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Old 30th May 2007, 01:12 AM   #11
Leolabs is offline Leolabs  Malaysia
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Limit the input bandwidth to something like 160kHz.
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Old 30th May 2007, 01:18 AM   #12
anatech is offline anatech  Canada
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One would think that 40~80 KHz might be a better target. 6 dB / oct, passive R-C low pass filter.

-Chris
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Old 30th May 2007, 03:06 AM   #13
jaycee is offline jaycee  United Kingdom
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The P3A does already have an ultrasonic filter formed with the 220pF capacitor on the input. It's -3dB down at about 360KHz.

I'd check the components on the input. The 220pF should ideally be a polypropylene and not a ceramic, although a monores ceramic might be ok here.

To try the steeper filter idea out, change it to 470pF for a cutoff at about 170KHz.
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Old 30th May 2007, 02:14 PM   #14
anatech is offline anatech  Canada
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Hi jaycee,
I'm thinking that the garbage coming out of the computer sound card may come in at 96 KHz, possibly lower. This is not a good situation. 44.1 KHz stuff would be much more difficult to get rid of. It may also be beating against power supply noise. $20 power supply, I wouldn't be surprised if this were to occur.

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Old 31st May 2007, 10:43 PM   #15
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Default FIXED

Found the problem. One of my 570ohm resistors was disconnected. Problem fixed.

Now I gotta fix my other channel. Blew one of my speakers when testing it. I think i have a bad C3 cap. Waiting for parts.
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Old 1st June 2007, 01:52 AM   #16
anatech is offline anatech  Canada
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Hi blap0220,
Good show!

-Chris
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