[sejarzo]

Not a DIY question, but a technical one nonetheless--and it seems this is the place to get straight answers, and quicker, than on something like the source forums.....

I get a lot of questions from new 0404 USB users about using the TRS output jacks to drive unbalanced amps, and I assure them that it's OK to plug TRS-to-RCA cables or adapters into those TRS jacks. That's plainly verified by the info in the E-MU manual.

However, I do know that some pieces of gear with only XLR connectors for balanced outputs use output stages that are not designed to allow the "cold"/inverted/pin 3 signal to be grounded....that one must allow pin 3 to float, and simply connect pin 1 to the RCA sleeve, pin 2 to the RCA pin if it's necessary to drive an unbalanced load from those outputs.

That begs this question, at least in my mind: Has anyone ever encountered a balanced source output on TRS jacks that is not compatible with TS plugs, and could be damaged simply by inserting a TS plug?

Thanks!

 

[nikongod]

TS plugs in TRS jacks is a BAD BAD BAD idea.

the risk (gaurantee!) of shorting out your junk is too great.

just float the out-of-phase connection. if you want to get super-fancy (which may actually help some devices) you can ground the out of phase connection THROUGH a resistor equal to the load.

 

[sejarzo]

Not necessarily........E-MU provides diagrams in the manual along with text that clearly show the proper way to connect the 0404 USB to an unbalanced load is via TS plugs into the TRS jacks.

I'm not an EE, but I believe the proper term may be "cross coupled balanced output stage" for the type of circuit that allows the inverted side to be grounded without harm. Analog Devices makes a chip called the SSM2142 "Balanced Line Driver" specifically for this purpose.

And considering that my 0404 USB has operated for over 1000 hours with TS plugs in the TRS jacks, it sure seems as if it's designed to be used that way!

I had presumed that most manufacturers, if the device couldn't operate properly in unbalanced mode with TS plugs, wouldn't even install TRS jacks and simply provide XLR's, because one must use a modified (as it were) XLR to short the cold side to ground....whereas there is no impediment to putting a TS plug in a TRS jack!

 

[amb]

You would short circuit an output to ground by using a TS plug in a TRS jack. Whether that is ok is implementation-specific. Perhaps it's fine in the EMU 0404 USB, and may indeed be a good idea in some cases (as in the SSM2142 example, see the last paragraph in the application section of its datasheet). However, since your thread title is "always OK?", I think the answer would be no.

 

[sejarzo]

Thanks, amb! It seems like RTFM and contact the manufacturer when in doubt are always the best options, eh???