Ah ok Then That's all my questions answered. Thank you All for all your help. Youve been brilliant!! :-D
Really appreciate it1
Tommy
Jeri says you are welcome.
Ratch
Ah ok Then That's all my questions answered. Thank you All for all your help. Youve been brilliant!! :-D
Really appreciate it1
Tommy
So why don't you let a sweet young thing like Jeri tell you how to do it without using any lame parts you might have.
When researching lamp stabilised Wien bridge oscillators some time ago I came across a great article from HP describing issues they had in designing the original oscillators they made.
They found that some oscillators were less stable than they should have been. Perversely, these were the ones with the best distortion figures. What they discovered was that it was the small non-linearities in the amplifying element that contribute to stability. I found this after making a rock-steady lamp stabilised sine wave oscillator using a cheap rubbishy op-amp, only to have the circuit become unstable and largely unusable when an ultra linear, low distortion, gold plated, hand assembled by nubile virgins, purchased at the cost of your first born child style of op-amp was transplanted into the circuit.
I have a hard copy of that article at home, I can pull it out as an interesting reference as to why you might actually prefer to use "lame" parts in your Wien bridge oscillator.
And curiously, after watching that video (I'm pretty sure I've watched it previously) we're actually talking about similar things.
Whilst I'm pretty sure this 1960 article from HP is going to go way beyond what tburn wants or needs, some of us might find it of interest.
The most important conclusion is in the second paragraph:
"It is shown that amplifier non-linearity so slight as to cause insignificant waveform distortion has a profound effect on envelope stability. In fact, if it were not for this slight non-linearity, it would be virtually impossible to build a simple lamp-stabilized RC oscillator with good stability over a wide frequency range."
And it goes on to relate the correlation with low distortion and envelope instability seen in practice.
ahhh yes
I learnt a long time ago that a thermistor or light bulb was needed in the R2 position
Dave
Getting back to the original question of setting the frequency, I found this page interesting when I was building up my oscillators.
This page covers a heap of practical issues and explains how the oscillator works. It also suggests a method of frequency control (over a limited range -- a decade) by varying a single resistor.
Of note is that the op-amp is given a beefier output stage to allow it to drive the low resistance feedback path (the part where the lightbulb is).
Getting back to the original question of setting the frequency, I found this page interesting when I was building up my oscillators.
This page covers a heap of practical issues and explains how the oscillator works. It also suggests a method of frequency control (over a limited range -- a decade) by varying a single resistor.
Of note is that the op-amp is given a beefier output stage to allow it to drive the low resistance feedback path (the part where the lightbulb is).