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Building the simple low pass from schem on TSP site :)

 
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theDIY



Fri Jul 31, 2009 3:13 am   Building the simple low pass from schem on TSP site :) reply with quote

Hi all!

So, I'm building (or should I say attempting to build) the low pass from the schematics page on the TSP website (thanks for that, BTW!!!). I knocked it out on perfboard, and it passes signal, but I think mebbe I misinterpreted the schematic somehow, because while the volume knob works, there is something funky (in a bad way) going on with the cutoff and res knobs.

The 500k dual pot seems to function as a simple volume control, and the 100k res pot seems to only be rolling off a few higher frequencies at the low end of its range, instead of behaving like a resonance knob should. Power is coming from a 9v battery, and the opamp I used is a simple 741. Below is a link to the board layout (I did it in this cool java perf/veroboard layout tool). I was hoping someone who has built the circuit (or who has more electronics knowledge than I) could shed some light on why my layout doesn't work as expected. Thanks!!


-Scott

My layout: http://www.divshare.com/download/8041823-0dd

and in case anyone's interested, the software I used for the board layout:
http://diy-fever.com/index.php?project=software

 

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para
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Fri Jul 31, 2009 6:06 pm   reply with quote

nothing jumps out at me at a glance. could be commonly overlooked stuff like are you certain that you have the tip and sleeve of each jack wired correctly? do you have a continuity tester that you can use to check all of the wiring for shorts and cold solder joints? is the 10u cap in the power section really 10u because the symbol used is for a smaller ceramic? haven't spent much time with the 741 ( yeah yeah, i know, more of a 258 fan myself ) so i'm not sure but do you want to have the offset null at pin 1 or 5 attached to Vref (ground) for a split supply? low battery? check check and recheck all of your actual perf to be sure that you didn't miss something. check all component values

probably not much help....

 

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theDIY



Fri Jul 31, 2009 6:51 pm   reply with quote

Actually, that's pretty good advice Wink

I got the pinout for the 741 from the manufacturer's website, so they should be the correct ones. Though, the naming for some of the pins differ from the ones on the schematic, the mfg.'s sheet had a schematic symbol, so I took the appropriate pins from the corresponding parts of that symbol. I just used the 741 because it was the only single 8 pin opamp chip I could find locally.

Anyhow, gonna get to it with my continuity tester. Thanks for the tips!

 

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Fri Jul 31, 2009 6:54 pm   reply with quote

here is some talk about the offsets, looks like i was thinking about them wrong. i keep meaning to spend a little time with these but it will be a while

http://www.play-hookey.com/analog/experiments/balance_offset.html

 

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