How to bias current source output dac?

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I can't seem to find the answer to this.
I have a PCM1795 I want to play with but it has a current source output which I am not familiar with.
The datasheet doesn't say what voltage output is optimal.
I'm guessing I just center it at the mid point like other dacs?
 
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Yeah I saw that but I don't quite get it, how can the current source go down to ground since there is no negative rail in the dac? Is it an unloaded high side current source internally? I'm guessing if I want to avoid a DC offset I need to use some form of current sink?
 
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Current output type DACs ideally want to drive A.C. virtual ground nodes. The D.C. level (aka, the common-mode offset) of such virtual ground nodes varies among DAC chips. For some, it's the midpoint of the D.C. supply, for others such as the PCM1795, it's at the supply ground level. (Do not reference the PCM1795 outputs to the supply midpoint.) Keep in mind, current output DACs swing signal current not signal voltage, so there is no negative signal voltage swing at the current output pins even though the PCM1795 drives a virtual ground node set at the supply D.C. ground level.

Among your experiments, I suggest trying a simple resistor I/V. Such an I/V has many dynamic performance (and subjective listening) advantages over an active I/V. The one clear drawback is that the measured THD will be a bit greater as the DAC distortion is lowest driving a virtual ground rather than a small resistance. For the PCM1795, I suggest utilizing 150 ohms or less for the I/V. Just connect the DAC current output pin to one side of the I/V resistor and the other side of the resistor directly to signal ground. The resulting signal voltage can be tapped from the DAC's current output pin and will be in the range of 200mVRMS or less, so it will need some voltage amplification.
 
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Just connect the DAC current output pin to one side of the I/V resistor and the other side of the resistor directly to signal ground. The resulting signal voltage can be tapped from the DAC's current output pin and will be in the range of 200mVRMS or less, so it will need some voltage amplification.

Or, you could just look at the data sheet and learn that the PCM1795 current output is a differential signal that is the difference between the output from the Iout+ and Iout- for each channel. It is not referenced to ground.

Oh, sorry, I forgot. You diyAudio folks NEVER look at datasheets.
 
Or, you could just look at the data sheet and learn that the PCM1795 current output is a differential signal that is the difference between the output from the Iout+ and Iout- for each channel. It is not referenced to ground.

Oh, sorry, I forgot. You diyAudio folks NEVER look at datasheets.

Apparently, you've looked but still didn't understand what you saw.

The farther above ground level the common-mode voltage the greater the DAC distortion. While the output currents are differential, the output pins are designed to operate in to a 0V (ground level) common-mode virtual-ground node. This is obvious from the application I/V converter circuits shown in the data sheet, if you had bothered to look at them, rather than accuse me of the ignorance you yourself have displayed. Ignorance and arrogance are a particularly distasteful combination of traits.

I looked at the datasheet multiple times.
I found nothing of what you spoke.
Could you elaborate?
I think you may have mis-interpreted the differential section as pertaining to the dac output instead of the I/V stage.

Hi, hellokitty, to whom are you addressing the above question? If it's to me, could you be more specific in what you're asking?
 
Or, you could just look at the data sheet and learn that the PCM1795 current output is a differential signal that is the difference between the output from the Iout+ and Iout- for each channel. It is not referenced to ground.

Oh, sorry, I forgot. You diyAudio folks NEVER look at datasheets.

The Iout current "exists" (starts to flow) only if there is a path from Iout pins towards the ground...

The ground "point" for the purpose of the I-to-V conversion, on page 54, is the NE5543 pin 2. This is somewhat difficult to understand until one draws the output stage of the operational amplifier, and then follows the current flows between the output transistors and the Vcc / Vee & power supply ground, which is connected to a "global" circuit board ground (as shown on the page 54 circuit diagram)

With a proper choice of the OP, the dynamic impedance of that "ground point for the purpose of the I-to_V conversion", could be very close to 0 ohms.

Walter Jung depicted the AD811 current feedback circit diagram that does the above: "High_Performance_Audio_Stages_Using_TransZ_Amps.pdf"

It works execeptionally well, escpecially with a very low Iout DAC's like 1704
 
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