I hope there is a quick answer!  I'm doing a new studio build, lots of hardware, plus PC, displays, amps, all manner of electrical devices.
 
Question:  to avoid or minimize unwanted noise/hums, as a general rule, is it better to have EVERYTHING on/in ONE circuit, or is there a better way? 
 
If it's not the way to go, is there a short answer as to which "group" or "groupings" of "devices" (e.g., rack gear or amplifiers) should be on a one circuit, while another "group" (e.g., PC/display/MIDI controller) should be on a different circuit?  I only put it in these terms because on Marshall's site they advise that everything that is "connected" should be powered from a single circuit - does that logic extend to everything in the studio, if possible?
 
I know there are a million variables, so I don't need those listed, but for a starting point I need to decide whether I need to have the whole studio hooked into one circuit (or more than one). 
 
Right now the studio's outlets/plugs go to unknown circuits shared with my residence upstairs.  It's a small additional cost to add an additional circuit strictly for the basement/studio.  For purposes of my question, let's assume I don't need more than one circuit, power-wise.  After a bad experience, I'm on a hum/noise-killing spree.
 
Should I do it?  Will it help mitigate at least some of the myriad sources of potential noise?
 
Thanks in advance!

I have put in a totally separate power supply which nothing in the entire building except studio gear is connected to (and added a second for lights and whatever I might have to connect which should not affect studio gear)

So yes my experience was that having all studio gear on the same line works brilliantly. I used to have grounding issues with some USB devices before ... but since the single power supply (with nothing else on it - I believe that's what makes the diffetence) everything is fine ...

plus it also allows to hook the entire studio quickly into UPS if power supply gets flaky (thunderstorm season)

Thank you!  That's the best news I've heard all day...

One potential issue.  Even with one AC power line for everything a "ground loop" hum problem can appear.  I've seen this many times.  Fixes for ground loop hum problems include lifting the AC power ground on one device, using a device such as the Ebtech hum eliminator; or if its because of two units both mounted to the same rack rails, isolating the device causing it from the rack rails (commercial "hum frees" are sold for this purpose).
 
Sorry to hijack the thread but thought this needed brought up.
 
If you are going to run a special AC power line for recording, consider a 20 amp circuit and an "isolated ground" line with a Hubbel 5262 (orange) receptacle.  With an isolated ground circuit the ground wire is connected directly to the ground bus in the AC power panel and directly to the AC power receptacle, not to a conduit ground or just grounded to the outlet box.  Thus the "isolated" ground.  When I worked as a LAN/WAN Network Manager, all our computer equipment (including servers, printers, workstations, etc) was connected to isolated ground circuits, which minimized noise on the AC power line.  I don't know how much that would add to the cost of a "standard" AC circuit but ultimately may be worth it.  
 
 

Thank you - you anticipated my next concern! It's very helpful to know that ground loop hums are still a possibility because it gives me the starting point for troubleshooting... that I won't need. 🎸

I hope!

Not to get too technical, but ground loop hum is caused by a difference in potential of grounding points in circuits. Ideally, all grounds should be at the same potential, otherwise, you will have current flow between them (and hum). The easiest (and usually cheapest) way to eliminate the possibility of loops is to set up a ground bus that is as close as possible to AC source and then run equipment chassis grounds back to that bus.
 
If possible, I would have a separate circuit for amps and another for any air conditioners or microwave ovens. A separate circuit would be a separate breaker supplying a set of outlets (not a extension cord plugged into the wall someplace).
 
Since you are doing a build, you might want to test things as you go (connect your mixer, listen for noise, connect some preamps, listen again, etc.) rather than connecting everything and then try to figure out what is causing the noise. 
 
hope that helps!
 
h 

you want to create a dedicated power source (single phase on the box, or UPS, or other power conditioner) for your electronics and music gear - and ensure all grounds are star-based. separate circuit(s) for lighting. also, make sure your lines are clean from induction motors, noisy dimmers, etc. here's a paper on the ground loop issues by John Brandt (a seriously good studio designer) http://www.jhbrandt.net/wp-content/uploads/2014/11/Grounding-Wiring-Zero-Loop-Area.pdf  and some detailed technical background on the subject: http://web.mit.edu/~jhawk/tmp/p/EST016_Ground_Loops_handout.pdf 
 

BTW I should have mentioned that I also use a power conditioner, but that may be just a placebo ... but I got it and I use ... it should also do some extra surge protection (yet, this conditioner thing didn't fix my problems before I redid the entire power line setup)
 

hbarton
If possible, I would have a separate circuit for amps and another for any air conditioners or microwave ovens.

 
As said above I think that's key ... I actually tapped into the 380V power supply (I'm in Europe so things work different here) that enters the building and had 3 separate 220V lines installed from that which are separately secured with circuit breakers, etc.
 

hbarton
Since you are doing a build, you might want to test things as you go (connect your mixer, listen for noise, connect some preamps, listen again, etc.) rather than connecting everything and then try to figure out what is causing the noise. 

 
Yes, it would make sense to add gear stepwise and listen (especially if you have some equipment with hum problems identified)

I'm not really picking on your Fireberd, your post was good, but I'm afraid you offered some dangerous advice.
 

fireberd
One potential issue.  Even with one AC power line for everything a "ground loop" hum problem can appear.  I've seen this many times. 

 
This is true - ground noise comes from many places. and even a properly designed technical power system can still have ground loops.

However, ground loops aren't really the problem, it is current flowing in the ground loops that is the problem, and more to the point, poorly designed equipment that allows the ground loop current to interfere with the audio.
 

fireberdFixes for ground loop hum problems include lifting the AC power ground on one device, using a device such as the Ebtech hum eliminator; or if its because of two units both mounted to the same rack rails, isolating the device causing it from the rack rails (commercial "hum frees" are sold for this purpose).

Not true!
 
You should NEVER lift the SAFETY ground! This is an old wives tale that, sadly can reduce noise problems, but it can also create a lethal power problem where you become the low impedance path between an energized conductor and ground. NEVER life the SAFETY ground - it is called that for a reason.

So how do you build a noise free audio system? Turns out we've know for a very long time, we just forget every now and again.

#1 - clean power! You don't have complete control over the power that enters the building, but there are numerous ways to clean it up once it gets there. Probably the most cost effective solution (in most situations) is called a separately derived panel, fed from an isolation transformer. If that sounds like greek then I'd strongly suggest hiring a qualified electrician to install one.
 
#2 - properly designed balanced gozintas and gozoutas - if you have these then no ground current can affect your audio. It's really that simple. Any properly designed balanced input (active or transformer) will have sufficient ability to reject common mode noise.
 
#3 - twisted pairs - shields do nothing for power line noise,they are effective against radio frequencies, but at 60 Hz they are invisible.
 
#4 - proper termination of grounds - this gets tricky because (a) if everything else is good it becomes less of an issue, and (b) there are two perfectly acceptable solutions - "star ground" and "mesh ground" - and neither is particularly easy to implement. Good thing it isn't critical.
 
If it were me, and I were the curious type (which I am) I'd read Philip Giddings "Audio Systems Design and Installation" it is still considered the gold standard. It was out of print for a long time, and used copies used to command very high prices. PostToronto has recently reprinted it at a very reasonable cost of about $70 CDN.
 
After reading that I'd find everything I can on the topic of "The Pin-1 Problem". The late Neil Muncy first published his paper on this in 1996 and it was a real eye opener. Be prepared to diagnose and solve problems with existing gear.

I'd also check out most of the Rane Notes. There is a wealth of information there.
 
It is neither difficult nor expensive to build an electrically quiet system. If you can find your way around Sonar you can do this. Do you want this becomes the problem, and if you don't there are plenty of folks that can. I'd strongly suggest finding a local resource, I've tried helping people build studios remotely and it can become a wee bit frustrating for all concerned.