TRS cables.

D

doug662

Member
I have a focusrite 18i8. And I have the 1/4 male TRS outputs. I ran TS and got a hum. My Mackie monitors have a TRS input. Now, I did run these into the RCA RCA Inputs. No hum. But I will have to use the RCA input when I install my sub woofer. So, my question is are the new TRS cables I ordered w
fix the hum?
 
I have some 18i8s. I never worry too much about balanced/unbalanced cables. I'll plug anything into anything.
Never experienced hum on the 18i8.
Some of my sources do not have balanced outputs.
I bought a whole load of TRS cables for my SSL Big Six, but I still connect unbalanced stuff to them.
Maybe you could try an unbalanced cable to the monitors.
 
Hi @doug662
Doesn't sound like a straight forward one.
Normally I'd say get TRS to TRS cables to resolve your issue, as TS cables are not balanced,
but your RCA to RCA worked fine and that's not balanced either.

I'd guess maybe there's a problem with your cables, or the 1/4" inputs/outputs
or, little bit of a long shot, your TS cables were longer and ran closer to some transformer or similar?

If your TS cables are long try coiling them up and/or moving them away from other mains powered devices.
 
You might consider adding a cheap multi-meter to your kit to check continuity of cables. (Or, get a cable tester box).

Audible hum probably suggests an open ground in a cable, and probably just needs to be identified with one of the above, and then corrected with a soldering iron, solder, and maybe a replacement plug. Just buying new, good quality cables every time something doesn't work can get pretty expensive.
 
Slouching Raymond said:
I have some 18i8s. I never worry too much about balanced/unbalanced cables. I'll plug anything into anything.
Never experienced hum on the 18i8.
Some of my sources do not have balanced outputs.
I bought a whole load of TRS cables for my SSL Big Six, but I still connect unbalanced stuff to them.
Maybe you could try an unbalanced cable to the monitors.
Click to expand...
That’s what I would do. Usually it’s not an issue connecting unbalanced equipment to balanced equipment and just using unbalanced cabling, but it is always best to consult the manual. In some cases, more often with more vintage electronically balanced equipment (as opposed to transformer balanced), it is critical how you interface it with unbalanced gear and instructions have to be followed or damage can result. And sometimes you try an unbalanced cable and it doesn’t work, either no signal or there hum, so you then try a balanced cable…and vice-versa. In your case it could depend on how the shields of the devices interface the rest of the guts, but I’d do like @Slouching Raymond suggests and try an unbalanced cable, and if that doesn’t work you may need to lift the shield at one end of your cable and I’d suggest doing that at the monitor end of the cable. Do the monitors and the 18i8 have grounded power cables? Are they both plugged into the same power circuit?
 
I wonder if using a TS cable to connect an impedance balanced output to an electronically balanced input could be the issue. I seem to recall having that problem in the past.
 
I would stay with best practice and connect using TRS cables. The 18i8 uses a 12V power supply and it is very unlikely to carry mains earth through to the interface so a ground loop is unlikely.

I don't know if the Focurite's outputs are impedance balanced or 'symmetrical' amplifiers but if the latter it is not a good idea to use a TS plug. This shorts the ring amp's feed to screen which won't destroy it but will cause it to clip constantly and the clipped harmonics can pollute the tip signal.

Dave.
 
Make sure those cables are pushed all the way in . . . sounds dumb, but you would not believe the amount of times I've had that problem because I was careless inserting the cables!
 
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