Please help. Loud hum in New studio!?!

[DC-Choppah]

My next problem is that even with the grounds isolated (via transformers) between the upstairs live room and the Midas in the basement control room,
one of the JBLs (left) has his and noise present that the other (right does not).

The JBLs are plugged into different outlets.

I have each of the JBL Eons set at the same gain levels (+10 dB) on the channel, 0 dB on the master.

The right channel is silent with a bit of hiss in the tweeter array that is normal.

The left channel is very noisy.

I have made a recording of the noise using my iphone.

FYI I am moving my phone from the Tweeter down to the subwoofer over 6 secs. You can hear the noise and hum. It is much less noise than without the isolators. But still very loud and a show stopper.

Current noise after adding isolators between live room and control room in basement. Only left JBL Eon makes this sound.
https://drive.google.com/file/d/1XgXEod ... sp=sharing

[Hugh Robjohns]

I wrote 'unshielded' intentionally. It is my understanding that balanced signal cables do not need to be shielded since their balanced design is immune to interference as in a twisted pair, which is opposite polarity in the same location. So when the twisted pair picks up 60 Hz like a loop antenna, that hum cancels in the device connected. But I suppose if there is some imbalance between the two balanced lines (hot and cold) then the hum might not cancel?

In simple terms, the twisting helps to reject common-mode electromagnetic fields but doesn't do much for electrostatic fields like RF... which is why the screen is a standard addition.

I learned along the way that unshielded sounds better than shielded. But this may be controversial.

Controversial... or just nonsense, probaby related to shoddy equipment design that can't handle RF via the cable screen properly...

[ef37a]

Excuse my bluntness DC but, WTF have you got the speakers plugged into different outlets?

Simply put a 'diss strip ' on the quiet speaker's power socket and run a mains extension to the second. Then their grounds are "starred" back to the same mains ground.

Dave.

[Hugh Robjohns]

They are in different rooms, on different floors, of a large building on the other side of the Atlantic, Dave.

[ef37a]

They are in different rooms, on different floors, of a large building on the other side of the Atlantic, Dave.

Oh! Forgive me do! I assumed they were a stereo pair.

Dave.

[DC-Choppah]

Excuse my bluntness DC but, WTF have you got the speakers plugged into different outlets?

Simply put a 'diss strip ' on the quiet speaker's power socket and run a mains extension to the second. Then their grounds are "starred" back to the same mains ground.

Dave.

Dave you are right. My second problem in this thread is the residual hum/noise after adding the transformer isolators to the control room signal.

In the live room I have two JBL Eons to hear the keyboard. The left one still has some noise/hum.

https://drive.google.com/file/d/1aNBpIk ... sp=sharing

Please be blunt. No need to be excused. I need to fix this ASAP. Thank you!!

[DC-Choppah]

They are in different rooms, on different floors, of a large building on the other side of the Atlantic, Dave.

Hugh the transformer isolators in the signal path to the Midas in the basement has reduced the hum to zero in the right JBL Eon in the live room. But I use two Eons in stereo, and the left has some residual hum still.

[DC-Choppah]

Since the YC88 has a three conductor mains connector (IEC type 13) wouldn't you also need to isolate the piano from the control room/mixer?

BTW DC, I'm assuming it's a typo but you say "So a proper XLR mic cable should use a three conductor unshielded cable with a cable like:
Ground (bare metal) connected to pin 1
Hot (red for example) connected to pin 2
Cold (white for example) connected to pin 3"

That should read "XLR mic cables should use a three conductor shielded cable".

Thank you for your attention to these details Sam. Much appreciated. I wrote 'unshielded' intentionally. It is my understanding that balanced signal cables do not need to be shielded since their balanced design is immune to interference as in a twisted pair, which is opposite polarity in the same location. So when the twisted pair picks up 60 Hz like a loop antenna, that hum cancels in the device connected. But I suppose if there is some imbalance between the two balanced lines (hot and cold) then the hum might not cancel?

I learned along the way that unshielded sounds better than shielded. But this may be controversial. How fun!!! There may be an SoS article somewhere that squashes this myth. But perhaps it is confirmed?!?

Any thoughts are greatly appreciated.

Careful DC! You are sliding toward the murky regions of Russ Andrews cable claims. This will unleash wrath from many here, including myself!

There almost certainly CAN be a situation where the extra capacitance of a shielded cable causes an HF loss over an unshielded one but that is the 'fault' of the equipment driving the cable, not the cable itself.

You are also correct in saying that almost all of the external noise reduction of balanced working comes from the differential operation. However, such 'balancing' begins to fail at Radio Frequencies because amplifiers have a limited HF response and their "common mode" rejection capability fall off with increasing frequency. Basically an unshielded balanced cable will pick up all the RF **** in creation and it likely get demodulated in the gear and drive you nuts.

50+ years ago we ran 30 Ohm mics 100s of yards on twisted 'lamp chord' but there were no PMR taxis about and the mobile phone was only seen in Dan Dare at the Pictures!

Dave.

So cool. I love it. We will shield all of our mic cables in the studio.

Most are shielded but a few are not. Let me replace them now.

[DC-Choppah]

Excuse my bluntness DC but, WTF have you got the speakers plugged into different outlets?

Simply put a 'diss strip ' on the quiet speaker's power socket and run a mains extension to the second. Then their grounds are "starred" back to the same mains ground.

Dave.

I did this Dave. No change. Same noise/hash in the left side JBL Eon. But silence in the right.

Both are set to channel gain +10 dB, main 0 dB.

I found the problem. One of the channels on th JBL Eon mixer was set to max gain. Turning off all the channels except channel 1 fixes this problem.

Ok, back to ground loops.

[Hugh Robjohns]

Wow...

I get the impression you're out of your depth here DC. Leaving unused input channels on max gain is a really basic no-no.... and the ground loop issues are an obvious problem to any competent studio builder.

I said it before when you were discussing acoustic problems, it really would be worth consulting someone local with professional studio build experience. It would save you a lot of time and money in the long term, and you'd learn a lot along the way.

And it's often very difficult to remote diagnose from an ocean away. Things like open but unused input channels are obvious to an experienced eye in the room... but could lead to all kinds of potentially expensive mis-diagnosis via a remote forum.

[James Perrett]

I get the impression you're out of your depth here DC. Leaving unused input channels on max gain is a really basic no-no....

Though looking at the JBL website I would say the controls on the current Eon models are really badly thought out. There is absolutely no indication of where they are set. Looks like they brought someone in with no live sound experience to design them.

Mind you - that would instantly disqualify them from consideration if I was looking for PA speakers.

[ef37a]

Wow...

I get the impression you're out of your depth here DC. Leaving unused input channels on max gain is a really basic no-no.... and the ground loop issues are an obvious problem to any competent studio builder.

I said it before when you were discussing acoustic problems, it really would be worth consulting someone local with professional studio build experience. It would save you a lot of time and money in the long term, and you'd learn a lot along the way.

And it's often very difficult to remote diagnose from an ocean away. Things like open but unused input channels are obvious to an experienced eye in the room... but could lead to all kinds of potentially expensive mis-diagnosis via a remote forum.

Can't you and Paul raid the petty cash tin Hugh and pop over and sort him out?

Not had a good Studio SoS for ages!

Dave.

[DC-Choppah]

Wow...

I get the impression you're out of your depth here DC. Leaving unused input channels on max gain is a really basic no-no.... and the ground loop issues are an obvious problem to any competent studio builder.

I said it before when you were discussing acoustic problems, it really would be worth consulting someone local with professional studio build experience. It would save you a lot of time and money in the long term, and you'd learn a lot along the way.

And it's often very difficult to remote diagnose from an ocean away. Things like open but unused input channels are obvious to an experienced eye in the room... but could lead to all kinds of potentially expensive mis-diagnosis via a remote forum.

This is why I love you guys. Tell me what it is. I appreciate you.

[DC-Choppah]

Wow...

I get the impression you're out of your depth here DC. Leaving unused input channels on max gain is a really basic no-no.... and the ground loop issues are an obvious problem to any competent studio builder.

I said it before when you were discussing acoustic problems, it really would be worth consulting someone local with professional studio build experience. It would save you a lot of time and money in the long term, and you'd learn a lot along the way.

And it's often very difficult to remote diagnose from an ocean away. Things like open but unused input channels are obvious to an experienced eye in the room... but could lead to all kinds of potentially expensive mis-diagnosis via a remote forum.

I am determined to fix this. I need this studio to be noise free. I am always out of my depth. Yes I need some help though. I am looking for people local to help me.

Let me know if you have any suggestions - Washington DC USA area.

[Arpangel]

My tuppence worth, go around and unplug any unused mains equipment, then do the same with the audio cables, until the hum goes away, it will, as there is unlikely to be an equipment fault. Also substitute another keyboard, or audio source, and cables, repeat for other gear.
I've had issues like this, it’s normally a cable, or an earth loop produced by a mains connection. Do not disconnects mains earths, only experiment with audio grounds.

[ef37a]

"Let me know if you have any suggestions - Washington DC USA area."

Do you know of the forum homerecording.com DC? They are American based and I would say populated 90% by US people.

A rather, shall we say, more "relaxed" attitude than SoS forum but there are some technically good guys there. Maybe someone knows someone who's dad worked for RCA?

Do NOT of course desert us here!

Dave

[ef37a]

A thought has occurred, where you have a serious hum problem with a feed over a very long cable you might have to resort to different transformers and possibly two.

The transformer I mean is the "10k+10k line bridging" transformer and should have an inter-winding screen.
If the source is at a really low impedance say 100 Ohms or less then that can drive the line and the '10k' traff fitted at the remote, speaker end and close as reasonably possible, 6 feet or less. (see how I am keeping 'imperial' for you!).

If the source is not so good, a '600 Ohm' transformer can be used. Such a setup can send audio a very long way and is very resistant to RF signals. I used such transformers to send audio many 100s of yards in fields for PA jobs.

Of course such a setup compromises audio quality somewhat, mainly extreme HF loss but usually a small price to pay for no hum!

Dave.

[Hugh Robjohns]

Dave, I fear you're over complicating things and risk more confusion and inappropriate work.

The problem has already been identified and workable fixes have already been found.

[ef37a]

Dave, I fear you're over complicating things and risk more confusion and inappropriate work.

The problem has already been identified and workable fixes have already been found.

Well! Nobody told ME guv'nor!

Dave.

[Hugh Robjohns]

It's all in the thread...

[DC-Choppah]

Wow...

I get the impression you're out of your depth here DC. Leaving unused input channels on max gain is a really basic no-no.... and the ground loop issues are an obvious problem to any competent studio builder.

I said it before when you were discussing acoustic problems, it really would be worth consulting someone local with professional studio build experience. It would save you a lot of time and money in the long term, and you'd learn a lot along the way.

And it's often very difficult to remote diagnose from an ocean away. Things like open but unused input channels are obvious to an experienced eye in the room... but could lead to all kinds of potentially expensive mis-diagnosis via a remote forum.

I wanted to follow up on this thread. I took Hugh's advice and hired a studio specialist, and also and acoustician for the room acoustics. I will focus here on the ground loop problem which was solved by Dave Cannon.

Here is Dave Cannon, I will make a plug for him if any one in my region needs help. https://www.cannonsoundpro.com/

What Dave did to solve the problem completely is
- Changed to very short unbalanced cables coming from the YC-88 keyboard into a stereo direct box with ground lift, and balanced cables running to the JBL speakers in the live room. The unbalanced cables were previously too long and running near power cords which Dave identified as the worst problem.

- The balanced outputs of the YC-88 also go through a stereo direct box with ground lift and then into the snake (you may call it a loom) that goes to the basement Midas mixer.

Voila - no hum. All is silent.

Thank you for the inspiration Hugh. This was fixed right after your note, but I wanted to update anyone who follows along.

Now we have moved to the bass response of the control room and live room. I have a real acoustician for that. I may start a new thread. Very cool what they can do. Totally new to me.

[Hugh Robjohns]

Sounds very positive. Good work.