UI24R by Soundcraft +48 on TRS?

[Gizmo1977]

Hi there!

Has any of you actually measured with a tester if the Soundcraft provides +48 through the combo inputs including the TRS?

I know it's something quite unusual but I have read it in some FB Groups besides a few awkward issues and I find it quite dangerous (especially if someone plugs a TS, isn't it?).

Thanks in advance!

,

[Wonks]

The standard phantom power arrangement has current limiting resistors in series with the 48v supply of each output, so shorting the 48v with a TS plug (assuming there is 48v on the TRS connection) doesn't blow anything up in the interface, it just draws the maximum current that the sub-circuit can provide. But it's not a good thing to do, and on some interfaces with limited overall phantom power current available, it could compromise the operation of any XLR mic connections that need 48v.

No idea about the UI24R though.

[Mike Stranks]

Hi there!

Has any of you actually measured with a tester if the Soundcraft provides +48 through the combo inputs including the TRS?

I know it's something quite unusual but I have read it in some FB Groups besides a few awkward issues and I find it quite dangerous (especially if someone plugs a TS, isn't it?).

Thanks in advance!

I'm not sure I'd label it as 'dangerous'... The Tascam DR-680 (Mk 1) certainly had this anomaly as I discovered... It gave some weird artefacts if the phantom was on when the line input was used, but no permanent damage was caused.

Of course, still not to be encouraged, as users like me will forget to disengage the phantom before using the line-in.

Like Wonks, I have no idea if the Soundcraft does this...

[Hugh Robjohns]

Has any of you actually measured with a tester if the Soundcraft provides +48 through the combo inputs including the TRS?

I've not tested it myself, but I'd be surprised if Soundcraft allowed phantom on the TRS connections in the combi-XLR. The TRS connections provide a dedicated line input on that device. Phantom should appear only on the XLR connections when activated.

There are products that (shamefully) allow phantom on TRS connections, but they are rare... and Soundcraft do know how to do the job properly!

Testing
If you have access to the rack frame its easy to test with a multi-meter (or dedicated phantom checking tool, although you'll need a TRS to female XLR cable or adapter).

If using a multimeter, select a DC voltage mode (with a suitable range for 50V if not autoranging).

Engage phantom on the channel you wish to test and plug in a short XLR-XLR cable (this just makes it easier to identify the contact terminals).

On the female XLR at the end of the cable, look for numbers adjacent to the three contact holes identifying the sockets. Insert the red probe in the middle hole (3) and the black probe in an adjacent side hole (1).

The meter should read 48V (+/-4V).

If you move the red probe to the other side hole (2) the meter should read 48V again. And if you then move the black probe over to the middle hole (3) the meter should read zero.

Unplug the XLR-XLR cable and plug in a TRS-XLR (female) adapter cable and repeat the test exactly as above. The meter should read zero at all stages.

If you don't have an adapter cable, use s TRS-TRS cable. Hold the black probe on the sleeve (nearest the plug body) and touch the red probe to the tip. The meter should read zero, but 48V if phantom is present. Same with red probe on the middle ring.

I find it quite dangerous (especially if someone plugs a TS, isn't it?).

It's not dangerous in the sense it could hurt you... but it is dangerous in that it phantom power on the connection could damage or kill electronic instruments and other line-level sources. I have witnessed the demise of both a CD player and an expensive keyboard due to phantom power inadvertently appearing on the connection. (Neither occasion was caused by me, I hasten to add, but it is as a result of seeing that happen that I ALWAYS use DI boxes or line transformers when connecting my gear on stage, specigically to protect against accidental phantom.)

If phantom was present on a TRS socket, plugging in a TS plug would short the cold side to ground, drawing 7mA through its current limiting resistor, forcing it to dissipate 0.3 Watts continously. In a poor design that may result in the resistor burning out!

48V would remain on the Tip connection.

If anyone has access to a ui24 it would be good to confirm whether or not phantom appears on the TRS contacts of the combi inputs...

[Gizmo1977]

Thanks all for your answers. Hugh, as always so detailed and clear.
The UI24r is a piece of gear I'm interested in but I've read comments every now and then in user groups in FB that make me think it's not so reliable (dead channels, audio dropouts...). Issues I haven't read on other user groups which include Yamaha, A&H, Behringer.... Being Behringer a brand that can't be expected to be so reliable and, as being more affordable, having more options of being badly used due to lack of knowledge or experience.

One of the issues commented was that combo inputs drew +48 even on TRSs. Taking into account that inputs 1 and 2 can be used as HiZ with amp emulations, and taking into account that leaving +48 on isn't generally a problem ('cept frying phones/laptops, ribbon mics...), it would be too dangerous if someone had plugged a Beta91 for kick on 1, and afterwards try to record some guitar with his TS cable.

Thanks again.

[Hugh Robjohns]

The UI24r is a piece of gear I'm interested in but I've read comments every now and then in user groups in FB that make me think it's not so reliable (dead channels, audio dropouts...).

I understand your concerns. I know the smaller units (ui12/16) had WiFi connectivity issues due to different interface circuitry in combination with non-obvious configuration requirements. I've not heard consistent tales of unreliability in the ui24, though... but my user polling is not extensive! Most of my live-sound and band contacts have various A&H consoles, and they all love them!

One of the issues commented was that combo inputs drew +48 even on TRSs.

It is possible. Let's hope someone here can provide a definitive answer.

[Gizmo1977]

WiFi wouldn't be an issue using an external router I guess, which is something I always do when working with an XAirs or anytime I use my iPad to control a mixer.

My concerns goes about their reliability. I read about noisy/dead channels quite often, about 10 sencod dropouts, while people keep talking about investing in fans, UPS, AVRs...

Gear that should be recommended but never compulsory for a decent piece of gear in with stable power and not extreme weather (and good ventilation). Besides, if heat was an issue, no component would cool down enough in those 10 seconds.

I would expect frying a preamp in a cheaper piece of gear, or that it had a limited and too sensitive power supply... There are people who have posted really poor jobs with the thermal paste that might be one of the reasons but that would mean voiding the warranty by opening the unit.

Would love to read Soundcraft post something about all this, but you know that in case there was an actual problem it would be really difficult to see a company admitting it.

[Aled Hughes]

If I get a chance this week I’ll test on mine.

No reliability issues here by the way. I think it’s a fantastically versatile unit, with a few quirks (and a few things that could be expanded on a more expensive version)

[Hugh Robjohns]

Thanks Aled*, that would be very helpful.

*(Apols -- autocorrect renamed you and I hadn't noticed!)

[Gizmo1977]

Thanks all for your answers!