This video documents part 1 of the modifications I designed and tested for a Musical Fidelity Tri-Vista 21 Class A Tube DAC.
Beautifully built, the performance of this DAC is limited only by some parts choices. The 5532 op-amps are very good, even by today's standards, but may be bettered, at least to see if this improves things. I have bypassed electrolytic caps in the power supply and installed a matched set of NOS Raytheon 5703 tubes for the class-A output stage. I also replaced all electrolytic caps outside the main PSU board with high-temp, low-impedance types, replaced all the ceramic decouplers with mil-spec Siemens MKT. I changed a few filter capacitor values and critically, replaced the bi-polar electrolytic capacitors used for output coupling with premium film types.
The result was a big improvement to an already great-sounding DAC. Visit http://liquidaudio.com.au for more great restorations and repairs!