June 7 update (relative to my original post #3 in this thread):
OK, so I had the opportunity to spend more time with the RDAC, get a high-quality switcher for better A/B with other amps, so following are my impressions.
Initially, I theorized the volume is higher from the RDAC compared with my Metrum Amethyst DAC. It has been confirmed that RDAC outputs 2.5V whereas the Amethyst is outputing 2.0V
I wanted to further verify those spec numbers, so using my iPhone 6S with SPL meter app, Sennheiser HD600 headphones and a 1KHz tone playing... I confirmed that when RDAC fed the amp - the volume level was almost exactly 2dB louder. Tried various listening levels and the 2dB was pretty consistent. Introducing a passive preamp between RDAC out and amp input, volume knob max'd - the volume dropped by 2.5dB. So now, difference between 2 DACs is 0.5dB (this time, the Amethyst is the louder one, but only by 0.5dB).
Now, that I have a more even field signal levels feeding my A/B switch, I was ready to repeat my comparisons.
Let me recap my 2-DAC setup:
1.
Mac mini -> USB cable -> Gustard U12 -> Coax cable -> Metrum Amethyst ->
A/B switcher -> amp
2.
Mac mini -> USB cable -> Gustard U12 -> SPDIF (optical) cable -> RDAC -> passive preamp (to lower voltage) ->
A/B switcher -> amp
The
bold components are shared between 2 audio paths.
This time around, I have used Massdrop's LCX and CTH amps, as well as the Schiit Lyr3 (with stock Tung Sol tube).
I have used both the HD600 headphones as before, but also Mr. Speakers AEON Flow Closed.
After spending several hours, listening to MANY tracks from various genres (but mostly Rock, Pop Rock, Heavy Rock, Metal) here are my observations:
a. In most tracks I could NOT hear any difference at all. Switching back and forth (using the A/B switch, mid-song) I could not even tell the DAC was switched..... Just identical.
b. In very few tracks, the male and female vocals sounded tiny bit different. I thought the Amethyst might be a tiny bit more detailed? or maybe better dynamic range? Again, VERY small difference. Would never have heard it if not A/B during playback with a switch that takes zero time to change source.
c. In other very few tracks, the RDAC sounded a tiny bit better. Trying to describe it I would say maybe the whole presentation felt like fuller / thicker sound. So for those very few tracks I would give the tiny edge to the RDAC.
I must caveat that my hearing is good but I do NOT have golden ears, and I was never musically trained. So others with better hearing or golden ears might hear things I do not.
MY conclusions:
1. Both DACs sounded great! Very natural and musical. Not dry or analytical. Both made me want to keep listening to the music
2. Those observations did not change much switching between amps and headphones. So, I do not think it is a synergy thing, but a real (tiny) difference.
3. Knowing the sound difference is almost non-existant, and knowing the price difference is 3x between those DACs - I have no problem saying that:
If I were in the market today for a DAC, with a budget of $1000 - I would absolutely buy the RDAC!
(and it absolutely is worth the 6 months wait)
But, this project has taken longer than we anticipated (for different reasons, including getting the power supply to a high level) and so it has been best to ensure we had the samples in-hand so you could read several impressions on day one. I’m not only happy that we finally have it available and out of the bag, but I really like the sound and presentation.
