i am interested in getting an ac isolation transformer for a piece of
gear that has a ground loop in my studio. i see ones that are 110, 115
120v input voltage. my wall voltage is supposed to be 120v actually my
furman pl-plus meter shows about 125v. would i be okay using any of
these voltage inputs? or should i get one that is closest to my actual
wall voltage?

are the "medical grade" transformers ok for audio use?

wrote:

i am interested in getting an ac isolation transformer for a piece of
gear that has a ground loop in my studio. i see ones that are 110, 115
120v input voltage. my wall voltage is supposed to be 120v actually my
furman pl-plus meter shows about 125v. would i be okay using any of
these voltage inputs? or should i get one that is closest to my actual
wall voltage?

are the "medical grade" transformers ok for audio use?

Ground loop problems are better solved by solving the underlying
electrical ground issues. All of those voltages are within the
nominal specifications for wall current in the US. However, you
presumably are seeing different voltages at different outlets in the
same room. This tells me that you probably have undersized
electrical wiring feeding those outlets. LIkely to be within code,
but only meeting the minimums.
I suggest that your best solution is to hire an electrician and
have them install a couple of isolated ground circuits for your
studio. Using wire that is a couple of gauge larger than the
minimum size. If your studio is large enough, then it may be
better to bring in a larger power feed to a subpanel in the
studio, and establish a technical ground there.
Less expensive solutions are to eliminate unbalanced
signal connections between your equipment, moving everything
to balanced connections. Then break the signal ground
as needed in these interconnections to reduces ground loop
noise. Restore all the electrical safety ground connections,
leaving them as the only path to ground from each piece of
equipment.
If you find one particular piece of gear is the source of
ground noise, then send it out and have it repaired, or
replace it with a better quality one.

--Dale

On 18 Dec 2005 19:50:50 -0800, wrote:

i am interested in getting an ac isolation transformer for a piece of
gear that has a ground loop in my studio. i see ones that are 110, 115
120v input voltage. my wall voltage is supposed to be 120v actually my
furman pl-plus meter shows about 125v. would i be okay using any of
these voltage inputs? or should i get one that is closest to my actual
wall voltage?

are the "medical grade" transformers ok for audio use?
Yes. Just use the highest, 120V, which would be no different than
plugging directly into the wall (voltage wise)

The other taps were to correct low line voltage (that you don't have
g).

thx for the relpies. how will a transformer with a 115 input voltage
differ from one with 120 input, (both having 120v output) in a
situation like mine--getting around 125v from the wall? i have a 115v
transformer available to me and i'd like to use it if possible for a
"quick fix" i realize that it would be better to find the underlying
problem but unfortunately i'm in a rental apt so no messing with the
ac. also almost all my lines are unbalanced and i've run out of audio
isolation transformers! my only other option is lifting ac ground and
i'm not about to do that..

wrote in message
oups.com...
thx for the relpies. how will a transformer with a 115 input voltage
differ from one with 120 input, (both having 120v output) in a
situation like mine--getting around 125v from the wall?

It will raise the voltage by a factor of 120/115, so you'll get about 130v
out.

It would be better to wire it backward. Feed 125v to the 120v side and take
the output from the 115v side, which will deliver about 120v.

By the way, transformers should never be used at more than a few percent
above their rated voltage. Feeding 120v into a 115v transformer winding is
OK, but I don't want people come away with the impression that any
overvoltage is OK. If the overvoltage is more than slight, you'll saturate
the core and have a fire.

Anything designed to be connected to the AC line can tolerate maybe 10%
overvoltage or more, because the AC line varies.

wrote:
thx for the relpies. how will a transformer with a 115 input voltage
differ from one with 120 input, (both having 120v output) in a
situation like mine--getting around 125v from the wall?

US consumer electric power is nominally 110V, though I've seen it range
as low as 90 (in an old building with inadequate wriring) and as high as
130. In general, devices are designed to tolerate about 10% variation;
that 90V line *did* upset some equipment.

So unless your power supply is inadequately designed, running a 115V box
on anything from 110V to 120V shouldn't be a problem.

Just _don't_ try to plug it directly into a 220/240V outlet. That lets
the magic smoke escape...

mc, so you're saying that I plug the ac wall power into the "output" of
the xformer and the audio device into the "input" of the xformer?
would doing it backwards like this have any adverse effects on the
power quality or safety of the unitt?

In article , wrote:
On 18 Dec 2005 19:50:50 -0800, wrote:

i am interested in getting an ac isolation transformer for a piece of
gear that has a ground loop in my studio.

You should first solve the ground loop problem by checking your equipment,
your wiring and/or adding balanced isolation transformers on *signal* feeds.

An isolation transformer can be beneficial but IMO will be the wrong
solution.

i see ones that are 110, 115 120v input voltage

Isolation transformers usually have the same I/O voltages. Are you sure
you're not considering other types of transformers ?

Isolation transformers should have the same voltages under full load. With no
load expect to see 10-20% higher output voltage.

greg

are the "medical grade" transformers ok for audio use?

Medical grade isolation transformers are built to high standards, with very
low leakage current. They are of course OK for audio use.

In .com, on 12/18/05

at 07:50 PM, said:

i am interested in getting an ac isolation transformer for a piece of
gear that has a ground loop in my studio. i see ones that are 110,
115 120v input voltage. my wall voltage is supposed to be 120v
actually my furman pl-plus meter shows about 125v. would i be okay
using any of these voltage inputs? or should i get one that is
closest to my actual wall voltage?

If you are simply working through a problem with a home studio, do what
you need to do. If an isolation transformer on the power and/or signal
lines solves *THIS* problem, go for it. I say "*THIS*" problem, because
the next time you add a piece of equipment, you'll be fighting another
issue, and another, and another.

As other posters have stated, you should hire an electrician who is
familiar with low noise grounding practices and fix the underlying
problem with your electrical system. Don't hire the inexpensive guy
down the block because he could easily make the problem worse. Warning:
Good grounding requires discipline. A single violation of the rules
will ruin the result.

If you are not using balanced audio distribution, you'll be fighting an
uphill battle.

Your voltages are more or less normal and may vary during the day or by
season. (Power companies may adjust the local voltage in response to
seasonal demands, such as lots of airconditioners.)

are the "medical grade" transformers ok for audio use?

They would be excellent, but expensive. "Medical" electronics must have
very low, controlled leakage. These are desirable for your application.

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"Joe Kesselman" wrote in message
...
wrote:
thx for the relpies. how will a transformer with a 115 input voltage
differ from one with 120 input, (both having 120v output) in a
situation like mine--getting around 125v from the wall?

US consumer electric power is nominally 110V, though I've seen it range as
low as 90 (in an old building with inadequate wriring) and as high as 130.
In general, devices are designed to tolerate about 10% variation; that 90V
line *did* upset some equipment.

Hasn't been nominally 110V for half a century. Design center was 117V in
the 1960s, 120-125V today, I think. Someone once posted a very long and
detailed history of this.

So unless your power supply is inadequately designed, running a 115V box
on anything from 110V to 120V shouldn't be a problem.

Agreed!

wrote in message
ups.com...
mc, so you're saying that I plug the ac wall power into the "output" of
the xformer and the audio device into the "input" of the xformer?
would doing it backwards like this have any adverse effects on the
power quality or safety of the unitt?

Assuming it's really a transformer (and not something more complicated),
transformers are reversible. For example, a 120-to-12-volt transformer is
also a 12-to-120-volt transformer, depending on which way you connect it.

If you're not comfortable doing this, get help locally from someone with
electronics experience.

i see ones that are 110, 115 120v input voltage

Isolation transformers usually have the same I/O voltages. Are you sure
you're not considering other types of transformers ?

Touché! It could be an autotransformer that does not isolate and wouldn't
do him a bit of good.