Help with audio amplifier circuit

[rafaelandreatta]

Hello,

I'm a very beginner in electronics and want to make an audio amplifier circuit. The circuit will be based in the TDA2030 IC.

I reproduced the circuit "Typical Application with Split Power Supply" as in the datasheet ( https://www.electro-tech-online.com/custompdfs/2012/04/tda2030.pdf ).

I put in the circuit a wave generator giving a sine wave of 447mV of peak, as specified in https://en.wikipedia.org/wiki/Line_level for "consumer audio".

Although, the output wave is saturating, and I think it is a problem.

I took a screenshot from the circuit being simulated in Multisim 12

**broken link removed**

I changed the 22k resistor to a potentiometer. I think the problem is in that resistor's value, but I would like your opinion. The wave is fine when I make the value of the 22k resistor lower.

Could someone help me solving this issue? (is that really an issue?)

Thank you all

 

[audioguru]

ALL power amplifiers have an input volume control. Yours does not.
The input volume control allows an amplifier to normally have too much voltage gain so that low level inputs can be "turned up".
High level inputs can be "turned down". Add an input volume control and turn it down so the amplifier does not saturate.

If you use an audio-taper (logarithmic) volume control set to half then it attenuates the input about 10 times. So a 3V peak input becomes 300mV at the input of the amplifier. The amplifier has a voltage gain of 33 so the output peak is not clipped.

The datasheet warns about reducing the gain by reducing the value of the 22k resistor. If the gain is less than 24dB (a gain of 16 times) then the amplifier will probably oscillate at a very high frequency.

 

[rafaelandreatta]

ALL power amplifiers have an input volume control. Yours does not.
The input volume control allows an amplifier to normally have too much voltage gain so that low level inputs can be "turned up".
High level inputs can be "turned down". Add an input volume control and turn it down so the amplifier does not saturate.

If you use an audio-taper (logarithmic) volume control set to half then it attenuates the input about 10 times. So a 3V peak input becomes 300mV at the input of the amplifier. The amplifier has a voltage gain of 33 so the output peak is not clipped.

The datasheet warns about reducing the gain by reducing the value of the 22k resistor. If the gain is less than 24dB (a gain of 16 times) then the amplifier will probably oscillate at a very high frequency.

Hello audioguru, thank you for the reply.

About the volume control, this circuit I showed is the power amplifier itself. It will have a preamplifier before the input, which will have the volume control. Let me show you how I thought it should be.

**broken link removed**

The input signal will enter in C3. Voltage control is R7. LF353 helps us making a low pass filter for the subwoofer (B, on the right). There will be 3 TDA2030 amplifiers, 2 for left, right and 1 for the subwoofer. A amplifier should go after the LF353(B). Also, for stereo, there should be 2 copies of this circuit, one for left, another for right (both without the low pass filter, of course), and one power amplifier in each part. I'm googling how could I put the low pass filter in order to sum or something, the signals from both left and right (or what is the best way to put the low pass filter).

But, let's go by parts. The volume control you told is needed is in the preamplifier. Is that correct?

So, if I understood correct, the saturation is normal, and will happen when you amplify too much high level inputs, so you have the flexibility of the variety of input levels. Is that correct?

If you have any other good suggestion of this circuit (specially how to add the low pass filter), I would be grateful.

Thank you

 

[audioguru]

The datasheet and I warned that the gain of the TDA2030 should not be less than 16. Then why is yours only (1.9K/680) +1= 3.8??
It will oscillate like crazy!!
Where can you buy a resistor with the strange value of 1.9K??

I guess you did not learn the simple calculation for a coupling capacitor which is why you have a huge 10uF electrolytic input capacitor C3 instead of a non-polarized 0.1uF or 0.22uF film capacitor??

Why is C1 such a huge value that it passes frequencies down to 7.2Hz?? Oh, i guess you did not learn about the simple calculation.
It should cutoff the low frequencies produced by the subwoofer. Then it can be a non-polarized film capacitor.

Your gain control pot R7 adjusts the gain from 1 to 7.7 so it is amost useless. Make it a preset pot to vary the gain 30 times so the preamp output never clips then add a REAL volume control which is a voltage divider on the signal at the input of the power amp.