LM4780 and noise (question)

john_lenfr · 4th July 2005, 11:30 AM

My problem is:

I can hear a very low noise (into speakers) when I sleep in my room (so it's very low but when I turn at max volume, it increases).

How can I remove this thing?

Frank Berry · 4th July 2005, 11:36 AM

Quote:

Originally posted by john_lenfr
My problem is:

I can hear a very low noise (into speakers) when I sleep in my room (so it's very low but when I turn at max volume, it increases).

How can I remove this thing?

Are you using a preamp?
If the noise increases when you increase the volume, the noise may be coming from your preamp or from your source (CD player, etc.).

We really need more information before we can offer too many suggestions.

john_lenfr · 5th July 2005, 04:07 PM

Of course!

So, I plug my mp3 player on it.

When I turn off my mp3 player, I can hear the noise.
I want to use my mp3 player+amplifier as an alarm clock.(I plug it with a RCA to Jack cable, 1.5 meter)

=>So I must turn on my amplifier when I sleep.

How can I remove this?

asgorath · 5th July 2005, 10:25 PM

some background noise is common with grounding problems. lots of problems and lots of solutions for that, so check that area.

john_lenfr · 6th July 2005, 06:28 AM

What I search for?

The keyword is "Grounding" in the search section? But for my application must I choose acurate solution?

Leolabs · 6th July 2005, 01:51 PM

Check your PCB layout and grounding.

asgorath · 6th July 2005, 04:25 PM

few tips....

keep signal ground (0V) seperate from power ground. Watch AC sources as they'll add noise to everything. Isolate and shield as much as possible. Connect signal ground to power ground with a resistor

john_lenfr · 7th July 2005, 06:25 AM

What value of the resistor must I choose ?

SRMcGee · 7th July 2005, 12:02 PM

I've used 10 ohm 0.25 watt resistors, which worked very well.

jackinnj · 7th July 2005, 01:06 PM

Quote:

Originally posted by john_lenfr
My problem is:

I can hear a very low noise (into speakers) when I sleep in my room (so it's very low but when I turn at max volume, it increases).

How can I remove this thing?

Is it a "random" noise (like the inter-station FM noise), or an "oscillatory" noise like motorboating? IF you havent' used the supply bypass caps which national semiconductor recommends -- THEN use the supply bypass caps which national recommends. (100nF in parallel with 10uF).

also check the DC offset of the amplifier -- the noise on the supply lines is amplified through the ampchip.

4th July 2005, 11:30 AM	#1
john_lenfr diyAudio Member Join Date: Jun 2005 Location: France	LM4780 and noise (question) My problem is: I can hear a very low noise (into speakers) when I sleep in my room (so it's very low but when I turn at max volume, it increases). How can I remove this thing?

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5th July 2005, 04:07 PM	#3
john_lenfr diyAudio Member Join Date: Jun 2005 Location: France	Of course! So, I plug my mp3 player on it. When I turn off my mp3 player, I can hear the noise. I want to use my mp3 player+amplifier as an alarm clock.(I plug it with a RCA to Jack cable, 1.5 meter) =>So I must turn on my amplifier when I sleep. How can I remove this?

5th July 2005, 10:25 PM	#4
asgorath diyAudio Member Join Date: Jun 2005 Location: Seal Beach, CA	some background noise is common with grounding problems. lots of problems and lots of solutions for that, so check that area.

6th July 2005, 06:28 AM	#5
john_lenfr diyAudio Member Join Date: Jun 2005 Location: France	What I search for? The keyword is "Grounding" in the search section? But for my application must I choose acurate solution?

6th July 2005, 01:51 PM	#6
Leolabs diyAudio Member Join Date: Dec 2004 Location: Bukit Mertajam	Check your PCB layout and grounding.

6th July 2005, 04:25 PM	#7
asgorath diyAudio Member Join Date: Jun 2005 Location: Seal Beach, CA	few tips.... keep signal ground (0V) seperate from power ground. Watch AC sources as they'll add noise to everything. Isolate and shield as much as possible. Connect signal ground to power ground with a resistor

7th July 2005, 06:25 AM	#8
john_lenfr diyAudio Member Join Date: Jun 2005 Location: France	What value of the resistor must I choose ?

7th July 2005, 12:02 PM	#9
SRMcGee diyAudio Member Join Date: May 2004 Location: Wynnewood, PA	I've used 10 ohm 0.25 watt resistors, which worked very well.

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