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Old 13th May 2011, 02:55 AM   #1
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Default still having low pass filter issues

still having problems with my low pass filter! when i apply an audio signal to my filter it works perfect and i get full output from the amp module connected to it (stk4050) but when i connect the left and right main amps (stk4048) using a standard rca splitter cable the output of the sub amp drops off dramatically.the main amps are not affected i still get full power from them. i found out if i remove the grounds at the input of the filter the 4050 comes back up to full power!! anyone have any idea whats happening here? I have inserted the schematics for the circuits that i am using...amps,filter(with input buffer)and my input signal detecting auto power on circuit. the 4048s use one power supply the 4050 uses another power supply the filter uses its own supply and the power on circuit uses an always on supply of its own(single ended) Everything is star grounded except the single ended supply. why is this happening??
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Old 13th May 2011, 04:39 AM   #2
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I see no inserted schematics. Sure sounds like some kind of impedance issue. "Standard RCA splitter cable" raises a flag, but we really could use some kind of diagrams.
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Old 14th May 2011, 12:08 AM   #3
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I scanned the schematics but file size in pdf format was to large for the forum. any computer wizards know how to shrink pdf files
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Old 14th May 2011, 01:14 AM   #4
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I'm not a Distiller owner so I just use a lower dpi when scanning. But the real answer is not to use pdf.
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Old 14th May 2011, 01:30 AM   #5
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changed dpi
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File Type: pdf scan0001.pdf (109.1 KB, 36 views)
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Old 14th May 2011, 01:50 AM   #6
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Now I need the main amps, please.
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Old 14th May 2011, 01:54 AM   #7
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here are a few pics of my project. Its built in a nema3r enclosure and is installed under the floor of my screenporch
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Old 14th May 2011, 02:01 AM   #8
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heres the amp schematics
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Old 14th May 2011, 08:44 PM   #9
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First of all, I wouldn't call that a true buffer; it's a variable gain summing amp. But whatever you want to call it, it has a very high Zin. Versus the relatively low 56k ohm Zin of the main amp. So the main amp gets most of the current, and most of the voltage consequently. The LPF is starved for input signal.
I'm unsure of the standard remedy. Seems to me you could add 56k ohm resistors to the left side of the L & R 39k ohm resistors to ground. Then the signal source should see 56k on each of the four inputs, or about 28k per channel. That should cure the problem.
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Old 14th May 2011, 10:04 PM   #10
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As far as I can tell, your circuits should work. My only conjecture would be perhaps the ground and signals are reversed going into the filter, but it is floating relative to your source, so would work until a ground path between input and source is added when everything is put together. (this is guess work since I think your schematics are correct - I would see if you got output out of the bass amp with all the grounds connected together. YMMV
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