Nest Theater Part Twenty Two ~ Pro ADC For Final 'Final Vinyl' 05Apr23

Whoa. I started simply with a new turntable & pre-amp but wasn't satisfied. I dove on pro analog to digital (A2D, ADC, A>D) converters used in studios to digitize  analog from mics, etc. to replace my $15 gizmo currently in service in the NestT to send phono to the miniDSP EQ. I found I could mostly only afford "vintage" gear like the venerable Apogee SD-500E (48KHz/16bit), lauded for "that Apogee sound," or similar, as the modern versions cost ~$2.5K or more. I almost pulled the trigger on eBay for vintage but kept diving and found a German team, RME, with a much less expensive but modern system, their ADI-2 FS, seemingly equally lauded, though much more recently. It's probably a lot less expensive (but not cheap) due to the rudimentary UI of just LED lights. They had higher end stuff with LCD panel UIs. I didn't care about that as it does what I want at up to quad sampling: 192Khz/24bit and is electrically ultra-quiet. I'm just gonna "set it and forget it" and hide it anyway. I did also care that pro reviews of this half rack converter were strong, as were its tech specs. I'd say it's a prosumer/small studio ADC. I pulled the trigger on Amazon and it arrived from a 3rd party quickly. The fact that it is somewhat small is good as I don't have much rack space. More importantly, my testing shows it is excellent ~ displaying something I will now call "that RME sound." Grrr... it did not come in black; that is, per se; a Pro version with LCD did come in black with the same A>D function & quality, but was $2K more!

I strapped up a test setup in Blodgett to assure I did not need to immediately return it for some reason. I drove the analog out from my Onkyo DP X1 mobile system into the ADC and set the ADI-2FS to resolve to 192KHz/24bit in real time, and sent that digital signal over SPDIF to my Schitt Gungnir Multibit DAC /Mjolnir AMP stack, then balanced to my ears via Mr Speakers planar magnetic headphones. I was listening to the latest Screaming Females. Holy crap ~ no latency or loss of fidelity! One should not even attempt to play a high rez digital file through a DAC and analog out through an AMP (in this case both internal to the DP X1) to a different ADC to a DAC to an AMP... unless it is really good gear. This audio path is insane ~ but it is what I need to pump up the vinyl on the NestT. The test cleanly showed that this ADC upgrade will improve the "Final Vinyl" system of the NestT to Final "Final Vinyl." Woohoo... I will integrate it and measure results soon ~ after all, closing day at Keystone is next week.

It was a smooth integration into the NestT, except for some placement hassles (the new ADC is larger) and the fact that I needed to convert digital COAX to fiber as I could not get the fiber out of the ADC directly to work well enough for me; vinyl playback is now complete liquid butter. Here's the install and the modified connection diagram. Again, using an ADC on vinyl is NOT a classic audiophile move, but getting the miniDSP module in the mix on phono playback as well is simply much better for these speakers and this room - plus, I can always defeat it to hear LPs unadulterated.

This may raise the price of an LP to $20-$30 or so (to include vinyl) from my current $10 digital files only buys. But I buy so few it'll be worth it for some visceral feel and handling fun; I'll always get the digital version with the vinyl anyway. I've always loved the album covers & liner notes, and one gets a certain feeling hearing the scritch scritch meaning side A is over and then spinning the 180gram album to play side B... now the sound is very worthy as well. I did acquire some new vinyl to try.

Measuring 20Hz-20KHz sound pressure levels on the NestT before (with Mosou A2D) and after (the new RME A2D) did not show significant differences, as shown in the 1st graph; I expected this as the speakers, tubes and room dominate the frequency response of the system. But the Mosou introduces >2X higher distortion (THD) of 3.6% than the RME at 1.6%, as show in the next graph. Finally, the measured latency or processing delay in the Mosou was 3X the .1 msec of the RME ~ not a huge deal but longer. Further, to my ear, I noticed improvement in dynamics and clarity, especially on the low & high ends, and on the full range delivered, as I played real vinyl. I'll take it ~ audiophile mods are often nuanced.

UPDATE 05May23 ~ Elimination Of Two Media Converters... Today I updated the NestT along the vinyl audio path. I built my own cable for converting COAX/SPDIF to AES, which is compatible with my new REM A2D, to get it's digital output to my DAC's AES input. It's a weird cable but I rewired the ends of an existing RCA to XLR cable to make it. Using it allows a direct connection where I previously had to convert COAX to fiber and then fiber to AES via lots of cabling and 2 boxes powered by wall warts. The best news is that it works! I replaced this mess with a single custom cable because I found s setting on the A2D that enabled electrically higher signal output (required for AES use) on the COAX/SPDIF. There is no measurable difference in the sound from this change ~ it's just digital.

Of course I like less active stuff, and less cabling, in an audio path. The updated new NestT connection diagram is now as below.