Preamp Ground Loop Problem

Vipul Kumar's picture


Joined: Jan 05, 2019

Replies: 0
Preamp Ground Loop Problem
January 5, 2019 - 4:22pm

i recently built a preamp but one problem is very critical that when i amp connecting microphone to the preamp along with the laptop in charging mode i am getting a very static strong ground loop or hum noise.

Case1- when all things connected just removed charger from laptop noise goes away 

case2- when all then are connected just make volume all the way down noise goes away 

case3- when all thing connected just mic is removed then all noise goes away 

can any one here who can help me i went so many forums but no one able to give me solution which could solve my problem this forum is my last hope WhatsApp Image 2018-10-14 at 8.20.30 PM.jpeg open this to see what the noise

Aswinth Raj's picture


Joined: Aug 16, 2016

Replies: 917
Ground isolation
January 7, 2019 - 12:03pm

Hi Vipul,

Your video does not show the hardware connections. So the questios are

1. What is your laptop doing here? Is it powering the circuit through the USB or providing arduino signal instead of the microphone?

2. How is the output speaker connected? Does it also have its power source or it just a simple speaker?

This should very likely bee a isolation problem. the reason why no was able to help could be because of the lack of hardware information.


Sourav Gupta's picture


Joined: Feb 12, 2018

Replies: 12
Seems like 50 Cycle Hum
February 14, 2019 - 12:58am

I completly agree with Ashwinth...

Lack of hardware information is critical. It is impossible to fight with something that we can not see or feel.

Have you tried different power source possibly a battery?

Based on the case studies you provided, I think it  is 50 cycle hum noise  and it is very common.

Here are few possibilities to check:-

1. Check for the power outlet where the laptop charger is conencted, do you have proper earthing? Please connect a multimeter and recheck what is the voltage in between earthing and live (The voltage should be near accurate same as the voltage between live and neutral) and then check the voltage between earthing and neutral (Should be less than 1V, the lower is better).

2. Add two filter capacitor close to the transistor, 10uF 12V and .01uF 16V.

3. Create PCB with proper ground plane.

4. If still the problem remains, Use a 2.2 Meg resistor from the ground to the earthing (If you want to use it with the laptop).

5. Still problem? Use a high pass sallenkey filter after the transistor and then add an op-amp.

I think the problem will be solved.

STOLIE's picture


Joined: Feb 14, 2019

Replies: 1
February 14, 2019 - 6:39am