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What's wrong with my RME Audio Interface?

restorer-john

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Where "ground" comes in is consideration of balanced, and there, the ONLY thing that matters is equal impedances to ground. Equal voltages to ground aren't necessary for balanced transmission and reception.

Absolutely true. Except they were clearly created from a single ended source that was referenced to GND/0V in the first place. We are, remember, discussing outputs, from a DAC in this thread.

The DAC was, and is, not remotely floating, balanced or differential, apart from the fact that it has two +/- outputs from the IC/OPT itself. The original source signal was never differential or balanced. It was NRZ at its core.
 
OP
peniku8

peniku8

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I don't even know what's going on anymore. I fed the signal back like I did in my first post (negative connected to ground, positive to hot) and saw some wierdness again, played it back through my speakers and it sounded audibly distorted. The following wave form was recorded during the first test (which is also to be seen in post 1):

zdSFsuq.png


I then changed the output reference from +4dbU to HiGain and back to +4dbU again and recorded the waveform again (not gain matched to above measurement):
lTPQnpG.png


So.. I am confused now
 

MRC01

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Originally, you said you measured 1.9 V on + and 1.3 V on - so they seemed unequal. But all voltages are relative to something, they are the difference between 2 points. What if the reference point (call it "ground") that you used for these measurements is off? If you picked a different reference point 0.3 V above the original, you'd measure the same 1.6 V on each. Yet this way of measuring each signal against a ground is in some sense artificial because if some downstream device received both signals and simply differenced them against each other, it would get perfect doubling without the need for a separate ground.

I think this is the point that RME was making earlier.
 
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peniku8

peniku8

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Originally, you said you measured 1.9 V on + and 1.3 V on - so they seemed unequal. But all voltages are relative to something, they are the difference between 2 points. What if the reference point (call it "ground") that you used for these measurements is off? If you picked a different reference point 0.3 V above the original, you'd measure the same 1.6 V on each. Yet this way of measuring each signal against a ground is in some sense artificial because if some downstream device received both signals and simply differenced them against each other, it would get perfect doubling without the need for a separate ground.

I think this is the point that RME was making earlier.
That makes sense, I didn't take into account that the signal might've used a difference "zero reference" (what would the correct technical term for this be, if I don't use "Gound"?). If I understand this correctly, there is no need for "ground" for the differential signal, but the ground will be needed as a common reference after the differential signal has been converted back to single-ended.
 

SIY

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The DAC was, and is, not remotely floating, balanced or differential, apart from the fact that it has two +/- outputs from the IC/OPT itself. The original source signal was never differential or balanced. It was NRZ at its core.
If you look at the output of the DAC, it is absolutely differential. It is also absolutely balanced.
 

pma

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That makes sense, I didn't take into account that the signal might've used a difference "zero reference" (what would the correct technical term for this be, if I don't use "Gound"?). If I understand this correctly, there is no need for "ground" for the differential signal, but the ground will be needed as a common reference after the differential signal has been converted back to single-ended.

Ground reference is always needed otherwise you get into CMV (common mode voltage) problem if the components are floating each against other. The input allowed CM voltage is exceeded though differential voltage is OK.
 
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