Strange noise form lm3875

velikan · 21st February 2005, 06:47 PM

It all looked to good to be true. :-(
I assemblied new lm3875 board, listen it for a some time and then something strange happend to sound from one speaker. Yes, before that i volumed up the music and then sound become distorted and stay like that. I can't realy describe that sound. It has high freq and it is similar to the sound from radio station when it is tuned. It can be played loud and every segment of sound (low, middle, high) is infected.
Other channel is OK.

What could it be?

Upupa Epops · 21st February 2005, 06:57 PM

This amp is probably oscilating. Control again all connections and devices.

velikan · 1st March 2005, 05:45 PM

Well, i finaly found some time to examine the problem.
Now things aren't as i said before. I CAN connect noise with volume control or with bass witch is producing most of it.
I examined all elements and noticed some strange black fluid on pin 4 (neg pole). Does anyone know something about it?
Then I tried to measure the resistance between pin 4 and lm chassis and that connection wasn't shorted.
As I said in my first post, this happened when i turned the volume up to the limit.
I have non-inverted version with 22k/680 gain and 2x20 Vac secondaries.
What is the problem? Me or LM?

21st February 2005, 06:47 PM	#1
velikan diyAudio Member Join Date: Jan 2005 Location: Zagreb	Strange noise form lm3875 It all looked to good to be true. :-( I assemblied new lm3875 board, listen it for a some time and then something strange happend to sound from one speaker. Yes, before that i volumed up the music and then sound become distorted and stay like that. I can't realy describe that sound. It has high freq and it is similar to the sound from radio station when it is tuned. It can be played loud and every segment of sound (low, middle, high) is infected. Other channel is OK. What could it be?

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21st February 2005, 06:57 PM	#2
Upupa Epops diyAudio Member Join Date: Aug 2003 Location: Prague,Czech Republic	This amp is probably oscilating. Control again all connections and devices.

1st March 2005, 05:45 PM	#3
velikan diyAudio Member Join Date: Jan 2005 Location: Zagreb	Well, i finaly found some time to examine the problem. Now things aren't as i said before. I CAN connect noise with volume control or with bass witch is producing most of it. I examined all elements and noticed some strange black fluid on pin 4 (neg pole). Does anyone know something about it? Then I tried to measure the resistance between pin 4 and lm chassis and that connection wasn't shorted. As I said in my first post, this happened when i turned the volume up to the limit. I have non-inverted version with 22k/680 gain and 2x20 Vac secondaries. What is the problem? Me or LM?

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