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Digital noise and ground loops

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Re: Digital noise and ground loops

PostPosted: Wed Jul 24, 2019 10:26 pm
by James Perrett
jellyjim wrote:Thanks James
The USB carries multi-channel audio too which is a big feature, not just MIDI

So why do you need to connect an audio cable from it to the Apollo?

Re: Digital noise and ground loops

PostPosted: Wed Jul 24, 2019 10:36 pm
by jellyjim
Just different workflows/use cases I guess

Plus irksome to have a part of a setup problematic and unresolved

Do prefer MIDI over USB, tidier

But I take your point

Re: Digital noise and ground loops

PostPosted: Wed Jul 24, 2019 10:40 pm
by jellyjim
And thanks for your help/suggestions, it's appreciated!

Re: Digital noise and ground loops

PostPosted: Wed Jul 24, 2019 11:22 pm
by jellyjim
More info for the mix ...

I bought a Focusrite Octopre to expand the number of inputs to the Apollo. That connects to the Apollo via optical ADAT. I still get the noise when the MODX is plugged into the Octopre! Wtf? Surely isn't the MODX to Apollo connection now optically isolated?

I'm baffled.

Re: Digital noise and ground loops

PostPosted: Wed Jul 24, 2019 11:42 pm
by cyrano.mac
One thing that I seem to remember that hasn't been touched yet, is that -some- ModXes are very sensitive to external magnetic fields. Stack them on top of, or near a power amp with a hefty transformer and you'll have hum everywhere.

So did you move it recently? Or did you put something else next to it?

What also sometimes helps, is reversing the flat power plugs that you find on ungrounded equipment in the EU. Dunno if that's easy with UK plugs. Because of the fact that stealing ground is legal in the UK, I'd try that too, to see if your room's wiring isn't at fault.

As far as USB isolators go, the real industrial ones, providing 5 kV or even 10 kV isolation are very pricey, but work well with audio gear. The rest doesn't and in some cases isn't even providing any isolation at all.

The JitterBug isn't an isolator and doesn't pretend to be one. It's just a plain old RC filter on the 5V line from the USB connection. That might help with noisy computer PSU's and USB powered equipment, but I doubt sincerely if it would help your case as it isn't PSU related.

Re: Digital noise and ground loops

PostPosted: Fri Jul 26, 2019 12:15 am
by jellyjim
cyrano.mac wrote:One thing that I seem to remember that hasn't been touched yet, is that -some- ModXes are very sensitive to external magnetic fields. Stack them on top of, or near a power amp with a hefty transformer and you'll have hum everywhere

So did you move it recently? Or did you put something else next to it?.

Nope but I changed from a USB to a Thunderbolt interface.

cyrano.mac wrote:What also sometimes helps, is reversing the flat power plugs that you find on ungrounded equipment in the EU. Dunno if that's easy with UK plugs. Because of the fact that stealing ground is legal in the UK, I'd try that too, to see if your room's wiring isn't at fault.

Not possible with UK plugs I don't think. Are there other ways to test my rooms wiring?

cyrano.mac wrote:As far as USB isolators go, the real industrial ones, providing 5 kV or even 10 kV isolation are very pricey, but work well with audio gear. The rest doesn't and in some cases isn't even providing any isolation at all.

I've ordered a couple of the cheaper type to try out. If they don't work I'll take advantage of my distance selling consumer rights and return them. I don't like doing that to manufacturers/retailers but I'm at a loss :(

Re: Digital noise and ground loops

PostPosted: Fri Jul 26, 2019 12:20 am
by jellyjim
Hugh Robjohns wrote:I haven't had a chance to go through the list in details, but it does seem likely that the problem is an absent ground reference, rather than a loop.

A quick and easy test is to get a standard guitar lead, and touch the tip at one end to the metal screw securing a mains wall socket. At the other ends touch the tip to the earthy contact of any audio socket on any of the hardware. That will provide a reasonable ground to the whole system, and that may well cure the noises. If it does, we can work out a more permanent solution.

Thanks Hugh. Stupidly my plug is in a really hard to reach spot. I can reach and feel the plug to pull it in and out and turn it on and off but I can't reach it or see it clearly to do what you suggest. Will there be a spot on an extension cable I can rely on instead?

Re: Digital noise and ground loops

PostPosted: Fri Jul 26, 2019 9:35 am
by Martin Walker
jellyjim wrote:
cyrano.mac wrote:As far as USB isolators go, the real industrial ones, providing 5 kV or even 10 kV isolation are very pricey, but work well with audio gear. The rest doesn't and in some cases isn't even providing any isolation at all.

I've ordered a couple of the cheaper type to try out. If they don't work I'll take advantage of my distance selling consumer rights and return them. I don't like doing that to manufacturers/retailers but I'm at a loss :(

Let us know your thoughts when they arrive Jim - I'm always keen to update my 'USB audio problem solvers list'


Martin

Re: Digital noise and ground loops

PostPosted: Fri Jul 26, 2019 9:37 am
by Martin Walker
jellyjim wrote:
Hugh Robjohns wrote:I haven't had a chance to go through the list in details, but it does seem likely that the problem is an absent ground reference, rather than a loop.

A quick and easy test is to get a standard guitar lead, and touch the tip at one end to the metal screw securing a mains wall socket. At the other ends touch the tip to the earthy contact of any audio socket on any of the hardware. That will provide a reasonable ground to the whole system, and that may well cure the noises. If it does, we can work out a more permanent solution.

Thanks Hugh. Stupidly my plug is in a really hard to reach spot. I can reach and feel the plug to pull it in and out and turn it on and off but I can't reach it or see it clearly to do what you suggest. Will there be a spot on an extension cable I can rely on instead?

Try making up an earth connection by connecting up a length of single core flex to the earth pin of your UK mains plug. Then you can plug this in and touch the other end of this 'ground connection' as Hugh described above.


Martin

Re: Digital noise and ground loops

PostPosted: Fri Jul 26, 2019 10:29 am
by jellyjim
Martin Walker wrote:
jellyjim wrote:
Hugh Robjohns wrote:I haven't had a chance to go through the list in details, but it does seem likely that the problem is an absent ground reference, rather than a loop.

A quick and easy test is to get a standard guitar lead, and touch the tip at one end to the metal screw securing a mains wall socket. At the other ends touch the tip to the earthy contact of any audio socket on any of the hardware. That will provide a reasonable ground to the whole system, and that may well cure the noises. If it does, we can work out a more permanent solution.

Thanks Hugh. Stupidly my plug is in a really hard to reach spot. I can reach and feel the plug to pull it in and out and turn it on and off but I can't reach it or see it clearly to do what you suggest. Will there be a spot on an extension cable I can rely on instead?

Try making up an earth connection by connecting up a length of single core flex to the earth pin of your UK mains plug. Then you can plug this in and touch the other end of this 'ground connection' as Hugh described above.


Martin

Thanks Martin

So ... as is often the way with these gremlins ... I've eradicated it but could I tell you how exactly? No!

I can repeat it. MODX direct to MacBook USB. Thunderbolt to Apollo. MODX audio to Apollo line in. I get my noise.

MODX audio to Octopre. Octopre to Apollo via ADAT. MODX USB to USB hub. USB hub to MacBook. No noise!

But the weird thing is, I know for certain I'd previously done this as I've it written down with a tick next to it!

So what changed?

Possibly some audio cables
Possibly the order in which USB devices are plugged in
The other USB port is now in use, it wasn't before

It was late last night that I had success so I went to bed. Maybe I'll spend time getting to the bottom of it, maybe I'll just count my blessings and deal with the next horror ...

:headbang: :headbang: :headbang: LATENCY :headbang: :headbang: :headbang:

Thanks all for your help.

Re: Digital noise and ground loops

PostPosted: Fri Jul 26, 2019 7:18 pm
by jellyjim
jellyjim wrote:Lots of reviews from audio people saying this was helpful or is it just snake oil?

https://www.amazon.co.uk/iDefender-Grou ... B01N3XKOLG

https://ifi-audio.com/products/idefender3-0/

And I just picked this up from an Amazon locker and ... would you believe it ... it works incredibly well! I might make a video. Standby ...

Re: Digital noise and ground loops

PostPosted: Sat Jul 27, 2019 7:15 am
by ef37a
Very interesting J, now I don't mind paying £49 for the device if it solves an otherwise intractable problem but a nifty for wall rat is taking it some!

Farnell do a 5V 1A jobby for about a fiver. I will admit the single page manual does say "any low noise 5V suppply will work".

I would however like to try my idea of just having the data lines connected to the USB ports? I suspect this is basically what the wee dongle is doing in effect.

Dave.

Re: Digital noise and ground loops

PostPosted: Sat Jul 27, 2019 7:24 am
by jellyjim
Yes, ouch at fifty but I didn’t expect it to work and was all set to return it. Not sure what to do now! I only got the dongle, not the companion PSU. It did come in a very nice box ...

I did try mangling a USB cable in various ways arriving eventually at just the data lines and it killed the noise but also the connection! No USB device found. It might work in other contexts as I found various posts online where people had had success.

Re: Digital noise and ground loops

PostPosted: Sat Jul 27, 2019 7:52 am
by ef37a
jellyjim wrote:Yes, ouch at fifty but I didn’t expect it to work and was all set to return it. Not sure what to do now! I only got the dongle, not the companion PSU. It did come in a very nice box ...

I did try mangling a USB cable in various ways arriving eventually at just the data lines and it killed the noise but also the connection! No USB device found. It might work in other contexts as I found various posts online where people had had success.

Have you tried connecting a 5V supply? I suspect something needs to detect 5V in order to work, even if the current pull is minimal.

Don't know about you but I must have at least half a dozen 5V supplies about the place and several at other voltages.

Dave.

Re: Digital noise and ground loops

PostPosted: Sat Jul 27, 2019 8:04 am
by jellyjim
Don’t need the supply. It’s all working.

No dongle, noise from the MODX’s USB port. Put dongle between MODX and USB cable. Noise gone!