Orson Cart
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Not actually tunable in my opinion. Im contrast to a Wien bridge, you can adjust the frequency by a small amount without affecting the performance too much. Tunable would imply a wide frequency range of 1:10 or more. In addition, it should be mentioned, that amplitude stabilization by zener diodes or similar voltage limiters involves more distortion than a variable gain element.One is even tunable witrh a single pot.
If you adjust the gain very exactly, distortions can be low. If you do the same with a FET regulated oscillator, distortions will be even lower, presuming a suitable circuit design.The claim that clipping involves more distortion is not true. Both circuits can be adjusted for a very small amount of clipping which is then further reduced by the low pass nature of the phase shift networks.
I'm not neglecting FET distortions, just referring to the fact, that a FET generates less distortions than a zener clipper or similar circuit. I prefer however a linearized FET variable resistor. The FET circuit in your circuit 3 doesn't use this option. A linearized FET can handle higher AC voltages than only 50 mV. Some results have been in reported in a previous thread https://www.edaboard.com/threads/129234/Also, you are neglecting the large amount of distortion that is introduced by the nonlinear resistance of the FET.
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Unfortunately, the single resistor "tuned" oscillator needs the gain to be tuned together with frequency variation. So both advantages claimed for the circuit, single resistor tuning and low distortions are mutual exclusive.
The upper circuit is a 2nd order low pass filter followed by an integrator for a 3rd order output.
P.P.S.: Circuit #1 also isn't a double integrator oscillator. Apparently, I tend to see circuits that I would expect in this place rather than those, that are actually there.
Yes, this has been granted.I wish you had studied my schem more closely so more of your comments actually applied to it.
..........I wish you had studied my schem more closely so more of your comments actually applied to it. I will forgive you .........
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davenn;909650 [I said:Current work is in building a couple of long period seismometers they will be ~ 10sec period (0.1Hz) and will record the big events anywhere in the world.[/I]
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