TDA2003 Buzzing Problem.

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TiPEX360

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Joined 2016
#1
Hi all,
I have build an amplifier circuit using the TDA2003 IC and this circuit: http://www.electronicspoint.com/attachments/7w-tda2003-audio-amplifier-circuit-gif.13252/

The amp works great at very low volume, and when i bring the volume up a loud buzz suddenly appears. If I bring the volume up higher, the buzz stays at the same volume and the audio gets louder so it can be heard over the buzz, but it's still very annoying as it's always present.

So I came here hoping someone would have a suggestion on how to get rid of this problem.
Thanks.
 
#2
If the buzz suddenly appears as you slowly bring up the volume, it is probably oscillation. Add a 2k2 resistor in series with the input followed by a 500pf cap from input to ground. I also recommend using the datasheet circuit. Be sure no high currents from the speaker return are flowing in the small signal ground areas of the circuit.
 
#3
Thy circuit is wrong, because there is too much feedback, so indeed the amplifier is oscillating. The TDA2003 is stable for a closed-loop amplification of at least 50, or was it 20? Reduce the 47 Ohms resistor to 10 Ohms (and possibly leave out the 1822pF+100Ohms and raise the 1 Ohms resistor to 2,2 Ohms), and it shall work.
 
#5
High frequency stability and damping at upper limit frequency is a point to look for in circuits around audio ICs. Some op-amps like NE5532 are stable no matter which gain, while most power ICs need certain amounts of gain in order to keep phase difference between +in and -in within Pi/2.
 
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