MA12070 Audio Noise/artefacts

[Audio-guru-CPH]

The problem we have is that the right channel on our 2xBTL MA12070 amplifier board has a noise issue.
The left channel works perfectly (the sound is absolutely clear), but the right one makes a quite loud noise.

[Audio-guru-CPH]

The problem relates to that the input jack (CN1) has no board GND connection.

When left floating, all kinds of spurious common mode signals can get into the input of the amplifier.

I have successfully cured the problem by jumping pin 1 and 4 to ground (please see picture) and the amp now plays beautifully.

Looking at your layout/design I have one note on PVDD pins 41 and 42.

For best stability, close capacitive decoupling of these pins are necessary. Place 1U0 to 10U close to these pins and return directly to GND.

[Audio-guru-CPH]

We've used your advice and re-worked our amplifier board, connecting pins 1 and 4 of the input jack CN1 to the ground. A colleague who tested the amplifier board after the correction stated that the condition of the right channel had improved significantly, but there is still a slight noise, and the sound is not as clear as on the left channel.

Did this case happen to you after the correction of the amplifier board? Do you think this slight noise will be removed entirely after re-designing and creating a new version of the amplifier board?

[Audio-guru-CPH · Accepted solution]

Grounding the input jack, greatly improved the noise problem.

In an analog audio input system, care should be taken when doing ground layout so that “dirty” ground lines in the system does not inject noise into the input ground.

Also, high frequency spurious (>> 20kHz) should not be allowed to pass into the input of the amplifier.

In my lab setup, with an Audio Precision Analyzer and a laboratory power supply, i was able to cure the problem by grounding the CN1 directly.

If you could separate the analog input ground from the power ground, having them connected right at your PVdd bulk supply capacitor, it would be good.

Also close decoupling of the PVdd pins on the device, directly to ground, is mandatory.