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beginner question about filters


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5/30/2000 10:44 PM
aron
 beginner question about filters
Here's a question:  
 
What's the difference between this:  
 
signal---||----^^^^^---grnd  
 
and  
 
signal---^^^^^---||---grnd  
 
I've seen both used for filtering with the 2nd version being more common.  
 
How do you calculate the first version? Obviously signal also is sent to the next section of the pedal....
  
5/30/2000 11:12 PM
jason
They are in series. Same,same. Doesn't matter if the resistor is first or the cap (if I understand your drawing). Example...TS9 feedbackloop has a 4.7k in series with a .047uF cap...or the tone control in a TS9 a 220 ohm resistor in series with a .22uF cap. Is that the type filter you are refering to? If so, they are the same. Resistor or cap can be first. Now if you are talking about the signal coming out of the junction of the 2 components then the first is a high pass and the second is a low pass.  
jason
  
5/31/2000 12:11 AM
aron
Wow. Interesting.  
 
To reiterate, in the TS9, feedback loop example - with the 4.7K in series with the .047uF cap to ground...  
 
You could put the 4.7K resistor first and then the .047uF to ground and it's the same....??  
 
Well, look at that... the Shaka Braddah 3 does just that.  
 
Thank you, this has been bothering me for a while!  
 
Aron
  
5/31/2000 2:09 AM
Cole
FYI, the formula to caluclate the bass rolloff (ie: w/TS-9 4k7 and .047u cap) is:  
 
1/(pi*2*R*C)  
 
Where R is the resistor's value in meg-ohms (so 4k7 would be .0047) and C is the cap value in uF. So the bass rolloff of the TS-9 is:  
 
1/(3.14*2*.0047*.047) = 720Hz  
 
The same formula applies for low pass and high pass filters as well.
  

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