• Registered: 2011-11-20
  • Posts: 22

Topic: UFX analog out 1/2 -> RCA pinouts

I'm sorry if this has already been asked, but I have been looking on the board and can't find what I would call a definitive answer.

I am building a pair of adapter cables for the UFX which need to go to an RCA input on my AHB mixer.  I thought I understood this just fine until I read this in the manual:

"The electronic driver circuit of the XLR outputs does not operate servo-balanced!  When connecting unbalanced equipment, make sure pin 3 of the XLR output is not connected.  A connection to ground will cause higher THD!"

OK, that's good to know, but I have a factory built XLR to 1/4" TRS cable and pin 3 of the XLR is wired to the TIP of that cable.  So what does this mean?  Nothing connected to the tip?

I'm confused now and I would love some clarification.  I should also note that I am enjoying the Fireface very much and this is the only confusing thing I have found in the manual.

Best to all,
Bill

  • From: Houston, TX
  • Registered: 2007-05-11
  • Posts: 1,191

Re: UFX analog out 1/2 -> RCA pinouts

I believe you are lumping unbalanced RCA cables in with your balanced TRS cable.  Your TRS cable is balanced (tip, ring, sleeve = 3 conductors for balanced transmission) and should be wired Pin 1 to Sleeve; Pin 2 to tip, Pin 3 to ring (sounds like yours has inverted polarity based on your observation).

You don't want to short Pin 3 to Pin 1 for unbalanced 1/4" TS (tip/sleeve) or RCA connections.  In this case, Pin 1 goes to shield/sleeve, and pin 2 ("hot") goes to tip/center-pin.  Pin 3 (the inverted output) would be left un-connected for unbalanced (2-conductor) operation.

cool

MADIface-XT+ARC / 3x HDSP MADI / ADI648
2x SSL Alphalink MADI AX
2x Multiface / 2x Digiface /2x ADI8

3 Reply by wjniemi (edited by wjniemi 2011-11-20 22:10:34)

  • Registered: 2011-11-20
  • Posts: 22

Re: UFX analog out 1/2 -> RCA pinouts

Thanks a $million for your quick response.

I am not sure why my 1/4" TRS to XLR are wired with tip to pin 3, but I bought 6 of them from a company called BTX and 4 of them are in place and working in my rack.  Weird.

However, I am very thankful for your help, and if you would prefer your thanks in a different currency I could understand completely.

Cheers,
Bill

Quick edit... OH, I get it... it's the INVERTED output!  Doh!

  • From: Houston, TX
  • Registered: 2007-05-11
  • Posts: 1,191

Re: UFX analog out 1/2 -> RCA pinouts

Lol - Your thanks is more than sufficient :-)

There is not a de-facto standard for XLR pin-outs, but it is generally accepted that Pin 2 is "hot/+" and Pin 3 is "inverted/-" - but plenty of gear is wired Pin 3 "hot/+".  Using cables of opposite polarity shouldn't harm your balanced equipment, but will have the same effect as flipping the "phase invert" button on that channel (waveform polarity is inverted).  This can have a drastic effect on the audio if combined with other correlated signals - or it can have little to no audible effect depending on the exact scenario at hand ("Relative polarity/phase" versus "absolute polarity").

If the "Pin 3 -to- Tip" cables are working in your setup, you are probably alright, but be aware that polarity issues might creep up as your setup and techniques change.

Regardless, you should go with "XLR Pin 2 -to- RCA Center Pin" and leave XLR Pin 3 unconnected for your unbalanced RCA cables.


And while we are on the topic, a Q for RME:
Since it is stated that the XLR Outs shold not have Pin 3 shorted, is the same true for the UFX's 1/4" TRS outputs, or are they using a different line driver stage (otherwords, are there any issues using regular unbalanced 1/4" TS cables in the 1/4" TRS outs?).  I don't own a UFX, but am curious since this topic came up...

cool

MADIface-XT+ARC / 3x HDSP MADI / ADI648
2x SSL Alphalink MADI AX
2x Multiface / 2x Digiface /2x ADI8

5 Reply by MC

  • MC
  • MC
  • Administrator
  • Offline
  • From: Germany/Thailand
  • Registered: 2007-04-06
  • Posts: 25,599

Re: UFX analog out 1/2 -> RCA pinouts

The UFX XLR outs are the same as all our others, - should not be shorted to ground.

Regards
Matthias Carstens
RME

MC's Website

  • From: Houston, TX
  • Registered: 2007-05-11
  • Posts: 1,191

Re: UFX analog out 1/2 -> RCA pinouts

I don't own the UFX so I haven't reard the manual, but I'm assuming there is also a blurb about not using standard 1/4" TS plugs on the TRS Outputs (will short Ring to Sleeve at the UFX, correct?)?  These types of cables are very likely to be plugged into an output (like a 1/4" TS to RCA) - more so than an XLR with pin 3 shunted to ground IMO...

Just looking out for the UFX users with unbalanced output needs :-)

cool

MADIface-XT+ARC / 3x HDSP MADI / ADI648
2x SSL Alphalink MADI AX
2x Multiface / 2x Digiface /2x ADI8

7 Reply by MC

  • MC
  • MC
  • Administrator
  • Offline
  • From: Germany/Thailand
  • Registered: 2007-04-06
  • Posts: 25,599

Re: UFX analog out 1/2 -> RCA pinouts

?????

Same as with your ADI-8, no problem...

Regards
Matthias Carstens
RME

MC's Website

  • From: Houston, TX
  • Registered: 2007-05-11
  • Posts: 1,191

Re: UFX analog out 1/2 -> RCA pinouts

MC wrote:

?????

Same as with your ADI-8, no problem...

Ah - I thought your initial response stated otherwise:

The UFX XLR outs are the same as all our others, - should not be shorted to ground.

I thought you were saying the XLR's should not be shorted to ground just like all other RME Outputs (meaning the TRS outputs as well) - but the XLR outs apparently use a different line driver than the TRS outputs.

Thaks for the clarification.  cool

MADIface-XT+ARC / 3x HDSP MADI / ADI648
2x SSL Alphalink MADI AX
2x Multiface / 2x Digiface /2x ADI8

9 Reply by wjniemi (edited by wjniemi 2011-11-22 00:36:45)

  • Registered: 2011-11-20
  • Posts: 22

Re: UFX analog out 1/2 -> RCA pinouts

Tearing my hair out in the Turtle Bowl....

OK, I have built a short adaptor cable to make AN1/2 available to my board and I know something can't be right.  The main symptom... it's not working. (LOL sorry I had to say that because I used to hear it all the time when I did support).

Here's my cable:  XLR female to TRS female

          PIN 1 XLR => pin 2 TRS (ring)
          PIN 2 XLR => pin 3 TRS (tip)

I have ohmed this out through the actual cable I'm using to the mixer and pin 1 XLR goes to outer ring of RCA, pin 2 XLR goes to center of RCA.

* The actual cable is a RCA - TS 8 channel snake.

I apologize if I misunderstood something in the previous post, but I'm scratching my head in utter amazement that it's not working.  The two wires are NOT shorted to each other, and pin 3 of the XLR is connected to thin air.

Could some kind soul please set me straight on this?

Many thanks in advance....

Bill

PS  The "Turtle Bowl" is in the middle of the United States, some also refer to this part of the world as "flyover country".  I'm OK with it, I've traveled around the world as a musician and am happy with my little cottage studio, and so far I've not seen one turtle in it.

  • From: Houston, TX
  • Registered: 2007-05-11
  • Posts: 1,191

Re: UFX analog out 1/2 -> RCA pinouts

Sounds like it should be working - are you sure you are getting signal at the UFX XLR's?

How are you adapting the 1/4" TRS (from the XLR -to- TRS cable) to the RCA -to- TS snake?

Can you test if the RCA -to- TS cable works in one of the UFX's 1/4" outputs?

cool

MADIface-XT+ARC / 3x HDSP MADI / ADI648
2x SSL Alphalink MADI AX
2x Multiface / 2x Digiface /2x ADI8
  • Registered: 2011-11-20
  • Posts: 22

Re: UFX analog out 1/2 -> RCA pinouts

Hi, and thanks again,

According to the meters on the front of the unit and the software mixer application, there should be signal at the XLR ports. Greenness on the two lower left slivers...

OK... the TS snake is plugged into the TRS female jack.  It connects to the tip and ring, and this rings out with my meter at the RCA end from the XLR end.  Pin 1 XLR to ring of the TRS, Pin 2 of the XLR to the tip.  That leaves the sleeve pin in the TRS connector unconnected, and also pin 3 of the XLR.

I have the other 6 TS leads plugged into the Analog outs 3-8 and connected to the RCA inputs on the board.  They are working just fine.

I was wondering if I might have hosed something up in the UFX by grounding something that shouldn't have been grounded.  When I went to build these, I scavenged a Neutrik female XLR connector and a chunk of 2 cond shielded from a mic cable in the "fix-it" box.  I attached the TRS female to that cable (wrong) and then corrected that and it still wasn't working so I opened up the XLR connector and there was a jumper between the ground and the shield (DOH!) so I clipped that.  Funny I didn't notice that when I clipped the wire on pin 3.  My eyes aren't what they used to be, thanks to the aging process.

So I'm wondering if the device has some way to shut itself off to keep from being blown up by nincompoops who keep hooking up cables with wrong pinouts and shorts?  If I pull the connector out of AN1 and stick a meter lead into pin 1 or 2, I can ohm it out on the RCA connector as expected.

I appreciate your thoughts.  There may be something odd going on with the software mixer, too, though.  In submix mode whenever I change the output of the playback to a different analog out, the entire playback section changes to that same output.  I am not sure if that's the way it's supposed to work.  However, I have been able to move the meter on the AN 1 output so if that's truly an indication of signal on the XLR jack we've got it.

Curious. 

Cheers,

Bill

12 Reply by MC

  • MC
  • MC
  • Administrator
  • Offline
  • From: Germany/Thailand
  • Registered: 2007-04-06
  • Posts: 25,599

Re: UFX analog out 1/2 -> RCA pinouts

Randyman... wrote:
MC wrote:

?????

Same as with your ADI-8, no problem...

Ah - I thought your initial response stated otherwise:

The UFX XLR outs are the same as all our others, - should not be shorted to ground.

...same as all our other XLR outputs...  :roll

Regards
Matthias Carstens
RME

MC's Website

  • From: Houston, TX
  • Registered: 2007-05-11
  • Posts: 1,191

Re: UFX analog out 1/2 -> RCA pinouts

Pin 1 XLR to ring of the TRS, Pin 2 of the XLR to the tip.  That leaves the sleeve pin in the TRS connector unconnected, and also pin 3 of the XLR.

I believe that's part of the issue - XLR Pin 1 should go to the Sleeve/Shield of the TRS and/or RCA.  XLR Pin 2 should end up at the Center Pin of the RCA ("hot"), and XLR Pin 3 is not connected.

If you are handy at soldering, you can easily chop off the 1/4" TS connectors on your snake's channels 1/2, and wire an XLR directly onto the cable (XLR Pin 1 to Shield, and XLR Pin 2 to Center Pin).


Roger that, MC :-)

cool

MADIface-XT+ARC / 3x HDSP MADI / ADI648
2x SSL Alphalink MADI AX
2x Multiface / 2x Digiface /2x ADI8
  • Registered: 2011-11-20
  • Posts: 22

Re: UFX analog out 1/2 -> RCA pinouts

I hate to cut up a brand new $120 snake.  I will try to get my adapter working first... then hold that in reserve.

If I ring out pin 1 from the XLR adapter to the end of the snake it gives me 0 ohms on the outside ring (shield) of the RCA.  So by all rights it should be working.  Of course, by all rights I should be dead at least twice from medical mistakes and arguably once from sheer dumb luck.

I will do some more checking and let you know shortly what I have discovered.  THX!!!!!!!!!!!!
Bill

  • Registered: 2011-11-20
  • Posts: 22

Re: UFX analog out 1/2 -> RCA pinouts

OK, I didn't make any changes to the cable and as far as I can tell, I didn't make any changes to the Matrix (love the name.) 

But now the cable is WORKING.  I don't know how to attribute this one.  I left the rack power off overnight, so maybe something inside of it reset?  For whatever reason, it's working and I can proceed with building the second one and getting back to work.

One thing I did notice is that just connecting the tip wire was sufficient to operate the channel.  I assume this is because I have 23 other ground connections from the 3 ADAT output banks to serve as the second conductor.  I guess I will leave it connected because it doesn't seem to hurt anything and it does shield the 3" of cable between the XLR and the 1/4" jack.

I do love a good mystery once in a while, maybe there's even some supernatural stuff going on.  Like help from the ghosts of the 7 turkeys I didn't eat while I was a strict vegetarian.  Whatever.

Thanks, Randyman, and should I not post back before Thanksgiving, have a very good one.

Best regards,

Bill