In 1972, I built a three channel color organ using 4 op amps and this exact circuit. Mind you, the op amps were industry samples given to me by a distributor. I was 14-15. I designed it using the above filter from the Burr Brown op amp handbook. Worked decently. later, received a price list of these one inch by two inch epoxy rectangle op amps and found I had built a color organ with around a thousand dollars worth of laboratory grade op amps. I had mixed feelings about that.
Wow, what are the odds of two twin tee notch filter videos released on the same day? Free Electron did one on using twin tee notch filters to analyze distortion. Great video, thank you . Regards, David
Thank you for providing instruction and entertainment together. Also, this is a pleasant brain exercise. Great circuit, and explanation. Provides more insight into the gyrator operation (for me at least) when the circuits are compared. Now this makes me want to see "Tone Control" and "AGC" circuits explained in a way I can understand too.
Equally important, the phase change around the feedback loop must be 2n pi radians to get positive feedback. This happens for both T's only at the right frequency.
Understand how it oscillates at the set frequency but can't see why it doesn't run to the rails and give a square wave output. Think I recall a thermistor or even a small bulb being used to limit gain so the cct only just oscillates and avoids the harmonics that would ruin the clean sine wave.
WOW ! if you put two pots in there at the 'T junction' of both filters you have a Baxandall Tone control set up. Exactly what I'm playing with but having a hard time working out how it functions, this is quite a big shove for me !! I'm not sure how to pick a value for the pots, because in an example circuit I have they give no explanation of why the values are what they are and they dont say whether they are LOG or LIN ? I think LIN but who knows, maybe I can think from another angle....cheers !!
Interesting! Twin T is a notch filter, definitely not a bandpass! It oscillates because only at the notch frequency, the phase shift crosses zero very sharply, going from +pi to -pi. Since your gain is very large (A=111) and the notch is not perfect, your overall loop-gain AB probably becomes nearly 1 and the phase shift AB is 0 degrees only at the notch frequency. For oscillations, overall loop-gain AB should be 1 angle 0 degrees, as in Wien bridge and other oscillators that use a bandpass filter in the feedback path.
Can you tell me how much distortion there is on that sine signal? With a four-fold potentiometer and replaceable capacitors, it can become a nice little sine generator! But the distortion must be low.
I often see weird and wondrous circuits in the thumbnail. I am sure I am not alone when I say "Holy cow. How does that work? I better watch the video and find out." So in other words, these thumbnails are a kind of click bait. Lol. PS - Ohh.. now I sort of get it. A high pass filter and a low pass filter combined. It does make a nice sine wave 👍
Well that just doesn't seem right. Don't know why, but it doesn't matter. It's a sunny warm day here in the north country and the wife just told me to get away from the computer and do some much needed yard work after the long snowy winter. Sigh!
Still yelling at the screen... Combine a low order low pass with a low order high pass filter and you get a lousy notch. That requires a cascade (series) arrangement. But these are in parallel. So the phase response of the two T's comes into play. Do the circuit analysis and you find that there is a zero in the transfer function at that frequency. Zeros make really good notches.
In 1972, I built a three channel color organ using 4 op amps and this exact circuit. Mind you, the op amps were industry samples given to me by a distributor. I was 14-15. I designed it using the above filter from the Burr Brown op amp handbook. Worked decently. later, received a price list of these one inch by two inch epoxy rectangle op amps and found I had built a color organ with around a thousand dollars worth of laboratory grade op amps. I had mixed feelings about that.
This notch/bandpass plot twist was a revelation - thanks!
Educational and entertaining what more could you want.
Good Circuit. Good concise explanation. Thanks. Ize beez luvs me some circuit o' the day!
4:50 I was about to say it's a notch filter... 😂😂😂
i thought the same, low pass and high pass in parallel is a notch, in series is a band pass
Wow, what are the odds of two twin tee notch filter videos released on the same day? Free Electron did one on using twin tee notch filters to analyze distortion. Great video, thank you . Regards, David
Thank you for providing instruction and entertainment together. Also, this is a pleasant brain exercise.
Great circuit, and explanation. Provides more insight into the gyrator operation (for me at least) when the circuits are compared.
Now this makes me want to see "Tone Control" and "AGC" circuits explained in a way I can understand too.
Nice presentation. Looking forward to more. Thanks!
Equally important, the phase change around the feedback loop must be 2n pi radians to get positive feedback. This happens for both T's only at the right frequency.
Pretty interesting :)
Positive and negative feedback combined to work together!
Understand how it oscillates at the set frequency but can't see why it doesn't run to the rails and give a square wave output. Think I recall a thermistor or even a small bulb being used to limit gain so the cct only just oscillates and avoids the harmonics that would ruin the clean sine wave.
Merci for this video.
Would be so interesting to compare it with the phase shift oscillator, almost the same component requirements / number.
I have vc hi pass filter coupling this to vc low pass filter creates really awesome noises, noises you might not expect.
Cool circuit this T-bridge.
Nice video as usual 🤷🏻♂️ does types of capacitors and resistors makes a difference?
It would be very interesting to find a way to control this fine sine wave oscillator with voltage, like a VCO
I think the filter is a Twin T Notch Filter...
WOW ! if you put two pots in there at the 'T junction' of both filters you have a Baxandall Tone control set up. Exactly what I'm playing with but having a hard time working out how it functions, this is quite a big shove for me !! I'm not sure how to pick a value for the pots, because in an example circuit I have they give no explanation of why the values are what they are and they dont say whether they are LOG or LIN ? I think LIN but who knows, maybe I can think from another angle....cheers !!
You didn't cover the positive feedback loop. It wouldn't work without it and too much would probably cause you to loose the pretty sinewave.
Interesting! Twin T is a notch filter, definitely not a bandpass! It oscillates because only at the notch frequency, the phase shift crosses zero very sharply, going from +pi to -pi. Since your gain is very large (A=111) and the notch is not perfect, your overall loop-gain AB probably becomes nearly 1 and the phase shift AB is 0 degrees only at the notch frequency. For oscillations, overall loop-gain AB should be 1 angle 0 degrees, as in Wien bridge and other oscillators that use a bandpass filter in the feedback path.
@IMSAI Guy, glad you are doing synth stuff
Can you tell me how much distortion there is on that sine signal?
With a four-fold potentiometer and replaceable capacitors, it can become a nice little sine generator! But the distortion must be low.
watch the video I link in the description.
How do i make it respond exponentially to 1v per octave? :P
What if you connect the + (non inverter) pin of the op amp to ground. Would it still oscillate?
What's the power supply to the op-amp look like? Single ended or bipolar?
Nice vid thank you. Has anyone ever tried circuit simulation apps for android?
For dullards, that doesn't seem to have any input signal. What starts the oscillation?
random noise.
@@IMSAIGuy Thank you. I'll give it a buzz
What type of capacitors are those. They look like tantalums.
just common ceramic, but not common (these days) axial leads
I often see weird and wondrous circuits in the thumbnail. I am sure I am not alone when I say "Holy cow. How does that work? I better watch the video and find out." So in other words, these thumbnails are a kind of click bait. Lol.
PS - Ohh.. now I sort of get it. A high pass filter and a low pass filter combined. It does make a nice sine wave 👍
like wow man! this really resonated with me!! I got the vibe!!
gota learn how 2 skii...
Well that just doesn't seem right. Don't know why, but it doesn't matter. It's a sunny warm day here in the north country and the wife just told me to get away from the computer and do some much needed yard work after the long snowy winter. Sigh!
Watch from Pakistan
Still yelling at the screen...
Combine a low order low pass with a low order high pass filter and you get a lousy notch. That requires a cascade (series) arrangement. But these are in parallel. So the phase response of the two T's comes into play.
Do the circuit analysis and you find that there is a zero in the transfer function at that frequency. Zeros make really good notches.
Won't work, you are not feeding any current to the circuit 😁🇨🇦