Get Rid Of Unwanted Frequency from Audio InPut

Thread Starter

Adfly

Joined Dec 31, 2019
27
If you solder 1 to 2 then the opamp tries to amplify 22 times the +5V or +2.5V feeding R2 which causes it to stop amplifying.
The circuit is wrong anyway. The low value for R1 kills the output level from the mic and the opamp gain is too low for a mic.

Here is how I amplify an electret mic:
Sir is it a balanced circuit?
 

Audioguru again

Joined Oct 21, 2019
6,673
A SIR is knighted by the Queen of England. I am not a SIR and I have never met the Queen.

Shielded audio cables from China are very poor quality and are very cheap.
Maybe the layout of the traces on your pcb pickup rfi. Put the pcb inside a grounded metal box.
 

Thread Starter

Adfly

Joined Dec 31, 2019
27
A SIR is knighted by the Queen of England. I am not a SIR and I have never met the Queen.

Shielded audio cables from China are very poor quality and are very cheap.
Maybe the layout of the traces on your pcb pickup rfi. Put the pcb inside a grounded metal box.
Ok audioguru i will be careful next time onwards that u ought not to be knighted by a queen.
Ok sir i will build the circuit and let you.
Sir is your suggested circuit is a balanced circuit.
One more this my laptop charger does not have the ferrite core choke at the end of the lead will it make any difference in the interference if a add one ferrite core at the end of charger
 

MrChips

Joined Oct 2, 2009
30,711
Adding a ferrite core will do absolutely nothing to help get rid of your hum.
The ferrite core works at RF, not at 50Hz LINE frequency.
 

Audioguru again

Joined Oct 21, 2019
6,673
I am not a SIR so please stop calling me a SIR. A criminal might say SIR to a judge of law in court.

A balanced mic has two output signal wires and one ground wire. My unbalanced mic has only one signal wire and a ground wire. Your mic preamp uses an inverting opamp circuit, mine uses a non-inverting opamp circuit.
 

AnalogKid

Joined Aug 1, 2013
10,986
1. If C1 and C3 are ceramic capacitors, add another one in parallel with C2. This cap and C2 should be as close as possible to the U1 power pins.

2. Add another 470 nF and 22 uF in parallel from the junction of R3 and R4 to GND. This sill filter the noise in the bias circuit.

3. Use the input stage in the post #18 schematic. It has a larger boas resistor for the mic, which will increase its output voltage. It also has a separate filter for the mic bias voltage.

4. If the 5 V source is coming from the computer or a switching type wall wart, that is a problem. Both of those sources have a lot of noise. This can be dealt with using more filtering on the +5 V input.

AND

5. The 5532 is not designed to run with a single 5 V supply. It requires a minimum of +/-3 V, or +6 V and GND. Note that other 5532 parts, such as the NE5532 from TI, require 10 V to operate.

ak
 

Thread Starter

Adfly

Joined Dec 31, 2019
27
I am not a SIR so please stop calling me a SIR. A criminal might say SIR to a judge of law in court.

A balanced mic has two output signal wires and one ground wire. My unbalanced mic has only one signal wire and a ground wire. Your mic preamp uses an inverting opamp circuit, mine uses a non-inverting opamp circuit.
Is there any way to make an unbalanced two-terminal mic capsule to balanced by using 2 mic capsule connected in series
like image in below
1577864551584.png
 

Thread Starter

Adfly

Joined Dec 31, 2019
27
1. If C1 and C3 are ceramic capacitors, add another one in parallel with C2. This cap and C2 should be as close as possible to the U1 power pins.

2. Add another 470 nF and 22 uF in parallel from the junction of R3 and R4 to GND. This sill filter the noise in the bias circuit.

3. Use the input stage in the post #18 schematic. It has a larger boas resistor for the mic, which will increase its output voltage. It also has a separate filter for the mic bias voltage.

4. If the 5 V source is coming from the computer or a switching type wall wart, that is a problem. Both of those sources have a lot of noise. This can be dealt with using more filtering on the +5 V input.

AND

5. The 5532 is not designed to run with a single 5 V supply. It requires a minimum of +/-3 V, or +6 V and GND. Note that other 5532 parts, such as the NE5532 from TI, require 10 V to operate.

ak
1577864913386.png
 

bertus

Joined Apr 5, 2008
22,270
Hello,

Try this:

mic_preamp.png

The noise getting to mic is filtered by the 100 Ohms and the 22 uF capactor.
The + input is decoupled by the other 22 uF capacitor.

Bertus
 

Audioguru again

Joined Oct 21, 2019
6,673
All your schematics wrongly show a 5V supply for the NJM5532 but it will not work with only 5V, its minimum is 6V when it barely works. An NE5532 is the same. Your 9V battery will work fine if the sounds are not loud.

Also, it has many wrong value parts:
1) R4 and R5 should be 470k each. Then the capacitor to ground between R3 and R4 to ground can be only 2.2uF.
2) R2 should be about 10k if the sounds are not loud.
3) C3 should be removed and C1 should be 330nF film type (marked 333).
Then a voice at conversation level about 10cm away from the mic will produce about 500mV RMS at the output of this preamp.

Why do you want a balanced mic when single electret mics are used in millions of products? Two mics create phase cancellations at frequencies depending on the distance between the mics. Two mics in series need an 18V supply to power them. Two mics have double the impedance of one then the capacitance of a shielded cable cuts more high frequencies.

Have you tried connecting a short piece of wire to ground instead of the mic to see if the noise radiated from the laptop power supply is gone? If the noise is gone then wiring to the mic is picking up interference.
 

Thread Starter

Adfly

Joined Dec 31, 2019
27
Hello,

Try this:

View attachment 195789

The noise getting to mic is filtered by the 100 Ohms and the 22 uF capactor.
The + input is decoupled by the other 22 uF capacitor.

Bertus
I tried this no improvement at all what is the absolute solution? to get rid of the Problem
should i have to give you the sample how the buzz sounds?

Low pass filter solution also not worked

Audio guru what is happening with me why i am not able to get rid off irritating rfi humm
no solution is working
 

Audioguru again

Joined Oct 21, 2019
6,673
Since the noise only happens when the laptop is connected to the charger and the mic preamp is powered by a battery then the noise must be radiated into the wiring of the preamp.
1) Did you try replacing the electret mic and its cable with a short piece of wire?
2) Did you connect the pcb and mic with its cable into a grounded metal box? Connect the box to the preamp ground.
 

Thread Starter

Adfly

Joined Dec 31, 2019
27
Since the noise only happens when the laptop is connected to the charger and the mic preamp is powered by a battery then the noise must be radiated into the wiring of the preamp.
1) Did you try replacing the electret mic and its cable with a short piece of wire?
2) Did you connect the pcb and mic with its cable into a grounded metal box? Connect the box to the preamp ground.
I will do it in the morning and let you know
What should i do with mic should i remove the mic and add online a piece of wire to ground and input each? Can you pls briefly explain what did you say? I did not understand properly
 

Audioguru again

Joined Oct 21, 2019
6,673
1) REPLACE the mic and its cable means to remove them. Add a short piece of wire from where the mic output cable was connected and to the circuit ground instead.
2) Put everything inside a grounded metal box.
 

Audioguru again

Joined Oct 21, 2019
6,673
An unused opamp not connected to anything has a very high gain and can easily oscillate and cause a lot of interference. It should be properly disabled.

A NE5532 opamp will not work properly if its input connects to its negative supply voltage that is 0V in your circuit. Make it a voltage-follower by connecting its (-) input to its output then connect its (+) input to the +2.5V you made with the two 10k resistors in series. Then its gain will be only 1 and it will not produce any interference.
 

Thread Starter

Adfly

Joined Dec 31, 2019
27
An unused opamp not connected to anything has a very high gain and can easily oscillate and cause a lot of interference. It should be properly disabled.

A NE5532 opamp will not work properly if its input connects to its negative supply voltage that is 0V in your circuit. Make it a voltage-follower by connecting its (-) input to its output then connect its (+) input to the +2.5V you made with the two 10k resistors in series. Then its gain will be only 1 and it will not produce any interference.
I will do what you suggested but see here what he did in this video
i tried this got almost no interference but still have little bit
 
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