[andyr]

When you have DC '+ve' and DC '-ve' wires running from a PS to a PCB, should these be twisted together (like ac wires) or should they be kept separate?

If the answer is "twist them" ... why?  What benefit does this provide? 

Thanks,

Andy

[JoshK]

Good question....I've no clue.  In the past I've twisted them but didn't really know if it mattered.  If your amp isn't strictly class A then there is likely some HF artifacts on those wires, not just DC.  Also there is always some ripple.  Just thinking aloud here...

If the current through the wires isn't AC then I can't imagine having any EMI rejection by twisting.

[andyr]

Good question....I've no clue.  In the past I've twisted them but didn't really know if it mattered.  If your amp isn't strictly class A then there is likely some HF artifacts on those wires, not just DC.  Also there is always some ripple.  Just thinking aloud here...

If the current through the wires isn't AC then I can't imagine having any EMI rejection by twisting.

Thanks, Josh.

I was thinking it wasn't so much twisting helping with EMI rejection as twisting maybe reducing inductance (so that the DC current would flow more easily)?

When you twist speaker wires together, you end up with a lower inductance cable - which helps the current flow more easily.  But that is twisting 'hot' with 'ground' ... when you're dealing with DC rails from an amp PS, twisting '+ve' with '-ve' seems to me to be a different kettle of fish! 

Regards,

Andy

[Speedskater]

Twisting keeps the two (or 3) conductors very close to each other. Being close to each other reduces the loop inductance (and source impedance) this allows the supply to better deal with high frequency noise and fluctuations that the amplifier generates.

[andyr]

Twisting keeps the two (or 3) conductors very close to each other. Being close to each other reduces the loop inductance (and source impedance) this allows the supply to better deal with high frequency noise and fluctuations that amplifier generates.

Bingo! 

Thanks, SS.

Andy

[jneutron]

There will be no significant difference between twisting the two rail wires and not.

1.  Twisting per se does not reduce the inductance of two wires.  What is does is keep them close together, that is the key to reducing inductance.

2.  Keeping two wires close together to reduce the inductance only works if the wires are carrying the same current.  The only way that would occur in a two rail amplifier, is if there is cross conduction of the output transistors.  Otherwise, the current will flow in one rail wire to the pass transistors, through the load, then back to the supply via the ground path....not the other rail wire.

As speedskater said, twist the two rail wires with the ground return wire.

Cheers, John