More fun with digital
Here a few more modifications to the Alpha DAC:
1)
Digital volume setting now at 47.0, down significantly from the previous settings I was using before (~53.0). It took months to realize, but the output section can be overdriven at higher settings, with a slightly euphonic and less-resolving character as the program got more complex. This volume setting ended up maintaining the DAC's high resolution and clean sound with all tough material I have tried, and tamed treble energy a little bit.
2) The output section's corner frequency has been lowered to ~68.5kHz (from ~193kHz), using Vishay 1837s in a 31nF configuration in the output RC filter [first picture], for more natural treble, much closer to my analog rig's.
3) At the urging of a fellow WBF member - who contacted me actually about my XP-25 phono mods and suggested that I try out different diodes in the power supply - I decided to replace the Alpha's diodes with them first. They are the
Vishay HEXFRED VS-HFA15TB60-M3, 600V/15A continuous, "state of the art ultrafast recovery diode" [second picture, wrapped in heat shrink for protection] -
https://www.mouser.com/datasheet/2/427/vs-hfa15tb60-m3-1351136.pdf - cost about $1.06 each, and that's considered expensive. By contrast, the stock ones appear to go for roughly $0.16 retail.
Well, the results here were just shocking, so I already blindly put them into the phono as well, though I still do not have my A90 back from repair to listen to. The other WBF fellow says he's replaced his Pass XS Pre and Phono's diodes with these as well.
The increase in speed (attack and settling) was quite obvious - from piano to snare drums - as was the additional smoothness in the midrange and treble, with a tighter and more well-defined bass, and indeed, more resolution than ever before at the highest of program levels, finer micro dynamics, and greater body, and of course, even better timbre and articulation. The Berkeley Ref3 doesn't sound like this at all, and neither do the Vivaldi 2.0 and others I've had in here at various times. The one exception again being the Spectral SDR-4000SV player, which continues to be my digital reference in terms of crispness, vividness and clean sound - it really is that good, and I continue to prefer it over the $100K+ Vivaldi 2.0 stack and everything else I've heard. The other DACs and players seem to want to make digital sound beautiful, rather than accurate in the best analog sense. Different strokes for different folks.
Al M - who visited - and I were talking about the cost of digital products, and how dangerous it is to spend a lot of money on it, when: a) there are true diamonds in the rough that can be modified with spectacular results; and b) the pace of improvement in the digital world is so fast.
We played a Shostakovich symphony, piano solo, piano/string sonatas, vocal, jazz, winds, etc - and the DAC's sound simply shocked me. Well, we do know that the quality of the power supply is paramount, so why can't more manufacturers spend a dollar per diode?!?!?
So there we have it: the sound of an ultra-fast, beautifully engineered diode - fascinating!