Noise problem with LM3886 gainclone - diyAudio
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Old 9th April 2008, 07:25 PM   #1
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Join Date: Nov 2005
Location: Mauritius
Default Noise problem with LM3886 gainclone

I have the atatched ain clone amp am planning to use as tweeter amp. It has been built on pcb will attach the pcb layout soon. The amp is producing a low frequency noise but its not a hum. (like when you touch the input lead of an unterminated amp)

When the input is shorted to the ground the noise dissapears.

If i connect it to my active xover the noise is even stronger.

With only gnd connected but signal removed the noise is lower. As signal is connected noise appears( Could it be the opamps TL072 offset in my xover?)

The chip is getting hot(Could be the noise/oscillation)

If i substitue the gain clone with one of discrete amps with same psu and connected to same xover there is no noise/hum

Sorry i don't have any scope to measure the output voltage.

Can the atatched circuit be modified to remedy to the problem?

Thanks

P.S PSU is 4X4700uF Followed by one LM7815 and 1 LM7915 for Xover supply
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Old 9th April 2008, 07:32 PM   #2
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Default PCB layout

Attached is the pcb layout. Sorry for the mess but had to draw it bit by bit in eagle.
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Old 12th April 2008, 08:31 PM   #3
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Default In case it can help anyone with sme problems

In case it can help anyone with sme problems:-

Removed my AN7815 and AN7915 from the PSU. Xover and all other circuits had no power. checked the sound from the ampsm the hum and noise had decreased dramatically i had to press my ears hard against the speaker to hear what remained and it was very faint.

Going ahead with using seperate bridge with 2 resistors in front of ac taken from transformer + 10R in series with main transformer ground to regultors. I'll post the result as its done
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