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As a newcomer in electronics as a hobby field, before starting, my humble request to everyone is to not get annoyed by my questions which sometimes may be little silly.

So lets get started: I have started studying a little about opamps for audio amplifying and the IC I am using is a TDA2030. In previous circuits, I used to have a potentiometer to control the gain of the opamp, and that method worked very well,

Then I realized that I can't use a potentiometer everywhere to control gain of this IC so I found another formal way to do this; the diagram is shown below:

schematic

simulate this circuit – Schematic created using CircuitLab

When I start this circuit up, I get very high noise for a few seconds from starting time, every time. The noise goes away automatically after a while; it takes almost 1-2 mins to get pure sound without any noise. So what I want is: as soon as I start the circuit, the noise is removed.

First Question:

Am I missing some other components which is making it behave so? If yes so what are those and please explain their functionality. And what is the cause of this startup-time noise?

Last question:

When I discharged the Capacitor C1 before running the amplifier, this produces same noise for few seconds again. Why so? Does the capacitor's charged or discharged state matter here? Or is it the original functional procedure of the IC?

Thanks for your precious time, and please always put a schematic with example for my better understanding which will be more preferable to me.

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    \$\begingroup\$ Inputs must have same DC bias \$\endgroup\$ Jan 11, 2021 at 13:35
  • \$\begingroup\$ Same dc bias meaning same value resistor to be connected between the non-inverted and 12 volt ? \$\endgroup\$ Jan 13, 2021 at 13:15
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    \$\begingroup\$ R2 biases Vin- with 0V for silence. So Vin+ needs same value as R2 to gnd to null input bias current offset voltage. \$\endgroup\$ Jan 13, 2021 at 13:21

1 Answer 1

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The problem is that you haven't got a pull-down resistor on the non-inverting input: -

enter image description here

Transistor amplifiers of this type (and op-amps) need to have their inputs biased correctly and that means adding resistors where appropriate. The inverting input on your schematic is fine because the input is biased by the feedback resistor (R2 in your schematic).

So, because you have a single sided supply, you need to do this: -

enter image description here

You also need to add power supply decoupling capacitors as indicated by C3 and C5 in the diagram at the top of my answer. And, in case you still get some noise, you might need to do this: -

enter image description here

Image from TDA2030 data sheet.

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  • \$\begingroup\$ The second schematic works! Just made a voltage divider using 2 x 100k and biased the non-inverted with this divider and this works very well! And , the pulldown resistor method doesn't seem to work. \$\endgroup\$ Jan 12, 2021 at 14:55
  • \$\begingroup\$ Sounds like good news @SubhaJeetSikdar. It's good to get feedback. \$\endgroup\$
    – Andy aka
    Jan 12, 2021 at 14:56
  • \$\begingroup\$ Well, last question, though I have used 100k resistors, what should be the actual value of them for best performance? \$\endgroup\$ Jan 13, 2021 at 13:21
  • \$\begingroup\$ The circuits came from the data sheet so I would leave them as is @SubhaJeetSikdar \$\endgroup\$
    – Andy aka
    Jan 13, 2021 at 13:46

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