Reducing hum, noise and ground loops?

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canidoit

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I was doing a mix the other day using all outboard gear through my balanced patchbay and summing box back into my DAW and I noticed that I was getting hum/noise from some of my outboard gear which I never did when I was just daisy chaining my outboard gear for mono/stereo insert bouncing. They are all routed using balanced cables into my balanced patchbay.

Some hum/noise came from my DIY outboard which I built with ground lift switches on them but they didn't reduce or stop any hum/noise when I toggled them.

I was reading online that having all my gear plugged into one power socket could be a solution which I cannot do, due to the spread of the equipment and I am concerned that it may put a strain on one socket having all the equipment plugged that way?

I read that using a UPS could be a possible fix so that I isolate the outboard gear and help stop the ground loop from happening. Is this plausible to have my outboard onto a UPS, even if you mix with other equipment that is on the-same patchbay that has equipment not using a UPS?

How many outboard gear can one of these pure sine wave UPS handle - CyberPower VP1600ELCD Value Pro 1600VA / 960W. I have a few DIY tube compressors, preamps, equalisers, power amp, 500 series chassis, effects, synths that I will likely use with the UPS if this is a possible solution.

Is there generally a rule on how you group your equipment to the-same power source to prevent hum/loop noise?

Any tips on resolving this issue?

Thank you.
 
A meta thread or something on grounding or hum would be cool.
Found this real quick on the hard drive. Maybe it can get some ideas going while waiting for others to chime in.
 

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Sounds to me that you may have an issue with how your patchbay is wired in terms of 'Ground' / Chassis/ 0V connections.
Maybe interacting with a piece of kit with a "Pin 1 Problem".
Is the outboard in a metal rack ? If so are they electrically isolated to it / connected to it / a mix ?
Build the signal chain one connection at a time and see when you get a problem.

fwiw it generally takes a load of small signal audio kit to give a socket a problem (Caveat - I'm not familiar with Australian electrics)
 
I was doing a mix the other day using all outboard gear through my balanced patchbay and summing box back into my DAW and I noticed that I was getting hum/noise from some of my outboard gear which I never did when I was just daisy chaining my outboard gear for mono/stereo insert bouncing. They are all routed using balanced cables into my balanced patchbay.

Some hum/noise came from my DIY outboard which I built with ground lift switches on them but they didn't reduce or stop any hum/noise when I toggled them.
Ground lift switches are potentially dangerous. If you have a fault to chassis with the safety ground path open, the entire chassis will be energized.
I was reading online that having all my gear plugged into one power socket could be a solution which I cannot do, due to the spread of the equipment and I am concerned that it may put a strain on one socket having all the equipment plugged that way?
Should not be necessary with well designed gear.
I read that using a UPS could be a possible fix so that I isolate the outboard gear and help stop the ground loop from happening. Is this plausible to have my outboard onto a UPS, even if you mix with other equipment that is on the-same patchbay that has equipment not using a UPS?

How many outboard gear can one of these pure sine wave UPS handle - CyberPower VP1600ELCD Value Pro 1600VA / 960W. I have a few DIY tube compressors, preamps, equalisers, power amp, 500 series chassis, effects, synths that I will likely use with the UPS if this is a possible solution.

Is there generally a rule on how you group your equipment to the-same power source to prevent hum/loop noise?
no
Any tips on resolving this issue?
Search "pin 1 problem". Identify the unit that is humming, review its input stage design.
Thank you.
JR
 
My advice is to get a copy of "Audio Systems Design and Installation" by Giddings. If you have a studio with outboard gear, you should really consider reading it.
 
Ground loops are caused by pieces of equipment in the audio system having more than one path to ground. PERIOD!
Safety ground (as in the third pin on the power cord) should never be defeated.
The most common ways systems get set up with ground loops are from the physical mounting ( the standard is for the equipment case to be connected to the power connector ground pin).
You can use isolation hardware to mount you gear in rack (PIA) or just use wood rack rails.
Audio cable shields are often the cause of ground loops, having a balanced signal interface has no effect on weather ground loops are created or not (but it is much easier to avoid creating them with balanced interfacing). Telescoping shields, or single point shielding, is the most simple and reliable way to eliminate audio shield induced ground loops.
As to your AC power system questions, you need to know how much power is being drawn to know how much capacity needs to be supplied.
Of utmost importance is to have the entire system on one phase of power, either all one one single phase or all on dual phase.
 
Ground lift switches are potentially dangerous. If you have a fault to chassis with the safety ground path open, the entire chassis will be energized.

Should not be necessary with well designed gear.

I assume (I know !) that the "Ground Lift" discussed referred to 'lifting' the Signal 0V from Chassis / Mains Earth either completely or leaving it connected via a resistor or parallel RC. Rather than removing the chassis from the Mains.
But yeah - Don't Do that. No 3 to 2 pin 'adaptors' with Class 1 equipment please.
 
Ground lift switches are potentially dangerous

I assumed if someone said "ground lift" it always meant whether signal cable pin 1 was connected to chassis or floated (like how the term is used on DI boxes).
Have you actually seen builds where someone put a switch in the power line earth ground connection?!
 
I have no idea what is inside the OPs DIY build.

I see way too many people using and advocating use of 3 prong to two prong adapters to lift safety grounds.

FWIW years ago when I still partied like it was years ago, I installed a 3 prong to 2 prong adapter on an outlet in my living room for the live band to use. Afterwards I discovered that my house wiring has zero safety grounds, so catching the outlet face plate screw ground was wishful thinking.

JR
 
Just as a starting point the Bill Whitlock presentation he gave to the Indiana AES section is really good, and has some specific troubleshooting advice starting on page 101:
Whitlock grounding and shielding seminar

The preceding 100 pages explain the electrical basis behind the various noise mechanisms. There are lots of drawings, the text is not dense, so don't be put off by seeing "100 pages."

using all outboard gear through my balanced patchbay and summing box

Is all of the gear actually balanced? Or some is unbalanced? If some is unbalanced, how is the unbalanced connection wired through the patchbay?

I was reading online that having all my gear plugged into one power socket could be a solution

Gear that has problems with voltage differences on power line protective earth can avoid that by connecting all the gear to the same PE point, like using a power strip, but if this is in your home there will not be much difference between different sockets in the same room. Don't worry too much about that unless you are running a cord down the hall to a power outlet in a different room.

I read that using a UPS could be a possible fix

That is usually just a variation on using a power strip to get all the gear power connections together. Most UPS devices just pass through wall power until there is a power failure, but there are some known as "online" UPS which regenerate power all the time. Those are large, hot, and expensive, and the Cyberpower model you linked is not that type. It is known as a "line interactive" UPS, which means if there is a short drop in voltage it can boost it up without dropping to full battery backup mode, but as long as the incoming power is within specified voltage it will be exactly the same as using a power strip with several outlets on it.

Any tips on resolving this issue?

I would start with the balanced gear (assuming that when you said "synths" that implies there may be some unbalanced equipment).
Follow the troubleshooting tips in the Whitlock document to narrow down which of the balanced equipment (if any) has a problem, and if you are capable of and comfortable with doing so, fix the design problems in that equipment (probably "pin 1 problem" designed or built in).

After all the balanced gear is working properly, then figure out how to incorporate the unbalanced equipment into the setup. Some may be relatively trouble free, some may need a transformer based isolator or DI box to work well. You may also need some custom cables (e.g. wire the unbalanced equipment as balanced, but do not connect the cable shield at the patchbay end, so that the unbalanced equipment ground goes all the way through the patch bay without connecting to anything except the equipment at the other end of the patch). The exact configuration which will work will depend a lot on whether the unbalanced equipment has a protective earth connection or is floating. It is possible to make some educated guesses to what will work better for unbalanced gear, but you eventually just have to try it and see.
 
The source of hum can be several different things. Analyzing a complex system with multiple pieces of outboard gear, a summing box, custom gear and an audio interface is really not possible. One incorrect wire can create hum that cannot easily be traced back to the source. Your only real option is to break down and isolate things to reduce the complexity of the problem. Actually I would go all the way and start with just the audio interface to get a baseline. Then incrementally add gear to see what happens.

More specifically, use one high quality cable as a "loopback" from audio interface out, to audio interface in. Then use some software to generate a tone and FFT. Adjust the output so that the input is 0dBFS. Then back off the output -20dB and capture an FFT. That is your baseline.

Then incrementally add gear. Start by running a cable out to a mult on the patchbay and back. Or some patch point where you can just connect an output XLR to an input XLR or similar. If you get noise, you know the patchbay has a problem.

Note that patchbay connectors get corroded after a while and need to be cleaned. Put some 99% isopropyl on a jack and inert / twist / remove / insert / twist / remove , ... etc. Don't use deoxit. I hear that leaves a residue. Try different patch points.

Start with that and report back. It could be so many things ...
 
For what it’s worth…ran into a problem many years ago. One XLR connector had pin 1 connected to the shell inside the connector. This caused Audio ground - pin 1 - to be connected directly to chassis ground when the plug was inserted. I changed the connector and no more problems. This is easy to check with an ohm meter between pin 1 and the shell. Hope this helps.
 
For what it’s worth…ran into a problem many years ago. One XLR connector had pin 1 connected to the shell inside the connector. This caused Audio ground - pin 1 - to be connected directly to chassis ground when the plug was inserted. I changed the connector and no more problems. This is easy to check with an ohm meter between pin 1 and the shell. Hope this helps.
Pin 1 of an XLR is not audio ground. It is a shield and should be connected directly to the chassis. The audio signal exists only between pins 2 and 3. Check out "the pin 1 problem"

Cheers

Ian
 
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Only if the output signal is ideal transformer balanced,
if not, then that statement is incorrect.
It's essentially true for any flavour of balanced / differential output.. Of course nothing is "perfect". And "ideal transformers" exist only in simulation.
But we deal in models of actual behaviours so the statement is valid in context.
 
It's essentially true for any flavour of balanced / differential output.. Of course nothing is "perfect". And "ideal transformers" exist only in simulation.
But we deal in models of actual behaviours so the statement is valid in context.
It is not. From any electronically balanced output you can take the signal from pin 2 referenced to pin 1. So the audio signal exsist between pins 2 and 1 also. It is just usually 6dB lower.
 
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