"The Nucleus"

 
It is always exiting to discover and learn about new companies in this wonderful hobby of ours known as personal audio.  Covalent-Audio, founded in 2013, is one such company based in Chatsworth California. Covalent-Audio owner Ronnie Holtzman, once of Theta-Digital in the glory days working for Mike Moffat, had a goal of offering headphone fanatics a high-quality, high-value headphone amp.  After listening to and spending some time with their first offering, it looks like Ronnie has definitively achieved that goal with the Covalent-Audio Nucleus headphone amplifier / preamplifier.
 
The Nucleus is a solid-state headphone amp with very well-implemented features.  It sports a three position toggle switch on the front-panel which selects between the two analog inputs or mutes the Nucleus’ outputs. On the back, there is a power switch, Hi/Lo gain setting switch, two analog inputs on RCA jacks and a pair of “active” pre-amp outputs on RCAs that are controlled by the mute switch and volume control on the front panel.  The Nucleus amp has a very clean and simple industrial look to it. The amp feels solid and is built like a tank – there are no plastic covers or knobs anywhere.  The chassis of the Nucleus is constructed out of non-ferris aluminum, which minimizes external stray magnetic field interference.  Volume control duties are handled by an ALPS Blue-Velvet Pot, which works and feels great during use.  And yes, it is smooth like velvet.  Finally, the nucleus comes with a two year manufacturer’s warranty which exceeds the typical one year warranty most electronics have.
 
The Nucleus product brief on Covalent Audio’s website is as follows:
“Powerful, detailed, warm sound and versatility are exactly what the Nucleus headphone amplifier delivers. With over 1.5Watts (rms) of output power per channel and the current capability to go with that, the Nucleus is able drive a wide variety of high performance dynamic headphones, IEMs and many ‘more power hungry’ orthodynamic models with ease.  You’ll marvel at what your cans are capable of when you listen to them through the Nucleus.”
 
For those that enjoy the technical details about such things, the Covalent-Audio website has very detailed information on the makeup of the Nucleus amp’s circuitry.
 
Now Down To Business…
I have been an audiophile for more than 20 years, and believe I know good sound from listening to and owning hundreds of components from different price brackets and manufacturers.  After burning in the Nucleus amp for more than 100 hours, I connected the amp to my Muto DAC with Kimber Kable KCAG silver interconnects and began listening with my Ultrasone SIGNATURE PROs.  Since the SIG PROs are very easy-to-drive headphones, I set the Nucleus’ gain switch to the “Lo” setting and listened.  The sound coming out of the SIG PROs was well balanced, transparent, detailed and musical.
 
 
Important to note is that the Nucleus is able to drive many different CANS with various sensitivities because the “Hi/Lo” gain switch features “sensible” spacing between the two gain settings.  Many other amplifiers I’ve come across do not always offer gain setting options that are sensible spaced apart or even offer any gain options at all other than one fixed gain setting thus making this amp highly versatile in regards for use with a wide variety of headphones.
 
Condensed Points - As for the sound:
Bass: Was controlled, detailed, deep and musical -- What else can we ask for - right?
 
Midrange: Very detailed, but still musical, never too forward, or analytical.
 
Highs: Detailed, airy, present, not overwhelming, extended as the source permited.
 
Moving Onward…
Next I paired the Nucleus up with my HiFiMan HE500s, which are my hardest to drive headphones.  I moved the gain switch to the “Hi” position and set the volume between 10 and 11 o'clock on the dial.  I have to say this little amp impressively drove the HE500s with full, powerful, detailed and dynamic sound.  I was pleasantly surprised at how well this small amplifier drove the HE500s.
 
Listening to Ray LaMontagne “This Love is Over”, the sound was so buttery smooth, romantic, detailed and dynamic at the same time.  I felt as if the sound was not missing anything.  The Nucleus is very good at letting you hear the recording as well as the source reproducing it.  This is one of those amplifiers that doesn’t add much of its own “signature” to the music.  It lets the music flow through like it is supposed to.
 
Leonard Bernstein conducting the New York Philharmonic playing “Barber’s Adagio for Strings” sounded fantastic.  All of the string instruments sounded natural, smooth and tonally real.  This is one of my favorite classical pieces and the Nucleus/HE500 combo rendered it in a marvelous manner.
 
“Strange Fruit” from Cassandra Wilson’s “New Moon Daughter” is my favorite from all of her albums. The details were just there, easy to hear without being analytical. Highs were extended yet smooth and non-fatiguing.  Bass was potent, tight, and detailed.  The vocals produced from the headphones felt in front of my face and in the middle of the soundstage, not just between the ears.
 
Unleashing the Mad Dog Pros form MrSpeakers on the Nucleus sounded almost exactly the same, just with a closed back headphone sense of presentation.  While I consider the Pros not as detailed as the HE500s, the Nucleus/Mad Dog Pro combo yielded a presentation that was detailed enough while still being crazy musical and smooth sounding showing that the Nucleus was able to walk those dogs well.
 
I then switched to my Aurisonics Rockets IEMs to see where the noise floor was with this amp when driving small headphones.  With the Nucleus’ gain set to “Lo”, the rockets (which even though they are IEMs, do appreciate an amp with some muscle behind it) sounded fantastic.  Again, the sound was powerful, rich, detailed and complete with tight bass.  No evidence of hiss was heard when driving these small IEMs.
 
 
 
 Apples to Oranges?...
Now in comparing the Nucleus amp to my reference amp, the Apex Peak outfitted w/ the optional Volcano power supply, I’ll have to admit that I felt that even though my Peak (which is a tube/MOSFET hybrid amp) sounded better, the differences were minimal which is very impressive for the Nucleus considering the big price difference between the two units.  I consider both to be true-to-the-source amplifiers.
 
 Another factor in my above mentioning is that through tube rolling, the sound of the Peak can be altered to one’s taste so to speak, where as the Nucleus, being a solid-state amp is more of a fixed affair.  Although the Nucleus dished out great sound, I felt that the Peak did it all a little bit better.  But when you look at the roughly $1600 price difference between the two amps, the Nucleus at 400 bucks, does indeed offer a lot of great sound and value for the money.
 
Beyond the Cans…
Using The Nucleus as a pre-amp driving my Audioengine A2 desktop powered speakers was yet another very pleasant experience.  Once again the Nucleus offered sound which was transparent with great bass and detail.   There is just nothing bad to say about this little amp sonically.
 
With the Nucleus’ simple industrial styling look, it may not be the number one choice when it comes to “drop dead gorgeous” appearances but it’s important to realize that audio gear with fancy chassis work, also has a fancier price tag to go with it.  Now don’t get me wrong, equipment that emphasizes appearance is not a bad thing, but not everyone wants to or can pay the money for it. In my case I don't sit and stare at the equipment, I just listen to the music and get lost in it!  The Nucleus allowed me to do just that.
 
Summing It Up…
The Nucleus amplifier is for anyone who wants to hear the recording and source with minimal added sonic signature from the amp.  In my opinion the Nucleus does what an amp is supposed to do and lets the music flow.  Also because of its good amount of transparency and balanced sound from the top to bottom octaves, this amplifier is capable of playing all different genres of music equally well.
 
Like I said at the beginning of this review, Ronnie from Covalent-Audio wanted to create an amp that sounded great and whose price point was reachable for most of us, and without a doubt he achieved his goal.  I highly recommend this amplifier especially for the people whose priority is good sound.
 
The Nucleus headphone amp can be purchased directly from Covalent-Audio for $399.
Website:   www.covalent-audio.com
Email:        info@covalent-audio.com