Unbalanced Connections: TRS Floating Ring Clarification (UltraLite-mk5)

[fredrick]

I'm getting conflicting information from this forum and the manual, so I'm hoping for some clarity regarding exactly which 1/4" connections need to be TRS floated ring. The interface I'm using is the UltraLite-mk5.

Rear 1/4" Outputs:

There seems to be no ambiguity about this one. The manual states clearly on page 23 that:

Quarter-inch line outputs are not cross-coupled. Therefore, when connecting them to an unbalanced input, use a TRS plug with the ring disconnected. Not floating the negative terminal will short it to the sleeve ground and cause distortion.

And every everyone on the forum seems to agree.

Rear 1/4" Inputs:

The manual, on page 10, states:

Equipped with very high quality 24-bit 192 kHz converters, these six line inputs are balanced TRS (tip/ring/sleeve) quarter-inch connectors that can also accept an unbalanced plug (with the ring disconnected). Use them for keyboards or other line level analog sources.

Which contradicts many comments I found on this forum and elsewhere, where everyone was saying that the rings only needed to be floated for the outputs. Granted, all the comments I found were directed at older models, so maybe this is something new with the UltraLite-mk5? Or is it a typo in the manual?

Front 1/4" Inputs (i.e. the centers of the combo jacks):

If page 10 is correct about inputs needing floated rings then these front two might be exceptions, because on page 55 it says of those jacks:

Balanced or single ended

"Single ended" I take to mean TR plugs (as opposed to TRS), which indicates that floated rings are NOT necessary for these two jacks at least. There is no other mention of "single ended" in the manual.

So my takeaway from the manual is that, for unbalanced connections, TRS plugs with floated rings should always be used for both outputs and inputs, except maybe the front two. Is this correct?

But if there's one single question I'd like answered the most, it's this: For unbalanced connections, Is there any reason why I shouldn't just use floated ring TRS plugs for EVERY input and output on the UltraLite-mk5? I'm making my own cables.

[mikehalloran]

It applies to unbalanced connections only for the Line In/Outs. The first version of the User Manual for the M2/M4 said the exact same thing except it warned of potential damage if this wasn't followed, now that manual refers to the outputs only and only warns of distortion.

Balanced connections must TRS. Period. You can't have a balanced connection if you float the ring.

This does not apply to the CombiJacks.

None of my keyboards output line level signals—most don't, in fact, and those are barely audible if plugged into the Line Ins of my M2 or M4 (again, not an issue with the CombiJacks that handle those levels fine). I use the passive Morley/Ebtech LLS 2 (an excellent step-up transformer) or an active DI like the Radial J+4. In both cases, unbalanced cables are not an issue since the outputs are balanced only and the cables going in can be balanced or unbalanced—just doesn't matter.

Since distortion is the issue, you might want to see if your units have enough level to drive the Line Ins of your UltraLite-mk5 without a DI before making special cables.

[HCMarkus]

Haven't looked at that specific unit, but I can confirm unbalanced TS to TS connections to my 828ES Inputs have been trouble-free.

I floated the Outputs as needed per MOTU's directive. For most situations, floating the Output rings is a simple as using TRS to TRS cables with unbalanced gear... the ring won't see any contact in an unbalanced (TS) jack.

[mikehalloran]

Yes, the 828es reads like the M2/4 in that it only refers to the Line Outs,

TRS quarter-inch analog inputs and outputs

Quarter-inch analog inputs and outputs are
balanced (TRS) connectors that can also accept an
unbalanced plug. The outputs are DC-coupled, so
they can be used for CV control output.

☛ Quarter-inch analog outputs are not
cross-coupled. Therefore, when connecting them
to an unbalanced input, use a TRS plug with the
ring disconnected. Not floating the negative
terminal will short it to the sleeve ground and
cause distortion.

I just looked it up. Actually, the UltraLite-mk5 refers to the Line Outs only and no longer says the same about the Line Inputs.

TRS quarter-inch line inputs/outputs

Quarter-inch line inputs and outputs are balanced
(TRS) connectors that can also accept an
unbalanced plug. The outputs are DC-coupled, so
they can be used for CV control output.

☛ Quarter-inch line outputs are not
cross-coupled. Therefore, when connecting them
to an unbalanced input, use a TRS plug with the
ring disconnected. Not floating the negative
terminal will short it to the sleeve ground and
cause distortion

I can confirm that, when I was testing all this with my Yamaha P125 and other keyboards, my only issue was not enough signal from the Line Inputs without a DI. I did not float the rings on TRS plugs.

[fredrick]

I just looked it up. Actually, the UltraLite-mk5 refers to the Line Outs only and no longer says the same about the Line Inputs.

The mk5 manual does still refer to line inputs on a different page, as I quoted in the OP.

If I want to keep things simple, can I use floated ring with all outputs, inputs and CombiJacks on the mk5? (here I'm speaking purely in the context of unbalanced connections) That way I can repurpose the cables from one jack to the other without worrying about rewiring them. I only ask because some manuals for other (non-Motu) devices specifically call for the ring and sleeve of TRS plugs to be bridged when used for unbalanced inputs.

And your earlier point about DI boxes is well taken, I'm keeping that in mind.

[EMRR]

Balanced connections must TRS. Period. You can't have a balanced connection if you float the ring.

You don't get the noise rejection of a balanced cable run, true. If they are impedance balanced inputs, floated ring preserves the balance at the input jack itself, not sure what that's worth versus seeing one side grounded, small to negligible benefit.

I haven't noted anything wrong with unbalanced input to the 16A.

[mikehalloran]

I just looked it up. Actually, the UltraLite-mk5 refers to the Line Outs only and no longer says the same about the Line Inputs.

The mk5 manual does still refer to line inputs on a different page, as I quoted in the OP.

MOTU removed floating the rings from the Line Ins from the body of the manual, as they did with the M2/4. I had one of the first M4s and still have an M2 with its original print manual. Leaving it in the description of the jacks is certainly a proofreading error.

As MOTU Manual mistakes go, this one’s pretty benign.