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Re: Hmmm...

10/7/2005 11:41 PM
Jon BlackstoneRe: Hmmm...
> Although I didn't actually spell it out I was comparing the 50pf  
> treble cap to a more common value like 250pF. Xc would be 5 times  
> higher for the 50pF cap as compared to the 250pF cap, but in my  
> experience there isn't that big of a difference between the two.  
 
That tone stack seems to be taken right out of a Vox AC-30. Looking at it in my spice modeling program, it appears there would be a very substantial difference between a 50p and 250p. With the bass maxed and the treble at 12:00 (how I would set AC-30 controls), the mid notch with the 50p is centered at about 1KHz and is quite deep. With a 250p the mid notch would be very shallow and centered around 600Hz.  
 
That's assuming the treble pot is log taper, as in the Vox. And I've got the output Z of the cathode follower as 612 ohms.  
 
Jon Blackstone  
BlackstoneAppliances.com