audio recording circuit

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ritelec

Senior Member
Location
Jersey
hi all,

doing some home recording and would like to eliminate noise from dimmers, motors, ground loops, etc.

there's advice to run conductors in conduit, bring seperate grounds, cross other circuits perpendicularly, sub panel, etc.

been reading about isolation transformers. 120v in 120v out with the center tap on the secondary being grounded. which gives 120v phase to neutral, 60 v phase to ground and 60 v neutral to ground.

has anyone wired a recording studio with this iso transformer?

any and all comments welcome.

thank-you in advance.

rich
 

dbuckley

Senior Member
These balanced power systems are pure snake oil, they come from the same people who make high defintion udio cables and dpower cords that cost $1000.

The key to a silent audio system is (a) use balanced audio signals, and (b) have equipotential grounding of all the auido kit. I don't do recording studios, I do live theatre with temporary kit, and I dont have noise problems.
 

dereckbc

Moderator
Staff member
Location
Plano, TX
dbuckley said:
These balanced power systems are pure snake oil.
The key to a silent audio system is (a) use balanced audio signals, and (b) have equipotential grounding of all the auido kit.

Not true on the snake oil. Balanced and Isolated power are proven techniques that work from the same basic principal. Any type of isolation transformers will provide anywhere from 40 to 140 db common mode noise reduction, which is all the noise found in AV equipment. Your common every day dry type transformers provide a impressive 40 db of cmnr, and specialty transformers (like those used by equitect and others) provide up to mind boggling 140 db of cmnr. If decibels is a foriegn subject it is a logrythmic expression, In this case 40 db equal a ratio of 10,000:1, and 140 db ratio of 100,000,000,000,000:1.

What equitech and others are doing is eliminating the grounded circuit conductor, turning it into 120/60 VAC, and eliminating the grounded circuit conductor which is the source of commom mode noise problems induced from equipment that place filters from L-G and N-G.

I do agree using balanced tranmission goes a long ways, using a balanced power system just takes the same concept to the power source and eliminates ground as a reference point or signal path.
 

dereckbc

Moderator
Staff member
Location
Plano, TX
Rich, back to answering your questions. I have worked with Equitech on a commercial scale using balanced power in data centers. Not in a recording studio environment. However there is no difference between the two applications.

If you use one of the plug-n-play units that require no external wiring; you can use it in a home recording studio if you can afford to do so. However you cannot use the transformers made for premises wiring unless you can meet certain code requirements, specifically requirement 647.3(1) which states for industrial or commercial occupancies. Trust me your home does not qualify.

I doubt you need to go this far or to that expense. There are two far more less expensive routes. One is similar to balanced power is to buy a plain ole Tripp-Lite 1500 VA, plug-n-play isolation transformer if it meets you power requirement. Plug it into the wall, then plug in your equipment and you are ready to go.

The other method is to hire an electrician and run you a dedicated 20-amp quad circuit, and power all the equipment from that circuit.
 

ritelec

Senior Member
Location
Jersey
I am an electrician. Seperate circuits are there.

dimmers in the house, clothes dryers, you get some humms and noise, clicks and pops.

yes, i've read that grounding the center tap on that transformer doesn't follow with code practices.

also installed some isolation "sola" transformers for fedex for there scales but did not ground the center of the secondary side as discussed.(there may be 2 or 3 left).

also read that these isolation transformers are used in high end studios.(although they conflict with code practices). "is that commercial"? and if so , whats the difference if its installed there or here?

I'll check into the trip-lite you suggested.

looking for no noise and 100% safe. and yes 60v neutral to ground is something to think about.

thanks
r
 

brian john

Senior Member
Location
Leesburg, VA
There lots of different beliefs on installing power systems in studios. I have used isolation transformers and they work fine.

But I have also been in studios with hum issues, (very critical elebrorate studios) and simply by correcting the wiring issues, we resolved the PQ issues.

Start with proper NEC compliant wiring practices, if there issue check out your wiring practices. If there are still issues then take the next steps.
 

dbuckley

Senior Member
dereckbc said:
Not true on the snake oil.

I disagree, but lets not fall out over it :)

The AC power that goes into a <fill in piece of audio equipment here> goes straight into a transformer, the primary of which has no reference in the equipment to to ground, then the AC voltage is then rectified and stabilised, and that is where the ground reference is generated. Thats the extent of mains power.

The key to quiet audio is a quiet ground, and balanced power neither contributes nor detracts from ground. Gte the grounding right, and all the hums and buzzes go away.

There are also safety concerns about balanced power when used with equipment not designed for a balanced power supply. These concerns come from balanced power having two hots and no neutral, and only one of the hots is switched and fused. Equipment designed for balanced power use has double pole switching and fusing. Its exactly like 220V distribution but at half the voltage, where you have two hots, and an (optional) neutral.
 

dereckbc

Moderator
Staff member
Location
Plano, TX
dbuckley said:
The AC power that goes into a <fill in piece of audio equipment here> goes straight into a transformer, the primary of which has no reference in the equipment to to ground
Incorrect, input transformers are not used, haven't for the last 15 yesrs, they use switch mode power supplies. Any switch mode rectifies line voltage directly to DC, converts to high frequency AC, then into a transformer/rectifier circuit to derive the various DC voltages used by the equipment. But for the sake of argument lets say they do use an input transformer, the AC line is referenced to ground, why, there is a nuetral involved. In addition you have line input filters installed between L-G and N-G that discharge right into the chassis ground.

Either a isolation transformer or balanced transformer removes all noise from the line as they both are the same thing just tapped differently.

I agree most problems are eliminated by proper wiring techniques, but not common mode noise. Only device capable of effectively removing common mode noise is either an isolation transformer, motor-generator, or dual conversion UPS.

The safety problems involved with 120/60 systems are addressed in the code. Both phase conductors have to have OCPD and GFCI receptacles. In the case of the plug-n-play systems, all that is built into the box.

I am not advocating that balanced power is the only answer, it is the last resort. As Brian stated start with dedicated circuits, insure all the wiring of the facility meets code, and if that fails start taking steps.

Most of the noise like hum is caused by the equipment being sourced from multiple circuits that have small voltage differences induced onto the grounding conductors. These small voltage differences are picked up by the interconnected signal cables that use unbalanced transmission like coax where ground is used as a path. This is common mode noise.

There are lots of ways to deal with common mode noise like signal transformer, balanced signal lines, dedicated circuits, and isolation transformers. Start with the least expensive methods and work your way up. Personally I like optical, no problems.
 

dereckbc

Moderator
Staff member
Location
Plano, TX
ritelec said:
also read that these isolation transformers are used in high end studios.(although they conflict with code practices). "is that commercial"? and if so , whats the difference if its installed there or here?

Yes balanced power is used in high-end recording studios, and four data centers to my knowledge. It was born in Hollywood studios, which prompted article 647 to deal with it. Yes a studio is a commercial application as defined by local zoning laws, and your home is zoned residential, meaning you cannot install balanced power as part of premise wiring system. The way around it for a home owner is a plug-n-play box or a rack mount system which is regulated by the UL not NEC
 

ghostbuster

Senior Member
I agree 100% with "dereckbc" statements.In large tv and post production studios, the"total combined leakage ground current" from all the front end filtering on the rack equipment can sometimes be greater then 1 amp.This is real live ground current and creates real live ohms law I*R voltage potential differences between different pieces of rack equipment.This potential difference causes current to flow on the signal ground between this equipment.I believe the key to designing a proper studio is to understand this current will flow on the ground : you must design in proper safeguards as mentioned in earlier posts.
 

ritelec

Senior Member
Location
Jersey
safe safe safe....... i agree.

I'm ok with electricity.... electronics is not my forte...


checked out the trip-lite, still researching and with your help I'm sure we'll get it so we can get down to writeing some hit songs...

r
 
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