Firstly, sorry for the cross-post - trying to better my odds here :-)

I have a Piano lab that consists of a dozen Yamaha Clavinovas, a dozen
computers (9 I-Macs and 3 E-Macs) and a Teacher's Console that is connected
via MIDI cables to each station. Each station consists of the one keyboard
(note: I mean keyboard musical instrument throughout) and computer, and a
set of headphones whose only connection to the Console is a MIDI cable (the
students can then hear their own keyboard, hear the teacher's keyboard, and
can communicate (the headphones have a headset mic) with each other. The
teacher has the control to listen to any individual, groups, or entire class
from the console.

Everything works fine, but when everything's plugged in, there's an annoying
hum in the system (60-cycle hum I assume, since the pitch is roughly between
Bb and B - sorry, I'm more of a musician than electrician). I did some
trouble shooting and noticed the following:

If the computers are not plugged in, then there's no hum.

I can plug in the three E-Macs and there's no hum - as soon as the first
I-Mac goes in, it begins (though faintly) and as each successive one is
plugged in it gets worse.

Now, everything is plugged into outlet strips that are plugged into outlet
strips (I know, not the best idea). There are only 4 available outlets in
the room, and the entire system (25 plugs) are divided among two of those
outlets (the others or in places where students would be tripping over
them). I'm guessing there's only one circuit for the entire room.

I did try plugging all of the computers into one outlet line, and the
keyboards in another, but every combination yielded the same results.

So here's some other things I tried, and other info that I felt might be
worth considering:

The Yamahas have only 2-prong plugs.
It seems to me that the interaction of the MIDI system and the Computers is
at issue (???). Besides the computers running off the same outlets as the
keyboards, each computer is directly connected to the keyboard with a USB
MIDI adapter (MIDISport UNO). Which seems to interact thusly:

If I unplug the USB port (connecting the MIDI to the keyboard), the hum is
gone.
If I unplug the Computer or the Keyboard the hum is gone.
If I unplug the MIDI cable from the Console, the hum is gone.

So it may in fact be the interaction of all three. Obviously though, we have
to use them all though..

Some stations hum more than others, and no matter which cables, outlets,
computers, etc. I tried, the same stations always hummed the same way - and
I noticed a correlation between the model of Clavinova and the hum.

I haven't been able to do things like see what happens if the teacher's
console is off, or if the offending stations are off or on. I do hear some
other noises in the system (like hard drives whirring, but I can live with
that).

One more thing, when I flip on the lights (fluorescent) in the room, they
hum pretty loud - more so than what I'd expect.

If anyone can offer any suggestions or potential fixes I'd be most
appreciative.

TIA,
Steve

You probably have ground loops. Ideally, "everything" should be connected to
the same outlet! This is electrically possible, but rather clunky from a
practical point of view.

You should start by reversing the power plugs on the keyboards, one at a
time, to see if you can get the hum to drop.

"William Sommerwerck" wrote in message
...
You probably have ground loops. Ideally, "everything" should be connected
to
the same outlet! This is electrically possible, but rather clunky from a
practical point of view.

I had thought about that, because I've been in situations with PAs where if
everything's not plugged together, you get noise (and potentially shocked,
but from a different cause).


You should start by reversing the power plugs on the keyboards, one at a
time, to see if you can get the hum to drop.



What do you mean - reversing the blades (they're all polarity plugs, but I
think they might go both ways)?

Steve

Disconnect everything from the AC mains except for the main part of the
system. Add one thing back at time, to see where the cause is. It is
possible that there is a defective power supply, or a ground loop, or a
problem of how the power is distributed. If it is a distribution problem, a
knowledgeable electrician will be required.

--

JANA
_____


"Steve Latham" wrote in message
news:huLHe.33077$S%5.26075@trnddc06...
Firstly, sorry for the cross-post - trying to better my odds here :-)

I have a Piano lab that consists of a dozen Yamaha Clavinovas, a dozen
computers (9 I-Macs and 3 E-Macs) and a Teacher's Console that is connected
via MIDI cables to each station. Each station consists of the one keyboard
(note: I mean keyboard musical instrument throughout) and computer, and a
set of headphones whose only connection to the Console is a MIDI cable (the
students can then hear their own keyboard, hear the teacher's keyboard, and
can communicate (the headphones have a headset mic) with each other. The
teacher has the control to listen to any individual, groups, or entire class
from the console.

Everything works fine, but when everything's plugged in, there's an annoying
hum in the system (60-cycle hum I assume, since the pitch is roughly between
Bb and B - sorry, I'm more of a musician than electrician). I did some
trouble shooting and noticed the following:

If the computers are not plugged in, then there's no hum.

I can plug in the three E-Macs and there's no hum - as soon as the first
I-Mac goes in, it begins (though faintly) and as each successive one is
plugged in it gets worse.

Now, everything is plugged into outlet strips that are plugged into outlet
strips (I know, not the best idea). There are only 4 available outlets in
the room, and the entire system (25 plugs) are divided among two of those
outlets (the others or in places where students would be tripping over
them). I'm guessing there's only one circuit for the entire room.

I did try plugging all of the computers into one outlet line, and the
keyboards in another, but every combination yielded the same results.

So here's some other things I tried, and other info that I felt might be
worth considering:

The Yamahas have only 2-prong plugs.
It seems to me that the interaction of the MIDI system and the Computers is
at issue (???). Besides the computers running off the same outlets as the
keyboards, each computer is directly connected to the keyboard with a USB
MIDI adapter (MIDISport UNO). Which seems to interact thusly:

If I unplug the USB port (connecting the MIDI to the keyboard), the hum is
gone.
If I unplug the Computer or the Keyboard the hum is gone.
If I unplug the MIDI cable from the Console, the hum is gone.

So it may in fact be the interaction of all three. Obviously though, we have
to use them all though..

Some stations hum more than others, and no matter which cables, outlets,
computers, etc. I tried, the same stations always hummed the same way - and
I noticed a correlation between the model of Clavinova and the hum.

I haven't been able to do things like see what happens if the teacher's
console is off, or if the offending stations are off or on. I do hear some
other noises in the system (like hard drives whirring, but I can live with
that).

One more thing, when I flip on the lights (fluorescent) in the room, they
hum pretty loud - more so than what I'd expect.

If anyone can offer any suggestions or potential fixes I'd be most
appreciative.

TIA,
Steve

What do you mean -- reversing the blades (they're all polarity plugs,
but I think they might go both ways)?

Yes.

In rec.audio.pro,rec.audio.tech, On Tue, 02 Aug 2005 14:32:45 GMT,
"Steve Latham" wrote:

Firstly, sorry for the cross-post - trying to better my odds here :-)

At least it's not as far and wide as we've seen, but anyway...

I have a Piano lab that consists of a dozen Yamaha Clavinovas, a dozen
computers (9 I-Macs and 3 E-Macs) and a Teacher's Console that is connected
via MIDI cables to each station. Each station consists of the one keyboard

...

If I unplug the MIDI cable from the Console, the hum is gone.

This is the standard 5-pin DIN connector that MIDI has always used?
A MIDI cable should never make a difference in hum. Whether you have
a MIDI cable plugged in should definitely not affect anything. MIDI
cables have three connections, the + and - current loop, and ground.
IIRC, ground is only connected at the connector at the transmitting
("MIDI out") end, and the receiving end is both opto-isolated and
intentionally missing the ground connection at the connector.
Apparently a "MIDI in" connector has a ground connection where it
shouldn't. For someone handy with a soldering iron, it should be easy
enough to make a short "ground lift" male-to-female MIDI cable that
has only the two signal pins connected. Perhaps Hosa makes such a
"MIDI ground lift" thing that you can buy at Guitar Center.
The old standard MIDI connection is the one thing that should
always be isolated, and never cause a ground loop.
Also, don't confuse this with a power cord "ground lift" adapter.
You don't want to use one of those, regardless of whether it "solves"
your hum problem. MIDI ground lift good, power ground lift bad.

So it may in fact be the interaction of all three. Obviously though, we have
to use them all though..

Some stations hum more than others, and no matter which cables, outlets,
computers, etc. I tried, the same stations always hummed the same way - and
I noticed a correlation between the model of Clavinova and the hum.

I haven't been able to do things like see what happens if the teacher's
console is off, or if the offending stations are off or on. I do hear some
other noises in the system (like hard drives whirring, but I can live with
that).

One more thing, when I flip on the lights (fluorescent) in the room, they
hum pretty loud - more so than what I'd expect.

Do you mean the acoustic sound directly from the lights, or that
you hear extra hum coming through your headphones?

If anyone can offer any suggestions or potential fixes I'd be most
appreciative.

TIA,
Steve








-----
http://www.mindspring.com/~benbradley

Ben Bradley wrote:
This is the standard 5-pin DIN connector that MIDI has always used?
A MIDI cable should never make a difference in hum. Whether you have
a MIDI cable plugged in should definitely not affect anything. MIDI
cables have three connections, the + and - current loop, and ground.
IIRC, ground is only connected at the connector at the transmitting
("MIDI out") end, and the receiving end is both opto-isolated and
intentionally missing the ground connection at the connector.
Apparently a "MIDI in" connector has a ground connection where it
shouldn't. For someone handy with a soldering iron, it should be easy
enough to make a short "ground lift" male-to-female MIDI cable that
has only the two signal pins connected. Perhaps Hosa makes such a
"MIDI ground lift" thing that you can buy at Guitar Center.

Many MIDI devices out there violate the spec horribly and allow ground
loops to be created. There are a number of optoisolator boxes out there
that exist to fix the problem; I know Markertek sells one.
--scott


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

"JANA" wrote in message
...
Disconnect everything from the AC mains except for the main part of the
system. Add one thing back at time, to see where the cause is. It is
possible that there is a defective power supply, or a ground loop, or a
problem of how the power is distributed. If it is a distribution problem,
a
knowledgeable electrician will be required.

Yeah, I tried that. I tried swapping all of the power supplies. It may be
time to call in an elexctrician.

Thanks.


--

JANA
_____


"Steve Latham" wrote in message
news:huLHe.33077$S%5.26075@trnddc06...
Firstly, sorry for the cross-post - trying to better my odds here :-)

I have a Piano lab that consists of a dozen Yamaha Clavinovas, a dozen
computers (9 I-Macs and 3 E-Macs) and a Teacher's Console that is
connected
via MIDI cables to each station. Each station consists of the one
keyboard
(note: I mean keyboard musical instrument throughout) and computer, and a
set of headphones whose only connection to the Console is a MIDI cable
(the
students can then hear their own keyboard, hear the teacher's keyboard,
and
can communicate (the headphones have a headset mic) with each other. The
teacher has the control to listen to any individual, groups, or entire
class
from the console.

Everything works fine, but when everything's plugged in, there's an
annoying
hum in the system (60-cycle hum I assume, since the pitch is roughly
between
Bb and B - sorry, I'm more of a musician than electrician). I did some
trouble shooting and noticed the following:

If the computers are not plugged in, then there's no hum.

I can plug in the three E-Macs and there's no hum - as soon as the first
I-Mac goes in, it begins (though faintly) and as each successive one is
plugged in it gets worse.

Now, everything is plugged into outlet strips that are plugged into outlet
strips (I know, not the best idea). There are only 4 available outlets in
the room, and the entire system (25 plugs) are divided among two of those
outlets (the others or in places where students would be tripping over
them). I'm guessing there's only one circuit for the entire room.

I did try plugging all of the computers into one outlet line, and the
keyboards in another, but every combination yielded the same results.

So here's some other things I tried, and other info that I felt might be
worth considering:

The Yamahas have only 2-prong plugs.
It seems to me that the interaction of the MIDI system and the Computers
is
at issue (???). Besides the computers running off the same outlets as the
keyboards, each computer is directly connected to the keyboard with a USB
MIDI adapter (MIDISport UNO). Which seems to interact thusly:

If I unplug the USB port (connecting the MIDI to the keyboard), the hum is
gone.
If I unplug the Computer or the Keyboard the hum is gone.
If I unplug the MIDI cable from the Console, the hum is gone.

So it may in fact be the interaction of all three. Obviously though, we
have
to use them all though..

Some stations hum more than others, and no matter which cables, outlets,
computers, etc. I tried, the same stations always hummed the same way -
and
I noticed a correlation between the model of Clavinova and the hum.

I haven't been able to do things like see what happens if the teacher's
console is off, or if the offending stations are off or on. I do hear some
other noises in the system (like hard drives whirring, but I can live with
that).

One more thing, when I flip on the lights (fluorescent) in the room, they
hum pretty loud - more so than what I'd expect.

If anyone can offer any suggestions or potential fixes I'd be most
appreciative.

TIA,
Steve

"Ben Bradley" wrote in message
...
In rec.audio.pro,rec.audio.tech, On Tue, 02 Aug 2005 14:32:45 GMT,
"Steve Latham" wrote:

Firstly, sorry for the cross-post - trying to better my odds here :-)

At least it's not as far and wide as we've seen, but anyway...

I have a Piano lab that consists of a dozen Yamaha Clavinovas, a dozen
computers (9 I-Macs and 3 E-Macs) and a Teacher's Console that is
connected
via MIDI cables to each station. Each station consists of the one
keyboard

...

If I unplug the MIDI cable from the Console, the hum is gone.

This is the standard 5-pin DIN connector that MIDI has always used?

Yes.

A MIDI cable should never make a difference in hum. Whether you have
a MIDI cable plugged in should definitely not affect anything. MIDI
cables have three connections, the + and - current loop, and ground.
IIRC, ground is only connected at the connector at the transmitting
("MIDI out") end, and the receiving end is both opto-isolated and
intentionally missing the ground connection at the connector.

These stasions use a Headseat consisting of phones and mic that plug into a
box that plugs into the keyboard phone jack on one side, and the MIDI cable
on the other. My assumption (as it's the only possibility) is that the MIDI
cable is actually carrying Audio somehow (across one of the pins could work,
couldn't it?). I mean, it must be, as there's no other audio connection
between the teacher's head set, and the student's. I'm beginning to wonder
now if any MIDI is carried at all by those cables. I couldn't experiment
with this because I couldn't be in two places at once, but I know when a
student plays, the teacher is hearing the audio through her phones (which
are plugged into the console whose only other attachment to any of the
stations is via a standard MIDI cable. I'm wondering now if ONLY audio is
being carried an no MIDI data at all. I'd have to try to trigger one
keyboard with another, but it's now sounding like that could be a big cause
if those cables are not grounded at one end.

Apparently a "MIDI in" connector has a ground connection where it
shouldn't. For someone handy with a soldering iron, it should be easy
enough to make a short "ground lift" male-to-female MIDI cable that
has only the two signal pins connected. Perhaps Hosa makes such a
"MIDI ground lift" thing that you can buy at Guitar Center.
The old standard MIDI connection is the one thing that should
always be isolated, and never cause a ground loop.

Unless they've done what I think they might be doing - carrying audio.

Also, don't confuse this with a power cord "ground lift" adapter.
You don't want to use one of those, regardless of whether it "solves"
your hum problem. MIDI ground lift good, power ground lift bad.

I don't like, or believe in those things, however, I keep running into
people solving (or at least as far as one aspect is concerned) noise
problems with them. My bass player had one and I said, are you crazy. Sounds
like electrocution just waiting to happen.

[snip]

One more thing, when I flip on the lights (fluorescent) in the room, they
hum pretty loud - more so than what I'd expect.

Do you mean the acoustic sound directly from the lights, or that
you hear extra hum coming through your headphones?

Acoustic.

Steve

If you unplug the USB cable or unplug the MIDI cable the hum is gone?


Try routeing those cables together so as to minimize the area of the
loop created by them.

In general try to minimize the area of "loops" created by wiring things
together and keep those loops away from electro magnetic motors or
transformers.



Mark

"Scott Dorsey" wrote in message
...
Ben Bradley wrote:
This is the standard 5-pin DIN connector that MIDI has always used?
A MIDI cable should never make a difference in hum. Whether you have
a MIDI cable plugged in should definitely not affect anything. MIDI
cables have three connections, the + and - current loop, and ground.
IIRC, ground is only connected at the connector at the transmitting
("MIDI out") end, and the receiving end is both opto-isolated and
intentionally missing the ground connection at the connector.
Apparently a "MIDI in" connector has a ground connection where it
shouldn't. For someone handy with a soldering iron, it should be easy
enough to make a short "ground lift" male-to-female MIDI cable that
has only the two signal pins connected. Perhaps Hosa makes such a
"MIDI ground lift" thing that you can buy at Guitar Center.

Many MIDI devices out there violate the spec horribly and allow ground
loops to be created. There are a number of optoisolator boxes out there
that exist to fix the problem; I know Markertek sells one.

Scott, could you explain (in semi-layman's terms) a little more about this?
I just replied to Ben and I think one issue might be that those MIDI cables
are also (and may exclusively be) carrying audio - they are the only
connection between the teacher's headset phones/mic and the student's. It's
got to be carrying audio.

Is it likely that an isolator would fix this, or is there something like a
"grounded" MIDI cable - it seems to me it would be the same problem if I
were using unbalanced cables - maybe they should be like a Balanced MIDI
cable (like XLR) - course that depends on the devices I know. I'm sure the
keyboard's audio and headphone outs are unbalanced, and that's what goes to
this little connector box. I'm now thinking that an unbalanced audio out
(stereo 1/4") comes out of the keyboard into this box, to which the
headphones are connected (two cables, one for the mic, unbalanced miniplug,
and unbalanced stereo 1/4", and then these signals are combined and sen via
the MIDI cable to the teacher's workstation. I would doubt that this little
box is converting from unbalanced to balanced for the trip (some 30 feet or
more) and back to unbalanced for the console (which I'm assuming is standard
unbalanced signals like typical 1/4" stuff).

So that may mean that only two of the pins are actually being used in the
MIDI cable - 1 hot 1 ground? Does this seem reasonable?

Steve

"Mark" wrote in message
oups.com...

If you unplug the USB cable or unplug the MIDI cable the hum is gone?

Yes.



Try routeing those cables together so as to minimize the area of the
loop created by them.

In general try to minimize the area of "loops" created by wiring things
together and keep those loops away from electro magnetic motors or
transformers.

Easier said than done :-) I did experiment with moving various things in the
room, running the MIDI cables opposite side of the power supplies, etc. But
it didn't seem to help. The USB cable only goes from the Mac to the keyboard
directly to MIDI IN/Out. I've now realized the othe MIDI cable might no be
carrying any MIDI at all. In fact, I just now am thinking it can't. It's not
hooked up to the keyboard's MIDI outs. It's hooked to the headphone jack, so
it must be audio only. Stupid me. So now I'm thinking there's a problem with
the fact that this system is carrying audio over MIDI cables. Sound like a
possibility?

Thanks,
Steve

Steve Latham wrote:

Scott, could you explain (in semi-layman's terms) a little more about this?
I just replied to Ben and I think one issue might be that those MIDI cables
are also (and may exclusively be) carrying audio - they are the only
connection between the teacher's headset phones/mic and the student's. It's
got to be carrying audio.

I've never heard of that.

What I have heard of are MIDI interfaces that are designed without any
isolation, because it's cheap. It violates the spec, but most of the
time it works, except when it doesn't.

Is it likely that an isolator would fix this, or is there something like a
"grounded" MIDI cable - it seems to me it would be the same problem if I
were using unbalanced cables - maybe they should be like a Balanced MIDI
cable (like XLR) - course that depends on the devices I know. I'm sure the
keyboard's audio and headphone outs are unbalanced, and that's what goes to
this little connector box. I'm now thinking that an unbalanced audio out
(stereo 1/4") comes out of the keyboard into this box, to which the
headphones are connected (two cables, one for the mic, unbalanced miniplug,
and unbalanced stereo 1/4", and then these signals are combined and sen via
the MIDI cable to the teacher's workstation. I would doubt that this little
box is converting from unbalanced to balanced for the trip (some 30 feet or
more) and back to unbalanced for the console (which I'm assuming is standard
unbalanced signals like typical 1/4" stuff).

So that may mean that only two of the pins are actually being used in the
MIDI cable - 1 hot 1 ground? Does this seem reasonable?

Normally there is one send, one receive, and one ground, and that ground
should be isolated from the chassis ground. It is not always.
--scott

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

"Steve Latham" wrote in message
news:huLHe.33077$S%5.26075@trnddc06...

If anyone can offer any suggestions or potential fixes I'd be most
appreciative.

If the establishment has an engineering department, ask if there's an
electrical engineer who can advise.

But I'd guess that the various power supplies are causing some ripple on the
neutral line... which would be why as you add more devices the hum
increases.

Tim

a ground lift adapter can in general be dangerous to use, but it may be
useful for you to use only as a troubleshooting tool being carefull not
to hurt yourself....

If it solves the problem, then at least you know what the problem is
and need to find a safe way of solving it.

Mark

"Steve Latham" wrote in message
news:huLHe.33077$S%5.26075@trnddc06...


and a
set of headphones whose only connection to the Console is a MIDI cable
(the
students can then hear their own keyboard, hear the teacher's keyboard,
and
can communicate (the headphones have a headset mic) with each other.

How are these connected? I though a standard Mac had a single audio input
and single audio output, using mini jacks. I don't see how you could
connect a MIDI cable.

Is there some kind of connector device or expansion card at each computer?

Tim

Sorry Tim, we probably have to go back to my original info, which we've
snipped along the way.

Ok, there's two things. Each Mac is hooked into a keyboard by a MIDI/USB
connector.

Additionally, Each Keyboard is plugged into a console. There's a device
that's plugged into the headphone out of the keyboard, and into which the
mic (miniplug) and headphones (1/4" stereo) are plugged into. This little
box is connected to the main console via a MIDI cable. But, I'm now
convinced that this cable carries no MIDI, but only audio (i.e. the system
is using MIDI cables instead of XLR or 1/4 RCA, etc. because it needs to
carry the headphone and the microphone (talkback) signals. So maybe they
needed 3 leads and this was the easiest way to do it?) I can listen to audio
from any keyboard from the teacher's station (console). The MIDI cables do
not go to the teachers keyboard, so what I'm hearing must be audio. At one
point I thought that the console might have General MIDI sounds built in,
and the individual keyboards were using MIDI to trigger this module, which
the teacher could hear. But in thinking about it more, I realized the MIDI
out of the keyboard is not even hooked into this thing. So basically we've
got a Keyboard to computer in/out loop (running via MIDI/USB), and a
keyboard to console loop, via a single MIDI cable, but running from the
audio out (headphone jack) of the keyboard.

"Tim Martin" wrote in message
...

"Steve Latham" wrote in message
news:huLHe.33077$S%5.26075@trnddc06...


and a
set of headphones whose only connection to the Console is a MIDI cable
(the
students can then hear their own keyboard, hear the teacher's keyboard,
and
can communicate (the headphones have a headset mic) with each other.

How are these connected? I though a standard Mac had a single audio input
and single audio output, using mini jacks. I don't see how you could
connect a MIDI cable.

Is there some kind of connector device or expansion card at each computer?

Tim

"Steve Latham" wrote in message
news:RshIe.41192$MW5.14989@trnddc08...
Sorry Tim, we probably have to go back to my original info, which we've
snipped along the way.

Ok, there's two things. Each Mac is hooked into a keyboard by a MIDI/USB
connector.

Additionally, Each Keyboard is plugged into a console. There's a device
that's plugged into the headphone out of the keyboard, and into which the
mic (miniplug) and headphones (1/4" stereo) are plugged into. This little
box is connected to the main console via a MIDI cable. But, I'm now
convinced that this cable carries no MIDI, but only audio (i.e. the system
is using MIDI cables instead of XLR or 1/4 RCA, etc. because it needs to
carry the headphone and the microphone (talkback) signals. So maybe they
needed 3 leads and this was the easiest way to do it?) I can listen to
audio
from any keyboard from the teacher's station (console). The MIDI cables do
not go to the teachers keyboard, so what I'm hearing must be audio.

Right, so you're not using the computers' audio at all, all the audio
signals are generated by the microphones and Yamaha Clavinovas.

Now, the MIDI is opto-isolated, and the Yamaha Clavinovas will presumably
implement that correctly; so the keyboards' MIDI connections cannot be
involved in the hum.

But when you disconnect the MIDI-to-USB converter, the hum disappears.

As it happens, I have a hum problem myself, with an external USB device. I
have a Creative Audigy NX, which connects to a laptop via USB 2. I bought
it to record sound from live events. When I tried it beforehand it was
fine, but when I made the live recordings, there was a lot of hum.

As you can imagine, this was very irritating. I eventually discovered that
the hum was the result of interaction between the USB and the laptop's mains
supply. When I'd tried things out, I'd brought the laptop to the mixing
desk, and used its internal battery power rather than the mains.

I've not got to the bottom of the problem yet.

If I've got your setup pictured correctly, the headphone out of the
Clavinova goes into a local box. This box also takes the microphone signal
from the headset ... I think you said the students could hear each other
talk, so the mike signal presumably goes to the teacher's console via a
separate line to the Clavinova's audio out. But there's also an audio
signal from the teacher's console back to the Clavinova box. That means you
have three separate audio signals. I don't think you can do that with a
MIDI lead, because in a MIDI lead, only three of the five pins are
connected.

Wildly guessing: is it possible you're supposed to be using a DIN audio
lead and not a MIDI lead between the teacher's console ad the Clavinova box?
And by using a MIDI lead instead you're missing an earth connection?

Tim






















































..

Tim Martin wrote:

"Steve Latham" wrote in message
news:huLHe.33077$S%5.26075@trnddc06...

If anyone can offer any suggestions or potential fixes I'd be most
appreciative.

If the establishment has an engineering department, ask if there's an
electrical engineer who can advise.

But I'd guess that the various power supplies are causing some ripple on the
neutral line... which would be why as you add more devices the hum
increases.

Please explain how *RIPPLE ON THE NEUTRAL LINE* would affect hum ! If you can't
it might be better to shut up than post worthless snonsence. What the heck *IS*
" ripple on the neutral line " anyway ? Some curious invention of your own ?

Graham

"Tim Martin" wrote in message
...
[snip]
Right, so you're not using the computers' audio at all, all the audio
signals are generated by the microphones and Yamaha Clavinovas.

Correct.


Now, the MIDI is opto-isolated, and the Yamaha Clavinovas will presumably
implement that correctly; so the keyboards' MIDI connections cannot be
involved in the hum.

But when you disconnect the MIDI-to-USB converter, the hum disappears.

Hmmmm. That's true. But it also disappears when I unplug the computer's
power. So disconnecting the computer in either way removes the hum. Hmmm.

[snip].

If I've got your setup pictured correctly, the headphone out of the
Clavinova goes into a local box. This box also takes the microphone
signal
from the headset ... I think you said the students could hear each other
talk,

I don't know if they can hear each other, or only the teacher. The teacher
can talk to all of them. She can hear or talk to any one individual, all of
them, or the console allows subgroups too. But I don't think that Player 1
could talk to Player5.

so the mike signal presumably goes to the teacher's console via a
separate line to the Clavinova's audio out. But there's also an audio
signal from the teacher's console back to the Clavinova box.

I would think. Teacher to Console to Student. Student to Console to Teacher.
That's two leads and a common ground?

That means you
have three separate audio signals. I don't think you can do that with a
MIDI lead, because in a MIDI lead, only three of the five pins are
connected.

And yet, they are MIDI cables (although maybe they shouldn't be????). In
fact, all of the devices also say "MIDI IN" (or out) on them - which led to
my initial misconception.


Wildly guessing: is it possible you're supposed to be using a DIN audio
lead and not a MIDI lead between the teacher's console ad the Clavinova
box?

Possible. What's a DIN audio lead look like - is it a MIDI cable with more
wires connected internally? Obviously the ports on either end are Female
MIDI connectors (because a MIDI cable does fit in there, and they say
"MIDI", even though it's actually audio).

And by using a MIDI lead instead you're missing an earth connection?

Well that's beginning to sound very reasonable.


Steve

Steve Latham wrote:

"Tim Martin" wrote in message
...

But when you disconnect the MIDI-to-USB converter, the hum disappears.

Hmmmm. That's true. But it also disappears when I unplug the computer's
power. So disconnecting the computer in either way removes the hum. Hmmm.

I think you're on the right track here.

Now - *where* is it that the audio ground is connected to the PCs' ground ?

Graham

"Pooh Bear" wrote in message
...


Steve Latham wrote:

"Tim Martin" wrote in message
...

But when you disconnect the MIDI-to-USB converter, the hum disappears.

Hmmmm. That's true. But it also disappears when I unplug the computer's
power. So disconnecting the computer in either way removes the hum. Hmmm.

I think you're on the right track here.

Now - *where* is it that the audio ground is connected to the PCs' ground
?

I assume you mean the gound of the system that powers the audio.

The teacher's console is plugged in (with a two prong transformer) and
that's where these MIDI/Audio cables eminate. THe PC is plugged into an
outlet strip that initally was daisy-chained with others into the same
outlet as the teacher's console. However, I did try plugging them all in
different places, no daisy chains, etc. and the hum is still there.

Steve

"Steve Latham" wrote in message
news:huLHe.33077$S%5.26075@trnddc06...

Besides the computers running off the same outlets as the
keyboards, each computer is directly connected to the keyboard with a USB
MIDI adapter (MIDISport UNO). Which seems to interact thusly:

If I unplug the USB port (connecting the MIDI to the keyboard), the hum is
gone.
If I unplug the Computer or the Keyboard the hum is gone.
If I unplug the MIDI cable from the Console, the hum is gone.

So it may in fact be the interaction of all three. Obviously though, we
have
to use them all though..

What happens if you disconnect the Clavinova's MIDI cable from the MIDISport
Uno, leaving everything powered on?

In theory, this should make no difference, as there should be no electrical
connection between the Clavinova and the MIDISport. The MIDI-in ports at
each end are supposed to be isolated with opto-isolators, and the MIDI cable
shield is not supposed to be connected at the MIDI-in port. The cable
shield should not be connected to the plugs' shells.

If disconnecting the MIDI cable gets rid of the hum, that would suggest to
me that there is something wrong with the MIDI cables or the devices' MIDI
implementations ... presumably an earth connection over the MIDI when there
should be none.

Tim

"Tim Martin" wrote in message
...

"Steve Latham" wrote in message
news:huLHe.33077$S%5.26075@trnddc06...

Besides the computers running off the same outlets as the
keyboards, each computer is directly connected to the keyboard with a USB
MIDI adapter (MIDISport UNO). Which seems to interact thusly:

If I unplug the USB port (connecting the MIDI to the keyboard), the hum
is
gone.
If I unplug the Computer or the Keyboard the hum is gone.
If I unplug the MIDI cable from the Console, the hum is gone.

So it may in fact be the interaction of all three. Obviously though, we
have
to use them all though..

What happens if you disconnect the Clavinova's MIDI cable from the
MIDISport
Uno, leaving everything powered on?

Hum is gone.


In theory, this should make no difference, as there should be no
electrical
connection between the Clavinova and the MIDISport.

Well, it's "touching" the IMac, and I assume the metal in the USB housing is
connected to the motherboard, which is connected to the power supply, which
ends up plugged into the same outlet as the Clavinova (but the problem
exists even if they're not).

The MIDI-in ports at
each end are supposed to be isolated with opto-isolators, and the MIDI
cable
shield is not supposed to be connected at the MIDI-in port. The cable
shield should not be connected to the plugs' shells.

If disconnecting the MIDI cable gets rid of the hum, that would suggest to
me that there is something wrong with the MIDI cables or the devices' MIDI
implementations ... presumably an earth connection over the MIDI when
there
should be none.

What if those MIDI cables are carrying audio signals instead?

Thanks for you patience...
Steve

Steve Latham wrote:

What happens if you disconnect the Clavinova's MIDI cable from the
MIDISport
Uno, leaving everything powered on?

Hum is gone.

Therefore, it is a ground loop relating to the MIDI connection, which
is not really isolated.

In theory, this should make no difference, as there should be no
electrical
connection between the Clavinova and the MIDISport.

Well, it's "touching" the IMac, and I assume the metal in the USB housing is
connected to the motherboard, which is connected to the power supply, which
ends up plugged into the same outlet as the Clavinova (but the problem
exists even if they're not).

If you get an ohmmeter, is there continuity between the cases? Does it
change with the MIDI cable added or removed?

If disconnecting the MIDI cable gets rid of the hum, that would suggest to
me that there is something wrong with the MIDI cables or the devices' MIDI
implementations ... presumably an earth connection over the MIDI when
there
should be none.

Right. This is, as I said a week ago, a very common problem. Therefore there
are optoisolation boxes sold to deal with the issue. Markertek, as I said a
week ago, has some.

What if those MIDI cables are carrying audio signals instead?

Then they are not MIDI cables. They are something else. MIDI cables do
not carry audio.
--scott

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

"Steve Latham" wrote in message
news:MAQIe.1439$iE.630@trnddc06...

What happens if you disconnect the Clavinova's MIDI cable from the
MIDISport Uno, leaving everything powered on?

Hum is gone.

OK, so it sounds like a faulty MIDI connections between the Clavinova and
the MIDISport. You could try disconnecting separately the lead at the
Clavinova MIDI OUT socket, then the leadat the MIDI IN soclet.

What if those MIDI cables are carrying audio signals instead?

Eh? What? They shouldn't be ... and can't be, can they? Aren't they
connected to the Clavinova MIDI sockets? Do you have a MIDI sequencer on
the PC, and are the students using it to record and playback MIDI on the
Clavinova?

Well, it's "touching" the IMac, and I assume the metal in the USB housing
is
connected to the motherboard, which is connected to the power supply,
which
ends up plugged into the same outlet as the Clavinova (but the problem
exists even if they're not).

Do you have a multimeter with a resistance meter? On a MIDI lead, the
cable's shielding is connected to the centre of the 5 pins, and it's not
supposed to form an electrical connection betwen the two connected devices..
If you disconnect the cable at the Clavinova MIDI OUT socket, and measure
the resistance between the cable center pin there and the body of the
MIDISport, there should be infinite resistance. There should also be
infinite resistance between that pin and the metal of the computer. (But
it can be hard to measure resistance and be sure you're getting a correct
reading.)

Tim

Steve Latham wrote:

"Pooh Bear" wrote in message
...


Steve Latham wrote:

"Tim Martin" wrote in message
...

But when you disconnect the MIDI-to-USB converter, the hum disappears.

Hmmmm. That's true. But it also disappears when I unplug the computer's
power. So disconnecting the computer in either way removes the hum. Hmmm.

I think you're on the right track here.

Now - *where* is it that the audio ground is connected to the PCs' ground
?

I assume you mean the gound of the system that powers the audio.

The teacher's console is plugged in (with a two prong transformer) and
that's where these MIDI/Audio cables eminate. THe PC is plugged into an
outlet strip that initally was daisy-chained with others into the same
outlet as the teacher's console. However, I did try plugging them all in
different places, no daisy chains, etc. and the hum is still there.

You're saying that *all* the audio equipment is ungrounded ? The only ground
connection for all this equpipment is the PC ?

Graham

"Scott Dorsey" wrote in message
...


If you get an ohmmeter, is there continuity between the cases? Does it
change with the MIDI cable added or removed?

Cases? What do you mean?


If disconnecting the MIDI cable gets rid of the hum, that would suggest
to
me that there is something wrong with the MIDI cables or the devices'
MIDI
implementations ... presumably an earth connection over the MIDI when
there
should be none.

Right. This is, as I said a week ago, a very common problem. Therefore
there
are optoisolation boxes sold to deal with the issue. Markertek, as I said
a
week ago, has some.

Scott, I think I replied, and we may have missed each other, but I had some
more questions about that - like, what ehy are, what they do, etc. Sorry,
I'll go back and check the responses.


What if those MIDI cables are carrying audio signals instead?

Then they are not MIDI cables. They are something else. MIDI cables do
not carry audio.

Well, can't any wire basically carry audio. A guitar cable is a wire and a
sheath (which is a wire) with layers of insulating material. It's just two
pieces of metal. I could take two bare wires (or two pieces of conductive
metal) and connect them from an amp to a speaker (not that I'd want to). If
a MIDI cable has 5 pins, and each pin is connected by a wire to a pin at the
other end, that means you can pass electricity down it (which is how either
MIDI or Audio travel)- right?

Steve

"Tim Martin" wrote in message
news
"Steve Latham" wrote in message
news:MAQIe.1439$iE.630@trnddc06...

What happens if you disconnect the Clavinova's MIDI cable from the
MIDISport Uno, leaving everything powered on?

Hum is gone.

OK, so it sounds like a faulty MIDI connections between the Clavinova and
the MIDISport.

No, there's 11 of them. They can't all be faulty.

You could try disconnecting separately the lead at the
Clavinova MIDI OUT socket, then the leadat the MIDI IN soclet.

What if those MIDI cables are carrying audio signals instead?

Eh? What? They shouldn't be ... and can't be, can they? Aren't they
connected to the Clavinova MIDI sockets?

No, they're not.
There is the MIDISport IN Out MIDI cables which terminate in USB going to
the computer. Call that "loop A"

"Loop B" is:
The headphone jack of the Clavinova is connected via 1/4 stereo heaphone
plug to a little box which has a headphone jack, and miniplug jack into
which the headphones with the headset mic are plugged. Additionally, there
is a port marked "MIDI" which carries a MIDI cable back to the teacher's
console into a port marked "MIDI". Thus, even though the cables look
identical to MIDI cables (and are), and all of the ports are marked "MIDI",
those MIDI cables are not connected to anything on the Clavinova besides the
headphone jack. They MUST be carrying audio. There's no way for the
Clavinova MIDI signals to get to the headphone jack is there? (of course
not, but just to be thorough). It might be potentially possibly that this
teacher's console contains a GM sound set with no access controls whatsoever
and is being triggered by MIDI signals from those MIDI cables that are
plugged into it, but those MIDI cables terminate into that box that is only
connected to the Clavinova HP jacks. (you see why I was so confused
initally). The ONLY connection between the teacher's console and any
student's station is this "MIDI" cable plugged into the box plugged into the
HP jack. It's GOT to be carrying audio - right?


Do you have a MIDI sequencer on
the PC, and are the students using it to record and playback MIDI on the
Clavinova?

Yes.


Well, it's "touching" the IMac, and I assume the metal in the USB housing
is
connected to the motherboard, which is connected to the power supply,
which
ends up plugged into the same outlet as the Clavinova (but the problem
exists even if they're not).

Do you have a multimeter with a resistance meter? On a MIDI lead, the
cable's shielding is connected to the centre of the 5 pins, and it's not
supposed to form an electrical connection betwen the two connected
devices..
If you disconnect the cable at the Clavinova MIDI OUT socket, and measure
the resistance between the cable center pin there and the body of the
MIDISport, there should be infinite resistance. There should also be
infinite resistance between that pin and the metal of the computer. (But
it can be hard to measure resistance and be sure you're getting a correct
reading.)

Of course the MIDI In Out to the computer doesn't seem to be the issue. It
seems to be the "MIDI" cables connecting the teacher with the student (which
never terminate in anything MIDI).


Steve

"Pooh Bear" wrote in message
...

Sorry Graham, but I'm not much of an electrician. I might not be sure of
what grounded actually means.

All of the Clavinovas have only a two prong plug. I've always understood
that the third prong on any - are they Edison style? - plug is the Ground
(the round ones in the US if anyone's somewhere else). Then there's the two
"blades" (what I've been calling prongs).


You're saying that *all* the audio equipment is ungrounded ? The only
ground
connection for all this equpipment is the PC ?

What I meant is, the PCs are the only thing with 3 prong plugs. The
teacher's console, and all of the Clavinovas are all 2 prong. All of the
outlet strips and wall sockets are 3 prong.

Thanks for your patience,
Steve

Steve Latham wrote:

"Pooh Bear" wrote in message
...

Sorry Graham, but I'm not much of an electrician. I might not be sure of
what grounded actually means.

All of the Clavinovas have only a two prong plug. I've always understood
that the third prong on any - are they Edison style? - plug is the Ground
(the round ones in the US if anyone's somewhere else). Then there's the two
"blades" (what I've been calling prongs).

You're saying that *all* the audio equipment is ungrounded ? The only
ground
connection for all this equpipment is the PC ?

What I meant is, the PCs are the only thing with 3 prong plugs. The
teacher's console, and all of the Clavinovas are all 2 prong. All of the
outlet strips and wall sockets are 3 prong.

You mentioned PCs ( plural ). Are there several PCs connected in a single
'setup' ?

If not then you certainly don't have the classic 'ground loop' problem. It's
something else but I have no idea what.

Graham

Pooh Bear wrote:

Steve Latham wrote:

"Pooh Bear" wrote in message
...

Sorry Graham, but I'm not much of an electrician. I might not be sure of
what grounded actually means.

All of the Clavinovas have only a two prong plug. I've always understood
that the third prong on any - are they Edison style? - plug is the Ground
(the round ones in the US if anyone's somewhere else). Then there's the two
"blades" (what I've been calling prongs).

You're saying that *all* the audio equipment is ungrounded ? The only
ground
connection for all this equpipment is the PC ?

What I meant is, the PCs are the only thing with 3 prong plugs. The
teacher's console, and all of the Clavinovas are all 2 prong. All of the
outlet strips and wall sockets are 3 prong.

You mentioned PCs ( plural ). Are there several PCs connected in a single
'setup' ?

If not then you certainly don't have the classic 'ground loop' problem. It's
something else but I have no idea what.

Aaaaahhh ! I just re-read your original post.

You haven't explained about the 'teacher's console'. I'm betting that this is
simply to listen to each student - yes ? It *isn't* connected by MIDI cables at
all ! They're ordinary audio cables. They may simply look the same though but
they can't be carrying midi data if they're being used to listen to audio.

So, how many poles on the power plug from the teacher's console ? Was it custom
made by someone ? I'm betting that's the part of the setup causing trouble.

Graham

"Steve Latham" wrote in message
news:tDXIe.359$2j.104@trnddc07...

OK, so it sounds like a faulty MIDI connections between the Clavinova
and
the MIDISport.

No, there's 11 of them. They can't all be faulty.

I meant a faulty design with incorrect isolation. Bear in mind that the
MIDI standard was designed to handle live performance on stage, where there
is all kinds and vast amounts of electrical equipment and audio cables. To
avoid problems, the MIDI standard ensured electrical isolation. With
correctly-implemented MIDI devices, there is *no* electrical connection
between the device at one end of the lead, and the device at the other.

The MIDI lead has two wires inside; the current is sent by the transmitting
device through the "send" wire, activates a light emitter inside the
receiving device, and returns through the "receive" wire. The receiving
device also has a light detector, which responds to the light emitter. So
the MIDI signals are transmitted without there being any electrical
connection. And the MIDI cable shield is only supposed to be connected at
the transmitter end.

I spent a while on Google, trying to find specs for USB MIDI adapters, and
none of them said whether they implemented MIDI correctly. (I did find that
Yamaha make a USB midi adapter, the UX16.)

You could try disconnecting separately the lead at the
Clavinova MIDI OUT socket, then the leadat the MIDI IN soclet.

What if those MIDI cables are carrying audio signals instead?

Eh? What? They shouldn't be ... and can't be, can they? Aren't they
connected to the Clavinova MIDI sockets?

No, they're not.

What we have here is a failure in communication ... :-) Sorry, I failed to
be clear.

Your Clavinovas, as well as the headphone out and box and MIDI leads to the
teacher's console, also have MIDI leads connecting their MIDI in/out sockets
to the Midisport Unos, don't they?

In the original post, you said when you disconnect the USB lead between the
computer and the Midisport Uno, the hum disappeared. So I wanted to check
to see what happens if you disconnect the MIDI leads between the Clavinova's
MIDI sockets and the Midisport Unos. It *should* make no difference, as
there should be no electrical connection.

If disconnecting the leads between the Clavinovas' MIDI in/out sockets and
the Midisport does make a difference, that suggests the devices have faulty
MIDI design (and I'd assume it was the Midisports, as Yamaha would have been
one of the original MIDI consortium, and I assume it would not make devices
that could generate hum on stage.)

However, if disconnecting that MIDI connection makes no difference,but
disconnecting the USB lead does between computer and Midisport does, that
gets interesting ... :-)

Thus, even though the cables look
identical to MIDI cables (and are), and all of the ports are marked
"MIDI",
those MIDI cables are not connected to anything on the Clavinova besides
the
headphone jack. They MUST be carrying audio. There's no way for the
Clavinova MIDI signals to get to the headphone jack is there? (of course
not, but just to be thorough).

Agreed, there is no way.

The ONLY connection between the teacher's console and any
student's station is this "MIDI" cable plugged into the box plugged into
the
HP jack. It's GOT to be carrying audio - right?

Right

Of course the MIDI In Out to the computer doesn't seem to be the issue. It
seems to be the "MIDI" cables connecting the teacher with the student
(which
never terminate in anything MIDI).

However, disconnecting the USB cables makes the hum disappear, and there
should be no electrical connection between USB and the audio equipment. So,
first we need to eliminate the possibility of an incorrect MIDI
implementation causing an unwanted electrical connection between Clavinova
and Midisport.

Then, once we've eliminated that, we ponder how disconnecting the USB lead
could eliminate the hum.

There's also the matter of the audio connection between the Clavinova and
the teachers console. Disconnecting that eliminates the hum, too. For the
moment, I'm inclined to the view that there's somehow a small amount of hum
being generated at each Clavinova, that is sent down the audio connection to
the teacher's console, where all the hum is summed together and sent back.

So, you have Clavinovas 1-12 all connected, and with a hum. If you
disconnect Clavinova 1, its hum disappears; but what happens to the hum in
Clavinovas 2-12? Does it get quieter? It's probably hard to tell. But, as
you disconnect more Clavinovas from the teacher's console, does the hum in
the remaining Clavinovas get quieter?

If you have someone who is electrically qualified, you could see what
happens if you earth the audio signal shields. (I'm assuming this is some
kind of educational institution, where there will be insurance implications
if any ad-hoc wiring is carried out by anyone otherthan a qualified
electrical engineer.)

Tim

Steve Latham wrote:

"Scott Dorsey" wrote in message
...


If you get an ohmmeter, is there continuity between the cases? Does it
change with the MIDI cable added or removed?

Cases? What do you mean?

The chassis grounds on the two machines. If you touch a metal part of
the case, I bet you find it's connected to the ground pin on the MIDI
line (which is a no-no), and I bet you find that there is continuity
between the two grounds of the computer and the synth for some reason.

That's why you've got a ground loop.

Scott, I think I replied, and we may have missed each other, but I had some
more questions about that - like, what ehy are, what they do, etc. Sorry,
I'll go back and check the responses.

It's a box with an optoisolator module in it, that transfers MIDI without
having the grounds connected together. It basically provides the isolation
that a CORRECTLY designed MIDI interface should be providing already. It
is basically a workaround for dealing with this problem, with poorly
designed interfaces.

What if those MIDI cables are carrying audio signals instead?

Then they are not MIDI cables. They are something else. MIDI cables do
not carry audio.

Well, can't any wire basically carry audio. A guitar cable is a wire and a
sheath (which is a wire) with layers of insulating material. It's just two
pieces of metal. I could take two bare wires (or two pieces of conductive
metal) and connect them from an amp to a speaker (not that I'd want to). If
a MIDI cable has 5 pins, and each pin is connected by a wire to a pin at the
other end, that means you can pass electricity down it (which is how either
MIDI or Audio travel)- right?

Yes, but now it's not a MIDI cable. It's an audio cable, and you just
violated the MIDI spec completely. It's now not MIDI, but something
different. MIDI is a particular format. If you use a 5-pin DIN cable
for something else, it's not a MIDI cable any more.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

"Pooh Bear" wrote in message
...


Aaaaahhh ! I just re-read your original post.

You haven't explained about the 'teacher's console'. I'm betting that this
is
simply to listen to each student - yes ?

Yes.

It *isn't* connected by MIDI cables at
all !

They're ordinary audio cables. They may simply look the same though but
they can't be carrying midi data if they're being used to listen to audio.

Ok, well it looks like I need to make a distinction, which I've been trying
to do, and I thought was thorough - they look exactly like MIDI cables, they
are plugged into female jacks at either end marked "MIDI", but they must be
carrying audio signals (because they are not directly connected to any
actual MIDI jacks on the Clavinova - the signal passes via the headphone
jacks. I think all of the respondents are of the mindset that if a signal
carries Audio, then it's an Audio cable (no matter what it looks like). I'm
of the mindset that if it looks just like a MIDI cable, and I went up to GC
and bought it in a package (I didn't) that said "MIDI" cables on the
outside, then I' call them MIDI cables regradless of what data is being
carried over them. I think that's where some of the confusion is emanating.


So, how many poles on the power plug from the teacher's console ? Was it
custom
made by someone ? I'm betting that's the part of the setup causing
trouble.

Poles? Prongs? The teacher's console power supply is a "wall wart" - big
transformer with 2 blades (prongs) to plug in.
I don't think it's made by a major manufacturer (like Roland) and is
probably custom made by a small-ish company (that may make nothing else) -
I'm going back over there tonight and I'll look at the brand name (I'll be
embarassed if it's Yamaha or something!).



Graham

"Tim Martin" wrote in message
...


I meant a faulty design with incorrect isolation. Bear in mind that the
MIDI standard was designed to handle live performance on stage, where
there
is all kinds and vast amounts of electrical equipment and audio cables.
To
avoid problems, the MIDI standard ensured electrical isolation. With
correctly-implemented MIDI devices, there is *no* electrical connection
between the device at one end of the lead, and the device at the other.

Ok, this is interesting Tim, because there are 3 stations that don't hum,
and they all have a Mark of the Unicorn MIDI/USB box (these three are all on
the E-Mac - so it could also be not an I-Mac E-mac issue, but a MIDISport
vs. MOTU issue. If those MOTUs are isolated properly, then I should be able
to move them and cause the hum to move to different stations (it's non
existent when monitoring some, moderate on some, and annoying on 2)).


The MIDI lead has two wires inside; the current is sent by the
transmitting
device through the "send" wire, activates a light emitter inside the
receiving device, and returns through the "receive" wire. The receiving
device also has a light detector, which responds to the light emitter. So
the MIDI signals are transmitted without there being any electrical
connection.

Wow - I didn't know that. But I suppose a female MIDI jack could be wired so
that all 5 pins (if you wanted to) were actually connected to carry audio
instead?


And the MIDI cable shield is only supposed to be connected at
the transmitter end.


I spent a while on Google, trying to find specs for USB MIDI adapters, and
none of them said whether they implemented MIDI correctly. (I did find
that
Yamaha make a USB midi adapter, the UX16.)

The MIDI sports are 75 bucks, and therefore attractive from a cost
standpoint. They're also darn simple to use. In fact, it's plug it in the
USB and on a Mac, they work, on XP you have to trick the "Logo" test, but
other than that they work fine. We've had so many problems with the MOTU
stuff (the thru switches always broke, and the software was always not
recognizing the device) that these seemed like a great alternative (and have
been in every other situation, I have one at home in fact). They were
originally made by MIDIMan, and now M-Audio has taken them over (or changed
names). M-Audio makes "competitive" gear - so everytime something new comes
out, they make it - but cheaper - I would dare guess that this probably
means the specs might not be military, so to speak.

[snip]

In the original post, you said when you disconnect the USB lead between
the
computer and the Midisport Uno, the hum disappeared. So I wanted to check
to see what happens if you disconnect the MIDI leads between the
Clavinova's
MIDI sockets and the Midisport Unos. It *should* make no difference, as
there should be no electrical connection.

Ahh, I understand. I may have tried that before, but not taken note of it,
assuming that if electricity passed through the whole thing, it wouldn't
matter which end I pulled (and of course the USB port was handy). I'll try
that tonight. Thanks!


If disconnecting the leads between the Clavinovas' MIDI in/out sockets and
the Midisport does make a difference, that suggests the devices have
faulty
MIDI design (and I'd assume it was the Midisports, as Yamaha would have
been
one of the original MIDI consortium, and I assume it would not make
devices
that could generate hum on stage.)

Logical.


However, if disconnecting that MIDI connection makes no difference,but
disconnecting the USB lead does between computer and Midisport does, that
gets interesting ... :-)

With my luck, it will probably go this way!


Thus, even though the cables look
identical to MIDI cables (and are), and all of the ports are marked
"MIDI",
those MIDI cables are not connected to anything on the Clavinova besides
the
headphone jack. They MUST be carrying audio. There's no way for the
Clavinova MIDI signals to get to the headphone jack is there? (of course
not, but just to be thorough).

Agreed, there is no way.

The ONLY connection between the teacher's console and any
student's station is this "MIDI" cable plugged into the box plugged into
the
HP jack. It's GOT to be carrying audio - right?

Right

Of course the MIDI In Out to the computer doesn't seem to be the issue.
It
seems to be the "MIDI" cables connecting the teacher with the student
(which
never terminate in anything MIDI).

However, disconnecting the USB cables makes the hum disappear, and there
should be no electrical connection between USB and the audio equipment.
So,
first we need to eliminate the possibility of an incorrect MIDI
implementation causing an unwanted electrical connection between Clavinova
and Midisport.

Gotcha, I'll do that tonight, and that's a simple thing to check.


Then, once we've eliminated that, we ponder how disconnecting the USB lead
could eliminate the hum.

Thank you so much.


There's also the matter of the audio connection between the Clavinova and
the teachers console. Disconnecting that eliminates the hum, too. For
the
moment, I'm inclined to the view that there's somehow a small amount of
hum
being generated at each Clavinova, that is sent down the audio connection
to
the teacher's console, where all the hum is summed together and sent back.

So, you have Clavinovas 1-12 all connected, and with a hum. If you
disconnect Clavinova 1, its hum disappears; but what happens to the hum
in
Clavinovas 2-12? Does it get quieter? It's probably hard to tell. But,
as
you disconnect more Clavinovas from the teacher's console, does the hum in
the remaining Clavinovas get quieter?

Ok, no it's not so hard to tell. If I sit at the teacher's console, I can
listen to each station individually. Stations 9-11 do not hum. Stations 6-7
hum annoyingly. 8 hums a little. Stations 1-2 hum a little, and 3-5 hum a
little to - 3 and 4 about the same, and 5 about the same as 8 (I noticed a
rough corellation between the Clav models, so I haven't totally dismissed
that). (the 12th station, the teacher's is not connected by one of these
dubious "MIDI" cables). Each headset at each station has the same amount of
hum in it as heard in the teacher's station. After plugging (into the mains)
the last three first (9-11), I plugged in 8, no problem, plugged in 7, no
problem, plugged in 6 - problem. I could listen in station 7 headphones, and
plug in station 6, and the hume in 7 would increase. This is what led me to
believe it had to do with how all of them were connected together, rather
than it being the fault of any one station (other than the teacher's
console).


If you have someone who is electrically qualified, you could see what
happens if you earth the audio signal shields. (I'm assuming this is some
kind of educational institution, where there will be insurance
implications
if any ad-hoc wiring is carried out by anyone otherthan a qualified
electrical engineer.)

Oh, yes :-) - I don't touch electricity. One zap after crossing some leads
coming out of a power amp one time cured that.

Thanks again Tim.

Steve

"Scott Dorsey" wrote in message
...
Steve Latham wrote:


Well, can't any wire basically carry audio. A guitar cable is a wire and a
sheath (which is a wire) with layers of insulating material. It's just two
pieces of metal. I could take two bare wires (or two pieces of conductive
metal) and connect them from an amp to a speaker (not that I'd want to).
If
a MIDI cable has 5 pins, and each pin is connected by a wire to a pin at
the
other end, that means you can pass electricity down it (which is how
either
MIDI or Audio travel)- right?

Yes, but now it's not a MIDI cable.

Ok. I'm calling it a MIDI cable because it looks like a MIDI cable, not
because of the signal it carries.

It's an audio cable, and you just
violated the MIDI spec completely. It's now not MIDI, but something
different. MIDI is a particular format. If you use a 5-pin DIN cable
for something else, it's not a MIDI cable any more.

OK, understood. But now let's assume it is an audio cable (because it must
be, since it carries no actual MIDI signal) that "looks like" a MIDI cable.
If a stock MIDI cable was used to carry audio, that means the female jacks
at either end would need to be wired differently, right? Are the 5 pins in
what looks like a stock MIDI cable able to carry audio (leads and ground)
without any modification? If the female jacks were installed and wired to
carry audio, wouldn't it be very simple to take, say, pin 5 and carry the
ground and just ground pin 5's hole internally to the chassis (or electrical
ground). If the people who built this thing did that, that would be bad,
right?

Steve

Steve Latham wrote:

Wow - I didn't know that. But I suppose a female MIDI jack could be wired so
that all 5 pins (if you wanted to) were actually connected to carry audio
instead?

Yes, but then it wouldn't be a MIDI cable, it would be a DIN-5 audio cable.
And it wouldn't be marked MIDI on the jack, it would marked LINE IN and
it would be wired with pin 2 grounded, and signal on pin 1 and 3. Totally
different thing, completely unrelated. They use the same connectors, but
are not MIDI (and in fact predate MIDI by twenty years). You hardly see
that any longer but it was one of the original uses of the DIN connectors
back in the fifties.

If you have something marked MIDI on the input and something marked MIDI
on the output, my guess is that it's probably MIDI that you are dealing
with.

You have one or more MIDI interfaces that do not meet the spec and are
not optoisolated. Buy an isolation box and stop wasting your time.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

On Sat, 06 Aug 2005 14:18:17 GMT, "Steve Latham"
wrote:


"Pooh Bear" wrote in message
...


Aaaaahhh ! I just re-read your original post.

You haven't explained about the 'teacher's console'. I'm betting that this
is
simply to listen to each student - yes ?

Yes.

It *isn't* connected by MIDI cables at
all !

They're ordinary audio cables. They may simply look the same though but
they can't be carrying midi data if they're being used to listen to audio.

Ok, well it looks like I need to make a distinction, which I've been trying
to do, and I thought was thorough - they look exactly like MIDI cables, they
are plugged into female jacks at either end marked "MIDI",

Whoa... where are these jacks? What equipment are they on? Are any
of these jacks regular commercial gear, or is it all some sort of
custom manufacture?
Now my impression is that you have "MIDI cables" that connect to
5-pin female "DIN" connectors (just like the old IBM PC/XT/AT keyboard
connector) that carry audio, but the jacks are marked "MIDI" even
though they don't carry MIDI. I think this just might be a violation
of the MIDI standardd...


but they must be
carrying audio signals (because they are not directly connected to any
actual MIDI jacks on the Clavinova - the signal passes via the headphone
jacks. I think all of the respondents are of the mindset that if a signal
carries Audio, then it's an Audio cable (no matter what it looks like). I'm
of the mindset that if it looks just like a MIDI cable, and I went up to GC
and bought it in a package (I didn't) that said "MIDI" cables on the
outside, then I' call them MIDI cables regradless of what data is being
carried over them. I think that's where some of the confusion is emanating.

Any time a cable carries something other than the most common,
'normal' signal (or in this case, the ONLY signal until this thread
came up) for it, confusion is more likely than otherwise. The fact
that the jacks are actually MARKED "MIDI" doesn't just increase the
chances manifold, it just about guarantees confusion.
My personal beef is 1/4" phone connectors for amplifier outputs and
speakers. It allows you to physically plug an electric guitar into and
amplifier output or a speaker, but it doesn't make sense so do so. Too
many people with access to that kind of equipment aren't very
knowledgable, likely to have hangovers, etc.

So, how many poles on the power plug from the teacher's console ? Was it
custom
made by someone ? I'm betting that's the part of the setup causing
trouble.

Poles? Prongs? The teacher's console power supply is a "wall wart" - big
transformer with 2 blades (prongs) to plug in.
I don't think it's made by a major manufacturer (like Roland) and is
probably custom made by a small-ish company (that may make nothing else) -

This could explain a lot ...

I'm going back over there tonight and I'll look at the brand name (I'll be
embarassed if it's Yamaha or something!).



Graham



-----
http://www.mindspring.com/~benbradley

On Sat, 06 Aug 2005 14:40:08 GMT, "Steve Latham"
wrote:


"Tim Martin" wrote in message
...

...

The MIDI lead has two wires inside; the current is sent by the
transmitting
device through the "send" wire, activates a light emitter inside the
receiving device, and returns through the "receive" wire. The receiving
device also has a light detector, which responds to the light emitter. So
the MIDI signals are transmitted without there being any electrical
connection.

Wow - I didn't know that. But I suppose a female MIDI jack could be wired so
that all 5 pins (if you wanted to) were actually connected to carry audio
instead?

If it's carrying audio, then it's surely NOT isolated, and
certainly can be a path for a ground loop.

-----
http://www.mindspring.com/~benbradley