My Wien Bridge Oscillators output is 12Hz, 3.2V AC, 1.8mA, with RL = 4.7k to 9.4k. It works perfectly except it seems the current oscillates, so I'm trying to make it constant.
Target Constant Current is ~0.5mA to 4mA (like it should stay 1 value within that range), and lowering the AC voltage output is fine, but not increasing it. Frequency shouldn't change.
I have used this method, but the problem is across RL I get too high a Voltage Range (0 to 15V) and the current oscillates from 0-30mA. I have tried a few examples I saw on stackexchange but they lower the current and voltage to micro, and still oscillate the current (according to simulations).
Is there a method for Constant Current Source for AC, where the voltage still oscillates but current remains same?
https://preview.redd.it/2905lok8f5251.png?width=1513&format=png&auto=webp&s=d34e917914dde9c389c05b4f18947c483cd10830
This is a simulation of the circuit in multisim. It is a Wien bridge oscillator circuit(I'm using a LM386 Omamp), tuned at 1844Hz. I am mostly interested in generating sound of that frequency. It seems to work here in simulation but when I connect a speaker to the output, I dont get anything. Connected a LED as well, im getting nothing.
I am not sure where the problem is. Is the supply voltage of +/- 6V a reason? I am using a 12V power supply, split in half through virtual ground technique.
Any idea on where the problem might be?
So here is the wien bridge oscillator I've simulated and built on a breadboard:
Wien Bridge Oscillator Schematic
And here is the LTspice output for the above circuit with the shown values:
The simulation for the most part matches my hand calculations for the amplitude and frequency. And here is the LTspice simulation for the same spice schematic, except now I've incorporated a diode model for the 1N4003 diode, which I am using in my physical circuit:
f = 13.8 kHz (Note the change in frequency)
This more closely matches what I'm actually seeing in the physical circuit:
So adding a non-ideal diode reduces the amplitude and frequency of the output. The change in amplitude makes sense because the amplitude is very sensitive to the diode voltage drop according to my calculations. I find the positive limiting level by setting VB = V(-) + VD2 and V(-) = 1/3 * Vout, where V(-) is the voltage at the negative input. This yields L+ = 3 *(V*(R5/R6)+VD2*(1+R5/R6)) / (2 - R5-R6). By setting R5/R6 = R4/R3 the negative limiting level is the same value (just negative), this is also assuming VD2 = VD1 which should be the case more or less. R2 and R1 are also chosen to be much larger than R4 and R5 so that the gain drops out when the diodes turn on. So a change in VD1 and VD2 will change the the output amplitude. But what I don't understand is why it's changing the frequency. I know the diode will have a capacitance but the frequency is determined by the feedback bandpass network make up of Rs, Cs, Rp, and Cp, where Rs = Rp =R and Cs = Cp =C. This issue is much worse when I try to output a higher frequency. Changing C to 1nF should output a frequency of 159 kHz according to 1/2*pi*R*C. Using the generic LTspice diode model D outputs a frequency of 145 kHz so I guess the op-amp non-idealities also somewhat affect the frequency output? Or maybe it's still LTspice's generic diode model, I don't kn
... keep reading on reddit β‘Is free EDA software worth it?
I just spent wayyy too much time hacking away at gEDA and ngspice to make this circuit simulation work. I guess I learned a lot about gEDA/gaf, ngspice, and linux along the way, but I think video games might have been a more productive use of my time.
If you're like me and think this nerd shit is cool, or if you have questions about how it finally worked, please feel free to comment or message me!
Procedure overview:
- I started with a fresh install of Ubuntu 18.04, and then I installed gEDA/gaf, ngspice, and gwave.
- Next, I opened gschem and drew up my favorite analog circuit: the amplitude-controlled wien-bridge oscillator. This tight little circuit creates a very pure sine wave with no external inputs besides +/-12V power.
- I added some SPICE models for the opamp, JFET, and diode, and then used gnetlist to create a spice netlist for ngspice.
- I ran a transient simulation and exported a .raw file of the results.
- Finally, I used gwave to plot the simulation waveforms.
I attached a few shots of (1) the oscillator circuit schematic, (2) plot of some voltages during the startup transient, and (3) a zoomed-in view of the steady-state oscillation.
gschem schematic with spice models and syntax
full-length sim results (top: output voltage, bottom: rectifier voltage and JFET gate voltage)
zoomed-in sim results (top: output voltage, bottom: rectifier voltage and JFET gate voltage)
Pretty sine wave!
The wien-bridge is a really cool all-analog circuit which includes JFET gain control and a nice little negative feedback loop that stabilizes the sine-wave amplitude. The frequency is set by the "wien-bridge" of R-C components in the positive feedback path of the opamp.
freq = 1/(2*pi*R*C) = 7,234 Hz
The amplitude is not controlled to a specific reference voltage, but it does find steady-state stability. One more opamp could provide control to a desired reference voltage, but I am pretty much done with this for now.
Thanks for reading!
I was building a Wien bridge oscillator with a 741 op amp and it worked fine when I tested it with a frequency of about 750Hz. I tried increasing the frequency to about 8kHz and the sine wave distorts a lot to the point where it looks like a triangle wave and the peak to peak voltage dropped to about 3V on a +-5V supply. I would like to know if there are other dual supply op amps that can handle a 15kHz Wien bridge oscillator while providing an output current upto around 50mA. Rail to rail is better but not a must.
Thanks in advance, Harid.
So, I was looking at the schematic for my old HP 200CD oscillator (manual PDF: https://www.manualslib.com/manual/1250634/Hp-200cd.html) and doing some research on the Wien Bridge circuit.
All of the information I'm seeing holds that the resistors in the oscillator must match. I'm struggling to understand why one set of the resistors in the HP circuit has double the values of the other set.
To make matters even more confusing, I was reading this page: https://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/qst/1946/10/page29/index.html
Down the page, at Figure 4, the guy explains again that the resistors need to match, but the diagram itself shows different resistances and these aren't even neatly doubled like the ones in the HP schematic.
Needless to say, I'm a bit lost.
So my Wien Bridge Oscillator, when I hook it up to an oscilloscope to measure the frequency, outputs a square wave as opposed to a sine wave. Is this due to the capacitors not being large enough, so they reach max charge? In that case would using larger capacitors work? Thanks in advanced.
Here the second part of my tutorial on DIY vactrols , we're making a more responsive vactrol and using it to voltage-control the distortion parameter of a wien-bridge oscillator. In this design when the distortion resistor is too small the circuit stops to oscillate, so it can be used as a kind of trigger control.
I'm trying out some sounds using an LFO, everything is still pretty raw, I'll upload the updated schematic with notes on my blog soon, let me know if you want to make it and have any question!
a nice little tutorial on how I made a dual vactrol using an LED and two photoresistors to voltage-control a wien-bridge oscillator, this solution can be easily used to take control of any potentiometer, possibly grouping more under the same control voltage. I'm planning to use it in lots of different applications, some sweet noise is on it's way! Here you can find the schematic with some notes
As probably everyone on this subreddit knows, a bridge rectifier will take an alternating current and, as long as the components can handle the power, convert it into DC. I'm looking for an oscillator like that, something that can handle almost anything between 12 volts and 1 KV input and give a similar output. Does such a circuit exist? I couldn't figure out how to phrase it in Google, and I wasn't sure if tolerances was the right word.
It is asking me to analyze the behavior of the resistor diode feedback loop. I understand the voltage divider and the opamp but what do the diodes do? Do they limit the the AC between a certain voltage at that node?
https://preview.redd.it/6jpbjy5luwu41.png?width=256&format=png&auto=webp&s=83e13275f74245f350a364e86608270bbe637da9
Hi,
Getting started to studying circuits and this was described as a good beginner's case study, but not much details. Which are the negative and positive feedback and what do the other components do?
I was reading about the tacoma narrows and looking at youtube videos and i started reading about this one scientist who was living in an apartment at the time and made an oscillator that he set on the end of a bridge and it made the bridge wobble. if i remember correctly the oscillator used a weight that was less than 100 pounds and police came and arrested him and he ended up helping the U.S. military design weapons or tactics or something involving resonance or sound or something like that. I can't find his name for the life of me and im going back to searching right after i hit post. please let me know his name if you already do or are able to find it. thank you.
Either hard or soft. Wanna get a better understanding of the range of this parameter and thought this would be a fun way of going about it.
Here the second part of my tutorial on DIY vactrols , we're making a more responsive vactrol and using it to voltage-control the distortion parameter of a wien-bridge oscillator. When the distortion resistor is too small the circuit stops to oscillate, so it can be used as a kind of trigger control. I'm trying out some sounds using an LFO, everything is still pretty raw, I'll upload the updated schematic with notes soon on my blog, let me know if you want to make it and have any question!
Here the second part of my tutorial on DIY vactrols , I'm making a more responsive vactrol and using it to voltage-control the distortion parameter of a wien-bridge oscillator. Here you can see the first video, with a dual vactrol In this design when the distortion resistor is too small the circuit stops to oscillate, so it can be used as a kind of trigger control. I'm trying out some sounds using an LFO, everything is still pretty raw, I'll upload the updated schematic with notes on my blog soon, let me know if you want to make it and have any question!
