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Isolation Transformer Vs Balanced Power
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manman
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#1
10th February 2011
Old 10th February 2011
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Isolation Transformer Vs Balanced Power

Hi, please help to understand this.
So I have narrowed my search here:

Isolated Transformer:
  1. It separates the physical contact hot&neutral wire
  2. It have so called electrostatic screen

Questions:

a. Is ground from AC outlet connected to device chassis/ground?
b. Is electrostatic screen connected to common chassis/ground?
c. Will this isolation transformer prevent ground loop for device?
d. Is it still safe, cause chassis/ground could be isolated & little charged?


Power balanced:
  1. Same thing with electrostatic but voltage divided by 60v+60v
  2. Middle point is connected to ground
  3. It helps to eliminate hum, some extra harmonics

Questions:

a. Is middle point connected to ground & electrostatic screen &/or to ground of device?
b. Any safety issues?

Problem:

I use Bryston 4b and when its ground lifted its super silent, i'm trying to eliminate ground loop on amp. I have used multimeter and power consumption does not exceed 2.5A which is 2.5A*120V=300Watts

Possible solutions:

1. Buy Furman IT-Reference7i power isolation
2. Buy Ebtech Xhum(any safety issues?)
3. Buy transformer and build custom power supply
4. Buy those medical A/C isolation transformers commonly seen on ebay
Attached Thumbnails
Isolation Transformer Vs Balanced Power-289sch.gif   Isolation Transformer Vs Balanced Power-plitron-isolation-transformer.gif  
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10th February 2011
Old 10th February 2011
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Quote:
Originally Posted by manman View Post
Isolated Transformer:
...
Questions:

a. Is ground from AC outlet connected to device chassis/ground?
yes. A transformer can't "generate" a ground. A ground is more than just a reference voltage, it's like a big drain pipe than can sink an arbitrary amount of current. It has to literally be a (low-resistance) connection to the earth.

Quote:
b. Is electrostatic screen connected to common chassis/ground?
usually, yes, the shielding is much more effective if any charge that develops on it is shunted to ground. The ground "holds" the screen at ground potential.

Quote:
c. Will this isolation transformer prevent ground loop for device?
probably not. ground loops happen because connections to ground have resistance, and in particular because different paths to ground have different resistance. Fighting ground loops might involve ensuring that everything is connected to a common grounding point and connected with as little resistance as possible. Or lifting a ground here and there, depends on the particular ground loop. but the isolation transformer isn't really relevant to the problem.

Cleaning up the power can make the ground loops less problematic by reducing the amount of noise and EMI in the power lines. I think one of the primary benefits of balanced power is in fact that a pair of conductors that have inverse signals on them (which is what you get in a power cable carrying balanced power) radiates a lot less of a field than an unbalanced conductor pair. That's one of the reasons that balanced connections are used for very noise-sensitive signal transmissions in so many electronic designs.

Quote:
d. Is it still safe, cause chassis/ground could be isolated & little charged?
The chassis grounding should not change.

Quote:
Power balanced:
Questions:

a. Is middle point connected to ground & electrostatic screen &/or to ground of device?
It's actually the connection of ground to the center tap of the transformer secondary that causes the power to be balanced, i.e., +60 / -60. The output side of the center-tap transformer is happy to swing 60V in either direction around any voltage that you apply to the center tap, interestingly. (There are other ways to generate balanced power that don't involve transformers, but it's the same idea.)

But the main point is that ground is ground is ground. The grounding on everything is connected to the earth, which is ground. period. You have to have a good solid ground.

Quote:
b. Any safety issues?
The main danger with balanced power is that if there is an improperly wired device (which should never occur and should not get past UL certification etc.) that has the neutral conductor connected to the chassis instead of ground, then suddenly the case of that piece of equipment will have 60V AC on it instead of ground, which is bad. You want to check for that but it should never happen. Such a piece of equipment is dangerous even without balanced power.


It's hard to say whether something like balanced power would fix your problem, but what I think it is safe to say is that with balanced power there is a whole lot less 60Hz/50Hz hum radiating around your studio, and also with any good power conditioner there is a lot less crud on the hot and neutral conductors. I.e., the EMI environment of the studio is a lot better.

-synthoid
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12th February 2011
Old 12th February 2011
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AC Phase / Ground Iso

If you are having "ground loop" issues between your console and power amps, this is the method that I used/use in all my installations. This is also recommended in a long article on the RANE website.

I remove the ground (pin 1) on the send (female) XLR cable. This way the balanced input of the equipment "telescopes" out the shield/ground, but does touch the output of the previous device.

This also solves the issue where some equipment has an unbalanced output or is quasi (sort of) balanced, because it's a lot harder to design a circuit with a proper symmetrical balanced output. Balanced inputs are easy to design, because all OP amps are basically balanced.

This also works for transformer balanced equipment. I have designed a number of high end studios using this method and have never had a problem.

With regards to AC. Balanced AC is way to difficult to setup. Just make sure ALL YOUR AUDIO AC plugs - are from the same 120V phase from your 120/120=240 vac house panel. I.E. if your put a AC volt meter between the (hot) of any two ac outlets in your studio and you measure near 240v you need to either (a) not use that plug, or (b) have someone that knows about AC move the circuit in your AC box to the other phase. Try and make the phase that you use for the studio, NOT the one that has the fridge/fax machine/coke dispenser/cheap light dimmers, etc. If need be have the same electrician move some of these to the "other" phase.

All modern equipment has the AC ground wire tied to the metal chassis. This is required by law and can save your life! Some equipment has a switch that allows you the decouple the AC ground from the DC audio ground (pin 1). Use this switch similar to the switch on a Direct Box, which ever way is quieter is the way to leave it.

Good day
Ron O. Vermeulen
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Last edited by Ron Obvious; 12th February 2011 at 10:22 PM.. Reason: AC grounding
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13th February 2011
Old 13th February 2011
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Just Lift the ground on your equipment racks, or lift the ground on the Bryston. Things will be fine.
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manman
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13th February 2011
Old 13th February 2011
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Quote:
Just Lift the ground on your equipment racks, or lift the ground on the Bryston. Things will be fine.
Thanks, that's what I did, now Bryston is dead silent.

Is lifting ground on completely dangerous if current flows through chassis in case of malfunction? Should I install GFCI?

I am usually never around Bryston its behind the desk.
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13th February 2011
Old 13th February 2011
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No, it's not really safe to lift the ground from a power connection. If there is a fault then you can become the ground. No legitimate source would advise lifting the power ground off a chassis.

Check this - Pin 1 Problem and follow it - you should be good.

CC
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13th February 2011
Old 13th February 2011
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I did not read the whole thread but this is an affordable and safe way to solve ground related noise problems:

Ebtech - Audio Solutions
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manman
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14th February 2011
Old 14th February 2011
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Not so much info about Ebtech stuff, how does it work? I read somewhere it has diodes in parallel + resister, isn't it a ground lifting still?
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14th February 2011
Old 14th February 2011
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Hello Manman,

Sorry to step back in on this topic. I've given you the PRO answer to all the questions you have. Very simple doesn't cost anything extra!

Lift the ground on the AC plug answer - how amateur is that!!! Oh and you could die.

Buy some boogie whoogie, plug adapter, come on kids, we want REAL answers!

My solutions have worked fine for Skinny Puppy, AC/DC, Slayer, Shakira, REM, Rush, Nickelback, etc.

Last edited by Ron Obvious; 14th February 2011 at 02:59 AM.. Reason: spelling
ORC
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14th February 2011
Old 14th February 2011
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Quote:
Originally Posted by conleycd View Post
No, it's not really safe to lift the ground from a power connection. If there is a fault then you can become the ground. No legitimate source would advise lifting the power ground off a chassis.

Check this - Pin 1 Problem and follow it - you should be good.

CC
I am a professional mastering engineer with a degree in electrical engineering. Lift the ground on the Bryston, you'll be fine. Your amp will still be grounded through your rack gear/ monitor controller. Now, someone is going to chime in and say I'm incorrect, but my reply would be: "Obvously you've got a ground loop problem, most likely caused by the ground connection to your rack, and the ground connection to your amp sitting at different potential/voltage. Ideally the voltage at ground should be at zero, simply lift the ground on your rack, or your amp. Either will do." As far as safety is concerned, you'll be fine.

Now, someone has said, "This isn't safe," I would argue that both your rack and your amp are indeed grounded, otherwise it would be physically impssible to have a ground loop hum. Removing the ground from either the rack or the amp will negate the ground loop, and both rack and amp will remain grounded, but now through the same path. This is exactly what is done in say a multi amp guitar rig, One amp is grounded, and the others should be lifted, this way all amps share the same path to ground, resulting in less chance for electrical mayhem, or the player getting shocked.
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14th February 2011
Old 14th February 2011
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Quote:
Originally Posted by ORC View Post
I am a professional mastering engineer with a degree in electrical engineering. Lift the ground on the Bryston, you'll be fine.
And if the amp power supply faults then the current getting dumped through the signal ground and console is nothing to worry about?

Ron Obvious gave a comprehensive answer that cannot be bettered. You got free advice from someone with proven experience.


BTW - Ron, Bob Brooks says hi.
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14th February 2011
Old 14th February 2011
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Then lift the ground on the console, and ground the Bryston. If the power supply faults, the chassis ground will indeed remain.
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14th February 2011
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Ron has the right answer.


GR
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14th February 2011
Old 14th February 2011
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OK this is my last time in on this topic.

PLEASE, ORC - just lift the ground on the console supply????

OK, so now we have a guitar player with a dodgy setup. I.E. they cut the AC ground pin off, or had some "expert" mod their amp, or have the "AC polarity" switch in the wrong position, etc. They now happen to be holding the strings of their guitar as they touch your (quasi) ungrounded console. Much joy will be had by the guitar player, for a very short time (?) Maybe even a small light show!

Also grounding using the common "rack rail" is not a good idea. Oxidation and/or screws coming loose, can cause the ground to become weak or non exsistent. This of course happens slowly over time, so you don't really notice that the noise floor of your "recording setup" is going downhill. Then you will have days and days trying to find the problem.
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