The Simple Transformer Explanation…
There are a lot of reports and discussions about using a transformer as I/V stage for Sabre32/Buffalo DAC, but is it such a good idea?
There is simple explanation why it is not.
According to the specifications, and the Sabre DAC whitepaper, THD will increase from -120 db to -108 db if you use the DAC in voltage mode. That is the same as saying that you need to hold the output voltage at a constant value to obtain maximum performance/minimum distortion.
A transformer basic voltage equation is Vp=RtVs, where Vp is the voltage across the primary, Vs is the voltage across the secondary and Rt is the turn ratio.
For a 1:1 transformer then, Vs=Vp.
Thus if you expect a voltage across the secondaries, there will be a voltage across the primaries and therefore you cannot hold the output voltage of the DAC constant.