Advice solving ART DTI grounding issue

[jessemcgoldrick]

Hi all, thanks in advance for any help or advice.

I’m trying to connect a pair of balanced XLR outputs to a pair of unbalanced RCA inputs using the ART DTI but I get a really loud humming...

Sound source is mains powered with earth (3 pin)
XLR cables go from source XLR outputs into DTI XLR inputs.
RCA cables go from DTI RCA outputs to destination RCA inputs.
Destination is mains powered without earth (2 pin)

The issue seems to be with connecting the DTI’s unbalanced RCA outputs to a destination which doesn’t have a mains earth connection, as if I keep everything else the same but connect to a destination which uses a 3 pin earthed power supply the humming is gone...

Any ideas how I can solve this?

Thanks in advance for any help or suggestions!

[Hugh Robjohns]

Is the DTI box near something with a mains transformer?

Or it could be that the class-2 destination device doesn't like a floating input...in which case, try running a wire from the earth terminal on the input side to the sleeve/barrel of one of the RCA output connectors.

[shufflebeat]

Is the DTI box near something with a mains transformer?

Or it could be that the class-2 destination device doesn't like a floating input...in which case, try running a wire from the earth terminal on the input side to the sleeve/barrel of one of the RCA output connectors.

Not in a position to check at the minute but if memory serves the earth terminal isn't on later versions, or possibly earlier versions depending on which order mine were constructed.

[Hugh Robjohns]

Odd... it's been on all the ones I've used over the years.

An alternative test arrangement would be to plug a TRS-TRS cable into the input side, and then touch the sleeve of the other end against the outer collar of the RCA on the output side.

[shufflebeat]

Odd... it's been on all the ones I've used over the years.

vs

[Martin Walker]

Good evidence shufflebeat- odd to see ART abandon an earthing point for the sake of a single knurled screw connector in a hole that still exists in the chassis!

Martin

[Hugh Robjohns]

Wow. Fancy that! I've checked and all the ones I have here have the earthing screw, so it must be a relatively recent change...

But not one for the good, because there are situations where that lug is essential to the correct functioning and application of the unit, and I can't imagine its removal would save any significant component costs or production time.

[Tomás Mulcahy]

Something is amiss here.

My older one had no earthing screw, my newer one does. Unfortunately I sold the older one. The new one has a sticker saying it was manufactured 11/2010. It does not have the legs that Shufflebeat's one has either.

[jessemcgoldrick]

Hugh you’re a lifesaver. Connecting TS at input and linking sleeve to RCA output sleeve did the trick. I’ll come up with something more elegant now. Thanks so much!

Edit: My unit does have a chassis ground pin luckily, linking this to the RCA output ground did the trick and only required a few cm loop of wire. Brilliant.

[Hugh Robjohns]

Hugh you’re a lifesaver.

It has been known... ...but in this case it was simply the appliance of science!

Connecting TS at input and linking sleeve to RCA output sleeve did the trick. I’ll come up with something more elegant now. Thanks so much!

No problem, glad it solved your problem.

Edit: My unit does have a chassis ground pin luckily, linking this to the RCA output ground did the trick and only required a few cm loop of wire. Brilliant.

Quite -- it was provided for exactly this kind of scenario and that's why its apparent omission in (some) current units is rather disturbing!

[shufflebeat]

My older one had no earthing screw, my newer one does.

I wonder if that's the development timeline, "hey, we have the wherewithal to add a chassis earthing point for the price of a short threaded shaft and a nut, I wish we'd thought of this before we'd sold all those others".

I'd like to think it was that way round anyway.

[Wonks]

No, the current ART page for the DTI has no feet or ground knob. SO taht wil be the latest incarnation, although the ART manual still indicated a ground connection. The Thomann page for the DTI shows the grounded version, but without feet, but I'd expect that you'd get a non-ground knob version.

[merlyn]

It's not as neat or user friendly but if the internal connections are still the same (i.e. that screw is still earthed) it would be possible to loosen the screw, wrap a bit of wire around it, then tighten the screw.

Just in case anyone with the new model needs an earth.

[Sam Spoons]

I'd have thought it easy enough to replace the screw with a longer one with two nuts and a couple of washers between them. Use on nut to secure the panel and the other to sandwich a wire between the washers. Worth checking but it'll almost certainly be earthed via the internal thread in the chassis, if not then clean the paint off the panel around the hole.

[GrahamGrant2]

I’ve just got a new DTI box which does have an earthing lug on the output side of the box. Problem is I have no idea how to use it! I know I’ll put a bare earth wire in the lug, but what do you do with the other end? I know you attach it to an rca, but on the same (output) or opposite (output) side, and how do you attach it to the rca? Just wrap it around the sleeve? Solder it somewhere?

Cheers, Graham

[Hugh Robjohns]

There is no one-solution-for-all-applications here.

The ground lug is not needed in 99% of applications. It's only needed when the destination requires a ground reference from the source...

In that situation, you may be able to connect a wire from the lug directly to a suitable ground point on the destination device.

Alternatively, you could solder a wire to the sleeve terminal of one output RCA-phono plug, and bring that round to the earth lug.

Or for bodge-merchants, you could trap the wire between the RCA-phono plug shield connection and socket body...

[GrahamGrant2]

Thanks Hugh! I like the bodge merchant option, should the need ever arise…