The ground layout of your amplifier has a major effect on sound quality. With a properly designed grounding layout, the amplifier’s output will be completely silent when the source is connected and no music is playing. With a poorly designed ground layout, the amplifier can produce a very noticeable hum or buzzing sound. The key to a good grounding layout is to keep low current grounds separate from high current grounds. Low current grounds are the ground feeds to the input circuitry and feedback loop. High current grounds are the ground feeds to the power supply decoupling capacitors, the Zobel network, and the speakers. High currents flowing through the low current ground conductors will create a DC voltage that can show up at the amplifier’s input and get amplified as noise.

To separate the low current grounds from the high current grounds, we will create several ground networks:

Audio input ground: Ground for the audio input cable

Signal ground: Ground for the input circuitry – Rin, Cc, and Ri/Ci

Speaker ground: Ground for the speakers

Power ground: Ground for the power supply decoupling capacitors, Zobel network etc

These grounds should connect only once at a set of terminals called the main system ground. The main system ground is located as close as possible the reservoir capacitors on the power supply.

The main system ground will connect to the mains earth wire via a ground loop protection circuit (explained later), and the amplifier chassis.

The individual ground networks are connected to the main system ground so that higher current grounds are closer to the reservoir capacitors.

The diagram below shows how to order the ground connections: