LM386 amplifier buzz when not connected and connected to signal

Thread Starter

mrnmir

Joined Nov 1, 2022
6
Hello all,

I am using LM386 with transistor preamplifier to amplify microphone input. It works good with +3V Vcc, but awfully with +12V Vcc. Is it related to resistor values or biasing? How can i fix it?

1707376457944.png
 

ericgibbs

Joined Jan 29, 2010
18,854
Hi,
The mic Vs max limit is 10v.
I would add a Resistor/Zener diode, with decoupling cap, in the mic supply line, to reduce the mic supply to ~3v.
Do you know how to do that?
E
 

LowQCab

Joined Nov 6, 2012
4,075
You have a "Buzz" when what is not connected ?,
You didn't specify what "Input" means.

You also didn't show any details of your Power-Source, which is extremely important.

Any and All Chips REQUIRE a ~100nF Bypass-Capacitor connected as closely as possible
to the Power-Supply-Input-Pin of the Chip.
This is not shown in the Schematic, do You have one installed ?

Second item ...........
Don't use an LM386 for anything,
there are dozens of far-superior Amplifiers available for just a few Dollars more.

Please explain exactly what kind of performance that You expect from your Project,
and, what the specifications of your Speaker are, or provide a link to a PDF or web-page.
.
.
.
 

Thread Starter

mrnmir

Joined Nov 1, 2022
6
Hi,
The mic Vs max limit is 10v.
I would add a Resistor/Zener diode, with decoupling cap, in the mic supply line, to reduce the mic supply to ~3v.
Do you know how to do that?
E
Thank you for your advice. The only thing it still has a buzz when the mic is not connected. I guess either transistor or op-amp creates oscillations. Whatever I do, it doesn't go away. It gets even worse, when I touch the cables. Any ideas how to get rid of it?
 

Thread Starter

mrnmir

Joined Nov 1, 2022
6
MODERATOR NOTE
It is a school project
Welcome to AAC, @mrnmir. This thread has been moved to the Homework Help forum in accordance to AAC rules concerning help with coursework. The type of help permitted with such questions is limited to guidance with the student‘s own efforts to solve the problem. Complete solutions or information that isn‘t already potentially present are not allowed. In the future please post any school/coursework questions to this forum to make their nature clear. Thank you.
—MODERATOR

POST BEGINS BELOW
You have a "Buzz" when what is not connected ?,
You didn't specify what "Input" means.

You also didn't show any details of your Power-Source, which is extremely important.

Any and All Chips REQUIRE a ~100nF Bypass-Capacitor connected as closely as possible
to the Power-Supply-Input-Pin of the Chip.
This is not shown in the Schematic, do You have one installed ?

Second item ...........
Don't use an LM386 for anything,
there are dozens of far-superior Amplifiers available for just a few Dollars more.

Please explain exactly what kind of performance that You expect from your Project,
and, what the specifications of your Speaker are, or provide a link to a PDF or web-page.
.
.
.
I have a noise even when the mic is not connected. I don't understand if LM386 acts as AM detector or oscillator, or maybe it's due to transistor. Scope shows oscillations all over the circuit and adds noise.

I connected 220uF capacitor between pins 6 and 4, didn't help. Should I use 100nF?

It is a school project and tbh I don't know what I should expect from LM386.
https://www.taoglas.com/datasheets/SPKA.46.8.A.pdf
 
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