Just made an LM1875 amplifier. Having problems with humming

As you say, not as neat but it should work. The idea is to make each amplifier have it's own "star" ground point, a place where all ground currents return through their own paths and meet together. Your present design has a kind of "ladder" ground where each point is connected to a different step of the ladder and carries the strain of all the steps above it.

What you are experiencing is one of the bains of design. Ground connections and ground loops are notoriously hard to work around, especially when high currents are involved. Being an audio system where the effects are very noticable doesn't help. Wait until you try working with RF !

Brian.

Hello, i dont know if it is mentioned, but, you can keep the hum noise hiss etc far from entering the amplifier chip's input
by first using a metallic enclosure
and then by
1. using shielded signal cables
2. keeping power cables far from the signal cables/path
3. having power cables short and twisted,and place them near corners of the enclosure
4. using starground in pcb of each channel and keep both boards relatively close
5. using emi filter on ac mains
6. using regulator with good ripple rejection (you can use a regulator with opamp like ne5532 with good rejection)
7. having the earth coupled to the ground of your circuit with capacitor inline with resistor (i could get you values if you like)

there are many factors not described here that also could cause parasites,
however if you apply all the above probably you will no hear a noise anymore