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In the Forum: Melquiades Amplifier
In the Thread: Valve Preamplifier for Macondo/DSET
Post Subject: You may well be right...Posted by anthony on: 4/28/2019
...especially about the difficulty of making a transparent preamp.  It seems to be a general concensus.  

But I need gain for most of my sources apart from perhaps the FM Tuner.  The dac, pc streaming, future cd/bluray/dvd player all will have 2VRMS output or less and there is no way to change this.  Perhaps the phonostage will have enough gain, I am not 100% sure, but even in the best case 3 out of 5 sources will require more gain.  I just had a look at the thread about your new Placette gain stage and it looks like x4 is possible.  This is certainly enough for all sources but the Phasure dac as I run it now.  Perhaps I should do some experiments with less attenuation that -6dB as I am running now:  -3dB will give me 0.94V output, -1.5dB will give me 1.1V output.  Multiply those by 4 and we have enough gain.  Actually, I should run a sine wave through the dac and measure the output myself rather than relying on specifications.

I do really like the idea of just getting more output from the dac, but Peter seems reluctant.


 Romy the Cat wrote:
Ok, thanks for explaining. I few things I would like to note. 
  
I need to say that I am not exactly understand the Phasure ecosystems. It is DAC that works only from software player and if it so then why no one talk about the sources of the material that is being played. There is a huge difference between ripped CD and raw digital files, how the files were ripped and many other subjects. I do not understand the notion of volume control at software and DAC level and many other things. Not that I need to but I would certainly would like any attention at digital level to be wide open. It sounds to me that Phasure has SS chip in the output and this is where you can experiment. There are new op amps out there that reportedly good you can play with them; I so feel that the absolute transparency you will find at SS level not at tube level.  
 
Rgs,
Romy the Cat


The software that Peter has written, XXHighEnd, is very successful with minimising the effects of computer hardware on sound quality.  He has been doing it a long time and in my opinion is THE pioneer in the field...two steps ahead of the next guy and five steps ahead of most.  Much of this is because he not only writes the software but he designs the hardware (dac) as well, and he has set up an ecosystem that either sidesteps the cause of the problem in the first place or the software attempt to minimise the damage.

So the Phasure NOS1a G3 is a non oversampling dac using I think eight PCM1704K chips.  It is DC coupled, PCM only, has zero digital filtering onboard, and zero sound processing, upsampling, oversampling or anything like that, and no volume control.  It is also a single input dac...USB only from a computer.  The onboard FIFO buffering and galvanic isolation on the USB input is current state of the art...but the computer hardware and software still affects sound.  It is a one trick pony because it takes whatever the computer sends and does not mess with it...it just plays it, whatever it is.

The software on the computer, XXHE, does the upsampling and digital volume control.  Redbook is generally upsampled x16 (this is configurable) to 705k and digital attenuation applied to a 32bit upsampled file.  Also, the digital filters are applied during upsampling and there are a number of filters available including one called ArcPrediction which has zero pre or post ringing.  As far as I am aware this is the only zero ringing digital filter in existence and Keith Johnson of PM2 fame did not believe that such a filter was possible, but it is possible if the filter is applied in software before it is sent to the dac.

So the general workflow in XXHE is as follows:
  1. Create your playlist or select your albums in the XXHE library.
  2. Press play.  XXHE then upsamples your music, applies the digital filter, loads it all into RAM (sounds better), then shuts down the operating system so that only a handful of process remain running, slows down the cpu so that it is almost stalled, sends the music files to the dac, shuts down the computer screen and displays a wallpaper of what is playing.
  3. Then the music starts (and sounds great)
  4. You can change volume with keyboard commands, or if you are running the whole thing from a tablet (which I do) you just press a button on the tablet and the volume is changed.
  5. At the end of play, or when you cancel play, the screen comes back on, the operating system comes back to life, the cpu is sped up so things go faster and you are returned to the library in XXHE.


It is a different workflow to all other software, but it works and the sound quality is definitely improved.  It is a bit slow though.  Romy, you should hear the difference between various operating systems, even different versions of the same operating system.

So yes, as Rowuk mentioned above, Peter is definitely "experimental".  He is the bleeding edge of digital (just need 3V output from the dac).

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