From: info@turneraudio.com.au   
      
   Regarding the wien bridge oscilator.   
   I deleted the j-fet amplitube regulator. I could not sleep because it produced   
   a huge amout of THD. But at least the Vo did not bounce, and all F between 1Hz   
   and 1MHz had the same amplitude.   
      
   But after deleting the j-fet, I tried the ITT P564 thermistor and a an adjust   
   pot to see just how well it worked. I soon saw how badly the darn thing worked   
   with terrible V bounce. But THD was very low. But I could not get all the F in   
   100kHz to 1MHz    
   range to oscillate. I tried lots of things and had to delete the bloomin thing.   
      
   Then I built a high input Z rectifier to produce a max +Vdc of +3Vdc. This is   
   applied to a base of a common emitter stage which inverts the at the collector   
   output so that a Vdc can be derived to power a BC640 bjt with Re 180r so that   
   as it turns on it    
   feeds collector current up to 22mA through 4 series lams each rated for 12V x   
   50mA.   
   Suitable R + electro Cs slow down any change in lamp DC current and its the DC   
   though the lamps that causes the most change in their resistance, which varies   
   between 27r cold to up 115r with about 22mA.    
      
   I have not tried my 3 bjt Vo regulator yet, but it does seem to behave far   
   better than the j-fet, and up to a slightly higher Vo.   
      
   The ß just goes over 0.33 at 3.5Vrms input to my circuit.   
   But at turn on, ß = 0.1, so oscillations will be max and distorted until lamps   
   warm up SLOWLY.    
      
   This NFB is a much lower resistance circuit so I expect no troubles getting   
   all F between 100kHz and 1MHz   
      
   I should get far lower THD, because the VNFB produced has no visible THD on my   
   CRO, unlike the j-fet which produced several % 2H.   
      
   I removed the PSU from inside the box, and re-built it much better at the rear   
   of the back plate so I have to make a cover to screw over it. This   
   re-arrangment gave me room to put the Vo regulator in a nice board against the   
   inside of the rear panel. The    
   arrangment keeps noise extremely low.   
      
   I will ammend the circuit at my website when I try the new Vo reg and iron out   
   any unexpected bugs which always manage to accompany R&D when you get keen.   
      
   So, what did anyone else work on today? Or have you given up?   
      
   Patrick Turner.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)