• Registered: 2023-01-04
  • Posts: 29

Topic: ADI-2 Pro auto ref behaviour

ADI-2 Pro has a great auto ref feature; however it has a strange behaviour when using the TS jacks with the rear 1/2 output.

As described in the manual, the reference output is capped at +19 dBu for those outputs, but the way this is implemented seems strange. It all works as expected until reaching -5 dBr, which correctly sets the digital volume at 0 dBFS at +19 dBu. Raising the volume further to -4.5 dBr the display shows +24 dBu reference, but the actual output signal seems to drop by 5 dB (haven't measured exactly). Coming to 0 dBr volume from that point, we actually seem to arrive to the same output level as the one we had already at the -5 dBr volume setting.

I don't know if the device detects the jacks being plugged into the rear 1/2 output. If it does, it would seem to be possible to implement the volume control without this discontinuity. If it does not, perhaps a menu configuration could be made available to manually tell the device how it is being used.

Have I overlooked something?

ADI-2 DAC FS
ADI-2 Pro FS R BE

2 Reply by KaiS (edited by KaiS 2023-02-20 02:12:34)

  • KaiS
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Re: ADI-2 Pro auto ref behaviour

It‘s been irritating when I experienced this in the first place, I know.

The idea behind:
TRS and XLR should carry the same level.
But this is not possible above +19 dBu, as TRS would run into clipping.


Why:

XLR’s electronically balanced out uses two active pins 2=(+) and 3=(–).

TRS’s “impedance balanced” out uses one active pin only, Tip (+) and passive Sleeve=(ground).
Ring does not carrying an active signal, but being connected to ground via an impedance matching resistor.

Therefore XLR is capable to deliver twice the voltage, or 6 dB more level, before clipping.


TRS can”t go above nominal 19 dBu (in fact 22 dBu) so when switching XLR to the highest Reference Level of 24 dBu TRS can not follow.
But for XLR’s continuous volume ramp, the DAC, used commonly for both outputs, is switched back by 5.5 dB at the 19 to 24 dBu transition.
This makes the TRS step down by those 5.5 dB at this last transition point.


Hope the above is understandable.


My simple workaround to get an unbalanced out with continous volume control:
I made a cable only using XLR pin 2 (+) and pin 1 (ground) an leave the TRS alone.


BTW: The DAC doesn’t need to have this behavior, RCA out simply is 6dB quieter in level.

KaiS's Website

  • Registered: 2023-01-04
  • Posts: 29

Re: ADI-2 Pro auto ref behaviour

Thanks for your response, Kai.
You are completely right, XLR can be used instead and the output stage design is clear to me.

However, the device does have those TRS connectors built in, and if I understand correctly, the manual advocates their use for the unbalanced connection, using e.g. a TS/RCA adapter (sleeve and ring shorted).

My point was to suggest an improvement on the usability of the existing product feature without a need for a workaround, i.e. not using it.

ADI-2 DAC FS
ADI-2 Pro FS R BE
  • KaiS
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Re: ADI-2 Pro auto ref behaviour

WowFlutter wrote:

... My point was to suggest an improvement on the usability of the existing product feature without a need for a workaround, i.e. not using it.

I totally agree this behavior is irritating.

I don’t think it can be changed by firmware, as XLR and TRS aren’t fully independent in the hardware domain.

ADI-2 DAC’s 6 dB lower output on the RCA / unbalanced out vs the XLR is the better solution.
Even offers a good fit to the typical levels present in home-HIFI.

KaiS's Website

  • Registered: 2023-01-04
  • Posts: 29

Re: ADI-2 Pro auto ref behaviour

How is the ref level switch between +19 dBu and +24 dBu implemented in the electronics of ADI-2 Pro?
Asking because there is no relay click audible when switching between these two levels, unlike others.

ADI-2 DAC FS
ADI-2 Pro FS R BE

6 Reply by MC

  • MC
  • MC
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  • Registered: 2007-04-06
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Re: ADI-2 Pro auto ref behaviour

Electronic (analog) switch.

Regards
Matthias Carstens
RME

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