I recently finished another, perhaps final, round of modifications to my Musical Fidelity Tri-Vista 21 Class A Tube DAC.
Actually, I may do some more power supply modifications, but more on that when it happens. This is part three in an ongoing process to develop and evaluate the best performance modifications for the wonderful Musical Fidelity Tri-Vista 21 DAC.
My Musical Fidelity Tri-Vista 21 is serial-numbered in the low 1400’s, of 1500 built. This time I am replacing some of the larger plastic film capacitors on the main DAC board with premium ERO parts. I am especially keen to replace the 0.47uF capacitors in the signal path to the 5703 tube output stage. This will make quite a difference, any capacitor in the signal path influences the final sound in some way. My video, outlining the initial array of improvements I made to the MF DAC contains more details.
I am also replacing the 6 x LM4562 op amps I installed in my part 1 modifications, with good old NE5532 op amps in the I/V conversion stages and ridiculously expensive LT1028 op amps in the balanced to unbalanced conversion stage. I am implementing this as per the datasheet for the TI PCM1792 DAC chip. I figure that the engineers who’ve specified this arrangement have done so for very good reasons. MF could never have included $20 op amps in the Tri-Vista 21 for production cost reasons, but we can certainly do it now.
I could have left the original NE5532 op amps in place, but at least I got to try the LM4562 solution, which worked very well. Now I get to try this new arrangement. I may even go back to using the LM4562 chips in place of the 5532s, but that will come down to listening tests.
UPDATE: The LT1028 opamp does not work in this application, despite being the preferred solution by TI. The way MF have designed the balanced to unbalanced summing circuit, the LT1028 oscillates and draws too much current. They got so hot after a few seconds that I had to shut her down. I will stick with a pair of the outstanding LM4562 opamps in the balanced to unbalanced summing role.
I am also trying a third output coupling capacitor arrangement. I have removed the large Obbligato 10uF paper-in-oil caps I installed in part 2 of my mods, and will try some Russian paper-in-oils, as I’ve had good results with them. I will probably bypass them with styroseals.
UPDATE – no I won’t, I’ve decided to use some very cool ERO MKC film caps that I pulled from some medical gear a while ago. These are meant to sound amazing. I’ve bypassed them with the same Siemens film caps I’ve used throughout the DAC.
Finally, I’m removing the factory flying leads that connect the output jacks and installing aviation-grade Teflon-sheathed silver-coated copper wire. This is running straight into a pair of gorgeous CMC silver RCA jacks.
UPDATE: I have replaced the four filter caps located near the opamps. These provide a local reservoir of charge and provide the lowest impedance +/- 15 V rails. I had originally replaced the factory Jamicons with 100uF Panasonic FM – superb caps. This time I went with larger 220uF Panasonic FC low-impedance caps. This was a last-minute thing and I did it because I have all these premium parts in stock just sitting there, begging to be used!
The end result is that the Musical Fidelity Tri-Vista 21 sounds sublime, better than she ever has. This verifies all the modifications I have made to this great, limited-edition DAC. This is now easily the most analogue and relaxed sounding digital system I have heard in my home and one of the best I’ve heard anywhere.