Transformer sweeps as promised.
See notes at the bottom of each sweep. With and without C704.
Edcor 150-150 (Stock)
Edcor XS4400
Both 1:1 and 1:2 modes were tested (see plot titles). Note the fairly significant phase shift and attenuation at 20k (-.6dB) (even without the 15nF capacitor) when wired in 1:2 mode. (MKII)
Here are the sweeps for the LL1948 transformer. The configuration is described in the notes field for each. These are the best of the three however the nickel core transformers will out perform these by a large margin.
All measurements were done with the transformer wired 1:2 (parallel primaries, series secondaries with grounded center tap). 1st one is without C704. 2nd one is with C704. Notice the high frequency, distortion, and phase change with C704 installed.
Our transformer design goal is to improve the high-frequency errors present when using both the XS4400 (mk2 DAC) and LL1948 in 1:2 mode while maintaining a low THD at low frequencies by use of a high-quality nickel core.