Noise in Home Studio

[Ajax]

Hi Everyone,

I'm looking for help to eliminate 50HZ mains noise (Sydney, Australia) coming through my son's active monitors in his home studio. It has existed for a long time, including his hum-bucker guitars.

Environment:

• Residential Property with 3 phase mains power
• Home studio comprising a MAC laptop running Logic software as a DAW through a Universal Apollo interface into active speaker monitors, of which I have several
• 50hz hum is coming through all active speaker systems, when I connect each one to the system
  • Adam A7X
  • Yamaha HS8
  • Adam A7
• Studio is powered via Black Lion Audio PG-P Type 1 Power-board and Furman M-10X E Power Isolator
• Noise is present when speakers are plugged into power, even without XLR cable ttached
• Once XLR cables are plugged in, speaker noise level increases as more audio equipment is plugged in, i.e. Apollo Twin x PSU, and MacBook Charger
• Noise is less apparent when using USB Powered Interface and running MacBook on battery
• Working conclusion is that the noise isn’t entering on the audio path, but rather via Earth connection, or maybe environmental EMI

Prolinx Audio (technician Pat site visit)

• Pat visited the studio and noted noise was still present in the speakers without XLR plugged in
• Can hear 3 distinct noises:
  1. 50hz hum
  2. Hum related to monitor gain knob
  3. Buzz
• Pat hinks the earth in the speakers may need to be re-grounded post AC/DC conversion in the speaker’s built-in amp
• Noted the the Earthquake subs on my AV system in downstairs lounge room are producing noise as well
• Noted that SVS Subwoofers upstairs that are within a different AV system and on a different circuit are NOT producing noise. I plugged in the Adam A7X, the Yamaha HS8, and the Earthquake subwoofer into the same GPO as the SVS, however, they are all produced noise???
• Tried adding a noise isolator in the studio to the audio cables, but made no change
• Confirmed grounding issue in house by testing Cheap Digitech Amp with passive speakers

Speaker Hospital (tecnician Ian by phone)

• Ian thinks the house has a grounding issue - may be dangerous?
• MEN connection (neutral connection) loose? Or Earth Bar Loose?
• Reckons a mains electrician should check the place out
• Earthing or neutral issue?
• Suburb noise issue?
• Maybe a UPS (Uninterruptible Power Supply) would help? - need to find out wattage required - 400W

Next Steps to solve problem

• Call back Speaker Hospital, explain that SVS subwoofers don’t have an issue, but my downstairs Earthquake subs do
  • Ask why that may be the case?
  • Ask Ian to recommend an electrician who has experience with audio issues and can investigate the distribution board
  • post on ASR

 

[olds1959special]

Have you tried Morley Hum exterminators?

 

[Everett T]

Use an extension cord and run one speaker to a different circuit and see if you still get the hum (to rule out Earth)If no hum, then start unplugging everything that is plugged in, one thing at a time, and see if/when the hum goes away. A UPS isn't gonna solve the problem. Definitely sounds like ground loop issues.

 

[AudioJester]

Have you tried a DC blocker?

 

[Ajax]

Thank you all your replies, greatly appreciated.

We belive it is a ground loop problem.

FYI

1. we plugged the Adam A7X monitor (by itself) into as separate GPO on another circuit and no hum, however, the Yamaha HS8 did?
2. my son has run an extension lead to his studio from another GPO and the hum persists on all monitors

We have an AV installer and his audio electrician coming out and will pass on your suggestions.

Thank you again.

 

[DVDdoug]

That's a tough-annoying problem...

Have you tried a DC blocker?

DC offset can cause a transformer to hum/buzz/vibrate. It doesn't normally get into the audio but in active speaker it would be hard to tell if the noise is coming from the transformer or drivers. If the transformer inside is humming/vibrating the woofer will also hum/vibrate. I don't think this happens with switching power supplies.

The DC offset can be different on different circuits in the house.

I had this problem once. My amplifier would hum/vibrate mechanically when my TV was turned-on. But there was no noise from the speakers. At the time I didn't know about DC offset. It doesn't happen with my new TV.

We believe it is a ground loop problem.

That would be the "usual suspect" but with nothing plugged-in there is no ground loop, and balanced connections are mostly immune to ground loop noise.

including his hum-bucker guitars.

I'm not a guitar player but I'm sure you know that guitars often hum/buzz to some extent and as far as I know humbuckers aren't completely immune. High impedance coils are "hum antennas" and the high-impedance unbalanced connection "doesn't help". Active pickups can help (they boost the signal and lower the impedance) but any electro-magnetic noise from the pickup is still there.* Noise sensitivity is only reduced after the little amplifier inside the guitar.

I think the normal solution is a noise gate (or other noise reduction) as well as other sounds in the mix drowning-out the noise.



* The noise is actually amplified by the active circuitry but the signal is amplified too so the signal-to-noise ratio isn't worse (perhaps better) and with a stronger signal you can turn it down.

 

[nagster]

Please excuse the awkward English. I used Google Translate.
One of the causes that is difficult to notice is radiated noise from surrounding electronic devices.
For example, lighting fixtures, even if the lights are off, can affect audio equipment simply by being connected to the distribution board.
This is especially common with mixers, microphone amplifiers, audio interfaces, and phono EQ amplifiers.
External socket-type vacuum tube devices are also vulnerable.
If the directionality is sharp, moving the device by just 50cm can sometimes reduce the problem.
I haven't experienced this with speakers, but I can't rule out the possibility.

If I were to handle this,
first, to understand the situation correctly, I would ask him to record himself using a microphone for about 30 seconds.
The data may be useful not only now but also in the future. It's similar to photographic evidence or medical records.
SM57 and SM58 microphones are not suitable. Please prepare a microphone with sufficient response down to around 50Hz. Disable HPF and EQ in the recording path.
Posting the recorded file will make it easier for the members to understand. We can listen to it, or paste it into REW to obtain the FFT spectrum.

Next, create the minimum configuration shown in the picture.
It's tedious, but it's necessary to eliminate each suspect one by one. Currently, there are still too many suspects.
• MacBook
• Audio signal cable
• One speaker
• Portable Power Station or UPS (sine wave output)

Please disconnect all wiring except for the 3.5mm TRS cable and the AC cord for the speakers.
This eliminates the influence of ground loops, grounding, and the wall AC outlet.
If a Portable Power Station is not available, connect the power cord of the speaker (only one) to the wall outlet.
However, the influence of the wall AC outlet will remain.

Disconnect the power plugs of other electrical appliances as much as possible.
Shut down the switches on the distribution board as much as possible.
It will be dark, so prepare a cell phone flashlight or similar.
This eliminates the influence of other electronic devices.

Try moving the device to a completely different location, such as to the opposite side of the room.

Compare this to the previous symptoms.

If there is no change in symptoms even with the minimum configuration, the following causes are possible:
• RF interference or magnetic field interference from outside the room. >> Try in a different building.
• Device failure. >> Replace with a working device. (Other laptops, mobile phones, iPads, etc.)
While speaker failure is a possibility, the probability of all six speakers failing with the same symptoms is low.

The device at the following link may help identify the cause and benefit his future.
I hope your son's stress will be relieved.

https://www.amazon.com/dp/B000068O33/

https://www.amazon.com/dp/B000068O3S/

https://www.amazon.com/dp/B000068O4D/

https://www.amazon.com/dp/B0GD13M2SF/

https://www.amazon.com/dp/B0D921GV75/

 

[Ajax]

Dear All,

The Morley Hum exterminator did the trick, so many thanks to Olds1959 and to all who took the trouble to respond to my request for help. This is the basis of what good forums are about - learning and support.

Below is a thank you note from my son, who is 26 and starting a career as a music producer.

"Hi guys,

Thanks so much for your responses and help with getting rid of the noise in my speakers.

The solution that seems to have worked for me is powering my Adam A7 studio monitors and Apollo Twin interface off the same Furman power conditioner, installing the Morley Humno hum eliminator cable on one of the Adam A7Xs, running the audio cables through an ART DTI passive line transformer and making sure the charger is plugged into my laptop.

God’s honest truth, I don’t really know why this solution worked. I understand the general principles of ground loops in power and audio signals, and in theory with the Morley on one of the monitors and the TRS > XLR cables running through a line isolator, I’ve broken the loop on both the power and audio side.

The weirdest part of this whole thing is that none of this works unless the charging cable is plugged into my laptop. If the charger is unplugged, the noise instantly returns. This is really strange because before the Morley was installed, plugging my laptop charger in would actually introduce more noise into the speakers whereas now it seems to act like a hum eliminator.

The hum isn’t completely gone, but it’s now so quiet that I have to put my ear right next to the woofer to hear it. From my normal listening position (around 1.2m away), it’s effectively inaudible.

This solution works well enough for me. As much as I’d love to say the hum is completely gone, it’s definitely still there, just barely noticeable. I have a feeling there’s a grounding issue in the house, but these band-aid fixes seem to have minimised the symptoms enough for me to get back to work and stop worrying about it."

A couple of questions:
1. Can anyone sugest a reason why the noise returns when the laptop is not charging, i.e. running solely by battery?
2. Would adding a second Moley to the other monitor get rid of the hum altogether or would it be a waste of money knowing that my son is happy with the greatly reduced hum noise and what has been achieved.

 

[AnalogSteph]

So the cables from UAA Twin to <monitors> are 1/4" TRS to XLR, correct? You can get ones in TS to XLR as well, and those would preclude balanced operation and cause all kinds of trouble.

I have a feeling there may be something more than a "classic" ground loop involved, e.g. the "Pin 1 Problem" or mains leakage in combination with a floating PE. Kind of hard to tell without a diagram of the whole system.

Side note, Yamaha HS series monitors are prone to virtually all sources of interference you can think of, including Pin 1 Problem (improper ground routing) and RFI (poor shielding).

 

[olds1959special]

Dear All,

The Morley Hum exterminator did the trick, so many thanks to Olds1959 and to all who took the trouble to respond to my request for help. This is the basis of what good forums are about - learning and support.

Below is a thank you note from my son, who is 26 and starting a career as a music producer.

"Hi guys,

Thanks so much for your responses and help with getting rid of the noise in my speakers.

The solution that seems to have worked for me is powering my Adam A7 studio monitors and Apollo Twin interface off the same Furman power conditioner, installing the Morley Humno hum eliminator cable on one of the Adam A7Xs, running the audio cables through an ART DTI passive line transformer and making sure the charger is plugged into my laptop.

God’s honest truth, I don’t really know why this solution worked. I understand the general principles of ground loops in power and audio signals, and in theory with the Morley on one of the monitors and the TRS > XLR cables running through a line isolator, I’ve broken the loop on both the power and audio side.

The weirdest part of this whole thing is that none of this works unless the charging cable is plugged into my laptop. If the charger is unplugged, the noise instantly returns. This is really strange because before the Morley was installed, plugging my laptop charger in would actually introduce more noise into the speakers whereas now it seems to act like a hum eliminator.

The hum isn’t completely gone, but it’s now so quiet that I have to put my ear right next to the woofer to hear it. From my normal listening position (around 1.2m away), it’s effectively inaudible.

This solution works well enough for me. As much as I’d love to say the hum is completely gone, it’s definitely still there, just barely noticeable. I have a feeling there’s a grounding issue in the house, but these band-aid fixes seem to have minimised the symptoms enough for me to get back to work and stop worrying about it."

A couple of questions:
1. Can anyone sugest a reason why the noise returns when the laptop is not charging, i.e. running solely by battery?
2. Would adding a second Moley to the other monitor get rid of the hum altogether or would it be a waste of money knowing that my son is happy with the greatly reduced hum noise and what has been achieved.

I use two Morley hum eliminators on my pair of KRK S10 subs or they hum. I’m also adding some of the hum eliminators to my setup with Yamaha MSP5’s which had a terrible ground loop buzz. So I would say, yes, try one on each speaker.

 

[Torin Krell]

As a general rule the easiest way to minimize hum, RFI and EMI noise in a home studio is to use a star configuration for all the AC connections. All equipment should run off the same power strip or set of power strips with equal "arms" to each part of the "star". This will minimize noise by greatly reducing the ground differential between each AC powered component which will also maximize the faraday cage (or its like) that each component has or extends into the next component as well as for the interconnects between them. This is just my brief explanation and bit of advice. For a detailed technical explanation please read this excellent article in Sound on Sound magazine: https://www.soundonsound.com/sound-advice/understanding-solving-ground-loops