article online and thought it looked familiar and then I had it actually on the bookshelf all this time. What the hell. I really need to clean this house!

[@TheEmbeddedHobbyist]

Nice simple explanation of an rc oscillator, 9.30am on new year's day was a bit too early :) one thing you could have pointed out is that XC = 1/(2 pi F C) is the impedance of the capacitor at frequency F as its an important part of understanding an rc filter. Great video. Pcb has arrived but still waiting on 0805 components :(

[@GadgetReboot]

Glad the PCB arrived! Yes it’s kind of hard to tell where to begin and end with the information conveyed for a given topic. I didn’t want to get too deep and I know that some information is required to get the point across so it’s a balancing act. Stating the reactance of the capacitor at a given frequency might have been out of context because what we were doing was trying to simplify the whole equation down to calculating a frequency response with a certain configuration so we didn’t need to actually know how to derive or account for components discretely. Maybe in five years I will have an even different perspective from today where I convey things a little differently but I guess in the end we just need the formula to get the job done and understanding it’s derivation is optional based on the interest of the person. One thing I learned from all of my combined education and experience is I usually end up a little confused no matter what path I take and I just try to grab information from everywhere and fill in the blanks. So that’s why I try to put links in the description for more information if there is somebody with more knowledge than I who can get more out of the information. Overall I guess it’s good I didn’t get into Laplace transforms in this video because nobody needs to wake up on New Year’s Day seeing things like 1/sC in a weird equation. I still have nightmares of that from over 20 years ago. My knowledge and experience is all over the place. I know enough to know that I don’t know very much. So if I can either pass on some knowledge or at least the inspiration for someone else to move forward and learn on their own, it’s been a good day.

[@TheEmbeddedHobbyist]

​@@GadgetRebootMy mum who is visiting for Christmas and the new year wanted the stamps :) so no videos made while she's here with her two dogs. Don’t mention "Laplace Transforms" I never got my head around them. I could never see how to rearrange the first transform equation to the final one required transforming back to the real world. I just got used to the fact that I’d not get 100% in the exam if one came up as a question. Plus in the 40 years working in electronics and avionics since doing those exams I’ve never needed to use them.

[@GadgetReboot]

The reason there are an odd combination of stamps is because I have had those sitting around for years with no opportunity to use them up so you helped me de-clutter! Then the post office figured out the balance and put that other postage label on. I’ve never had to use most of the school math since the final exam in those courses. The only integrating and differentiating I’ve had to do is with op amps. But I still have all the text books and occasionally I turn a few pages just to see if there’s any application I can make use of in modern times, but usually my eyes glaze over before anything practical emerges.

[@electronic7979]

👍

[@gregwmanning]

Very interesting. I wonder what componet(s) need to be varible to adjust to get a stable output freq. Happy New year, LC&S Greg

[@aduedc]

good clip, It would be good to investigate the effect of mismatch in caps and resistors on phase noise. Also, since product of RC sets frequency. What value R and C gives us the best phase noise Xc>R, or Xc

[@gandsnut]

I'm going to have to excuse myself; my brain is full.

[@GadgetReboot]

And that was the edited down version. Sometimes these things can throw the mind for a loop but hopefully I can get things working in the real world eventually so that other people don’t have to go in circles to get things up and running.

[@unodos1821]

🎉🎊

[@AxiisMusic]

Do you know whether there's a way of varying the frequency using a pot? Obviously the capacitor size changes the charge and discharge time thus affecting the frequency, however which resistor alters the frequency

[@GadgetReboot]

The Twin T is intended to be a fixed frequency and the ratio of component values should stay balanced, where two resistors should always be identical and the other is half the value. So if any one changes with a pot, it's all messed up...

[@AxiisMusic]

@@GadgetReboot ah okay. Thank you