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RE: For analog balanced output ex a DAC, is there any significant difference between RCA unbalanced DAC input to XLR inp

Posted by Thorsten (M) on August 8, 2017 at 23:55:00

In Reply to: For analog balanced output ex a DAC, is there any significant difference between RCA unbalanced DAC input to XLR input? posted by John C. - Aussie on August 4, 2017 at 22:39:28:

Hi,

The "balanced input" is AES-EBU standard (more precisely AES-3).

Like any connection that has no separate clock link it has the exact same drawbacks as SPDIF.

Given that the difference between the nominal AES-EBU link impedance (110 Ohm) and the actual characteristic impedance of the XLR Plug is huge (much bigger than the difference in the RCA vs BNC debate) the signal degradation due to the plug impedance mismatch is way larger than for even RCA based SPDIF, causing greater problems with reflections caused by impedance mismatch.

Past that, actual true 110 Ohm balanced cables are not common and in fact manufactured by very few sources. So usually a poorly impedance matched twin & shield (aka microphone) cable is used, compounding the problems.

The current AES recommendation is actually called AES-3id and uses a BNC Plug, which offers much better impedance match but is (naturally) unbalanced.

I would also question claims of the inherent superiority of balanced outputs. In most DAC's and CD-Players that have come across my bench I found that the balanced outputs added an extra (Op-Amp) stage to provide balanced outputs driven from the single-ended output circuitry.

Similarly many Amplifiers/Preamplifiers use separate add-on balanced to single ended conversion circuitry in front of a single ended preamp circuit (and you guessed it, add on balanced outputs) and sound better on the unbalanced inputs (and outputs).

There are notable exceptions from a few brands, but I found in most cases the balanced outputs were INFERIOR in sound quality to single ended ones on almost any DAC/CDP tried (level matched comparisons, TVC passive preamp). And using Amplifiers/Preamplifiers with similar bolt on balanced input stages showed a serious degradation "going balanced" over the more direct single-ended connection.

So before going on about how great balanced is, it is better to evaluate how the actual circuit is designed, or just listen instead and draw ones own conclusions.

Thor

At 20 bits, you are on the verge of dynamic range covering fly-farts-at-20-feet to intolerable pain. Really, what more could we need?

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