From: phil_a@tpg.com.au   
      
   "Phil Allison"   
   >   
   > The final design operate at three fixed frequencies  ( 66, 998 & 5278 Hz )   
   > it employs a single LM308 op-amp in a Wien bridge notch filter followed by   
   > a TL071 x10 gain stage. The caps are all polystyrene, resistors all metal   
   > film and fine adjustment in each leg of the filter is done with a pair of   
   > 200ohm, 10 turn WW pots.   
      
      
   ** This schem has the same basic circuit.   
      
   http://www.tradeofic.com/uploadfile/ic-circuit/20097284957652.gif   
      
   In my version, resistor values were kept below 50k ohms for low noise and   
   the op-amp can be the readily available a OP07 type.  Cap values were 150nF,   
   10 nF and 1.8nF.   
      
      
   ...  Phil   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)