Core Audio Technology
Copper Level Mac Mini Music Server
List Price: $2,885
Dr. John Richardson
As of late, I’ve been focusing on power supplies and the effect they can have on the sound of my system. None of this is news, of course, since we all know that the better regulated and controlled our DC power is, the better our gear will perform. Look at my digital front end for example. I’ve replaced the inexpensive switching supply that came with my Antelope Zodiac DAC with an excellent custom linear power supply from the guys at Your Final System (or YFS), and it made a wonderful difference in the sound. Everything just seemed more grounded (pun intended...) and natural. Not content to stop there, I later added another linear supply from YFS to power my Sound Devices USBPre2 audio interface, which originally was powered by dirty usb power from my Mac Mini. Again, coupled with an improved usb cable, a worthwhile difference in sound quality was noted. As I worked up the digital chain I had to wonder about the power going to the computer itself: was I shooting myself in the foot by continuing to use the crappy stock switching supply that came with my Mac? And what else might be done to help clean up the RF nasties that reside in the chassis of most all computers? I kept going back to the old mantra that in computer audio everything matters. And I’ve been discovering first-hand that the more noise that I can eliminate from my signal chain, the more music, acoustic space, and detail I hear, which is all advantageous to a more enjoyable listening experience.
Back to the computer then. Computer audio is no longer a pipe dream or a passing fad. It’s not the future of audio reproduction or the sole domain of silly audiophiles. It’s here now, and it’s here to stay. And like many means of audio reproduction from our past, it’s finally starting to work through its tough adolescent years and grow into productive maturity and mainstream acceptance. Just visit any audio show and you’ll see what I mean.
In the audio world the computer is known as the music server. Its job is to retrieve the digital music bits from a storage device like an external hard drive and process them digitally using an audio engine (just a piece of software) before passing them off to the digital to analog converter (DAC). The computer also serves as our visual interface to our music files: we see our playlists and cover art while watching level meters dance on the monitor. Given that all of this business goes on in the digital domain, we shouldn’t have to worry much about the quality of the computer or how well regulated its power supply is, right? Wrong! Remember that bits are encoded as analog voltage/current pulses, and any fuzziness or distortion of these pulses results in jitter, which in turn translates into bad sound, even before they leave the computer.
For those of us who just want to listen to music, any computer will suffice as a music server. Either a stock Apple or Windows unit should do just fine. However, if you want to work toward perfectionist audio, then your options start to open up. If you’re cheap and handy, there are some nice dedicated DIY server recipes out there. If you’re like me, then it’s best to let someone else do the heavy lifting, meaning that you have some different types of choices to make. For instance, you could either go with a modified stock computer as your server, or you could have one built from the ground up. As an example of the latter, check out my review here in Stereomojo of the YFS Ref3 custom server. The subject of the present review, the Core Audio Technology modified Mac Mini, is a good example of the former. Each approach has its pros and cons. A custom unit can be made exactly to your specifications, and extensive pains can be taken to minimize EMI noise through careful layout of the interior coupled with extensive shielding and power supply design. The disadvantage is cost; these things get really expensive due to their custom nature.
In fact, I asked Core Audio’s head guy, Ryan Mintz, this very question. He responds:
“We build both, so I can say that both have the potential to sound really great. We license our power supplies to a number of PC-based music server companies and their products sound great too.”
“The triangle becomes cost, performance, and size. The Mac Mini has a great balance between all three. It's small, has excellent power for its size, and costs far less than the equivalent PC. The Mini is also much more reliable than a PC. We have Minis from 2007 running on our power supplies still. I've never had a PC-based system last that long.”
“Many network-type music servers can sound decent, but they lack versatility. With our Mac Minis we can listen to Spotify, which sounds great, watch Netflix, or for more serious listening play some hi-rez tracks via Audirvana or the like. It's just more flexible, and that flexibility really translates to higher performance potential.”
So, plus one for my fave Mac Mini then!
For most of us, the modification route will be the more realistic option. It’s cheaper since we’re letting the folks at Apple or other mega companies spend their billions developing the hardware technology and operating systems. All we have to do then is figure out how to best improve on their designs from the standpoint of shielding, power supply regulation, and a few additional bits and bobs. That’s the approach that the folks at Core Audio Technology and several of their competitors have decided to take, and it seems quite reasonable to me.
I was the recipient of the copper level Mac Mini-based media server package, priced at $2885. This is Core Audio’s middle-of-the-road server option and should be more than enough for most level headed enthusiasts. What you get is a stock Mac Mini computer (of course), along with Core Audio’s custom Kora linear power supply hard-wired via a nicely built shielded cable directly to the Mini (this was done to help eliminate noise on the DC side, according to Ryan). The package also includes a “six layered EMI shielding material” around the logic board to presumably decrease internal electronic noise to that sensitive part of the computer. For my evaluation, Mr. Mintz lastly tossed in a nicely built Katana power cord ($299) as well as the Atomic Mac Mini Isolation Platform ($350). The platform is a nifty device upon which the Mini sits that supposedly is in resonance with the Mini’s natural vibrations, thus absorbing them and making the computer itself sound better. It also looks pretty cool.
The various components arrived well-packaged and in good shape. The only thing I noticed was a bit of rattling in the power supply when it first came out of the box, which seemed to come from the area around the front panel, as if the panel itself were not tightly attached. Other than that, everything seemed to be in good order. Ryan gave me the heads-up that a few of the power supplies had suffered from a hissing noise resulting from a faulty resistor in the regulator section. Fortunately, mine didn’t seem to suffer from this malady, but I do wonder if these guys are still buttoning down quality control, especially in light of the slight rattling I heard coupled with the possible resistor issue. External build quality of the power supply was quite fine, but not exceptional. I was tempted to take a peek inside, but there was a label on one of the screws holding the top panel in place that warned that the warranty would be voided if the screw was tampered with, so I passed. Oddly enough, when I removed the power supply from my system at the end of the review time I gave it a good shake, and I got no rattling. Everything seemed tight as a tick, so go figure. Nighttime fix-it gremlins maybe?
I asked Ryan to enlighten me a bit more on the technology inside the Kora’s enclosure, which he was happy to do. A few excerpts of his lengthy, but informative treatise follow.
Ryan: “We do some neat things in our power supplies now to increase the performance and versatility. Because we use these same power supplies for dozens of different products we needed to be able to minimize heat dissipation, scale the current without creating noise issues, and have compatible grounding layouts so that the power supply is not only compatible with the device, but within the system which the device resides. The power supply operates at very high frequencies, so we've created special band gap filters in our regulation circuit so that internal regulator noise doesn't get amplified by the error amplifier or create instability. Heat and vibration really plague linear power supply designs because even a few degrees of heat really produces tremendous amounts of noise. Even capacitor ESR causes increased heat in capacitors, so we use banks of Organic Polymer Low ESR capacitors as well as large banks of X7R multilayer ceramics and feedthrough filters of various values to both reduce internal resistance, increase transient response, and help to eliminate any heat build up at higher currents.”
Sounds like there’s a great deal of technological innovation inside that box.
Setup was a cinch. Basically, all I needed to do was plug the Katana cord into the power supply and the opposite end into the wall. Ryan advised me that most customers indeed plugged the power supply directly into the wall for best sound, so I followed his advice. After attaching my own monitor, keyboard, and mouse, I fired everything up (note that the power supply does not have an on/off switch, so when it’s plugged in it’s on) and installed Pure Music as my preferred audio playback engine. After ripping a few of my favorite compact discs and homemade high-resolution LP transcriptions to the Mini’s hard drive, I was ready to go.
For the majority of my evaluation, I had the Core Audio Mac Mini server feeding digital data to my Sound Devices USBPre2 interface via a two-headed YFS (Your Final System) usb cable. One head of the cable powered the USBPre2 using a custom linear power supply from YFS, while the other head served as the data link. S/PDIF data were then sent to an Antelope Zodiac DAC powered by another YFS power supply. The analog signal from the DAC then went to my Klyne SK-6 preamplifier and then on to a Threshold SA 3.9e class A power amplifier which powered a set of Fritz REV7 or ATC SCM 11 (version 2) speakers. All components except for the server were plugged into my Spiritual Audio VX-9 power conditioner.
Compared to my absolutely stock Mac Mini, several improvements were immediately obvious. The Core Audio server most notably resulted in what I call a “popped” sound stage. What I mean is that the there was an immediate and noticeable change in the the dimensionality of the soundstage, with images becoming more holographic and precise along with an immediate increase in both breadth and depth of the soundscape. I also heard the same benefits of lowered noise floor that I’ve progressively heard as I’ve upgraded the power supplies on my digital front end. Specifically, such improvements include more of a sense of purity and presence of tone, as well as what I would call an overall less “digital” or “electronic” veiling of the notes - in other words, an increase in overall clarity. Each improvement I make yields a product that much closer to the analog benchmark. And here I mean really good analog.
Paying attention to noise reduction in the computer and its power supplies just seems like a natural extension of my prior findings with my digital front end, and it’s borne out as well from past experiences with really well-built music servers such as the YFS unit I mentioned earlier. My excitement over products such as Core Audio’s server is that excellent sonic performance can be achieved at real world prices along with tweak options that can be added easily after the fact as budgets allow (such as the fancy Katana audiophile power cord and the Atomic Isolation stand).
As I sit here and listen, I’m taking in the wonderful purity of tone that also seems to result from improved power regulation and shielding. Instruments and voices sound more real and natural. Vibraphones and marimbas take on a natural sheen and brilliance not heard before, but with a level of realism that belies my digital sources. With well-done computer audio, digital sort of stops sounding like digital, at least in the traditional negative ways. Check out the cello in Fussell’s “Right River” tone poem for cello and string orchestra (cd, Troy 883). I seem to hear more of the natural rosiny tone of the cello’s strings as well as greater interplay between the featured instrument and the ensemble backing it. Less hash and fuzziness leads to less ear strain and happier long-term listening sessions.
I’ve also really enjoyed listening to well-played jazz such as Gary Burton and Chick Corea’s collaboration “Like Minds” (24 bit/88.2 kHz download; HDTracks). As the system now stands, the vibes cut through the mix like a knife through butter, but with lots of clarity preserved in the performances of the rest of the artists.
Rather than prattle on about how much better music sounds using the Core Audio server, I decided to do a little experiment. Frankly, I’ve become quite used to the device after a month or so of listening through it exclusively. What would happen if I replaced it with my regular un-tweaked Mac Mini server? Let’s find out.
Alright, everything still sounds good. In fact, quite good. However, I did immediately notice a slight decrease in the immediacy or “sparkle” in the music. Transients seemed dulled a bit, and there wasn’t quite as much of a sense of air or spaciousness about the music. Cuts from “Like Minds” lost a little bit of their verve and attitude, with Gary Burton’s vibes taking a little bit more of a back seat position in the soundstage than before with the Core Audio server in place. While none of these are more than subtle changes, they are the types of things that those of us engaged in “perfectionist audio” will notice. In a sense, I just didn’t feel that the music had the same degree of focus and clarity that I had been enjoying previously, either in terms of tonal accuracy or soundstage precision. Can I live without a tweaked out Mini with a fancy power supply? Well, probably, at least for now, but I can tell you that I will miss that added bit of finesse that the Core Audio server brought to the table.
Of course, you’ll need a really resolving system to fully benefit from the improvements rendered by the Core Audio server. I heard the biggest differences when using the ATC SCM 11 speaker we recently reviewed here, which I find to be exceptionally resolving and sensitive to any changes made upstream. Such resolving power is not unexpected given this speaker’s heritage as a pro audio monitor. Your mileage, of course, may vary depending on what else resides downstream in your system. For me, however, the Core Audio Mac Mini music server shows what can be accomplished at a reasonable price point (at least by audiophile standards) for this important part of the audio chain. Yes, I believe we now need to consider the server itself, along with its accompanying hardware and software, as an individual audio component, very much like the digital transports of the days of yore. And an important one at that. Mr. Mintz and his team at Core Audio have truly provided me with some real food for thought...
I’ve long been a fan of the Mac Mini as a music server; it’s small, attractive, and does its job reliably and without fuss while still managing to sound quite good. Is it worth throwing more money at a stock Mini to make it even better? If your budget will allow, then of course! For a total outlay of less than $3000, one can have the versatility of a Mini-based server that can run with some of the best out there. And in the world of ever increasing computer audio, such a figure isn’t anywhere near what you could spend... The sky’s the limit in that regard, much like the rest of the audiophile’s dream world. As performance to price ratio values go, the Core Audio server setup is pretty hard to beat as a versatile turnkey option.
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