Mic Preamp Giving Ground Loop Problem

Thread Starter

Vipul Kumar 1

Joined Oct 20, 2018
79
when laptop is connected to the charger and just only preamp is connected to the laptop no problem here is the screen shot
upload_2018-12-22_20-17-24.png
now every thing is same just mic connected to preamp see the problem
upload_2018-12-22_20-19-31.png

now every thing is same as above just remove the charger from laptop
upload_2018-12-22_20-20-55.png
schematic that i used is attached below
upload_2018-12-22_20-23-12.png
can some body give me a correct and full proof solution for my problem
 

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wayneh

Joined Sep 9, 2010
16,401
Does the noise decrease as you move the microphone farther away from the charger? The circuit may be acting as an antenna and picking up interference from the switching power supply.

Also, is your 9V source sharing a ground with the laptop? Be careful if the 9V source is not isolated - you do not want to connect power supply grounds until you verify there is no current path. I'd use a 9V battery for testing first and only switch to a plugged-in source once things were working with a battery.
 

Thread Starter

Vipul Kumar 1

Joined Oct 20, 2018
79
Does the noise decrease as you move the microphone farther away from the charger? The circuit may be acting as an antenna and picking up interference from the switching power supply.

Also, is your 9V source sharing a ground with the laptop? Be careful if the 9V source is not isolated - you do not want to connect power supply grounds until you verify there is no current path. I'd use a 9V battery for testing first and only switch to a plugged-in source once things were working with a battery.
No Sir I Just Tried It is Not Decreasing Problem Remains the same
When used my mic with preamp in desktop same problem occurred
What should I do Sir??
pls find the video of the problem above this is how it sounds like
 

Thread Starter

Vipul Kumar 1

Joined Oct 20, 2018
79
Hello,

What happens when you split R1 into 2 X 4K7 and put a 10 uF capacitor from the middle of the 2 4K7's to ground?

Bertus
i tried but did not made any difference

Is there anyone One who can solve my Problem Pls help me ????
 
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wayneh

Joined Sep 9, 2010
16,401
What is your 9V source? Measure the actual voltage being supplied to the 7805 under operation.

Also, try posting a photo of your build and the wiring to the microphone.
 

MrChips

Joined Oct 2, 2009
22,107
How do you know that you have a ground loop problem?
What is the quality of the sound from the mic as heard through the speaker?
Have you tried connecting the mic directly to the mic input of the laptop?

btw, 1000μF for C3 is not the right value to use on a three-terminal linear voltage regulator. Check the IC manufacturer's datasheet.
 

Thread Starter

Vipul Kumar 1

Joined Oct 20, 2018
79
How do you know that you have a ground loop problem?
What is the quality of the sound from the mic as heard through the speaker?
Have you tried connecting the mic directly to the mic input of the laptop?

btw, 1000μF for C3 is not the right value to use on a three-terminal linear voltage regulator. Check the IC manufacturer's datasheet.
this is the video link of my problem it may be a ground loop or RF interference
mic sound quality is great when i used it with laptop(not in charging mode) i hv recorded many songs
i hv directly connected the mic to laptop input same issue but much less than with preamp
one more thing is when i move my 10k pot all the way down problem goes away. or if i disconnect the mic from preamp problem also goes away
you Sir Mr.Chips Sir can you help me to fix it????
 

bertus

Joined Apr 5, 2008
20,888
Hello,

It has already been asked before : post a picture on how all is connected.
It looks like there are some long lines that are picking up the noise.
As @MrChips said, the output capacitor of the LM7805 is not correct:

3-pin_low_power_regulators_with_capacitors.png


Bertus
 

Thread Starter

Vipul Kumar 1

Joined Oct 20, 2018
79

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