Bus powered Scarlett 2i2 3rd gen USB-C port sparks

[TrueComposer]

Hello folks.

This is probably an old discussion.

Recently I’ve been using a Scarlett 2i2 3rd gen for the first time.
I have a ViewSonic display and new KH-80 speakers. And a Scarlett. And a MacBook Pro 2016.

Why would I get small electricity flashes at the USB-C ports?

Is it the fault of the chain, electronics, the speakers, monitor, interface, MacBook Pro?

I'm posting here because I am wondering if I had a Clarett (because it's got a power source) it would be safer being more powerful?

Was considering the Clarett 2Pre but not as cheap of course.

The previous Clarett had a thunderbolt connection too.
Does the power supply from the Clarett ground the interface at all?

Thank you for any kind assistance!

Nicholas.

[James Perrett]

It could possibly be dry air due to the cold temperatures outside causing static electricity to build up which causes sparks when the charged item comes close to something grounded. I've noticed it recently when we had cold temperatures and snow. Provided the connectors and gear are well designed it shouldn't cause a problem.

Static shocks are a big problem working in cold places. I always used to get into the habit of leaning against something grounded (like a sink or pipe) before touching a tap when I was in Antarctica. If I forgot to do this I'd feel a jolt and hear a crack as I reached for the tap.

[Rockrooms]

The 2Pre power supply is a wall wart with a plastic earth pin, it doesn't ground the supply, so I don't think that's going to make a difference here.

Are the sparks persistent ? I.e if you remove the cable and try again they always occur?

If you have a radiator pipe handy, or other known grounded device, does touching the metal of the USB C connector to it show a spark, or if you have a multi meter hand see if there is a voltage difference between a pipe and the usb c connector. I've experienced what happens when two "earths" disagree by > 40 when fitting some tv ariel cable to an antenna.

I would start with just the Scarlett and the Mac book on battery, see if you get any sparks. Next try with the MacBook on mains power to see if it changes things.

Then with the MacBook on battery add the next mains powered item, try the usb C connector. Rinse and repeat with the Mac on mains / battery as you add speakers / monitor and any other powered devices. Make sure you physically disconnect each mains powered device as you try the different combinations.

Are all the mains powered devices on the same power supply, a 4 way or the like?

It would also be helpful to try another usb c device to see if you get sparks.

Some years ago, when BNC ethernet was common, I was visiting a client with a laptop and the bnc connector would spark as I connected it, but only if the laptop was on mains. It was an old building, but clearly ground meant different things at different places. It was an old cronky London office, but I'm very glad that was my one and only visit.

Joe

[Tomás Mulcahy]

Something for Martin to add to the list? This article is excellent but maybe could cover more about the issue happening with un-grounded gear that's so common now (that's not a complaint, just an observation).

https://www.soundonsound.com/sound-advi ... -my-studio

[TrueComposer]

Hello Folks,

The sparks ONLY occur when the Neumann KH-80's are switched BEFORE I put the USB-C cables are plugged in. The monitors are connected via balanced cables into the Scarlett 2i2 3rd gen.

I also have an external display connected to the MacBook Pro via Displayport to usb-c (ViewSonic VX3211-2K-MHD 32 Inch IPS WQHD 1440p Monitor).

If I switch on the monitors with the cables already in the MacBook, there are no sparks, but this is NOT a solution...just a workaround.

There are NO sparks if I leave the monitors switched off....

I have no idea what to do...

[Rockrooms]

From what you've described, my guess is you're getting sparks because there is a disagreement as to what ground is between the Mac USB power ground and the input ground on the monitors by some significant margin. This is not good and could potentially cause damage to the Scarlett, Mac or the monitors. The energy is going to end up being dissipated somewhere.

I note that the monitors themselves don't have an wired earth connection, I can't tell if the display monitor does or not. You mention the display is connected via USB-C , if you don't have the display connected, do you still get the same problem? I'm reluctant to say it's definitely the monitors as the problem could be the display, or the Mac, or some interaction between all three. I'm fairly confident another interface would have the same problem.

If you just try one monitor at a time does the same problem occur?

Putting a DI box between the Scarlett outputs and monitor inputs, with earth lift might help, but fundamentally something is misbehaving and the Scarlett is just at the end of the line where the fault is finally showing. If there was a fault in the Scarlett , it would only be a 5V short at the most, unlikely to spark and the device probably wouldn't work, the fact you don't get sparks if the monitor is off seems to confirm the signal vs power ground problem.

Joe

[James Perrett]

Have you got any properly grounded gear that you could plug the Scarlett into while it is plugged into the monitors? I suspect that capacitive coupling between the audio ground in the KH80's and the mains input could be causing the KH80's audio ground to rise up to a higher voltage than the ground on the Mac.

It is always a good idea to leave the monitors switched off while plugging/unplugging gear associated with them so I'd suggest that you have an easily accessible switch to control the monitor power.