Lamp-Stabilized Wien Bridge Oscillator Using LM386 Audio Amplifier

[@angelbertoascue1358]

I have built this circuit exactly like this one and im using it as my code practice oscillator.

[@electronics.tinker]

I guess the pure sine wave makes a pleasant tone. Do you drive a speaker or a headphone? I would not have thought that the oscillator is stiff enough to directly drive a speaker.

[@kensmith5694]

@@electronics.tinker I don't know about the case in question but headphones are common for such things. It cuts out the disturbing noises and also prevents the family from going crazy from the sound.

[@alabamacajun7791]

Interesting. I think the Heathkit ET3100 used a bulb Wien Bridge. I remember setting it to just where the bulb was nearly extinguished. 47 years later it is still working. I have not tested stability, will have to rebuild my old scope.

[@RixtronixLAB]

Nice video, well done, thanks for sharing with us :)

[@robinbrowne5419]

Quite an interesting video. Thank you. The little light bulb seems to do its job quite well, except for the fact that it is sensitive to vibration. I think that is why they developed chips like the XR2206. Cheers from Canada :-)

[@electronics.tinker]

Thanks for the comment. I think modern Wien bridge oscillators use JFET circuits to avoid the downsides of the bulbs. I like the bulbs because they are fun! The XR2206 is pretty old. I am not sure that new ones are available. Amazon sells XR2206 function generator kits. They do not produce high quality sine waves. There are numerous videos about them (and how to make improvements). Diode stabilized Wien bridge oscillators are a good compromise between simplicity and quality. Modern function generators use chips that synthesize signals digitally. The AD9833 is an example on the low end. They are fun to play with.

[@somedutchguy7582]

JFETs have their own downsides in this application. The late, great Jim Williams did a deep dive into this in Linear Technology's AN43.

[@kensmith5694]

A series parallel combination of 4 bulbs might work better. The cooler the bulb is, the less its temperature will vary over a cycle of the oscillator. With a really good op-amp, the variation in the bulb is the main source of distortion. The two op-amp version of the Wien bridge has the advantage of no variation in the common mode voltage. Common mode rejection is often not linear.

[@andymouse]

great video...cheers.

[@M0UAW_IO83]

Have recently bought a large number of Grain of wheat bulbs because I needed some to restore an old radio, I also have a reel of SMD LM386 chips so I can see some rainy day fun in the near future. Th circuit in the datasheet though, it very much looks like it's National Semiconductor/TI style drawing, wonder if it's in their datasheet too?

[@t1d100]

Kudos

[@discry]

Hi, I've tried to make this circuit. I'm trying to plug a speaker in to it to listen to the sine wave. At what point would I connect the speaker? Any other considerations?

[@electronics.tinker]

The circuit output is Vo as shown on the schematic at 1:00. But a speaker is a very low impedance device and speakers need a reasonable amount of current. I suspect connecting a speaker as the output load is likely to affect (probably stop) the oscillation. Resistor RL in the schematic represents the output load. I was testing with 300 Ohms. I bet you need a speaker driver circuit that presents a high-ish impedance to the oscillator. Try connecting the input of an audio amplifier as the load, either in place of or across RL. And use the pot to be sure that the oscillator output level is not too high, not more than 2V. This is to make the audio amplifier happy.

[@discry]

Thank you. I will try adding a preamp at Vo

[@discry]

As well as your suggestion across RL. Can you elaborate on what you mean by RL?

[@electronics.tinker]

RL is the load resistor. It is in the right side of the schematic shown in the video, connecting the output Vo to ground.

[@andrewandrosow4797]

I had done this generator several years ago. It works well - but on 50Hz amplitude decreases a bit. R1, R2 - it is a double variable resistor 47K. C1, C2 - are capacitors 56nF.

[@electronics.tinker]

Thanks for the comment. I have no ganged pots so I just changed the resistors in pairs.

[@dl1gsn]

This kzbin.info/www/bejne/hoHWdpJrgb-YatU might be related, an HP signal generator also using lamps for thermal compensation (if I understood correctly...), but even stranger: multiple bulbs, and one of them must be broken...

[@electronics.tinker]

That's a very interesting video. Thank you for pointing it out. I would not have guessed that a broken bulb would be used as an ambient temperature sensor. It shows how there is a wide gulf between concept circuits such as the one in the LM386 datasheet and the design of actual test equipment.

[@tubeDude48]

Your 1K POT is missing!

[@electronics.tinker]

It's the 1K pot at the top of the schematic at 00:51. Also the blue box on the right on the breadboard at 02:21.

[@tubeDude48]

@@electronics.tinker - Problem is, at the top is a 390Ω resistor, NO 1K POT.

[@wiwingmargahayu6831]

zamzam water

[@jonathanlister5644]

Jolly good but we've seen it all before.