Re: balanced power

[Scott Dorsey]

xy > wrote:
>i'm thinking this coming year is the year i finally drop $700 on a
>"box that does nothing".
>
>but seriously, since i'm such a low-noise freak, a balanced power box
>appeals to me.
>
>so two things if that's ok:
>1)can anyone convince me *not* to buy one of these power boxes? (that
>will be tough!)

Can you hear hum? If you can't hear hum, you don't have a chassis leakage
problem and balanced power won't fix it. Balanced power is a good way of
dealing with chassis leakage but it's not a fix for anything else, really.
It will do nothing about broadband thermal noise.

>2)why is the eta brand one so much more than the furman ones? it will
>be hard to convince me that the eta is "better", but maybe it is in
>some esoteric power-rail slew rate mojo...

Look at the data sheet. It should talk about CMRR, which you want as good
as possible. It should also talk about either effective output impedance
or about voltage drop with load (basically the same thing).

> furman makes i think the it-1210 and the it-1220. one of those uses
>a regular wall outlet and does not require one of those weird
>air-conditioner outlets. i like the idea of buying the "regular" one
>since my power requirements are modest.

You can get a dry isolation transformer with a center tap from your local
electrical supply for less than either.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[they call me frenchy]

On 9 Sep 2003 12:41:25 -0400, (Scott Dorsey) wrote:
<snip>
>Can you hear hum? If you can't hear hum, you don't have a chassis leakage
>problem and balanced power won't fix it. Balanced power is a good way of
>dealing with chassis leakage but it's not a fix for anything else, really.
>It will do nothing about broadband thermal noise.
<snip>

Scott,
Is the chassis leakage that you mentioned related to junk that certain
power supplies throw onto the ground?

I have a dell laptop powersupply with 3 prongs. It always causes lots
of noise in my audio, until I lift the GND prong, then all is fine.
Also, the other day I hooked a desktop computer to my laptop via
firewire (for filesharing) and I got a helatious noise in my audio
(that reacted to mouse movements) ..... as soon as I lifted the GND on
the desktop and the monitor, the noise completely disappeared.

I know I'm not supposed to be lifting everything, but if these certain
power supplies are throwing junk onto my audio system ground, then
what am I to do? Does this sound like a solution for balanced power
or do I have a different problem?

I am running everything from the same outlet. All my gear is located
within 15 feet from each other. All gear is low power (computers, RME
interface, lots of synths, preamps, mixers, midi patchbay,
etc)...audio and midi cables going everywhere.

Lastly, the other day when I plugged my firewire cable in there was a
huge spark (arcing). I am reasoning that my desktop computer chassis
is floating at some unknown potential (because it is lifted) and when
I plugged in the firewire cable, it forced the desktop GND to the
potential of my laptop/audio gear GND and momentarily sparked due to
the difference. I want to stop lifting my computers (I NEVER EVER
lift guitar amps). I should be able to plug in all 3 prongs of my
laptop, desktop, and everything shouldnt I?

Sorry for the question, but I just got a decent loan for my studio and
I want to know if I should consider balanced power, or if I just need
to be smarter about my grounding scheme.

thx,
frenchy

[Scott Dorsey]

they call me frenchy > wrote:
>On 9 Sep 2003 12:41:25 -0400, (Scott Dorsey) wrote:
><snip>
>>Can you hear hum? If you can't hear hum, you don't have a chassis leakage
>>problem and balanced power won't fix it. Balanced power is a good way of
>>dealing with chassis leakage but it's not a fix for anything else, really.
>>It will do nothing about broadband thermal noise.
>
>Is the chassis leakage that you mentioned related to junk that certain
>power supplies throw onto the ground?

Could be. Could be bad transformers with ground leakage. Could be badly
designed RFI filtering in front of the transformer. Could be bad switching
supply design too.

>I have a dell laptop powersupply with 3 prongs. It always causes lots
>of noise in my audio, until I lift the GND prong, then all is fine.
>Also, the other day I hooked a desktop computer to my laptop via
>firewire (for filesharing) and I got a helatious noise in my audio
>(that reacted to mouse movements) ..... as soon as I lifted the GND on
>the desktop and the monitor, the noise completely disappeared.

THIS is a switching supply issue. And it's not just the power supply,
it is everything on the computer tied to that safety ground and dumping
trash there.

>I know I'm not supposed to be lifting everything, but if these certain
>power supplies are throwing junk onto my audio system ground, then
>what am I to do? Does this sound like a solution for balanced power
>or do I have a different problem?

The real solution is to get an isolated ground outlet for the computer,
so it's not able to toss junk on the audio system ground.

A cheesy kludge is to use an isolation transformer that will allow you
to safely lift the ground on the computer. This will cost a lot less
than a balanced power transformer.

Another solution might be a better outboard supply for the laptop.

>I am running everything from the same outlet. All my gear is located
>within 15 feet from each other. All gear is low power (computers, RME
>interface, lots of synths, preamps, mixers, midi patchbay,
>etc)...audio and midi cables going everywhere.

WHY are you running everything from the same outlet?

>Lastly, the other day when I plugged my firewire cable in there was a
>huge spark (arcing). I am reasoning that my desktop computer chassis
>is floating at some unknown potential (because it is lifted) and when
>I plugged in the firewire cable, it forced the desktop GND to the
>potential of my laptop/audio gear GND and momentarily sparked due to
>the difference. I want to stop lifting my computers (I NEVER EVER
>lift guitar amps). I should be able to plug in all 3 prongs of my
>laptop, desktop, and everything shouldnt I?

Yes. DO NOT lift safety grounds unless you have some way to isolate
it. Lifting the computer is just as bad as doing the same thing to
a guitar amp. It does not fix the problem, it only hides it.

>Sorry for the question, but I just got a decent loan for my studio and
>I want to know if I should consider balanced power, or if I just need
>to be smarter about my grounding scheme.

A smarter grounding scheme is always a better idea. Isolation transformers
are handy to have around, though, if you have to mix analogue and digital
gear on the same circuits.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[they call me frenchy]

On 5 Mar 2004 14:55:22 -0500, (Scott Dorsey) wrote:
<snip>
>>I know I'm not supposed to be lifting everything, but if these certain
>>power supplies are throwing junk onto my audio system ground, then
>>what am I to do? Does this sound like a solution for balanced power
>>or do I have a different problem?
>
>The real solution is to get an isolated ground outlet for the computer,
>so it's not able to toss junk on the audio system ground.

I want to do the "real solution". I have the budget and I have the
desire. Can you point me to a "dorsey endorsed" reference that
outlines the real solution? Website? Book?

To this date, I have been purposely avoiding using different outlets
(different grounds) because then I get groundloop noises. I reasoned
that if I use one outlet (one ground) then ground loop problems go
away.....but then I run into the "dirty ground" problem.

>
>A cheesy kludge is to use an isolation transformer that will allow you
>to safely lift the ground on the computer. This will cost a lot less
>than a balanced power transformer.
>
Are you talking about an isolation transformer for the 120v mains? I
never thought of that as a possible solution. Can you point me to
some products that are on the market for this? I am interested in
learning more about these.


>Another solution might be a better outboard supply for the laptop.
>

I am using the "off the shelf" dell supply that came with the
laptop...it has a proprietary connector on the laptop end, but of
course I could do some splicing.


>
>>Lastly, the other day when I plugged my firewire cable in there was a
>>huge spark (arcing). I am reasoning that my desktop computer chassis
>>is floating at some unknown potential (because it is lifted) and when
>>I plugged in the firewire cable, it forced the desktop GND to the
>>potential of my laptop/audio gear GND and momentarily sparked due to
>>the difference. I want to stop lifting my computers (I NEVER EVER
>>lift guitar amps). I should be able to plug in all 3 prongs of my
>>laptop, desktop, and everything shouldnt I?
>
>Yes. DO NOT lift safety grounds unless you have some way to isolate
>it.

not sure what you mean here, but I look forward to a text that
outlines the proper way.


> Lifting the computer is just as bad as doing the same thing to
>a guitar amp. It does not fix the problem, it only hides it.
>
>>Sorry for the question, but I just got a decent loan for my studio and
>>I want to know if I should consider balanced power, or if I just need
>>to be smarter about my grounding scheme.
>
>A smarter grounding scheme is always a better idea. Isolation transformers
>are handy to have around, though, if you have to mix analogue and digital
>gear on the same circuits.
>--scott

do you mean isolation transformers for the audio or for the mains? If
you mean for the audio, then does that mean that I need 16 channels of
audio transformers for all the audio signals connected to my RME
interface (which would be considered digital gear)?

thx again!
frenchy

[Scott Dorsey]

they call me frenchy > wrote:
>On 5 Mar 2004 14:55:22 -0500, (Scott Dorsey) wrote:
><snip>
>>>I know I'm not supposed to be lifting everything, but if these certain
>>>power supplies are throwing junk onto my audio system ground, then
>>>what am I to do? Does this sound like a solution for balanced power
>>>or do I have a different problem?
>>
>>The real solution is to get an isolated ground outlet for the computer,
>>so it's not able to toss junk on the audio system ground.
>
>I want to do the "real solution". I have the budget and I have the
>desire. Can you point me to a "dorsey endorsed" reference that
>outlines the real solution? Website? Book?

Call an electrician. Tell him you want two isolated ground circuits
pulled to the room. This will at least radically reduce your problems.

There is a discussion of this in the NEC book, but the problem with the
NEC is that it tells how all this stuff is done, but it doesn't explain
why, and sometimes it takes some head scratching to figure out why the
code requires this or that or why you'd even want it.

>To this date, I have been purposely avoiding using different outlets
>(different grounds) because then I get groundloop noises. I reasoned
>that if I use one outlet (one ground) then ground loop problems go
>away.....but then I run into the "dirty ground" problem.

Okay, do you have a balanced connection between the computer and the audio
system? If so, you should just be able to lift the signal ground on the
audio line and be fine. If not, you can use a transformer to balance it.

The general rule is that everything should have one and only one ground path
to everything else.

>>A cheesy kludge is to use an isolation transformer that will allow you
>>to safely lift the ground on the computer. This will cost a lot less
>>than a balanced power transformer.
>>
>Are you talking about an isolation transformer for the 120v mains? I
>never thought of that as a possible solution. Can you point me to
>some products that are on the market for this? I am interested in
>learning more about these.

Right. You can isolate the power line ground instead of isolating the
audio ground. Stancor makes a bunch of line isolation transformers.
Square-D makes some bigger ones intended for installation. If you call
Cain Electronics in Hampton, VA and talk to Jeff, he can sell you a
cheap Chinese one.

>>Another solution might be a better outboard supply for the laptop.
>
>I am using the "off the shelf" dell supply that came with the
>laptop...it has a proprietary connector on the laptop end, but of
>course I could do some splicing.

Exactly. If you know what comes out of the supply, you can replace it
with a clean linear supply, but it will take some cut and paste work.

>>>Lastly, the other day when I plugged my firewire cable in there was a
>>>huge spark (arcing). I am reasoning that my desktop computer chassis
>>>is floating at some unknown potential (because it is lifted) and when
>>>I plugged in the firewire cable, it forced the desktop GND to the
>>>potential of my laptop/audio gear GND and momentarily sparked due to
>>>the difference. I want to stop lifting my computers (I NEVER EVER
>>>lift guitar amps). I should be able to plug in all 3 prongs of my
>>>laptop, desktop, and everything shouldnt I?
>>
>>Yes. DO NOT lift safety grounds unless you have some way to isolate
>>it.
>
>not sure what you mean here, but I look forward to a text that
>outlines the proper way.

An isolation transformer does just that... it gives you 120V on one lead
with respect to another lead, which are totally isolated from ground and
from the input. You can touch either lead while holding the ground, and
not get a shock. You can't touch both without getting a shock. If you
use an isolation transformer, it is now safe to lift the power line ground.

>> Lifting the computer is just as bad as doing the same thing to
>>a guitar amp. It does not fix the problem, it only hides it.
>>
>>>Sorry for the question, but I just got a decent loan for my studio and
>>>I want to know if I should consider balanced power, or if I just need
>>>to be smarter about my grounding scheme.
>>
>>A smarter grounding scheme is always a better idea. Isolation transformers
>>are handy to have around, though, if you have to mix analogue and digital
>>gear on the same circuits.
>
>do you mean isolation transformers for the audio or for the mains? If
>you mean for the audio, then does that mean that I need 16 channels of
>audio transformers for all the audio signals connected to my RME
>interface (which would be considered digital gear)?

If your RME is balanced, you have electronics in there that are effectively
the same thing as transformers (though they can't handle as high ground
offset voltages). This means you can probably lift the grounds on the audio
lines.

If you cannot lift the ground on the audio line, you can either use an
audio transformer to let you lift it, or you can use a power line transformer
to let you lift the power line ground.
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[they call me frenchy]

Scott,
Let me start by saying thank you very much!!! I really appreciate it.
I have my entire studio torn apart right now and the electrician is
coming today. I will rewire the studio power/GND system based on the
below discussion....


On 6 Mar 2004 09:58:28 -0500, (Scott Dorsey) wrote:

>they call me frenchy > wrote:
>>On 5 Mar 2004 14:55:22 -0500, (Scott Dorsey) wrote:
>><snip>
>>>>I know I'm not supposed to be lifting everything, but if these certain
>>>>power supplies are throwing junk onto my audio system ground, then
>>>>what am I to do? Does this sound like a solution for balanced power
>>>>or do I have a different problem?
>>>
>>>The real solution is to get an isolated ground outlet for the computer,
>>>so it's not able to toss junk on the audio system ground.
>>
>>I want to do the "real solution". I have the budget and I have the
>>desire. Can you point me to a "dorsey endorsed" reference that
>>outlines the real solution? Website? Book?
>
>Call an electrician. Tell him you want two isolated ground circuits
>pulled to the room. This will at least radically reduce your problems.

Did it. I have an electrician coming to run two separate circuits
that go all the way back to the circuit breaker. It is an old
building with the screw in fuses. I have a question: if one of the
circuits gets junk dumped on it by switching power supplies, wont the
noise go all the way to the circuit breaker box and then back to the
audio circuit ground?? I hope not, because then I am back where I
started.



>There is a discussion of this in the NEC book, but the problem with the
>NEC is that it tells how all this stuff is done, but it doesn't explain
>why, and sometimes it takes some head scratching to figure out why the
>code requires this or that or why you'd even want it.

So the NEC book accounts for professional digital/analog audio
systems? I'll try to find this book.




>>To this date, I have been purposely avoiding using different outlets
>>(different grounds) because then I get groundloop noises. I reasoned
>>that if I use one outlet (one ground) then ground loop problems go
>>away.....but then I run into the "dirty ground" problem.
>
>Okay, do you have a balanced connection between the computer and the audio
>system? If so, you should just be able to lift the signal ground on the
>audio line and be fine. If not, you can use a transformer to balance it.


The laptop to my audio breakout box is a proprietary cardbus/firewire
cable, so I will assume that the breakoutbox is part of the computer
system and I cannot isolate the GND at that point. There are 3 types
of connectors that plug into this box.

1) 16 channels of balanced TRS audio (8in/8out) So are you saying
that I need to lift the GND on all 16 TRS cables?

2) ADAT optical for an additional 8in/8out. I am assuming this will
never contribute to GND loop or dirty GND because there is no metal
(galvanic) GND connection.

3) Midi in/midi out. This is one of my quandries. Inevitably I have
gear that is audio and midi in one box..........so if I want to keep
the computer interface GND isolated from my audio system GND, then I
have to lift the GND on the midi in/midi out cables that go to my
computer interface..... is this correct?


>The general rule is that everything should have one and only one ground path
>to everything else.

So what about unbalanced rack gear? Should I let the chassis be
grounded to each other through the rack rails and then lift the GND on
the unbalanced TS cables?....or should I leave the TS cables in tact
and isolate the chassis from each other and from the rails? If the TS
cable is providing the one and only GND connection, then I need to use
a power isolation transformer on every 3-prong unbalanced peice of
gear AND isolate the chassis from the rails? This sounds like it will
be fun.

>>>A cheesy kludge is to use an isolation transformer that will allow you
>>>to safely lift the ground on the computer. This will cost a lot less
>>>than a balanced power transformer.
>>>
>>Are you talking about an isolation transformer for the 120v mains? I
>>never thought of that as a possible solution. Can you point me to
>>some products that are on the market for this? I am interested in
>>learning more about these.
>
>Right. You can isolate the power line ground instead of isolating the
>audio ground. Stancor makes a bunch of line isolation transformers.
>Square-D makes some bigger ones intended for installation. If you call
>Cain Electronics in Hampton, VA and talk to Jeff, he can sell you a
>cheap Chinese one.

The safety GND still works even though there is no galvanic connection
between the primary GND and the secondary GND??? hmmmmm. interesting.

>>>Another solution might be a better outboard supply for the laptop.
>>
>>I am using the "off the shelf" dell supply that came with the
>>laptop...it has a proprietary connector on the laptop end, but of
>>course I could do some splicing.
>
>Exactly. If you know what comes out of the supply, you can replace it
>with a clean linear supply, but it will take some cut and paste work.

I will consider this only if my two ground system doesnt work well
enough.....but darnit it should.

Is the two ground system, the way you would go? One for digital/noisy
gear and one for the audio system? I will plan on this.

thx very, very much,
frenchy

[Scott Dorsey]

In article >,
>>
>>Call an electrician. Tell him you want two isolated ground circuits
>>pulled to the room. This will at least radically reduce your problems.
>
>Did it. I have an electrician coming to run two separate circuits
>that go all the way back to the circuit breaker. It is an old
>building with the screw in fuses. I have a question: if one of the
>circuits gets junk dumped on it by switching power supplies, wont the
>noise go all the way to the circuit breaker box and then back to the
>audio circuit ground?? I hope not, because then I am back where I
>started.

Tell the electrician you want isolated ground circuits.
>
>>There is a discussion of this in the NEC book, but the problem with the
>>NEC is that it tells how all this stuff is done, but it doesn't explain
>>why, and sometimes it takes some head scratching to figure out why the
>>code requires this or that or why you'd even want it.
>
>So the NEC book accounts for professional digital/analog audio
>systems? I'll try to find this book.

Ask the electrician to show you his copy. The code handbook is expensive,
but it basically talks about every possible electrical situation. Sometimes
it can be very dense. But there are seperate sections for audio facilities,
television facilities, swimming pools, pipe organs, and what have you.

>>>To this date, I have been purposely avoiding using different outlets
>>>(different grounds) because then I get groundloop noises. I reasoned
>>>that if I use one outlet (one ground) then ground loop problems go
>>>away.....but then I run into the "dirty ground" problem.
>>
>>Okay, do you have a balanced connection between the computer and the audio
>>system? If so, you should just be able to lift the signal ground on the
>>audio line and be fine. If not, you can use a transformer to balance it.
>
>The laptop to my audio breakout box is a proprietary cardbus/firewire
>cable, so I will assume that the breakoutbox is part of the computer
>system and I cannot isolate the GND at that point. There are 3 types
>of connectors that plug into this box.
>
>1) 16 channels of balanced TRS audio (8in/8out) So are you saying
>that I need to lift the GND on all 16 TRS cables?

It's certainly worth trying, yes. Try using just one cable and keeping
the ground open on it.

You want to eliminate all ground loops. Anything that will cause two pieces
of gear to have more than one ground path between them should be eliminated.

>2) ADAT optical for an additional 8in/8out. I am assuming this will
>never contribute to GND loop or dirty GND because there is no metal
>(galvanic) GND connection.

Right.

>3) Midi in/midi out. This is one of my quandries. Inevitably I have
>gear that is audio and midi in one box..........so if I want to keep
>the computer interface GND isolated from my audio system GND, then I
>have to lift the GND on the midi in/midi out cables that go to my
>computer interface..... is this correct?

There are boxes that will let you lift MIDI grounds. They use optoisolators
and you can see them advertised in Electronic Musician and all the usual
magazines.

>>The general rule is that everything should have one and only one ground path
>>to everything else.
>
>So what about unbalanced rack gear? Should I let the chassis be
>grounded to each other through the rack rails and then lift the GND on
>the unbalanced TS cables?....or should I leave the TS cables in tact
>and isolate the chassis from each other and from the rails? If the TS
>cable is providing the one and only GND connection, then I need to use
>a power isolation transformer on every 3-prong unbalanced peice of
>gear AND isolate the chassis from the rails? This sounds like it will
>be fun.

Unbalanced stuff can be a nightmare, but put all your unbalanced stuff
together and treat it as one unit. Keep it seperate from the computer
sustem.
>
>>>>A cheesy kludge is to use an isolation transformer that will allow you
>>>>to safely lift the ground on the computer. This will cost a lot less
>>>>than a balanced power transformer.
>>>>
>>>Are you talking about an isolation transformer for the 120v mains? I
>>>never thought of that as a possible solution. Can you point me to
>>>some products that are on the market for this? I am interested in
>>>learning more about these.
>>
>>Right. You can isolate the power line ground instead of isolating the
>>audio ground. Stancor makes a bunch of line isolation transformers.
>>Square-D makes some bigger ones intended for installation. If you call
>>Cain Electronics in Hampton, VA and talk to Jeff, he can sell you a
>>cheap Chinese one.
>
>The safety GND still works even though there is no galvanic connection
>between the primary GND and the secondary GND??? hmmmmm. interesting.

The safety ground does not work. But there is no need for a safety ground
because there is no galvanic connection between the hot wire and the primary
ground. You can touch the hot wire and not feel anything, since there is
no path from the secondary system to the primary. It's isolated.

>>>>Another solution might be a better outboard supply for the laptop.
>>>
>>>I am using the "off the shelf" dell supply that came with the
>>>laptop...it has a proprietary connector on the laptop end, but of
>>>course I could do some splicing.
>>
>>Exactly. If you know what comes out of the supply, you can replace it
>>with a clean linear supply, but it will take some cut and paste work.
>
>I will consider this only if my two ground system doesnt work well
>enough.....but darnit it should.
>
>Is the two ground system, the way you would go? One for digital/noisy
>gear and one for the audio system? I will plan on this.

Probably. But you still need proper signal grounding.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[S O'Neill]

Scott Dorsey wrote:

> There are boxes that will let you lift MIDI grounds. They use optoisolators
> and you can see them advertised in Electronic Musician and all the usual
> magazines.


I thought all MIDI interfaces were opto-isolated by specification. That
is, the output is a current source that drives an input opto, and the
shield is grounded only at the MIDI OUT connector.

My copy of the MIDI spec says this, anyway. Or did they cheapen it?

[Scott Dorsey]

S O'Neill > wrote:
>Scott Dorsey wrote:
>
>> There are boxes that will let you lift MIDI grounds. They use optoisolators
>> and you can see them advertised in Electronic Musician and all the usual
>> magazines.
>
>I thought all MIDI interfaces were opto-isolated by specification. That
>is, the output is a current source that drives an input opto, and the
>shield is grounded only at the MIDI OUT connector.

That's what the spec says. This spec is routinely violated.

S-PDIF interfaces should also be isolated with a pulse transformer and
not share a common ground with the internal electronics. Guess how often
that is actually done on consumer gear?

>My copy of the MIDI spec says this, anyway. Or did they cheapen it?

It wasn't cheapened, just often ignored. Higher grade gear will be much
less trouble, though.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Kurt Albershardt]

they call me frenchy wrote:
>
> Did it. I have an electrician coming to run two separate circuits
> that go all the way back to the circuit breaker. It is an old
> building with the screw in fuses. I have a question: if one of the
> circuits gets junk dumped on it by switching power supplies, wont the
> noise go all the way to the circuit breaker box and then back to the
> audio circuit ground?? I hope not, because then I am back where I
> started.

The junk from switchmode power supplies is high frequency, so if you provide a shorter path to ground for HF, the junk will take it.

If they each have isolated ground wires running back to the panel and the panel is properly grounded, the junk will find giong to ground easier than going back up the other wire.