Hi all,

So - We've finally done the physical rearrangement of our home studio,
and I'm now hoping to to a really good job of wiring armed with the info
I got from my recent Internet research including lots of Q&A on this list...

So now, before I do anything, I'm trying to get an idea how each piece
of equipment is wired. I started with the Kork Triton Pro keyboard, and
that was easy. Outputs are unbalanced and I have electrical continuity
between the shield and the AC plug's 3rd pin.

Next, I took a look at the mixer, and I was surprised to realize that
the mixer's external rack-mount power supply uses a 2-pin power plug to
connect to the wall. Just to make sure I understand what's going on, I
check, and there's no continuity between either power plug pin and the
shield on a randomly chosen balanced input.

Questions:

1. Am I to assume that all shield connections to the mixer connect to
the chassis, but the chassis does not connect to anything else (except
the power supply chassis - I see there's a chassis ground pin on the
connector) since there's no safety ground connection?

2. Since the mixer does not connect to the safety ground, I presume that
all connections to the mixer should have shields connected to avoid
breaking THE RULE, and I would never want to lift a shield.

3. Since the mixer does not connect to the safety ground, do I still
want to make sure the mixer is on the same electrical circuit as the
rest of the gear, or should I assume the mixer has transformer-floating
power, and it doesn't matter where it's plugged in? (I'm going to make
sure use the same circuit anyway - I'm just curious)

4. What are my potential ground loop issues in a setup with a mixer with
a 2-prong power connection? I assume I could now have a potential
ground loop issue with any pair of 3-prong unbalanced (or imporoperly
designed balanced) devices that both have sheild connections to the
mixer, but I also presume that I don't want to have the shield lifted
between any device and this mixer. Is a transformer the only solution
if a ground loop issue arises in this setup?

Thanks,

- Steve J.

Sorry for typos "to to", :Kork", etc. I have to learn to use that spell
check button.

Steve Jorgensen wrote:
Hi all,

....

"Steve Jorgensen" wrote in message
...
Hi all,

So - We've finally done the physical rearrangement of our home studio, and
I'm now hoping to to a really good job of wiring armed with the info I got
from my recent Internet research including lots of Q&A on this list...

So now, before I do anything, I'm trying to get an idea how each piece of
equipment is wired. I started with the Kork Triton Pro keyboard, and that
was easy. Outputs are unbalanced and I have electrical continuity between
the shield and the AC plug's 3rd pin.

Next, I took a look at the mixer, and I was surprised to realize that the
mixer's external rack-mount power supply uses a 2-pin power plug to
connect to the wall. Just to make sure I understand what's going on, I
check, and there's no continuity between either power plug pin and the
shield on a randomly chosen balanced input.

Questions:

1. Am I to assume that all shield connections to the mixer connect to the
chassis, but the chassis does not connect to anything else (except the
power supply chassis - I see there's a chassis ground pin on the
connector) since there's no safety ground connection?

2. Since the mixer does not connect to the safety ground, I presume that
all connections to the mixer should have shields connected to avoid
breaking THE RULE, and I would never want to lift a shield.

3. Since the mixer does not connect to the safety ground, do I still want
to make sure the mixer is on the same electrical circuit as the rest of
the gear, or should I assume the mixer has transformer-floating power, and
it doesn't matter where it's plugged in? (I'm going to make sure use the
same circuit anyway - I'm just curious)

It may well be double-insulated (look for the little box-in-a-box symblo on
the back.

This is a Good Thing and will reduce the cahnce of a ground loop when
connected to grounded devoces like your Triron (though I'm suprise that it
ISN'T douoble-insulated).

4. What are my potential ground loop issues in a setup with a mixer with a
2-prong power connection?

Lower, until you connect more than 1 grounded device to it.

Just don't worry about a problem unitl you actually have one.

geoff

Geoff@work wrote:
"Steve Jorgensen" wrote in message
...

Hi all,

So - We've finally done the physical rearrangement of our home studio, and
I'm now hoping to to a really good job of wiring armed with the info I got
from my recent Internet research including lots of Q&A on this list...

So now, before I do anything, I'm trying to get an idea how each piece of
equipment is wired. I started with the Kork Triton Pro keyboard, and that
was easy. Outputs are unbalanced and I have electrical continuity between
the shield and the AC plug's 3rd pin.

Next, I took a look at the mixer, and I was surprised to realize that the
mixer's external rack-mount power supply uses a 2-pin power plug to
connect to the wall. Just to make sure I understand what's going on, I
check, and there's no continuity between either power plug pin and the
shield on a randomly chosen balanced input.

....

4. What are my potential ground loop issues in a setup with a mixer with a
2-prong power connection?


Lower, until you connect more than 1 grounded device to it.

Just don't worry about a problem unitl you actually have one.

The reason I am woryying about it is that I've had problems in pretty
much every previous significant wiring attempt. I want to make sure I
know what I should be trying to do and not do in this attempt to make
the problems less likely.

On Sun, 29 Jan 2006 16:53:29 -0800, Steve Jorgensen
wrote:


I was surprised to realize that
the mixer's external rack-mount power supply uses a 2-pin power plug to
connect to the wall. Just to make sure I understand what's going on, I
check, and there's no continuity between either power plug pin and the
shield on a randomly chosen balanced input.

Questions:

1. Am I to assume that all shield connections to the mixer connect to
the chassis, but the chassis does not connect to anything else (except
the power supply chassis - I see there's a chassis ground pin on the
connector) since there's no safety ground connection?

I don't know what to assume, but I'd probably run a safety ground to
the mixer in this case.

2. Since the mixer does not connect to the safety ground, I presume that
all connections to the mixer should have shields connected to avoid
breaking THE RULE, and I would never want to lift a shield.

No, what RULE is it you are trying not to break? The one main rule I
try not to break is never offer 2 paths to ground and to lift shields
as necessary so this doesn't happen.

I would ground the mixer chassis to AC ground and break audio shields
according to some standard configuration. 2 Ways that work are to
break ALL balanced line shields at a patch bay or to float all mixer
output shields but connect all mixer input shields.

3. Since the mixer does not connect to the safety ground,do I still
want to make sure the mixer is on the same electrical circuit as the
rest of the gear, or should I assume the mixer has transformer-floating
power, and it doesn't matter where it's plugged in? (I'm going to make
sure use the same circuit anyway - I'm just curious)

Connect the mixer chassis to ground and stop this train of thought!

4. What are my potential ground loop issues in a setup with a mixer with
a 2-prong power connection? I assume I could now have a potential
ground loop issue with any pair of 3-prong unbalanced (or imporoperly
designed balanced) devices that both have sheild connections to the
mixer, but I also presume that I don't want to have the shield lifted
between any device and this mixer. Is a transformer the only solution
if a ground loop issue arises in this setup?

Using balanced and unbalanced together is always a little dicey. Many
times equipment manuals for balanced equipment will recommend how to
handle it. The danger of plugging an unbalanced 1/4" into a balanced
1/4" for example is that you are shorting out the minus on the
balanced gear. For some gear that is OK, for others not. One way
that often works well is to connect the unbalanced equipment to ground
and hot on the balanced gear, floating the minus.

Julian

Julian wrote:
On Sun, 29 Jan 2006 16:53:29 -0800, Steve Jorgensen
wrote:



I was surprised to realize that
the mixer's external rack-mount power supply uses a 2-pin power plug to
connect to the wall. Just to make sure I understand what's going on, I
check, and there's no continuity between either power plug pin and the
shield on a randomly chosen balanced input.

Questions:

1. Am I to assume that all shield connections to the mixer connect to
the chassis, but the chassis does not connect to anything else (except
the power supply chassis - I see there's a chassis ground pin on the
connector) since there's no safety ground connection?


I don't know what to assume, but I'd probably run a safety ground to
the mixer in this case.

Well, I don't know what to assume, but I would go so far as to assume
that if Tascam designesd the mixer with a 2-prong plug, it's supposed to
work correctly and safely with just the 2-prong plug, and no safety ground.

2. Since the mixer does not connect to the safety ground, I presume that
all connections to the mixer should have shields connected to avoid
breaking THE RULE, and I would never want to lift a shield.


No, what RULE is it you are trying not to break? The one main rule I
try not to break is never offer 2 paths to ground and to lift shields
as necessary so this doesn't happen.

I would ground the mixer chassis to AC ground and break audio shields
according to some standard configuration. 2 Ways that work are to
break ALL balanced line shields at a patch bay or to float all mixer
output shields but connect all mixer input shields.

I guess I didn't fully explain my connundrum.

Treating each device separately, the way to have exactly one common
ground path between the device and mixer would be to have the shield
connected at both ends. With both devices connected, however, this is a
ground loop (not necessarily a problem, but definitely a loop). I could
lif the shield from one or the other, but that would leave one device
relying on the other one to make common ground path to the mixer by way
of the devices' shared safety ground. That doesn't seem like a good idea.

3. Since the mixer does not connect to the safety ground,do I still
want to make sure the mixer is on the same electrical circuit as the
rest of the gear, or should I assume the mixer has transformer-floating
power, and it doesn't matter where it's plugged in? (I'm going to make
sure use the same circuit anyway - I'm just curious)


Connect the mixer chassis to ground and stop this train of thought!

Again - the manufacturer didn't think it should be connected to a safety
ground, so I don't feel comfortable that it's best to connect one. At
least, I won't feel that way without getting multiple concurring
opinions first.

4. What are my potential ground loop issues in a setup with a mixer with
a 2-prong power connection? I assume I could now have a potential
ground loop issue with any pair of 3-prong unbalanced (or improperly
designed balanced) devices that both have sheild connections to the
mixer, but I also presume that I don't want to have the shield lifted
between any device and this mixer. Is a transformer the only solution
if a ground loop issue arises in this setup?


Using balanced and unbalanced together is always a little dicey. Many
times equipment manuals for balanced equipment will recommend how to
handle it. The danger of plugging an unbalanced 1/4" into a balanced
1/4" for example is that you are shorting out the minus on the
balanced gear. For some gear that is OK, for others not. One way
that often works well is to connect the unbalanced equipment to ground
and hot on the balanced gear, floating the minus.

I won't have trouble with how to make the balanced/unbalanced
connections becasue, in each case, the conenction is from an unbalanced
output to a mixer or A/D input designed to handle either balanced or
unbalanced input using TRS or TS rfespectively.

This really gets back to the 2nd part of this reply - when 2 devices,
each with chassis connected to safety ground have to be connected to a
mixer that isn't connected to safety ground, do I have any decent
options if there is a ground loop problem. If so, what might that be.
I know that sounds awfully hypothetical, except that I think I've had
just that problem in several previous wiring schemes.

Steve Jorgensen wrote:
Julian wrote:
....


Connect the mixer chassis to ground and stop this train of thought!


Again - the manufacturer didn't think it should be connected to a safety
ground, so I don't feel comfortable that it's best to connect one. At
least, I won't feel that way without getting multiple concurring
opinions first.


After arguing with you on this point (as if I know anything), I found
this article ...
http://www.epanorama.net/documents/g...udioracks.html
.... that backs up your statement and also clarifies what I didn't get.

I think I've got it now that, of course the mixer chassis should be
connected to the safety ground - it should be connected via it power
supply in the rack, then via the rack's connection (directly or
indirectly) to safety ground, which should be according to the star
grounding plan for the studio.

Am I finally on the right path?

On Mon, 30 Jan 2006 18:56:46 -0800, Steve Jorgensen
wrote:


After arguing with you on this point (as if I know anything), I found
this article ...
http://www.epanorama.net/documents/g...udioracks.html
... that backs up your statement and also clarifies what I didn't get.

I think I've got it now that, of course the mixer chassis should be
connected to the safety ground - it should be connected via it power
supply in the rack, then via the rack's connection (directly or
indirectly) to safety ground, which should be according to the star
grounding plan for the studio.

Am I finally on the right path?

There are several ways to avoid ground loops. This article explains
one of the 3 most popular methods, star grounding. In any system,
since the mixer probably has the most number of things referenced to
it is probably the single most important thing to chassis ground. I
don't think it actually matters to ground the power supply. If your
AC is clean the neutral on the 2 prong plug is referenced to ground
already. If your AC is dirty you'll have trouble no matter what you
do. For example if you put a voltmeter between ground and neutral and
there is any difference in voltage, you've got a problem that audio
wiring won't fix.

Julian

Julian wrote:
....

There are several ways to avoid ground loops. This article explains
one of the 3 most popular methods, star grounding. In any system,
since the mixer probably has the most number of things referenced to
it is probably the single most important thing to chassis ground. I
don't think it actually matters to ground the power supply. If your
AC is clean the neutral on the 2 prong plug is referenced to ground
already. If your AC is dirty you'll have trouble no matter what you
do. For example if you put a voltmeter between ground and neutral and
there is any difference in voltage, you've got a problem that audio
wiring won't fix.

Julian


Then there's something I still don't get.

If I leave the mixer unplugged from the wall, and with the power switch
in either the on or off positions, check for continuity between either
pin of the power plug and the chassis, I get nothing. If I check for
continuity with the sleive connection of an audio connector, likewise, I
see no continuity. How can the chassis be grounded by way of the
neutral power connector if there's no connection between neutral and the
chassis?

On the other hand, I do see how the chassis of the mixer (which is
electrically connected to the chassis of the power supply via one of the
wires in the power connector) could be tied to another rack via a ground
wire. Unfortunately, I now see that even if I got that right, the way
to do it can't be through the rack rails. Although I get continuity
between a screw on the back of the power supply and the sleive
connection on an audio connector, I don't get continuity to a rack rail.
The power supply doesn't even create electrical continuity from one
rail to the other, much less from a rail to anything else.

- Steve J.

On Mon, 30 Jan 2006 18:56:46 -0800, Steve Jorgensen
wrote:

After arguing with you on this point (as if I know anything), I found
this article ...
http://www.epanorama.net/documents/g...udioracks.html
... that backs up your statement and also clarifies what I didn't get.

I think I've got it now that, of course the mixer chassis should be
connected to the safety ground - it should be connected via it power
supply in the rack, then via the rack's connection (directly or
indirectly) to safety ground, which should be according to the star
grounding plan for the studio.

Am I finally on the right path?

Steve,

Thinking more about this, you must realize that it is possible to
design a completely balanced system that uses no audio shields at all.
It is called the phone system! It was set up with 600 ohm twisted
copper, no shields anywhere. I saw a radio studio that was set up the
same. None of the wiring had a single shield anywhere, but very
strict attention was paid to AC grounding and they made damn sure AC
ground was EXACTLY the same in every room of the facility and in no
place did the ground carry any current.

the engineer that built that facility went out to an old building a
client of mine was buying and we measured at some places the ground
was carrying almost 40% of the neutral current due to bad grounding
design and poor quality add ons over the years. I decided to
completely abandon the existing AC power in the building and install
all new isolated ground AC for the whole broadcast operation. Before
the AC was finished I did some testing and some computer equipment
that ran between 2 rooms wouldn't even work! The new AC got installed
and everything was groovy. We tested S/N between rooms that gave me
+30 dB headroom over FM radio specs!

Ground loops are mostly an issue when you connect rooms together
across a facility. At another radio station I visited all the shields
were connected in all the rooms, but all wires that went between rooms
came into a closet first where they were punched down and cross
connected from this central location. In this room, no shields were
connected anywhere. Although everything in every room except the
closet was fully safety grounded and all audio shields were connected,
no wires that went between rooms had any shields carried though.

This is very much like the recording studio I mentioned earlier where
all audio shields were connected everywhere, but all signals passed
through a patch bay between pieces of equipment. At the patch bay no
shields were connected anywhere.

Personally I've found I like to use the idea of connecting all audio
shields to equipment inputs, but floating all audio shields on
equipment outputs. I use 2c shielded cable. I just cut the shield
off at the output connectors, shrink wrap over it and don't solder it
onto the XLR or TRS or whatever. Then I carefully chassis ground
everything and all equipment racks too.

Star grounding has a great reputation also.

But all of this is unnecessary if the AC is perfectly clean, all
return current is carried by the neutral (not ground), and ground is
the exact same voltage at every location. If that is so, you don't
need any audio shields at all. Ground loops are not an issue because
a ground loop can only occur if ground is different at 2 pieces of
equipment. If ground is exactly the same everywhere, it doesn't
matter if you have 1, 2, 3 or 4 paths to ground.

Julian

On Tue, 31 Jan 2006 07:21:34 -0800, Steve Jorgensen
wrote:

Then there's something I still don't get.

If I leave the mixer unplugged from the wall, and with the power switch
in either the on or off positions, check for continuity between either
pin of the power plug and the chassis, I get nothing. If I check for
continuity with the sleive connection of an audio connector, likewise, I
see no continuity. How can the chassis be grounded by way of the
neutral power connector if there's no connection between neutral and the
chassis?

The chassis isn't grounded.


On the other hand, I do see how the chassis of the mixer (which is
electrically connected to the chassis of the power supply via one of the
wires in the power connector) could be tied to another rack via a ground
wire. Unfortunately, I now see that even if I got that right, the way
to do it can't be through the rack rails. Although I get continuity
between a screw on the back of the power supply and the sleive
connection on an audio connector, I don't get continuity to a rack rail.
The power supply doesn't even create electrical continuity from one
rail to the other, much less from a rail to anything else.

I'd run a wire from the AC ground directly to a screw on the mixer
that is connected to the chassis.

Julian

Steve Jorgensen wrote:
If I leave the mixer unplugged from the wall, and with the power switch
in either the on or off positions, check for continuity between either
pin of the power plug and the chassis, I get nothing. If I check for
continuity with the sleive connection of an audio connector, likewise, I
see no continuity. How can the chassis be grounded by way of the
neutral power connector if there's no connection between neutral and the
chassis?

It isn't. The neutral side of the AC supply may be referenced to ground,
i.e. at close to ground potential, but you must not rely on it or ever
try to use it as a ground connection. And for the same reason the mixer
ground (safety, signal or whatever) will never be connected to either
pin you your two-prong power plug.

Although I get continuity
between a screw on the back of the power supply and the sleive
connection on an audio connector, I don't get continuity to a rack rail.

If I read this right, you should be able to install, semi-permanently, a
wire from the screw on the back of your power supply to some point that
is connected to the ground of your AC supply - maybe another piece of
equipment that has a metal chassis with convenient grounding screw, and
which is always plugged in. Then your mixer signal ground is tied to a
real ground. Where your unbalanced signals come into balanced inputs on
the mixer, connect cable inner to +(hot) and cable ground (shield) to
-(cold), and don't connect anything the the mixer input ground.

I've run a CAT5 UTP cable (yes, UNshielded!) from a consumer
tuner/amplifier RCA output connector pair, one twisted pair for right
and one for left, all round the house and then to two balanced inputs of
a mixer and it's perfectly clean.

BTW, anywhere you have balaced-balanced connections, you might as well
connect ground at both ends. There may be a loop but with balanced
interconnects it doesn't matter.

--
Anahata
-+- http://www.treewind.co.uk
Home: 01638 720444 Mob: 07976 263827

"Steve Jorgensen" wrote in message
...


Then there's something I still don't get.

If I leave the mixer unplugged from the wall, and with the power switch in
either the on or off positions, check for continuity between either pin of
the power plug and the chassis, I get nothing. If I check for continuity
with the sleive connection of an audio connector, likewise, I see no
continuity. How can the chassis be grounded by way of the neutral power
connector if there's no connection between neutral and the chassis?

Chassis grounds are NEVER supplied from teh neutral. Netral *may* be bonded
to ground at the switchboard, but that's a different story.

On the other hand, I do see how the chassis of the mixer (which is
electrically connected to the chassis of the power supply via one of the
wires in the power connector) could be tied to another rack via a ground
wire.

It shouldn't necessarily. It may well be double-insulated, wwhich is great.
It removes one potential extra path for aground loop. Enjoy the lack of
complication !

geoff

On Wed, 1 Feb 2006 15:24:59 +1300, "Geoff@work"
wrote:

Chassis grounds are NEVER supplied from the neutral. Neutral *may* be bonded
to ground at the switchboard, but that's a different story.

Indeed, and a separately interesting one.

Also, let me add a big yeah! to everything that Julian
has posted in this thread. Great stuff, well put.

Good fortune,

Chris Hornbeck

Steve Jorgensen wrote:
Hi all,

So - We've finally done the physical rearrangement of our home studio,
and I'm now hoping to to a really good job of wiring armed with the info
I got from my recent Internet research including lots of Q&A on this
list...

So now, before I do anything, I'm trying to get an idea how each piece
of equipment is wired. I started with the Kork Triton Pro keyboard, and
that was easy. Outputs are unbalanced and I have electrical continuity
between the shield and the AC plug's 3rd pin.

Next, I took a look at the mixer, and I was surprised to realize that
the mixer's external rack-mount power supply uses a 2-pin power plug to
connect to the wall. Just to make sure I understand what's going on, I
check, and there's no continuity between either power plug pin and the
shield on a randomly chosen balanced input.

Questions:

1. Am I to assume that all shield connections to the mixer connect to
the chassis, but the chassis does not connect to anything else (except
the power supply chassis - I see there's a chassis ground pin on the
connector) since there's no safety ground connection?

2. Since the mixer does not connect to the safety ground, I presume that
all connections to the mixer should have shields connected to avoid
breaking THE RULE, and I would never want to lift a shield.

3. Since the mixer does not connect to the safety ground, do I still
want to make sure the mixer is on the same electrical circuit as the
rest of the gear, or should I assume the mixer has transformer-floating
power, and it doesn't matter where it's plugged in? (I'm going to make
sure use the same circuit anyway - I'm just curious)

4. What are my potential ground loop issues in a setup with a mixer with
a 2-prong power connection? I assume I could now have a potential
ground loop issue with any pair of 3-prong unbalanced (or imporoperly
designed balanced) devices that both have sheild connections to the
mixer, but I also presume that I don't want to have the shield lifted
between any device and this mixer. Is a transformer the only solution
if a ground loop issue arises in this setup?

Thanks,

- Steve J.

Thanks so much to all who have responded. I think I finally understand
what I need to have a chance of wiring up my studio to be noise-free
this time around.

My biggest headaches are going to be the many balanced/unbalanced
connections and the involvement of MIDI, USB, and Firewire lines, but if
I understand right, I can reduce the potential problems with my
unavoidable looped paths by following one single star grounding pattern
encompassing -all- categories of wiring and having shields lifted on
balanced/unbalanced paths that would otherwise make loops, then finally
lift shields on some balanced/balanced paths if and when that proves
necessary.

Do I finally seem to grok it?

On Tue, 31 Jan 2006 19:30:38 -0800, Steve Jorgensen
wrote:

Thanks so much to all who have responded. I think I finally understand
what I need to have a chance of wiring up my studio to be noise-free
this time around.

My biggest headaches are going to be the many balanced/unbalanced
connections and the involvement of MIDI, USB, and Firewire lines, but if
I understand right, I can reduce the potential problems with my
unavoidable looped paths by following one single star grounding pattern
encompassing -all- categories of wiring and having shields lifted on
balanced/unbalanced paths that would otherwise make loops, then finally
lift shields on some balanced/balanced paths if and when that proves
necessary.

Do I finally seem to grok it?

You are getting real close! Connecting your chassis grounds is the
first big step. A star ground system and making sure the AC ground is
exactly the same if you use more than one AC circuit should work. The
balanced / unbalanced question is still a possible snafu. I'd look at
the manual for any balanced equipment that you want to connect with
unbalanced equipment. Different manufactures have different
recommendations how to wire this.

Julian