LM4950 audio amplifier clicking sound and signal distortion?

Hi,

I am using LM4950 audio amplifier with DAC to amplify my audio signal. The output of the LM4950 is connected to the transformer and the output of the transformer is connected to ultrasonic transducer.

The shutdown pin is continuously high, which means that the amplifier is continuously on.

I generate 10ms of chirp signals (40kHz - 45kHz) which repeats after every 300ms.

When I play the sound, I hear some clicks from the amplifier and the signal at the output of the transformer is also distorted.

After debugging the circuit, I found out that when I remove the transformer, the clicking sound is completely gone and the signal at the output of audio amp. is also not distorted.

I am not sure why would the transformer distort the signal and also produce clicking sound.

Any idea?

Regards

Circuit schematic (particularly regarding transformer coupling), transformer specification?

faisal349 said:

and also produce clicking sound.

Click to expand...

Beacuse of the magnetic field. It appears when you apply the signal and some parts of your transformer are shifted over others which are fixed better. Example: \ / -> ||

The transformer is Prowave transformer K4000001. The link is http://www.prowave.com.tw/english/products/sr/transf.htm

The schematic is as follows:





Regards

Not sure if the transformer can handle the amplifier output voltage without core saturation. I would also suggest capacitive output coupling to avoid DC transformer current due to amplifier offset.

Try with increasing signal voltage.

Thanks.

Actually, when I reduced the input voltage, the wave distortion and clicking sound are gone. The input voltage to the transformer was 6Vp and when I reduced it to 5Vp it worked ok. The output voltage with 1:10 ratio is 50Vp.

One other thing that I noticed is that the waveform smoothens when I connect ultrasonic transducer (maybe because of capacitive behavior) to the output of transformer.

Regards

Hi,

* transformer core saturation
* yes, cpacitive behaviour

Klaus