Author Topic: Amplifier static  (Read 737 times)

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Offline digitalnomadjc

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Amplifier static
« on: October 04, 2016, 11:53:53 pm »
Hi I have an amplifier question.

The details are going to be a bit light because someone else asked me.

The amplifier design is a known working solution. The PCB is a old fashioned home etched single sided board.

When the amplifier is powered with no input cable plugged in there is no static
when the input cable is plugged in and there is no signal there is static
when there is signal (such as bass/loud sounds) the sound is crackly.

I'm thinking dry solder joints or some sort of grounding issue. I haven't seen the board yet.

any ideas?


 

Offline danadak

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Re: Amplifier static
« Reply #1 on: October 05, 2016, 03:16:27 am »
Grounding in cable shields, grounding in general.

Old caps, especially electrolytics, possibility.

Use a scope and start on output stage and work backwards.


Regards, Dana.
Love Cypress PSOC, ATTiny, Bit Slice, OpAmps, Oscilloscopes, and Analog Gurus like Pease, Miller, Widlar, Dobkin, obsessed with being an engineer
 

Offline digitalnomadjc

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Re: Amplifier static
« Reply #2 on: October 05, 2016, 01:33:36 pm »
Thanks  ;D
 

Offline digitalnomadjc

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Re: Amplifier static
« Reply #3 on: October 10, 2016, 10:57:55 pm »
Hey I worked out what it was.

working backwards from the output we replaced the 2200uF Cap and discovered the trace had lifted. Then the LM1875T looks pretty sick and after confirming that the output was not producing anything and the input was ok we replaced that too.

After that it came to life. Also worked out the power supply was under rated for the power amp and replaced it with a supply with 3 times the wattage.
 


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