A I/V stage that will handle the new differential ouput DAC's like the PCM179x is really needed in the DIY world. There are a few great projects out there using these chips (Rakk, EZDAC) that would be a lot better with a D1 or Jocko type I/V.
Isn't the problem that the 179x have a DC offset ? Or would you recommend just using coup[ling capacitors and not worrying about the offset ?
It is not a problem. I designed it for the TDA1541A which has 2 mA offset, while the PCM1798 has 3.5 mA offset. The offset current flows from the centre tap of the input transformer (ground) into the current outputs of the DAC. This current is in opposite direction at each half of the primary, so they cancel each other.
In the op-amp output stage version the current output of the DAC is at ground potential, and the offset current flows from the virtual ground into the DAC output (and the same current flows from the op-amp output to the virtual ground). The DAC pulls the necessary offset current from the ground always, regardless of wether it is hard tied to ground, connected to a virtual ground, or connected to a transformer that has a center tap on ground.
In the op-amp output stage version the current output of the DAC is at ground potential, and the offset current flows from the virtual ground into the DAC output (and the same current flows from the op-amp output to the virtual ground). The DAC pulls the necessary offset current from the ground always, regardless of wether it is hard tied to ground, connected to a virtual ground, or connected to a transformer that has a center tap on ground.
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