Is it bad practice for audio inputs and outputs to share a common ground?

Question

Say I have an audio AC input(RCA stereo). This is underlaid by a ground plane before being terminated and fed to the amplifier. The output is SE(stereo audio from the TPA3123D2), however is also underlaid by the same ground plane underneath the input.

Is this bad practice? Or should the grounds be separated? Blue is the ground plane, the three through holes at top left are the input. The 7-pin connector at the bottom is the output(significantly thicker traces).

[

Answer 1

In general the outputs have to share the ground with the inputs in audio amplifiers.

However, a lot of effort is needed to ensure that the high-currents flowing in the output do not contaminate the input signal.

Usually this means using a star-grounding where a common point is selected and input grounds and output grounds emanate from that point but no conductors have both the output current and input reference.

For devices such as the TPA3123D2 the manufacturer will have designed it with these constrains and their design recommendations should be followed. Such recommendations are usually in the data sheet or application notes.

See page 17 on the data sheet (TPA3123D2 datasheet)

Datasheet excerpt:

• Grounding—The AVCC (pins 19 and 20) decoupling capacitor and VBYP (pin 7) capacitor should each be grounded to analog ground (AGND, pins 8 and 9). The PVCCx decoupling capacitors and VCLAMP capacitors should each be grounded to power ground (PGND, pins 13, 14, 23, and 24). Analog ground and power ground should be connected at the thermal pad, which should be used as a central ground connection or star ground for the TPA3123D2.

Answer 2

The input and output are single-ended so they already have and need a ground reference which is a single ground.