From: sbench@aol.com   
      
   So, I thought as a curiosity,  I'd spend a couple hours in Spice land and see   
   if those interesting specs Patrick came up with could be achieved. Lets review   
   them... bass, mid, treble controls. At midpoint on all controls, +6dB at   
   100Hz, 0 at 400Hz, and +   
   6dB at 5kHz. Max bass, 10dB at 100Hz, min not too important. Mid, + and - 9dB   
   at 400Hz, with little effect at 200Hz znd 3.2kHz. Max treble, +15dB at 5kHz,   
   min not too important. I put a couple added constraints: power=250v, 12AX7s   
   only, overall more or    
   less unity gain, insensitive to input impedance or output loading, supports 1v   
   input level, and no inductors.   
      
   What I achieved uses 2 12AX7s and has the following characteristics.   
   Input Z, > 1meg, and insensitive to input Z.   
   Output: cathode follower and no effect on response by reasonable load.   
   Bass: mid, +6dB at 100Hz. Max, +10.5dB at 100Hz. Min, -1dB at 100Hz.   
   Mid: mid, 0dB at 400Hz, max, +10dB at 400Hz, min, -11dB at 400Hz. Effect of   
   the mid pot is less than a dB at 200Hz and 3200Hz.   
   Treb: mid, +6dB at 5kHz. Max, +15dB at 5kHz. Min, +3dB at 5kHz.   
      
   The bass and mid are implemented as tuned circuits, using a section of a 12AX7   
   each as gyrators. I was actually intrrested in seeing whether that would work   
   reasonably well; and it does.   
      
   Incidentally, setting things up for flat rather than boosted response provides   
   symetrical boost/cut for all 3 controls.   
      
   The pots for control are all 50k pots, and I alloeed for 1k residual   
   resistance at the pot extremes.   
      
   Anyone wanting the Spice file can email me.   
      
   -Stephie   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)