TH-cam decided I needed to see this video. Even though it seems to be six years old, it showed up on my feed. It brought back memories of when I was repairing audio gear in college. Our HP generator got a little unstable and I decided to crack it open. Imagine my surprise when I ran across a large (for something found inside a piece of gear), odd looking light bulb. Being young and dumb, I assumed the bulb was bad and ordered another one. I forget what was bad, but it's not a spoiler to report that it wasn't the bulb. Such a simple, elegant means of gain control. Great memories.
I too as a kid wondered why there were light bulbs in oscillators! One neat trick that I used ( I got it from an old book) is a radio squelch circuit made from two ten ohm resistors and two number 49 light bulbs. It's a bridge. I used it for years on a 6 meter SSB receiver. It goes between the speaker and the receivers audio out connection. You increase the audio gain until the lamps heat up enough to balance the bridge and then the speaker goes silent. Any signals that come in unbalance the bridge and un-mute the speaker.
One of my earliest electronics projects was a Wien bridge oscillator using a 741 op-amp. That was some forty or so years ago but I somehow clearly remember the struggle to get it to work and how I finally eventually succeeded. I had decided the problem was that the 741 could not drive enough current to warm up the lamp enough and I couldn't find a smaller lamp - the best I had was a bulb form a Christmas light string. In an attempt to solve that I put in an emitter follower stage to boost its current output capability. That could then easily drive the lamp but no matter how I adjusted it I could tell just by hearing that it was severely distorted. I then solved it in a different way. I replaced the lamp with an LDR. This acted as the gain controller. I then used the emitter follower transistor to drive the lamp which illuminated the LDR acting as the actuator for the gain control. With a lot of tweaking I finally got it to work. Many years later when I had access to an audio spectrum analyser at school I tested it and was pleased to find out it actually had very low distortion.
I never had children of my own, my wife has two grown kids from her earlier marriage, but had I had my own daughter I would have liked her to be very much like you.
Feedback loop oscillators reach stabilization when their closed loop gains reach 1. This is often done when the active device goes into saturation and the gain at the primary oscillation frequency is reduced while harmonics are increased. The use of an incandescent lamp, a device with resistance that has highly positive temperature co-efficience, allows loop gains to be reduced without the active device going into saturation; meaning oscillation reaches stabilization with much less harmonics (all active circuits are non-linear to some degree, even with heavy negative feedback). That is the primary benefit of using a light bulb to control oscillation. The other benefit is to assure reliable oscillation start-up because the resistance of the bulb is very low before voltage is applied. The ability to tolerate power supply voltage variation is a secondary benefit. By the way, Meacham described the use of lamp in a bridge to control gain in 1937, two years before Hewlett used it in his first product.
Thank you for the reminder. I have used one of those tiny indicator lamps in a reference 1khz oscillator that provided the synchronising bleep from the sound mixer to the audio recorder at the beginning of every take shot on a 16mm film camera. Everything was powered from the camera battery. I was amazed at the stability of the signal level that this simple technique provided.
Hi Jeri, Just seen your video regarding the Wien Bridge oscillator which reminded me of an interesting story relating to what I believe was the first use of a light bulb in this circuit. My story starts in 1967 when my college class mates wanted to build an audio generator as part of the practical element towards out final college exam. Out tutor, the wonderful Mr Dave King convinced the class to use the Wien Bridge circuit which used a glass thermistor in the feedback (pre op amps) circuit. Unfortunately, I was the only one in the class who had a glass thermistor and were too expensive even to purchase in bulk. Therefore, not wanting to abandon the project, Mr King went home that night and designed a circuit using a light bulb. As his design was so good, he published the project in one of the UK's leading electronic magazine, Practical Electronic. I still use my original audio oscillator in my workshop. It used to have a label on the front “May 1967). Therefore I believe our tutor was the first UK engineer to design this type of circuit. Regards Geoff.
Between you and Dave from EEVblog I have rekindled my interest in building stuff! Thank you. I was the only person at school who was interested in electronics, as a result there was no point in teaching this. I think I will be making my shack more focused toward construction when I move later next year.
I do not build any circuits like this, but it is great to watch your videos to help me stay up on the theory behind some of these circuits. Keep it up!
nice to discover your channel Ellie. I remember when I was a kid, I would be doing descartes 5th degree equations with either hand while watching TV, and I would also be thinking about op-amps with lightbulbs. :) coincindence.
I'm sorry. I've just come back to this video. Revisited, if you like. I GET IT. Thank you so much. Of all the videos out there trying to explain Wien bridge oscillation, *THIS IS THE ONE FOR ME* This is *MY LIGHTBULB MOMENT* Thank you so much lady. I am so excited right now, I need to go lie down. LOVE IT! FREAKIN' LOVE IT.
@cubemike99 The lamp is a 3V 15mA 'grain of rice' as used on model trains, get it on EBay. Resistor at the top of the diagram is a 1k pot. R1+2 is a10k dual pot with a 560R in series with each section. C1+2 100nF for about 200Hz to 2Khz. Opamp is a 741 or TL081.
Nice video, I just had the experience of building one for an am transmitter circuit! Took an annoying amount of tweaking to get the thing to work right
It's not just the non-linearity of the light bulb - it's the fact that it's time constant is long enough that it varies hardly at all over the period of the oscillator.
I never tought the light bulb to be lame in any circuit. Many times it was preffered instead LEDs. Since 8, when I build my first "lab" AF oscillator that was a Wien bridge with transistors only, I many times, used the Wien bridge as a stable and clean oscillator, with opams or transistors or even tubes even in RF (LC configuration with L or C variable). And, at first I wondered too what that bulb is doing there but, after opening the circuit, redrawing it and reading the explanation I understood their role in keeping the circuit stable. Strange is that Internet now (re)discover this circuit. Maybe soon you will find that existed many other configurations of oscillators RC, LC or even RL that were used before digital ones that are today.
Great demonstration! Actually the first resistance tuned oscillator with a non linear element (incandescent lamp) was Bill Hewlett's brainchild alone- It was his Stanford University thesis project in 1938. Dave Packard was on the east coast and had just been married. The partnership happened shortly thereafter, although they had met and been good friends throughout their time at Stanford. The other BIG advantage to using a lamp was amplitude stability over a very wide frequency range!
I love the elegance of this circuit! A light bulb as a thermistor. I remember seeing this one in some op amp circuit books and I too wondered what the hell a light bulb was doing in there. Now I know. :) Great video Jeri... thanks! Keep On Hackin!
Thorens used a Wein Bridge Oscillator in one of their old belt-drive turn tables, to drive an AC synchronous motor and still be able to have a pitch control and easy electronic speed adjust without having to move the belt to a different motor pulley. This was in the TD 124 or TD 125, I forget which. An excellent turntable if you put a good tone arm on it by the way. Many of the other Thorens turntables weren't all that great (and had flimsy integral tonearms) and the 1980s models with DC motors tended to have speed drift as the motor warmed up or aged; synchronous motors are really much more stable over time.
Nice to see the good old Wien bridge oscillator around. Like all oscillators of this type the main task is to overcome the losses to achieve a non decreasing amplitude of the sine wave. In the transfer function of the closed loop you easily spot out that the linear term in the denominator must be zero to reach a stable amplitude of the output. Here´s where the light bulb comes in. The bulb has a resistance which is dependent of the current flowing through it. The more current the more resistance. Filament heats up slowly resistance increases slowly. The "slow" behaviour is important to avoid a resistance changing according(along) to the sine wave. But you have to watch for the proper DC bias point because the bulb does not behave the same way in the whole current range. You have to spot out the highest slope of the resistance vs. current function R(I). Not every bulb works, if the slope is too flat you can´t compensate the lack of amplitude with the gain of the amp, because the gain would not grow enough due little resistance change of the bulb. Once you have figured out how to set the DC operation point of the bulb you also know the current which flows through the resistors for the negative feedback loop. That's one equation. The gain which is set by the negative feedback resistors is also a parameter for the oscillation criteria. You need just the right amount of gain to get the circuit oscillate with a stable amplitude. That's the other equation. Now the linear equation system can be solved for the two negative feedback resistors involving also the resistance of the bulb. For the frequency determining part, every circuit with the transfer function G=k/(as^2+bs+c) can be used it must not be necessarily an RC combination but also LCR or a crystal or whatever works. As long you compensate for the linear term "bs" this thing will oscillate sinusoidal.
Thank you!!!!!! So long I wondered why that light bulb. I searched halve the Internet but everyone besides me seemd to understand. You finally explained it so clear and easy. I subscribed and hope to learn a lot more.
There's a detailed analysis of the Hewlett Packard light bulb Wien circuit by Jim Williams, in the book www.amazon.ca/Art-Science-Analog-Circuit-Design/dp/0750670622
Thanks Jeri. I'm going to build a Wein Bridge Oscillator and test it through a VCF and VCA. What I liked about your video were the harmonics which aren't usually wanted but are desired for subtractive synthesis. I'll l try it with a thermister and a photocell. BTW, nice scope!
Excellent documentary, Jeri! I never knew why they'd use incandescent bulbs either, until now :) It reminds me of the use of 250V neon lamps as surge arrestors..
Mateo Aboy has a video "Wien-Bridge Oscillator: Amplitude Stabilization" which uses two diodes for stabilization. She refers to the lightbulb method as the HP method for obvious reasons :)
My General Radiotelephone tube-type CB radio has a feature called "Tone signal". It sends out a warbling tone to alert others via the transmitter. It uses a wien bridge oscillator with a neon bulb as part of the circuit - no transistors or IC's!
Light bulbs are still used in a lot of circuits. I took apart a giant Compaq robotic DLT tape library and the motor control circuits used a whole bunch of small (~50w) quartz halogen lamps in the power supply. Guessing part of the bus voltage shunt to bleed off voltage when the motors are decelerating.
There is an alternative version with 2 op-amps that gets around the fact that the common mode rejection ratio of most op-amps is quite non-linear. The theory of opperation is the same. The second op-amp gets the RC circuits and drives what in your circuit is the ground end of the lightbulb. It does about a decade better on the distortion values. This makes it good enough for testing audio circuits.
Great idea, that light bulb. Thanks for bring it to our attention. But I guess you can have a pick detector on your oscillator and then adjust the resistor that sets the gain of the oscillator. If C1=C2 and R1=R2 than your feed back factor beta is 1/3, and you need a gain of 3 out of your opamp, which means the ratio of R to Light bulb resistance should be 2. So, using a N type MOSFET biased in the ohmic region and a constant resistor can be replace your light bulb. Now you can make a peak detector and a feedback network to adjust the gate voltage of the NMOS, in order to get low phase noise. This can also cancel out the pushing (frequency change as result of supply voltage change.)
0:32 I remember a similar feeling when installing 10base2 network cards back in the 90s. There was a neon lamp attached to the BNC. These were for "modern PCs" and they were using something akin to a vacuum tube. Of course, later I found out why; the hard way. Those 10base2 NICs had a chassis ground. One place had bad electrical wiring. When I plugged in the BNC cable, I got zapped with 60 VAC and scared as the neon lamp flashed. But it did it's job as a GDT and saved the PC. Not lame at all.
I had the same experience, practically, in 1994, putting 10base2 into an IBM PC AT. Office had reverse-wired neutral and hot. I got a strong jolt. The PC survived but the network card did not. (This with the PC powered off but plugged in to mains).
I'd kill to get my daughter as interested in electronics as you are. I try all the time to get her into it, and she can hardly wait to change the subject. : ( Keep it up,Jeri!
I'm in love with your brain :) Personally I find it very useful to know the physics of basic materials used in electronics( light bulb filament heats up increasing resistance, etc. etc. ), not only does it help in understanding of how circuits work, it helps you find new implementations as well. P.S. You're such a nerd
It is said that the sound of the vacuum tube is legendary and the most desirable sound. A light bulb can be considered a single-element vacuum tube, so this oscillator is both a hybrid circuit and it has that Tube Sound that makes it so good.
A guy I know exploited the same property of a light bulb (increasing resistance with increasing current) to make a guitar compressor effect (just by wiring it in series between the guitar and amp). The cool thing is that it lights up when you play hard enough. If you wanted to do it yourself, I'd probably add a pot, though, since guitar pickup voltage output apparently varies by quite a lot from pickup to pickup.
I used a #1869 light bulb from Ratio Snack for a WBO, and found that it was 'microphonic'. The crimps on the ends of the filament were loose, and were ok when it was glowing since the hot filament wire expanded. But when the filament was just barely warm in the WBO, the ends made poor contact. Remember that the lifetime of this light bulb is extremely long because it doesn't get very hot. Thanks for the WBO explanation. I love a female who can talk tech like the guys!
That was wonderful! Good to see you doing these kind of videos again. The BEST part of this one was your "little helper". I gotta make one of those. The circuit was pretty cool also. Just kidding. I never knew that a light bulb in a circuit was doing what you showed. Thanks.
Great insight on a tiny non-linear resistive element :) I wonder about choosing the right parameters (nominal voltage and cold resistance; resistance-temperature characteristics) when designing the oscillator. Maybe Mr Carlson has something to say about it?
My friend has a collection of old HP products and yes, the old Wien Bridge is quite interesting. There's a write-up on the HP8903 distortion analyzer from the 80s in an old issue of the HP Journal, well worth reading to see how analog oscillators have evolved. By the way, ever seen distorting resistors caused by its voltage coefficient? You see these things when you build oscillator/analyzers down to a few PPM nonlinearities.
That or any other diode-based 'clipper' will work and I've done it too but the THD specification will be worse than the light bulb, provided that the light bulb has a time constant that is a lot longer than the output frequency.
We did this as a lab in Cambridge. We were given the components, and allowed to make any measurements we chose. Then we had to predict the frequency and voltage of the output. After that we built it and measured the output. My prediction was pretty close.
The AF has gone to these, but I still get by with the MSO4104. These mixed signal scopes are great when you do not need any more than 16 digital lines. It beats lugging around a huge HP rack mount logic analyzer.
One thing I didn't see mentioned here which I think should have been is resonance. The diameter of the bulb filament winding relative other parts is critical in some cases because of charge transition from part to part. This will help you prevent making those pesky artifacts for one, or you can apply such knowledge to making the first basic faster than light transmitter which used a heater coil (it's patented, search it). The key is physics, geometry, and ultimately the flower of life pattern which if used as a gauge for resonance among differing radius points, will also give you knowledge on predictive circuit building so it comes out right the first time. Eliminating thermal curve between caps of any kind (everything is a cap to some degree) will prevent burnouts and make cleaner waves.
Low-distortion oscillator design seems to be some fun stuff indeed. If anyone's interested, one example is to be found in the first of Cyril Bateman's "Capacitor Sound" articles that you can dig up someplace on the web. The problem of the circuit demonstrated here is that it apparently runs its OP at single supply between +Vs and ground, with a ground-referenced +in. Might work with an LM358, but not with most OPs. Better get +in DC to about +Vs/2, as suggested by kubarebo.
Could also try the more expensive PMOS CA3140. Also available is the CA3240 dual PMOS op-amp. For frequencies higher than audio the slew rate of the op-amp used becomes an important factor.
Did you know that a light bulb connected in series with a speaker and the amp output will work as an automatic gain control. as the filament get hotter,the resistance goes up. Crosley, Who was a radio pioneer of the 1930s, designed a radio that use a light bulb for AGC. It was called the expressinator tube.
Good demo of dynamic amplitude control. but with the light bulb in the circuit the sine wave appears to have some harmonic distortion: + peaks appears sharper than negative peaks (rounder).
I think I have the same meter that you have sitting there in the background. Love that meter. I just watched your scanning electron microscope video -- very cool...I'm very jealous. :)
It's just a filament of your imagination. But seeing you inspires me to build an osculator.. Anyone who molests power supplies is fixated on the rail, leading to a one-track mind. But you wreck my train of thought. I need distortion in my next project, which is an electric harmonica.
If you're speaking in general terms, there are materials which work either way. Some become more conductive with temperature, and some become more resistive. Look up NTC and PTC thermistors and the difference between them for more info.
TH-cam decided I needed to see this video. Even though it seems to be six years old, it showed up on my feed.
It brought back memories of when I was repairing audio gear in college. Our HP generator got a little unstable and I decided to crack it open.
Imagine my surprise when I ran across a large (for something found inside a piece of gear), odd looking light bulb. Being young and dumb, I assumed the bulb was bad and ordered another one. I forget what was bad, but it's not a spoiler to report that it wasn't the bulb.
Such a simple, elegant means of gain control.
Great memories.
I too as a kid wondered why there were light bulbs in oscillators! One neat trick that I used ( I got it from an old book) is a radio squelch circuit made from two ten ohm resistors and two number 49 light bulbs. It's a bridge. I used it for years on a 6 meter SSB receiver. It goes between the speaker and the receivers audio out connection. You increase the audio gain until the lamps heat up enough to balance the bridge and then the speaker goes silent. Any signals that come in unbalance the bridge and un-mute the speaker.
Thanks for interesting idea.
One of my earliest electronics projects was a Wien bridge oscillator using a 741 op-amp. That was some forty or so years ago but I somehow clearly remember the struggle to get it to work and how I finally eventually succeeded. I had decided the problem was that the 741 could not drive enough current to warm up the lamp enough and I couldn't find a smaller lamp - the best I had was a bulb form a Christmas light string.
In an attempt to solve that I put in an emitter follower stage to boost its current output capability. That could then easily drive the lamp but no matter how I adjusted it I could tell just by hearing that it was severely distorted. I then solved it in a different way. I replaced the lamp with an LDR. This acted as the gain controller. I then used the emitter follower transistor to drive the lamp which illuminated the LDR acting as the actuator for the gain control. With a lot of tweaking I finally got it to work. Many years later when I had access to an audio spectrum analyser at school I tested it and was pleased to find out it actually had very low distortion.
First time in my life i have read such a lengthy comment but to be honest i enjoyed it
This doesn't have enough distortion for indie bands. :)
I never had children of my own, my wife has two grown kids from her earlier marriage, but had I had my own daughter I would have liked her to be very much like you.
Wholesome
Feedback loop oscillators reach stabilization when their closed loop gains reach 1. This is often done when the active device goes into saturation and the gain at the primary oscillation frequency is reduced while harmonics are increased. The use of an incandescent lamp, a device with resistance that has highly positive temperature co-efficience, allows loop gains to be reduced without the active device going into saturation; meaning oscillation reaches stabilization with much less harmonics (all active circuits are non-linear to some degree, even with heavy negative feedback). That is the primary benefit of using a light bulb to control oscillation. The other benefit is to assure reliable oscillation start-up because the resistance of the bulb is very low before voltage is applied. The ability to tolerate power supply voltage variation is a secondary benefit. By the way, Meacham described the use of lamp in a bridge to control gain in 1937, two years before Hewlett used it in his first product.
that Jeri-style hair falling down over one eye is so beautiful
Thank you for the reminder. I have used one of those tiny indicator lamps in a reference 1khz oscillator that provided the synchronising bleep from the sound mixer to the audio recorder at the beginning of every take shot on a 16mm film camera. Everything was powered from the camera battery.
I was amazed at the stability of the signal level that this simple technique provided.
I built many Wien bridge oscillators though out the years. Another great tutorial for those beginning to understand analog circuits
Hi Jeri,
Just seen your video regarding the Wien Bridge oscillator which reminded me of an interesting story relating to what I believe was the first use of a light bulb in this circuit.
My story starts in 1967 when my college class mates wanted to build an audio generator as part of the practical element towards out final college exam. Out tutor, the wonderful Mr Dave King convinced the class to use the Wien Bridge circuit which used a glass thermistor in the feedback (pre op amps) circuit. Unfortunately, I was the only one in the class who had a glass thermistor and were too expensive even to purchase in bulk. Therefore, not wanting to abandon the project, Mr King went home that night and designed a circuit using a light bulb. As his design was so good, he published the project in one of the UK's leading electronic magazine, Practical Electronic.
I still use my original audio oscillator in my workshop. It used to have a label on the front “May 1967). Therefore I believe our tutor was the first UK engineer to design this type of circuit.
Regards
Geoff.
Between you and Dave from EEVblog I have rekindled my interest in building stuff! Thank you. I was the only person at school who was interested in electronics, as a result there was no point in teaching this. I think I will be making my shack more focused toward construction when I move later next year.
I do not build any circuits like this, but it is great to watch your videos to help me stay up on the theory behind some of these circuits. Keep it up!
It is 2018 and I just discovered this is the most elegant way to learn electronics. Thanks
nice to discover your channel Ellie. I remember when I was a kid, I would be doing descartes 5th degree equations with either hand while watching TV, and I would also be thinking about op-amps with lightbulbs. :) coincindence.
I'm sorry.
I've just come back to this video.
Revisited, if you like.
I GET IT.
Thank you so much.
Of all the videos out there trying to explain Wien bridge oscillation, *THIS IS THE ONE FOR ME*
This is *MY LIGHTBULB MOMENT*
Thank you so much lady.
I am so excited right now, I need to go lie down.
LOVE IT!
FREAKIN' LOVE IT.
@cubemike99
The lamp is a 3V 15mA 'grain of rice' as used on model trains, get it on EBay. Resistor at the top of the diagram is a 1k pot. R1+2 is a10k dual pot with a 560R in series with each section. C1+2 100nF for about 200Hz to 2Khz. Opamp is a 741 or TL081.
piezoelectric effect can be observed on the oscilloscope at 2:43
DestroManiak hey Sir i am ravi from india can i get your emails or other contacts
Please add the value of the items to the circle and can be used as a filter
When her hand hits the paper? How?
Polyurethane varnish is piezoelectric?!
@@iangrant9675 ceramic capacitors are everywhere and are piezoelectric.
Nice video, I just had the experience of building one for an am transmitter circuit! Took an annoying amount of tweaking to get the thing to work right
It's not just the non-linearity of the light bulb - it's the fact that it's time constant is long enough that it varies hardly at all over the period of the oscillator.
I never tought the light bulb to be lame in any circuit. Many times it was preffered instead LEDs. Since 8, when I build my first "lab" AF oscillator that was a Wien bridge with transistors only, I many times, used the Wien bridge as a stable and clean oscillator, with opams or transistors or even tubes even in RF (LC configuration with L or C variable). And, at first I wondered too what that bulb is doing there but, after opening the circuit, redrawing it and reading the explanation I understood their role in keeping the circuit stable.
Strange is that Internet now (re)discover this circuit. Maybe soon you will find that existed many other configurations of oscillators RC, LC or even RL that were used before digital ones that are today.
Thanks for this informative, concise and well produced video.
It's a nice unit. I'm still learning all of it's ins and outs.
Great demonstration!
Actually the first resistance tuned oscillator with a non linear element (incandescent lamp) was Bill Hewlett's brainchild alone- It was his Stanford University thesis project in 1938. Dave Packard was on the east coast and had just been married. The partnership happened shortly thereafter, although they had met and been good friends throughout their time at Stanford. The other BIG advantage to using a lamp was amplitude stability over a very wide frequency range!
Great technical explanation! Thank you, Jeri.
1938 - HP Audio Oscillator Model 200A&B, use of a light bulb was Bill Hewlett's idea. Thanks for the great video!
Excellent video!
Quality content, clear, concise, and useful!
that was amazing Jeri and entirely simplistic! Thanx 4 the upload
Gosh you are an amazingly clever person… I love seeing someone so driven
I love the elegance of this circuit! A light bulb as a thermistor. I remember seeing this one in some op amp circuit books and I too wondered what the hell a light bulb was doing in there. Now I know. :) Great video Jeri... thanks! Keep On Hackin!
Thorens used a Wein Bridge Oscillator in one of their old belt-drive turn tables, to drive an AC synchronous motor and still be able to have a pitch control and easy electronic speed adjust without having to move the belt to a different motor pulley. This was in the TD 124 or TD 125, I forget which. An excellent turntable if you put a good tone arm on it by the way. Many of the other Thorens turntables weren't all that great (and had flimsy integral tonearms) and the 1980s models with DC motors tended to have speed drift as the motor warmed up or aged; synchronous motors are really much more stable over time.
Pretty sure he used a Wien bridge o, not a Wein bridge o.
AWESOME history lesson and throwback circuit design!!!
Nice to see the good old Wien bridge oscillator around.
Like all oscillators of this type the main task is to overcome the losses
to achieve a non decreasing amplitude of the sine wave.
In the transfer function of the closed loop you easily spot out
that the linear term in the denominator must be zero to reach a stable
amplitude of the output.
Here´s where the light bulb comes in.
The bulb has a resistance which is dependent of the current flowing through it.
The more current the more resistance. Filament heats up slowly resistance increases slowly.
The "slow" behaviour is important to avoid a resistance changing according(along) to the sine wave.
But you have to watch for the proper DC bias point because the
bulb does not behave the same way in the whole current range.
You have to spot out the highest slope of the resistance vs. current function R(I).
Not every bulb works, if the slope is too flat you can´t compensate the lack
of amplitude with the gain of the amp, because the gain would not grow enough
due little resistance change of the bulb.
Once you have figured out how to set the DC operation point of the bulb
you also know the current which flows through the resistors for the negative feedback loop.
That's one equation.
The gain which is set by the negative feedback resistors is also a parameter for the
oscillation criteria. You need just the right amount of gain to get the circuit oscillate with a stable amplitude.
That's the other equation.
Now the linear equation system can be solved for the two negative feedback resistors involving
also the resistance of the bulb.
For the frequency determining part, every circuit with the transfer function
G=k/(as^2+bs+c)
can be used it must not be necessarily an RC combination but also LCR or a crystal or whatever works.
As long you compensate for the linear term "bs" this thing will oscillate sinusoidal.
Thank you!!!!!!
So long I wondered why that light bulb. I searched halve the Internet but everyone besides me seemd to understand. You finally explained it so clear and easy. I subscribed and hope to learn a lot more.
There's a detailed analysis of the Hewlett Packard light bulb Wien circuit by Jim Williams, in the book www.amazon.ca/Art-Science-Analog-Circuit-Design/dp/0750670622
Thanks Jeri. I'm going to build a Wein Bridge Oscillator and test it through a VCF and VCA. What I liked about your video were the harmonics which aren't usually wanted but are desired for subtractive synthesis. I'll l try it with a thermister and a photocell. BTW, nice scope!
I heard about it before but never thought that it would have such precision for what it is(Simplicity).
Great job Jeri, your explanation was concise and to the point. thank you for a great vid.
found that helpful in understanding these a tiny bit more, thankyou
Excellent documentary, Jeri! I never knew why they'd use incandescent bulbs either, until now :) It reminds me of the use of 250V neon lamps as surge arrestors..
loved seeing the harmonics!
hahaha ... that's meaning non linearity.
Mateo Aboy has a video "Wien-Bridge Oscillator: Amplitude Stabilization" which uses two diodes for stabilization. She refers to the lightbulb method as the HP method for obvious reasons :)
Great insight, thanks Jeri!
It's good to finally see Jeri again :-) Please make more of it :-)
Very nice video! Thanks for information. Very stable oscillation circuit.
Jeri I just had an oscillators class in Electronics in college and you explain it so much easier than my professor! Hahahaha. Thank you.
Awesome tutorial, Jeri!
Just recently saw the cancelled L4D game using your tech and then this popped up in my recommend. I must say, you are 10/10 amazing!!
My General Radiotelephone tube-type CB radio has a feature called "Tone signal". It sends out a warbling tone to alert others via the transmitter. It uses a wien bridge oscillator with a neon bulb as part of the circuit - no transistors or IC's!
I really admire you,self taught!! You are an inspiration!
Light bulbs are still used in a lot of circuits. I took apart a giant Compaq robotic DLT tape library and the motor control circuits used a whole bunch of small (~50w) quartz halogen lamps in the power supply. Guessing part of the bus voltage shunt to bleed off voltage when the motors are decelerating.
Digital scope with a very, very cool analog pointer!
There is an alternative version with 2 op-amps that gets around the fact that the common mode rejection ratio of most op-amps is quite non-linear. The theory of opperation is the same. The second op-amp gets the RC circuits and drives what in your circuit is the ground end of the lightbulb. It does about a decade better on the distortion values. This makes it good enough for testing audio circuits.
Great idea, that light bulb. Thanks for bring it to our attention. But I guess you can have a pick detector on your oscillator and then adjust the resistor that sets the gain of the oscillator.
If C1=C2 and R1=R2 than your feed back factor beta is 1/3, and you need a gain of 3 out of your opamp, which means the ratio of R to Light bulb resistance should be 2. So, using a N type MOSFET biased in the ohmic region and a constant resistor can be replace your light bulb. Now you can make a peak detector and a feedback network to adjust the gate voltage of the NMOS, in order to get low phase noise. This can also cancel out the pushing (frequency change as result of supply voltage change.)
0:32 I remember a similar feeling when installing 10base2 network cards back in the 90s. There was a neon lamp attached to the BNC. These were for "modern PCs" and they were using something akin to a vacuum tube.
Of course, later I found out why; the hard way. Those 10base2 NICs had a chassis ground. One place had bad electrical wiring. When I plugged in the BNC cable, I got zapped with 60 VAC and scared as the neon lamp flashed. But it did it's job as a GDT and saved the PC. Not lame at all.
I had the same experience, practically, in 1994, putting 10base2 into an IBM PC AT. Office had reverse-wired neutral and hot. I got a strong jolt. The PC survived but the network card did not. (This with the PC powered off but plugged in to mains).
wow ... that scope is off the chain.
thanks for explaining this.
Brilliant explanation, thank you !
Love a lady who knows her wy around an Op amp
Very nice vid, thanks!
Fun to see the spike at 2:45. :)
Greetings from Wien (Vienna) :)
Lightbulb Idea number one. Banging on-top of the board Idea #1. Time Place Location #1.
We might do that soon. This was filmed in the Valve lab.
Thanks for the great video. I learned a lot in that 5 minutes!
I'd kill to get my daughter as interested in electronics as you are. I try all the time to get her into it, and she can hardly wait to change the subject. : ( Keep it up,Jeri!
I'm in love with your brain :) Personally I find it very useful to know the physics of basic materials used in electronics( light bulb filament heats up increasing resistance, etc. etc. ), not only does it help in understanding of how circuits work, it helps you find new implementations as well.
P.S. You're such a nerd
Incandescents & IR sensors, love the one you're with.
Soo good! I love your youtube channel! Amazing! :) Thanks for the videos!
Really well done. Your videos are so much better than learning this from some book.
It is said that the sound of the vacuum tube is legendary and the most desirable sound. A light bulb can be considered a single-element vacuum tube, so this oscillator is both a hybrid circuit and it has that Tube Sound that makes it so good.
A guy I know exploited the same property of a light bulb (increasing resistance with increasing current) to make a guitar compressor effect (just by wiring it in series between the guitar and amp). The cool thing is that it lights up when you play hard enough.
If you wanted to do it yourself, I'd probably add a pot, though, since guitar pickup voltage output apparently varies by quite a lot from pickup to pickup.
I used a #1869 light bulb from Ratio Snack for a WBO, and found that it was 'microphonic'. The crimps on the ends of the filament were loose, and were ok when it was glowing since the hot filament wire expanded. But when the filament was just barely warm in the WBO, the ends made poor contact. Remember that the lifetime of this light bulb is extremely long because it doesn't get very hot. Thanks for the WBO explanation. I love a female who can talk tech like the guys!
That was wonderful! Good to see you doing these kind of videos again. The BEST part of this one was your "little helper". I gotta make one of those. The circuit was pretty cool also. Just kidding. I never knew that a light bulb in a circuit was doing what you showed. Thanks.
very nice video ! i really like old circuits !
That is really cool! Linear triumphs over digital, yet again.
Or rather, non-linear. When she replaces the (non-linear) light bulb with a fixed (linear) resistor, the performance is greatly degraded.
thank you for sharing, very helpful.
interesting stuff ! thanks Jeri
Great stuff. Its been nagging me to a bit. Thanks
Jeri, you are the sweetest thing! I love your gear, my God, the Tektronix! Your looks, they remind me of Elizabeth Mitchell.
Nice clear explanation.
You rock, Jerri! Totally awesome stuff :)
Great insight on a tiny non-linear resistive element :)
I wonder about choosing the right parameters (nominal voltage and cold resistance; resistance-temperature characteristics) when designing the oscillator. Maybe Mr Carlson has something to say about it?
Was admiring her all the time but I can always rewind
My friend has a collection of old HP products and yes, the old Wien Bridge is quite interesting. There's a write-up on the HP8903 distortion analyzer from the 80s in an old issue of the HP Journal, well worth reading to see how analog oscillators have evolved.
By the way, ever seen distorting resistors caused by its voltage coefficient? You see these things when you build oscillator/analyzers down to a few PPM nonlinearities.
That or any other diode-based 'clipper' will work and I've done it too but the THD specification will be worse than the light bulb, provided that the light bulb has a time constant that is a lot longer than the output frequency.
We did this as a lab in Cambridge. We were given the components, and allowed to make any measurements we chose. Then we had to predict the frequency and voltage of the output. After that we built it and measured the output. My prediction was pretty close.
my, we have similar history, and today I'm a full time inventor, cheers
Neat! I've never seen a circuit like that.
The AF has gone to these, but I still get by with the MSO4104. These mixed signal scopes are great when you do not need any more than 16 digital lines. It beats lugging around a huge HP rack mount logic analyzer.
One thing I didn't see mentioned here which I think should have been is resonance. The diameter of the bulb filament winding relative other parts is critical in some cases because of charge transition from part to part. This will help you prevent making those pesky artifacts for one, or you can apply such knowledge to making the first basic faster than light transmitter which used a heater coil (it's patented, search it). The key is physics, geometry, and ultimately the flower of life pattern which if used as a gauge for resonance among differing radius points, will also give you knowledge on predictive circuit building so it comes out right the first time. Eliminating thermal curve between caps of any kind (everything is a cap to some degree) will prevent burnouts and make cleaner waves.
Lightbulb between power supply and LM317 ,LM78xx can made easy constant current, constant voltage linear regulator for charging batteries.
Smart and beautiful!
Low-distortion oscillator design seems to be some fun stuff indeed. If anyone's interested, one example is to be found in the first of Cyril Bateman's "Capacitor Sound" articles that you can dig up someplace on the web.
The problem of the circuit demonstrated here is that it apparently runs its OP at single supply between +Vs and ground, with a ground-referenced +in. Might work with an LM358, but not with most OPs. Better get +in DC to about +Vs/2, as suggested by kubarebo.
Could also try the more expensive PMOS CA3140. Also available is the CA3240 dual PMOS op-amp. For frequencies higher than audio the slew rate of the op-amp used becomes an important factor.
I have one of the early HP oscillators and it does indeed have a light bulb in it.
Did you know that a light bulb connected in series with a speaker and the amp output will work as an automatic gain control. as the filament get hotter,the resistance goes up. Crosley, Who was a radio pioneer of the 1930s, designed a radio that use a light bulb for AGC. It was called the expressinator tube.
Very cool! great video thank you
What opamp were you using?
No idea how I missed you awesome channel for so long time. Useful stuff.
Good demo of dynamic amplitude control. but with the light bulb in the circuit the sine wave appears to have some harmonic distortion: + peaks appears sharper than negative peaks (rounder).
Interesting! I love circuits with macroscopic parts.
Well I had to watch this video for 2 times.
First time at her beautiful face
Second time understanding what she explains
Keep it up
creep
I think I have the same meter that you have sitting there in the background. Love that meter.
I just watched your scanning electron microscope video -- very cool...I'm very jealous. :)
It's just a filament of your imagination. But seeing you inspires me to build an osculator.. Anyone who molests power supplies is fixated on the rail, leading to a one-track mind. But you wreck my train of thought. I need distortion in my next project, which is an electric harmonica.
If you're speaking in general terms, there are materials which work either way. Some become more conductive with temperature, and some become more resistive. Look up NTC and PTC thermistors and the difference between them for more info.
I noticed some high end clipping on the output when using the resistor as opposed to the bulb; just another reason to use "lame" parts. :P
it's a pretty pure sine too, what about a vactrol in place of the bulb?