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Old 5th February 2005, 04:11 PM   #1
jarkaa is offline jarkaa  Finland
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Default HF noise problem

Hello,

I just finished a lm3886 gainclone with an inverting t-net topology.

There is no humming at the output and dc-offset is 7mV and 21mV. The Amp sounds pretty sweet but I get quite a bit of hissing HF noise.

There might be little oscillation because the chips get a bit warm without source signal.

Can any of you experts tell how to get rid of the problem?

I am using PMA:s audio buffer as preamp.

I have build several gainclones before and this is the first time I have problems with HF noise.

PSU is snubbericerad aŽla Carlos but the snubbers are located directly on the chip pins with 100nF bypass caps.
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Old 6th February 2005, 04:47 PM   #2
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I have a similar problem with my lm3886 GC... although, my HF interference seems to be in the form of radio stations This only happens with my input cable connected, however.

I have posted about this problem before, one thing that was suggested was a LP filter on the input with a 470 ohm resistor and 1nf cap just before the decoupling capacitor (if you use one). I tried it and found it didn't really help but also didn't hurt, so its worth a try. For me, the next thing to try is better sheilding as I have an open air amp and no sheilding on the interconnects.

my .02

-steve
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