"" I already have a wireless karaoke receiver with mics which
have 3.5mm audio out and a Bluetooth decoder board. ""
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"" I already have a wireless karaoke receiver with mics which
have 3.5mm audio out and a Bluetooth decoder board. ""
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Some Wireless karaoke machines have microphone level outputs for connection to microphone inputs, and some have line-level outputs.

 

Begging for Information can get tiresome after a while ...........
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If the mic is wireless then it will not have a line level output cord with a 3.5mm plug on the end.
The receiver will have the Bluetooth decoder board and does not need to be wireless so it will have the line level output cord with a 3.5mm plug on the end to connect to the power amplifier input.

 

Following is the image I took reference from (i have altered the pin 2 with 3 and vice versa) as it was wrong in diagram.

View attachment 301285

A couple of months ago I made a study, of the people asking for help in this and other electronics forums.
Of them, 13 out of 15 the issues were related to FLAWED circuits published on different web sites.

 

13 out of 15 the issues were related to FLAWED circuits published on different web sites.

I think many flawed circuits are posted on You Tube by students who have not learned about electronics yet and the students are payed MONEY by You Tube.

 

For the circuit that has excessive noise, consider that some opamps are created to have much lower noise levels. They ae marketed as "low noise", and you can check honest suppliers for which ones they are.
also, you can check the "schematics for free" website, which posts circuits of commercial audio equipment and see what devices those manufacturers use. Or even copy the circuits.
There is a very large spread of noise levels in electronic devices, and so you do need to read the data sheets.

 

Your second opamp has the + and - inputs reversed.

The first opamp needs a resistor on the input to set the gain.

Yep. AND...if you want FULL control of the output voltage, you need to have a non-inverting stage. An inverting stage can never go below a gain of 1.

 

Yep. AND...if you want FULL control of the output voltage, you need to have a non-inverting stage. An inverting stage can never go below a gain of 1.

The gain of an inverting op-amp stage is generally accepted as Rf/Ri, and while normally greater than unity it can also be much lower. Consider a 10K feedback resistor and a 100K input resistor, often used for summing in a DC level to adjust the output voltage "Q-point".
I think that KL7 has the inputs reversed.

 

Yep. AND...if you want FULL control of the output voltage, you need to have a non-inverting stage. An inverting stage can never go below a gain of 1.

A non-inverting stage can only go as low as unity.
but one would generally control the voltage output with a potentiometer with one end of the track connected to ground.