Hi Folks,

I'm a musician about to build a studio in my basement. I got tired of the half-wrong electrical "folk wisdom" on all the recording forums about how to wire a studio . . . so I thought I would seek out advice from real electricians. And judging from the responses to several searches, I know I'm in the right company.

Here is the situation:

I want to spend as little as I have to for my power to be safe, relatively quiet*, and reliable (i.e. enough of it!)

I don't know if I need just dedicated branch circuits, IG circuits, branch circuits from a subpanel, balanced power, separation transformers, etc. or a combination of the above . . . I have some ideas about what I would need, but I am curious to know what you would do if you were in my situation.

I will need power to:

1 computer & display (CRT)
6 audio components (including mic pre-amps, interfaces, small mixer)
2 guitar amplifiers
1 power amplifier
Various small peripherals (USB hubs, etc.)

I have a small ADC UPS and Furman power conditioner (electrically speaking I think it is a glorified strip plug w/ some filtering and surge protection)

I already have some "dirty" power down there for lights and receptacles . . . but what do you think I would really need to do to meet my goals for the sensative audio gear?

Thanks,
Mike

*I don't know what the measurement parameter would be for line noise. . . but, in practice, this would mean the noise floor of the system could never interfere with the recorded sound.

Mike,

You pose an interesting question from a design standpoint. I am assuming at this point that you are not asking for instructions on how to do this yourself, which would be outside the scope of this Forum.

Bill

Bill,

I'm mainly aksing what approach an electrician would take to achieve the goals I mentioned.

I'm not looking for you guys to walk me through how to wire an outlet, but to steer me in the right direction. I may hire an electrician- but I want to know enough be able to thoroughly explain what it is that I need . . . and I think I might know better after getting some of your opinions.

In short . . . if you guys were putting in a recording studio in your basements on a budget . . . How would run the power?

Thanks,
Mike

Mike,

Sounds like an interesting project.

Typically, an Electrican will only install what has already been engineered. I would contact a local design/build Electrical Contractor and explain to them what you are looking for. A design/build contractor is the best of both worlds. The in-house design team will engineer and consult with you on your preferences while the Electrican team will perform the installation.

Mike,

Figuring out how many circuits are needed and laid out will depend on your loads and which ones will be used at the same time and where this equipment will be. Look at your nameplates and add the values together. An Electrician should have no problem installing wiring for equipment that you have if you can tell him where and how it will be used.

IMHO the interesting, and more difficult part of this project has to do with power quality and ways to control different types of noise. Is that what you're asking about?

Bill

Mike,

In terms of the number of branch circuits needed, a single 20A branch would provide up to 2400 watts, which should be ample for your list of equipment. (Unless that power amp is big enough to blow out the basement walls ).

I've seen some studio designs recommend balanced power, but frankly I think that in a basic set-up such as this it's overkill.

Unless your power grid is particularly noisy, I think you'll find that having a dedicated branch circuit back to the main panel would be sufficient. It might be worth opting for larger cables than code would require, as this would help keep the supply impedance down thereby reducing noise fed back into other equipment from items such as class B power amps.

If you're particularly concerned about keeping induced hum to a minimum, then maybe go with a metallic conduit installation so that the conduit will act as an electrostatic shield.

mchimes, I use to do pro audio and recording systems before i got into the electrical field. I have some 10 years experience in that area. I would run a seperate sub panel for all you recording equipment and install a Transient Voltage Surge Suppressor on that sub panel. Now Gronding and Bonding is the key for clean audio. All Racks and Rack mount gear HAS to be effectively bonded. Seperation of you audio and power cabling is a MUST!

Email me if i can be of any help....and yes dont you love paying $125 for a Furman power conditioner that is little more than an outlet strip...lol

I have been involved in wiring audio and video editing suites in the past, both power and signal wiring.

For minimum hum and noise, a "balanced" power configuration was used. Critical equipment branch circuits (those feeding equipment racks, mainly) were fed from a special isolation transformer with a center tapped secondary, with the center tap grounded. Voltage from "hot" to "neutral" blades of receptacles is 120 V, but hot or neutral to earth ground is 60 V. All circuits were isolated ground, as well. RF noise filter installed on the power entrance to each rack.

All racks and cabinets bonded together with 2" wide copper strap, running back to the distribution panel, and on to the main service ground.

All power wiring in EMT for RFI shielding, with care taken to avoid parallel runs of power and signal wiring.

One basic way to reduce noise is to use at least 1 size larger wire than required for the load and put your circuits "in phase" - Most panels this means using every other breaker position.

Be certain that your electrician thoroughly understands and applies {1999} NEC Articles 640, 530 and 250 and the components served from transformer-isolated sources in 640-7(b.), 530-70, -71, -72, -73, 250-146(d) and 410-56(c).

The NEC derfines this 60/120V source as technical power. There is the potential for some serious abuse with all the currently advertised so-called “balanced-power” isolation transformers furnished with NEMA 5-15 or 5-20 receptacles, that seem to contradict 530-73(a)(4) All 125-volt receptacles used for 60/120-volt technical power shall be uniquely configured and identified for use with this class of system. Don’t overlook acceptable grounding methods for the center tap of the isolation transformer.

Also, anticipate that triac-based light dimmers can very effectively interfere with audio signals.




[This message has been edited by Bjarney (edited 04-07-2003).]

Thanks guys . . . this is exactly the dialogue I was looking for.

Couple of questions:

"If you're particularly concerned about keeping induced hum to a minimum, then maybe go with a metallic conduit installation so that the conduit will act as an electrostatic shield." From Pauluk

But wouldn't this increase the liklihood of capacitive reactance (coupling high freq. currents on the conduit w/ the IG conductor)?

I was talking to an authority in this area today (whose not an electrician, but understands electricity very well) who suggested that I run the insulated ground back to the service entrance grounding point in it's own conduit . . . separate from the hot and neutral. Now I've read that "for safety reasons," you can't run an IG equipment-grounding conductor in it's own conduit.

But why would that be unsafe assuming it follows an effective fault current path?

He also suggested that I use a heavier gauge wire for the ground to lower the impedance thereby reducing the possibility of parallel resonances.

Any thoughts?

Oh and one more thing you guys should enjoy!

He said that running a 220V outlet would be "balanced" by definition. But he admitted that he wasn't sure how one could get their gear hooked up to it. I know my computer is switchable to 220V, but I can't imagine how many codes I would be breaking by doing that.

One more . . .

Is there an advantage (as far as getting cleaner neutrals and grounds)to running branch circuits (for the sensative loads)from a 40 amp subpanel (w/o a transformer in between) over running them from the mains box? Is that one in the same?

OK . . . enough questions for now.

Thanks alot for your patience and expertise!
Mike

The balanced power system is only permitted in commerical or industrial occupancies. See 647.3(1).
The equipment grounding conductor is required by 300.3(B) to be in the same raceway or cable as the power conductors. On high amperage circuits a remote equipment grounding conductor will have a high impedance because of the inductive reactance.
Don

Don,

Thanks for the reply . . . I know of several companies that market balanced power systems for the home studio market. Do such products then represent code violations?

So running the IG conductor in its own conduit breaks 300.3(B) . . . and running the IG conductor w/ the power conductors cause high impedance (which I understand contributes to line noise).

So why is running the IG conductor in it's own conduit unsafe?

Not trying to annoy, just fully understand why the code is there to begin with.

Thanks,
Mike

Oops, you miss read Don's reply. Go back and read it and you will find out that running the ground separately causes a high impedence grounding situation. This is a big problem during a fault condition and may cause the circuit breaker (or fuse) to not be able to clear the fault which would lead to a fire. When the ground is run in the same conduit this is not a problem.

A ground conductor that is dedicated to the equipment it serves or otherwise isolated from other loads it will not cause noise problems but will help clear them up.

Shane

Mike,
Are these balanced power supplies for home use permanently installed or is everything cord and plug connected? If they are cord and plug connected, they are outside the scope of the NEC. If they are hard wired, they are a violation of 647.3(1).
As far as the EGC, the code requires it to be run with the circuit conductors. In a low amperage circuit, the impedance increase is not really great enough to prevent or even slow the operation of the OCPD (overcurrent protective device) as long as the EGC is not in a magnetic raceway. In a magnetic raceway, choke effect from running a single conductor in a ferrous raceway could effect the operation of the OCPDI don't see how running this conductor by itself would change anything as far as noise goes. The only source of noise is that from the circuit conductors and the equipment itself. How could running the ground remotely decrease the noise generated by the circuit and equipment.

I did one studio for my brother. The building was already on a subpanel seperate from the house. Surge protectors were used in the sub panel and main panel. We used 20a 12g circuits for recepticals. They were not dedicated or isolated ground. The recepticals were not shared with anything elce. I think he had a power conditioner as part of his sound board. No Dimmers or floresent lights in building. No problems.

Tom

Thanks alot,

Judging from your replies, it seems that just running a couple dedicated 20A branch circuits with heavier gauge wire may do the trick. But would connecting them to a subpanel be even better?

After reading this:
http://www.equitech.com/support/techgrnd.html

It seems like having an isolated ground point in a subpanel (fed directly from the main service ground . . . not the bonded neutral/ground point in the main panel) would be even better. I could then run insolated curcuits whose ground was bonded straight to the main service ground.

BTW- that link is from one of the balanced power companies I mentioned and they cite NEC codes everywhere so they must have specific criterion for there products.

Am I getting any closer?

Thanks,
Mike

My two cents:

I think Paul's suggestion to used metal conduit is good. It will significantly reduce the electromagnetic field.

Another solution is to use braided wires. (I mean that the wires are braided together, not that the core of each wire is braided.) I don't know if you can find that in the US, though. As you will still have to use conduit (plastic), the metal conduit is most likely a better choice.

If you wnat the wires braided, you can use "BX" cable. The wires inside are braided, around 1 wrap per foot. And the metal armour would act as an electrostatic shield.

Also, shielded power cords are made (Belden) with shielding braid around the wires, with IEC connectors (like those on PCs). Those can help keep the hum down inside your equipment racks. The shield is connected to the green wire.

Oh, and don't pay $600 for the shielded power cords.

Funny you should ask...I'm a guitar player (26 years) and have put together a few studios of my own (ALWAYS on a budget). Without writing a novel, here's a few basic tips I hope will help you...

1. Pipe in all power anywhere even near your equipmet to avoid AC hum (EMT, well grounded of course)

2. If you have any fluorescent lighting in your house, either get rid of it or make sure it's off and remains off during recording.

3. Don't let any audio cables, no matter how well shielded, lay over concrete. This may be difficult to impliment, but well worth the trouble in avoiding hum infiltration.

4. Make sure you have enough ampacity and outlets to handle your equipment. Put extra outlets and/or 4S boxes than you need, and outlets even where you think you will not need them, because you will...

5. Use XLR balances cables whenever possible. They are designed to cancel out unwanted sound, and are far superior to even the most well-shielded single conductor cables.

6. Not related to electrical persay, but install a "phone flasher" (available at Radio Shack for around $25) and turn off your ringer permenantly if you have a phone down there. In fact, turn off all your ringers in the house. A perfect performance is sometimes hard to get and easy to ruin...

And most important, have fun and good luck!

-S Cannon

You could always put in these receptacles: http://www.wattgate.com/prod-381.htm

comments?

Kale — Foolsgate is probably a more accurate term.

I'm sure the gold plated strap holding the receptacle in place makes a world of difference to the sound......

This high-end "audiophile" stuff makes me wonder how carefully the people who buy it stop to figure out the situation. Haven't they realized that the PoCo isn't using gold-plated connections? Or that the record company that cut the disc didn't use $2000 cables?

Hi Mike;
I just finished building a recording studio in my basement. We have the Korg D1600 board chained to a Mackie 16 channel mixer as so not to take up all the inputs on the Korg. We've investigated the construction side to the proper wiring of a sound room. The info is unlimited. One problem we ran into was the proper wiring of extending the inputs to the next room for instruments. We used a 18ga twisted shielded cable for this. Seems to have eliminated static hum and noise. Also we grouped A/C separate from power. Another thing I've done is wrap some of the twisted cable in aluminum foil for addtional RFI and EMI protection. The only noise problem we've had so far was using my line6 212 spider amp. It's programing I belive is over driving or over gaining. I belive a DI box or like cannon mentioned using XLR. Y9ou could run a 16 channel snake into the instrument room possibly. Hope your project works out good, good luck.
~Ange

Thanks guys,

Couple of things:

I'm planning on having power cable runs on only one side of the room . . . The other side will have audio cable runs. I plan on using a 19 channel Mogami snake for the audio and 20A isolated ground branch circuits for the power.

Zapped . . . why would running audio over concrete induce hum? . . . provided it is away from the power runs?

Thanks,
Mike