When making a cable umbilical cord coming off the back of a rack, should the audio + data + control cables be bundled separately from the power cables to the rack PDU ?

When dressing the cables into the back of the rack should one side of the rack be used for audio + data + control cables and the other for power cables ?

If you can do so, yes. The installations I've seen with a lot of power cable to stow were done on racks that had about three inches of empty width outside the rack rails. Power cabling was stowed in that space. That's a good idea since you then don't have to worry about getting custom length power cables. Also, jamming cables into that space gives you at least a slightly random arrangement of wires, with randomness being less conducive to noise ingress than nicely arranged wires are.

If you can do so, yes. Wouldn't it be nice if manufacturers decide on a side to ALWAYS use for power?

I think I'd like to make that decision myself. Manufacturers already make enough decisions.

What happened to your idea that a bit of randomness helps to avoid noise?

I don't understand your question. Are you saying that my call for manufacturers to put all the power cords on one side is a call for not randomizing, if you will, the placement of power cords?

You might say that, but you'd be ignoring the fact that power cords all bunched together on the opposite side of a component are less likely to cause interference than power cords run for any length right next to signal wires.

If there is a turntable, dress the power wiring opposite the arm and keep the arm as far away from transformers as possible.

When practical, keep signal wiring away from power transformers and cross power and signal cables at right angles. Keep signal wiring away from modular power supplies.

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Years ago I was working on a tube power amplifier that had hum in the speakers. The obvious candidates for replacement were the power supply filter capacitors, but this did not help much. I noticed that the hum did not track the Volume control. This was not shocking, but then I noticed that there was hum when all of the tubes were removed. Stepping back, I observed that the power transformer and output transformers were very close and their laminations were in parallel. Not a very glorious solution, but I moved the output transformer off chassis and the hum was gone. (Rotating one transformer 90° was not good enough)

I pull all my power cables up the the front rails and manage them in there.

I would say that best practice is to try and keep signal cables well away from power cables, and we always try and do this by using opposite sides of the rack for each, and yes Ernie you are right, it would be great if all equipment had the power plug on the same side!

That being said, even when we have been unable to distance power and signal cables, I cant ever remember an instance of where we have had mains induced hum. whether that's due to current equipment standards or just pure luck, I don't know!

I agree that turntable level signals may be more prone to this than others but in the instances where the turntables are remote from the amp we typically install a phono preamp next to the turntable and then send the normal line level output over a Cat cable using baluns to the rack amp. The rack amps don't normally have phono stage inputs anyway.

I separate as much as possible.  Using a larger (wider & deeper) rack like Middle Atlantic BGR can help compared to working with a narrow skeleton rack where you don't have as much room for cable management.

Using custom length power cables can also help vs. zip tying a bunch of 6ft power cables into small bundles.  I've been using Middle Atlantic Signal Safe power cables for 4-5 years now.  They're affordable, available in lots of different lengths and have twisted conductors to reduce the potential for interference:

[Link: middleatlantic.com]

Vertical power strips/distribution devices also help and will often let you use really short 1ft or 2ft power cables.