Connecting XLR to RCA adapter to FPIII's RCA input?

[audiblesoundwave]

Hi,

Is there any problem/issue for connecting from XLR output of a DAC through a XLR-to-RCA adapter with the RCA interconnect into the FPIII's input?

DAC's XLR output --> XLR-to-RCA adapter --> RCA interconnect --> FPIII SE input

XLR-to-RCA pin connections; XLR pin 2 to RCA hot.  XLR pin 3 and 1 to RCA 'ground'!

Will this damage FPIII and/or the DAC?

Thanks!

Happy holidays to everyone,
Milton

 

[JC]

I would be concerned about the DAC output.  To be on the safe side, I would start by leaving pin 3 on the xlr open.  Leaving it connected to pin 1 may end up grounding something you would rather not have grounded, like the output of an amp which would not be happy with you.

 

 

[audiblesoundwave]

Thanks Jim for the reply!

However, I want to make sure I understand the 'not connect pin 3 of the XLR'.  I thought pin 3 is the 'return', not the 'grounding'

Happy holidays,
Milton

 

[Paul Joppa]

For lots of information, go to the jensen transformers web site http://www.jensen-transformers.com/ then "white papers" then AN-003, "Interconnection of Balanced and Unbalanced Equipment". There is a lot of valuable background information in this paper.

Unfortunately, Whitlock shows more options for connecting unbalanced outputs to balanced inputs, compared to the reverse which is your case. Both of his suggestions involve a transformer. Also note that he assumes the balanced output is 12dB louder so his circuits proved 12dB of voltage attenuation - hard to say whether you need that or not, without more information.

In the text (but not diagrammed) he describes how a source device with an output transformer can be can be connected with no additional transformer; this assumes the output of the OPT is not center-tapped or grounded in any way. He does not describe using one side only of a "typical balanced output" as implemented with opamps - this is the arrangement proposed by JC and Grainger49.

A quick search for adapters provides this phrase, used in most descriptions: "Wired according to IEC 268-12: pin 2 = signal pin 1 and 3" - the same as described by audiblesoundwave. JC's concern is valid when examined in light of the Jensen paper's circuits, leaving some confusion! I have not been able to find a reliable answer in a quick search this morning, so I advise that you ask the DAC manufacturer for their advice - possibly quoting the description of the adapter you propose to use so they have a specific configuration to address. If you do this, please post what you hear back!

 

[JC]

Actually, if pin 3 has the "-" signal of the balanced pair, that is not a "return", but another signal that is equal to and 180 degrees out of phase with the "+" signal on pin 2.  You could easily use the "-" signal of the balanced pair as your "hot" going into an unbalanced input and it would work just fine.  This is a useful technique when you wish to reverse the phase in the signal chain for some reason.

But, as a fully functional signal in its own right, the "-" on the balanced output of a piece of gear most likely comes from the output of an amplifier.  It could also come from the balanced secondary of an output transformer, but this is far less likely in recent years: an amp-on-a-chip is generally cheaper than a transformer, so that's what gets used.

The manufacturer of the DAC will know which his product uses, and will very likely have an authorized procedure for connecting its output to an unbalanced input.  Paul's suggestion to contact the manufacturer is an excellent one.

But, failing that, your best bet is to never "ground" either pin 2 OR pin 3 of a balanced output, or cause it to be grounded by the next piece in the chain.  By simply using EITHER the "+" OR the "-" signal line and leaving the other floating, you will almost always get your unbalanced signal and not run the risk of hurting anything.

 

[audiblesoundwave]

Thank you Paul and Jim, and everyone else.

Happy Holidays to you all,
Milton

 

[JC]

And, Happy Holidays to you!

I have been giving you the "better safe than sorry" approach; I will definitely be interested in hearing what you ultimately decide to do and how it works out.

 

[audiblesoundwave]

Sorry Jim!  I did not come back and read your reply until today.

Anyhow, I decided not to use the XLR to RCA adapter due to too many uncertainties.  Instead, I am building a XLR to RCA converter.  This is a more expensive route but safer route to convert XLR to line level single ended RCA!  This converter will also give me the flexibility on 'rolling' opamps! 

Milton