From: phil_a@tpg.com.au   
      
   "Alex Pogossov"   
   >   
   > Note that op-amp IC1 is firtually out of the GNFB loop. It is only as a   
   > preamp with gain of 15 and for DC stabilisation.   
      
      
   ** IC1 has four jobs:   
      
   1. An inverting stage with gain of 15 times making the total gain 56 times.   
      
   2. A DC offset servo with C2, R4 & R5.   
      
   3. A sub sonic filter, -3dB at 13Hz and -20dB at 5 Hz.   
      
   4. With R11 fitted, it clamps the input signal so the max power becomes   
   half.   
      
   These last three together make to 405 safe to use with an ESL57.   
      
      
   ...  Phil   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)