Promitheus Audio DAC and Bursons Discrete Op Amps

The above is the Promitheus Audio DAC which uses the non over sampling concept and has 2 separate output transformers, one for each channel. The DAC uses 2 IC Op Amps, one for each channel - the Phillips 4532.

The Bursons Audio discrete Op Amps replaces the stock IC Op Amps and a separate power supply capable of supplying +/- 18V regulated is added and the difference is clearly shown in the photos below. Before and after the changes.




This was done a few months back and the problem was the output of the Bursons Op Amps are not null (not zero) and cannot be adjusted. Hence a small dc voltage is fed to the output transformers. Although the output is still pure ac since the transformers block dc voltage from going to the secondary coils, the primary coils are slightly magnetised due to the dc voltage. I checked with Promitheus' Mr Nicholas Chua and he explained that a very small dc voltage is advantegous - small in the order of up to 20mV. But mine was way above that level. So, I ended up with dc blocking (coupling) capacitors - some 40uF each side, temporarily. I complained to Bursons, more on that later...