ENS-76 VCF OPT2 Probs.

[gstopp at fibermux.com]

     Something is wrong, somewhere....
     
     The 100K/220ohm dividers should work just as well as the 10K/22ohm 
     dividers. Both dividers will provide the same attenuation ratio - the 
     only reason they went to the 10K/22ohm is that the compensation cap of 
     30pf is easier to work with than 3 pf. Just make sure you don't have 
     100K/22ohm - 10K/220ohm should work but the 3080's will be overdriven.
     
     Sounds like there's a mistake in there somewhere. Re-check everything. 
     I have one of these filters in my original modular and it works fine. 
     Where are you seeing the inverted version of the input? At the LP, BP, 
     or HP output?
     
     - Gene


______________________________ Reply Separator _________________________________
Subject: ENS-76 VCF OPT2 Probs.
Author:  "A.S.P." <ms20 at zebu.serv.net> at ccrelayout
Date:    4/18/96 6:24 AM


I recently built two of these Option 2 filters out of Electronotes.  I'm 
not having any luck with them.  I only get an inverted version of the 
signal I put in at the outputs, no resonance, no real filtering.  
     
     
At the end of the article it says this:
     
Note that while the optimum value 3pf seems smaller than the 10pf used 
in option 1, since the attenuating resistor is 100k in Option 2 while it 
was only 10k in option 1, the Q(?) here is equivalent to 30pf for the 10k 
attenuator.  In fact, persons building this circuit new should make R26 
and R28 10K, and R27 and 29 equal to 22 Ohms, and then about 30pf to 
compensate for Q.
     
------
(You'll probably have to look the circuit up to make sense of what I'm 
typing.)
     
I built the circuit with the original values.  Could this be why it's not 
working?
     
Also, is there a simple way to check if a FET (MPF102) is still ok?  I 
use the diode checker function on my multimeter for regular transistors, 
but I don't think that it is meant for FETs.
     
Romeo
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