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	Security (anti-spam) Question: How many dits in 72?
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Description	Record # 18
RevDate	Sun, 19 Apr 5936 13:42:48 -0600
Details	Preliminary design for an active low-pass AF filter. Since we don`t have any op-amps to play with, I had to go to a throwback design using discrete transistors. LTSpice says this circuit should have a corner frequency a little above 1 kHz and about 12 dB of gain in the passband. Looks like it has about the expected 40 dB/decade roll-off on the upper end. There is a bit of an increase in gain again after bottoming out at 18 kHz. But if you can hear those frequencies, you either have excellent hearing or are a dog. I originally designed the circuit to have no gain, but decided to add the final amplifier just in case it is needed. If not, Q3 and its associated biasing resistors can go. Since I don`t have an AF signal generator, I need to track down some PC soundcard software which will perform the same function. I know such a thing is out there. Once I do, I will build the circuit and sweep it to see if reality matches LTSpice. - Jason, NT7S 29 Nov 2006 Since it seems that I will have the parts to do it, I decided to add a second filter stage to the circuit. Because this is now a four pole filter, the upper skirt has a nice steep slope of 80 dB/decade. - Jason, NT7S 8 Jan 2007
Schematic=NT7S_Active_AF_Filter.gif   AuxFile=NT7S_Active_AF_Filter.zip                   Return to SEARCH

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