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previous: dave chun Hm, it seems in trying to find a on... -- 12/10/1997 7:46 PM View Thread

Re: fixing the TS-x bass rolloff...

12/11/1997 9:25 AM
R.G.
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Re: fixing the TS-x bass rolloff...
Changing that 4.7K changes gain (drive) at the same time, unfortunately. That RC pair to ground from the (-) input in conjunction with the drive control sets the gain and bass rolloff of the clipping stage.  
 
If we call that resistor R-, the midband gain is 1+ (Rdrive/R-). At frequencies where the reactance of the capacitor becomes significant compared to the value of R-, the bass starts rolling off at 6db per octave.  
 
For the stock values, the rolloff knee is at  
1/(2piRC) = 720Hz if I remember the values correctly. I personally think that this relatively  
high rolloff of the clipper gain is perhaps what is responsible for the smooth clipping nature of the TS - it steadily diminishes the amount of clipping on the fundamentals of the notes below 720 Hz. Cuts out a LOT of muddy distortion problems.  
 
A more effective although less smoothly variable way to do this is to switch select one of two or more capacitor values to select a different rolloff point.  
 
In fact, now that I think about it, that RC network offers some interesting possibilities. You could switch select from a couple of different values of RC's to get not only different bass responses, but different gain values, too. One interesting thing to do is to just switch parallel the RC with another identical one that would let you double the gain by switching it in; this is an alternate way to implement the "boost" feature.

 
Replies:
jason [I personally think that this relat... -- 12/11/1997 12:14 PM
John Greene I brought the FD2 with me again tod... -- 12/16/1997 2:28 PM