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Patchbay + di-boxes + synths + unbal fx units - ground loop issues, anybody to help?

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Patchbay + di-boxes + synths + unbal fx units - ground loop issues, anybody to help?

Postby foliasound » Sat Feb 22, 2020 2:54 pm

Hello, SOS community, here's Paul, your years long reader!

I'm having some major issues with my patchbays and outboard gear and thought it is high time I solved it, maybe SOS people can help me?

I'm owning 2x Samson S-Patch Plus balanced bays that I feed into my RME UFX and two ADAT units. As for outputs, some of my synths are balanced and go straight to the pb, some are not, so they run through di-boxes. Same with fx units - unbalanced outs get di-boxed first, then go to pb.

The problem occurs when I try to connect anything from the bay to my unbalanced fx, which are Eventide H9, Korg KP3+ and Boss SL-20. Though running literally everything that is interconnected via audio/usb/fw/video cables from one power outlet, I get massive computer ground loop type hum, especially on my H9 unit. It actually comes from my FW cable checked on that.

When unbalanced effects inputs are not in use on patchbay side, I get constant 50 Hz hum (European) that is... panned a bit left on H9, a bit right on SL-20. Input signal levels match perfectly between left and right channels, though.

When I use thepatchbay to incerconnect the synths and unbal effects, ground loop noise is... carried to the output of the synth, too (but only to the one that is physically connected)!

Last night I literally disconnected all the studio, checked on every audio cable, PSU, power strip, made sure all my gear is connected to one power socket (using really good Brennenstuhl power strips). I tried to resolder bal to unbal cables using Crokwood schemes:

https://crookwood.com/blog/dealing-with-unbalanced-gear-in-the-studio/


And the problem persists!

Also some strange behavior on my Blofeld: ground loop noise is present when running through di-box and gnd lift pressed and... it's gone when lift gnd not pressed on the di-box.

This is pure madness, I just stopped having a single clue what's up. Anybody?
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Re: Patchbay + di-boxes + synths + unbal fx units - ground loop issues, anybody to help?

Postby Hugh Robjohns » Sat Feb 22, 2020 6:59 pm

You have my sympathy. Connecting balanced and unbalanced gear through a patchbay is a potential nightmare scenario and it has to be designed with considerable care, knowledge and understanding.

Powering everything from a single mains outlet via star-radiating plugboards is the right way to do things, so a tick for that.

There are three likely reasons for the hums on different devices: a ground-loop, an absence of a ground, and magnetically induced hum into the transformers of DI (and line isolation) boxes...

The last one is easy to avoid. Makes sure the DI box (or line isolation box) is kept well away from anything with a mains transformer in it, or any mains cables.

As an aside, I wouldn't personally use standard DI boxes in this application, just because they are designed to reduce the signal level which isn't needed in a patchbay. A line isolation box is usually a more appropriate choice.

Ground-loops usually only occur between mains-powered devices which have a safety earth connection (class 1 devices). So step one is to identify all such equipment connected to the patchbay. These devices will need to be connected using the relevant wiring schemes or isolation boxes as appropriate -- wired so as to interrupt the audio ground connection.

Devices which don't have a mains safety earth -- double insulated or class 2 devices -- need an audio ground connection and will usually hum badly if they don't have one. So step two is to identify all these devices and ensure that they receive an audio ground connection one way or another. You can still use transformer boxes to resolve balanced/unbalanced issues, but you may need to make up bespoke cables to deal with individual situations.

I find it easiest to draw everything out on a big sheet of paper, identifying the class 1 and class 2 devices, and all the balanced and unbalanced inputs and outputs. The idea is to have everything on the patch bay appear to be balanced (and normal line level). So you can then work out which connections need special arrangements to deal with balancing/unbalancing -- which could be transformer boxes in some cases, or specially wired cables -- and which connections need to maintain a ground path and which don't.

I'm afraid there is no simple 'always do this' type of solution. You have to deal with each connection on a case by case basis.

And where devices have other grounded connections (such as USB, digital cables etc) you need to take those into account too...
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Re: Patchbay + di-boxes + synths + unbal fx units - ground loop issues, anybody to help?

Postby ef37a » Sat Feb 22, 2020 10:07 pm

My sympathy as well!

I have a dim recollection of a problem with Firewire such that on very rare occasions you can get a ground loop that defies just about any and all fixing?

Maybe if Hugh's expert advice does not improve things try the UFX on USB?

Dave.
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Re: Patchbay + di-boxes + synths + unbal fx units - ground loop issues, anybody to help?

Postby foliasound » Sun Feb 23, 2020 2:17 pm

Hugh Robjohns wrote:Powering everything from a single mains outlet via star-radiating plugboards is the right way to do things, so a tick for that.

Yep, I took care of it at the very beginning.

The last one is easy to avoid. Makes sure the DI box (or line isolation box) is kept well away from anything with a mains transformer in it, or any mains cables.

No transformers nor mains cables around DI-boxes.

As an aside, I wouldn't personally use standard DI boxes in this application, just because they are designed to reduce the signal level which isn't needed in a patchbay. A line isolation box is usually a more appropriate choice.

My levels after di-boxing are quite fine, no need of using too much gain on ADATs, s/n ratios on RME input meters between 90 and 100 dB.

Ground-loops usually only occur between mains-powered devices which have a safety earth connection (class 1 devices). So step one is to identify all such equipment connected to the patchbay. These devices will need to be connected using the relevant wiring schemes or isolation boxes as appropriate -- wired so as to interrupt the audio ground connection.

No ground loops between such devices, only my unbalanced inputs are affected, and they all use mains transformers, no earth connections.

Devices which don't have a mains safety earth -- double insulated or class 2 devices -- need an audio ground connection and will usually hum badly if they don't have one. So step two is to identify all these devices and ensure that they receive an audio ground connection one way or another. You can still use transformer boxes to resolve balanced/unbalanced issues, but you may need to make up bespoke cables to deal with individual situations.

I believe all my unbalanced rig is equipped with signal ground connections, but my guess is they are guilty here. I also tried all balanced to unbalanced custom soldered cables (hard bal to hard unbal, hard bal to floating unbal, floating unbal to hard bal, floating bal to floating unbal), all according to crookwood guidelines mentioned before.

BUT: when I touch the bay, hum rises. I suppose that this is also an issue with my patchbay grounding (or actually lack of it) and my next idea would me to terminate ALL grounds at patchbay, both balanced and unbalanced. What do you think about this?

I find it easiest to draw everything out on a big sheet of paper, identifying the class 1 and class 2 devices, and all the balanced and unbalanced inputs and outputs. The idea is to have everything on the patch bay appear to be balanced (and normal line level). So you can then work out which connections need special arrangements to deal with balancing/unbalancing -- which could be transformer boxes in some cases, or specially wired cables -- and which connections need to maintain a ground path and which don't.

I have as complete scheme of my studio and I'm aware of every single connection, mains, audio, usb. I can transfer drawing to a PDF for sure!

I'm afraid there is no simple 'always do this' type of solution. You have to deal with each connection on a case by case basis.

Yep, totally. Thanks for your you advices, that was all very informative and competent!

And where devices have other grounded connections (such as USB, digital cables etc) you need to take those into account too...

That is also taken into account. All usb ports are running with ground usolators and all are fine, the problem is with UFX fw connection, it does carry a ground loop, both when a computer is on the same socket with all the rest and when it has a separate mains ground. I'll try to provide this connection with parallel ground, as a ground wire is vital for fw data flow and can't be terminated at any end.
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Re: Patchbay + di-boxes + synths + unbal fx units - ground loop issues, anybody to help?

Postby foliasound » Sun Feb 23, 2020 2:28 pm

ef37a wrote:My sympathy as well!

I have a dim recollection of a problem with Firewire such that on very rare occasions you can get a ground loop that defies just about any and all fixing?

Maybe if Hugh's expert advice does not improve things try the UFX on USB?

Dave.

Hi Dave, I get worse latency results when using USB, I really feel like sticking to fw connection here...
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Re: Patchbay + di-boxes + synths + unbal fx units - ground loop issues, anybody to help?

Postby ef37a » Sun Feb 23, 2020 3:23 pm

foliasound wrote:
ef37a wrote:My sympathy as well!

I have a dim recollection of a problem with Firewire such that on very rare occasions you can get a ground loop that defies just about any and all fixing?

Maybe if Hugh's expert advice does not improve things try the UFX on USB?

Dave.

Hi Dave, I get worse latency results when using USB, I really feel like sticking to fw connection here...

But does USB fix any of the hum issues? I remember one review of an RME interface that said latency was the same for USB as FW. Not sure if that was the UFX?

Oh and when peeps say "touching things reduces hum" that indicates a lack of an earth AND makes me cringe!

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Re: Patchbay + di-boxes + synths + unbal fx units - ground loop issues, anybody to help?

Postby foliasound » Sun Feb 23, 2020 4:39 pm

But does USB fix any of the hum issues? I remember one review of an RME interface that said latency was the same for USB as FW. Not sure if that was the UFX?

Oh and when peeps say "touching things reduces hum" that indicates a lack of an earth AND makes me cringe!
Dave.

Yes, I'm good on usb soundwise, but my performance i seally lower, I won't tell you now why, there is surely a reason for that.

Touching thingz (a patchbay) increases hum, which is quite obvious, as I'm serving it another ground reference :D But maybe I should think about grounding it plus terminating shields of my cables?
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Re: Patchbay + di-boxes + synths + unbal fx units - ground loop issues, anybody to help?

Postby foliasound » Sun Feb 23, 2020 4:45 pm

But does USB fix any of the hum issues? I remember one review of an RME interface that said latency was the same for USB as FW. Not sure if that was the UFX?

Oh and when peeps say "touching things reduces hum" that indicates a lack of an earth AND makes me cringe!
Dave.

Yes, I'm good on usb soundwise, but my performance i seally lower, I won't tell you now why, there is surely a reason for that.

Touching thingz (a patchbay) increases hum, which is quite obvious, as I'm serving it another ground reference :D It's k8nd of verticalky strapped, but maybe I should think about grounding it the other wayplus terminating shields of my cables?
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Re: Patchbay + di-boxes + synths + unbal fx units - ground loop issues, anybody to help?

Postby Hugh Robjohns » Sun Feb 23, 2020 6:20 pm

foliasound wrote:Touching thingz (a patchbay) increases hum, which is quite obvious, as I'm serving it another ground reference :D

I don't get no hums when I touch any of my patch bays!

The frame work really should be grounded. Some designs achieve that through being mounted in a grounded rack. Some have dedicated technical earth connections. And some rely on the grounded screens of connected cables.

It seems yours is floating...

As I said, you need to draw everything out so that you can see -- and optimise -- the earthing paths for the entire system as a whole.
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Re: Patchbay + di-boxes + synths + unbal fx units - ground loop issues, anybody to help?

Postby foliasound » Sun Feb 23, 2020 7:59 pm

I don't get no hums when I touch any of my patch bays!

The frame work really should be grounded. Some designs achieve that through being mounted in a grounded rack. Some have dedicated technical earth connections. And some rely on the grounded screens of connected cables.

It seems yours is floating...

This is Samson S-Patch Plus. It's nothing special and it does seem to be floating at the front panel, jacks are vertically strapped and grounded through cables.

I have a full drawing of the studio and I know every connection, I'm afraid I lack electric knowledge to diagnose the problem properly.

I can provide you with a drawing, what ya say?
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Re: Patchbay + di-boxes + synths + unbal fx units - ground loop issues, anybody to help?

Postby foliasound » Thu Mar 05, 2020 7:29 pm

Ok, guys, got re-amp boxes from Palmer, problem fixed, thanks to all support and replies!
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Re: Patchbay + di-boxes + synths + unbal fx units - ground loop issues, anybody to help?

Postby Hugh Robjohns » Thu Mar 05, 2020 8:10 pm

Er... great. Glad its sorted and thanks for the update...

But can you explain where you've used the Palmer reamp boxes to fix the problems, please ?
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Re: Patchbay + di-boxes + synths + unbal fx units - ground loop issues, anybody to help?

Postby DanDan » Tue Mar 24, 2020 11:30 pm

My levels after di-boxing are quite fine, no need of using too much gain on ADATs, s/n ratios on RME input meters between 90 and 100 dB.

DI boxes typically have a 20-40dB step up or down.
This this could result in unnecessary gain to restore level, raising the noise floor.
Reamp or 1:1 boxes seem sensible. ART have a nice range, although they do make odd choices of earthing sometimes. (Easily rewired internally or by adding an external dedicated earth) There is a world of information on patch bays out there. Neil Muncy seems to be a valuable source. Also the Tech Library at Rane.com
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