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previous: Trace ):q{How about some ... -- 9/22/1999 1:38 PM View Thread

Re: Silr Mica Caps

9/23/1999 10:10 AM
Steve A.
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Re: Silr Mica Caps
Trace:  
 
 
 
    Thanks for your suggestions! Since my amp uses a pre-PI MV I went with the values you mentioned for a JCM800. On the eyelet board I used a 270pF treble cap and the 47k slope resistor (I didn't have a 250pF cap). I wired up a switch to kick in the alternate stack you mentioned: 470pf treble and a 39k slope resistor (well, actually 490pF and 38.2k).  
 
 
 
    Here's a trick for you (since you aren't crazy about math): if add in a 220k resistor in parallel with a 47k resistor, the result is roughly 38.2k (close enough to the 39k value you mentioned). Of course you know that adding a 220pF cap in parallel with the 270pF cap on the board results in a 490pF capacitance. So I wired up the switch on a p-p pot to select between those two stacks; the on-board values are great for the cleaner settings while the alternate values work better for the high gain sounds.  
 
 
 
    I'm not sure if you know the formula for figuring out what value resistor (R2) to add in parallel to an existing resistor (R1) to result in a specific resistance (RT):  
 
 
 
R2 = (R1 times RT)/(R1 minus RT)  
 
 
 
    That's a variation of the one we all know:  
 
 
 
RT = (R1 times R2)/(R1 plus R2)  
 
 
 
Steve Ahola  
 
 
 
P.S. So what values do you usually use for Rk and Ck on the initial gain stages? Thanks!

 
Replies:
Trace q{P.S. So what values do you usuall... -- 9/23/1999 1:47 PM