Holo Audio Spring DAC - Level 1 "Base Model"

T Bone

500+ Head-Fier
Pros: R2R architecture with a non-oversampling mode. Native DSD support
Cons: Lackluster USB performance. Sounds best with the help of expensive supporting gear. Limited & annoying display.
This is a pretty long review.  For the benefit of those with short attention spans, let’s cut right to the chase.
  1. The “entry level” Holo Spring DAC is good – very good!  It is transparent, detailed and handled just about every format I could throw at it. 
    With the level 1 DAC retailing for $900 less than the level 3; I think it’s a bargain.
  2. I found that the Level 1 Holo performs exceptionally well; especially in the non-oversampling mode (NOS). 
    I haven’t found a case where I preferred any of the oversampling modes to NOS mode. 
  3. I found the performance of USB input somewhat lackluster. 
    The I²S input performed significantly better with the help of a Singxer SU-1.
KitsuneSpring-10.jpg KitsuneSpring-1.jpg
The Holo Spring is a very interesting DAC.  Its primary draw is that it is an R2R DAC with a non-oversampling mode. 
The Spring uses a patented linear compensated R2R network.  Not being an engineer, I understand this to mean that the Spring uses two R2R “ladders”.  The second R2R ladder essentially provides error correction or “compensation” for resistor tolerance in the first.  This results in a very precise and linear output.  The Spring has one R2R network for PCM and a completely separate R2R network for DSD.  The R2R circuit board has the same resistor ladder on the top and the bottom as illustrated in the pictures below.
bottom.jpg top.jpg IMG_0933.jpg
The 3x oversampling modes are enabled using an AK4137 sample rate converter. 
In NOS mode, this circuit is bypassed completely. 
The Spring offers RCA and XLR outputs and a full complement of inputs including: USB, Optical, SPDIF, AES and I2S. 
The coax, optical and AES inputs can handle PCM 24/192kHz and DSD64 content.
The USB and I2S input are capable to handling higher PCM at rates up to 384khz and up to quad-rate DSD512.
The I2S input is particularly interesting.  This input bypasses the internal AK4118A receiver and pretty much sends the signal straight to the digital/analog conversion.  This is one of the reasons that so many Holo owners have paired their Holo DACs with the Singxer SU-1 USB bridge.
Finding the Right Level
The Spring DAC is available in 3-different configurations; Level 1 through 3.  There is a $900 difference in retail pricing between the “entry level” Spring DAC (being reviewed here) and fully pimped-out version.  The “core” of the DAC – the R2R network – is identical across all levels.  To help me understand the different configurations, I created a chart of the upgraded components in each level and the corresponding price increase. 
Level 1
Level 2
Level 3
Retail Price
Price Difference
+ $200
+ $700
"Red Label" 6N Copper
"Red Label" 6N Copper
99.99% silver hand wound
PSU Capacitors
standard capacitors
4x Jensen 4700μF/63V
4x Jensen 4700μF/63V
Input Capacitors
Mundorf Silver Oil
1.5mm Silver
Internal Connectors
PCB plugs
PCB plugs
hand soldered
standard fuse
standard fuse
Audio Horizon Platinum Reference fuse
Being a man of modest means (a polite synonym for “cheap b*stard”)  I opted for the Level 1 DAC.
I did not know if I could cost justify the small differences that the upgraded components would make.  …but primarily – I’m cheap! 
I placed my order with Kitsune HiFi here in the US and the DAC shipped directly from China.  If you are unfamiliar with this process know that shipping takes a little longer than Amazon Prime; you will need some patience.  In my case, I was pleasantly surprised to have my unit delivered in just 2 weeks.  Not bad at all!
The DAC came “double-boxed”.  The outer box arrived fully wrapped in orange shipping tape.  The inner box was unlabeled and devoid of any branding.  Inside the DAC was wrapped in a plastic bag and securely held in place with sturdy molded foam.  There was no manual, no power cord, no cabling - just a DAC in a bag. 
Out-of-the-box Experience
After removing the DAC from the packaging, the first thing I noticed was the casework.  The chassis is very solid and is deceptively heavy.  The copper colored side panels are interesting and attractive, but invisible in the location where I put my DAC.  Overall, I am very impressed with the quality of the chassis. 
Since the Spring DAC doesn’t ship with a power cord, I sourced a Shunyata Venom 3 (~$125) to connect the DAC to my PS Audio P3 Power Plant AC regenerator.
…oh, and that Singxer SU-1 I mentioned - it doesn’t ship with a power cable either.  If you don’t already own all of the necessary cabling – both signal and power - you will want to budget accordingly and plan to see a lot of your friendly UPS driver. 
The Spring’s power switch is on the rear of the chassis.  That might not be a problem depending on your installation.  Since my DAC lives on a shelf in my office, the power switch is completely inaccessible.  Therefore the Spring stays powered-on 24x7 and I use the standby mode when not in use.
I connected the DAC to my HeadAmp GS-X mk2 amplifier with a pair of WireWorld XLR interconnects and connected the DAC to my laptop with a non-descript USB cable.
Usability & First Impressions
Whenever I get new gear, I like to pay special attention to my initial impressions.  Over time you can get used to a product’s unique quirks.  I like to capture those first impressions before they fade into familiarity.
There aren't many features on the front of the Spring DAC.  You have a giant a digital display and four attractive copper colored buttons.  The switches engage positively but noisily. 
The display is large and very bright.  If you live in an apartment complex your neighbors will be able to see if you’re playing “44.1K” or “DSD64” content.  …yeah, it’s that big. 
The “Display Intensity” button steps through several brightness levels with each press.  At first I didn’t think the button worked at all.  In reality there is very little brightness difference between the first several button presses.  I counted 16 different illumination levels between full bright and off.  That’s right – if you want to shut off the overly bright display – press the button 16 times!  You will find yourself hitting the display button with all the speed and fury of a 14-year old banging on a Playstation controller.
Pressing the “over sampling” button naturally cycles the DAC through all four of its sampling modes.   The mode flashes on the display for about 5 seconds and then returns to displaying the sample rate.  …and that can be a bit of problem.  There is no indication on the display unit telling you what sampling mode the DAC is currently operating in.  Did you leave the unit in “NOS” mode 2 hours ago or was that “OS PCM” mode?  Now you have to cycle through all four modes to make sure the correct mode is selected.  I wish the first press of the over sample button would display current mode instead of changing it.
Since we’re on the topic of usability, I would really like to see a power lamp on the front panel.  It would be a nice touch.  If you completely dim the display, there is no indication that the unit is powered up. 
Initial Listening
I began my critical listening tests trying to assess straight USB performance.  I found that playback was good but in a word - lackluster.  Most notably, I found a fairly narrow soundstage.  Cymbals crashed instead of shimmered.  Crowd noise in live recordings like Eric Clapton’s Unplugged album felt two dimensional. The acoustic guitar in R.E.M.’s  “Drive” from “Automatic for the People” just didn’t feel realistic.  Michael Stipe’s voice sounded a little wooden.  It was pretty clear that straight USB was not going to cut it.  …at least not in my system.  I could tell that I was leaving something on the table. 
If you stopped reading this review at this point you would be left with an incorrect negative perception of Level 1 Spring DAC. 
Improving Performance
Undeterred, I reached out to Tim @bimmer100 at Kitsune HiFi for his thoughts.  Tim graciously agreed to send me a Singxer SU-1 and an Intona USB isolator to evaluate. 
(crack dealers employ the same business strategy.  “Hey kid, try a hit of this new DDC convertor and USB isolator”.  Next thing you know you’re slinking around the Kitsune website at o-dark-thirty trying to get another Head-Fi hit.) 
Each device made a significant improvement to the sound of the DAC.  Both the Intona and the Spring broadened the soundstage and increased detail.  Used together, the veil that I felt covered the music was finally lifted. 
I think it is important to note that the majority of the lackluster USB performance I encountered is due to the quality of my source.  A 4-year old Windoze 10 laptop isn’t exactly an audiophile grade source.  Could the Spring’s USB implementation be improved?  Most certainly.  By way of comparison, I recently reviewed a Benchmark DAC3 using the same laptop source.  The Benchmark dealt with the whatever nastiness came out of my USB port and performed admirably whereas the Spring struggled.  I would wager an uneducated guess that Benchmark’s USB implementation is superior to the Holo’s.
I believe that a different source, say a quality CD transport, streaming server or a MicroRendu, would have yielded different results.  Being a cheap bast*rd, I did not have an alternative source with SPDIF or AES output to compare USB performance against.  I had to make the most of my PC source.  The combination of an Intona (~$300) to clean up my USB signal and a Singxer SU-1 ($400) to convert it to I2S format worked for me.  …so much for my so called budget.
I was not thrilled at having to throw an additional ~$700 at a $1,700 DAC.  It certainly felt like throwing money at a problem.  (This is headfi after all – it’s what we do!)  That being said, the combination of supporting hardware seems to have been the right solution for my personal setup.  Whether it made economic sense or not is entirely debatable.
Do you need a Singxer SU-1 and a USB decrapifier to get the most out of your Holo?  That will depend on the quality of your source.  YMMV. 
DSD Playback
Over the years I have dabbled with the SACD format and have collected a fair number of DSD encoded titles.  Therefore, DSD playback and performance was an important consideration in my DAC choice.  It’s the primary reason that I did not buy the well regarded Schiit Yggdrasil.
The Holo Spring provides native support for DSD.  That means that you do not need to use “DSD-Over-PCM” or “DoP”.  When describing DoP; the analogy I like to use is that DoP is like stuffing a DSD “letter” into a PCM “envelope”.  The receiving device has to unpack the PCM stream to extract the original DSD content.  You can find a more detailed explanation here.
The benefit of native DSD is that your media player can skip the resource intensive process of packaging DSD into a PCM stream. 
Since DSD playback was a key feature for me, I was keenly interested in the Spring’s dual R2R network.  Many DACs handle DSD by first converting the DSD signal into a PCM stream before performing the digital-to-analog conversion.  The Spring DAC is unique in that it has a completely separate R2R network exclusively for DSD playback.  DSD is never converted to PCM - they are kept separate.
The Ghostbusters said it best – “Don’t cross the streams”.
I played DSD64 encoded tracks from Pink Floyd, Queen, Peter Gabriel, Dire Straits, Michael Jackson and David Bowie.  (guess who grew up in the 80’s?)  I have been very pleased with all of the DSD content I’ve tried.  Nothing has sounded artificial or unnatural to my ears. 
I found one notable, irritating quirk during DSD playback.  There is an audible click present at the start of most DSD encoded tracks.  This noise is also present when one DSD track ends and another begins.  I did not notice this behavior during PCM playback.  It’s more of annoyance than anything.
Oversampling Modes
If I were at a Head-Fi meet and someone asked me to demonstrate the difference that the oversampling modes make; I would queue up the first minute of Alison Krauss & Union Station’s track “Let Me Touch You For A While”. 
I found that in OS PCM mode; Alison’s voice had a certain unrealistic wooden edge to it.  Switching to NOS mode seemed to lift the veil (to my ears at least) from her vocals.  I found that same characteristic present in Rebecca Pidgeon’s “You Got Me”. The acoustic guitar in this track seems to present an unnatural resonance in OS PCM mode that is absent in the NOS mode.  I lack the eloquent vocabulary to describe it better than my inner redneck who just says “that ain’t right son”. 
After much listening and experimentation with the other modes, I am thoroughly convinced that I prefer the non-oversampling mode.  None of the oversampling modes did anything for me. 
More Listening Impressions
Having finally cleaned up my USB signal path and hidden the AMEX bill from my spouse, I was ready for some more critical listening.
One of my favorite test albums is Doug MacLeod’s “Exactly Like This” published by Reference Recordings.  The album is available on DVD as 176.4kHz/24bit uncompressed WAV files.   
On the track “Serious Doin’ Woman”  you can hear Doug’s chair creaking while he plays.  There are a couple of finger snaps early in the track that have that realistic, fleshy sound.  The Spring does an admirable job of rendering minute details like that. 
I have always been a big fan of live performances.  I am captivated by the sound of the crowd, the musicians talking between songs and overall “imperfection” that is a live performance.  The first track from Eric Clapton’s Unplugged album is called Signe.  The Spring is able to present a wide soundstage on this track giving the giving the crowd noise a realistic 3D quality.  The highs ring true and roll off naturally and the guitars are upfront and rich.  It’s everything that you want from a live performance – this DAC takes you there.
Macy Gray’s “I Tried” from her Stripped album on HDTracks is another great track for evaluating a headphone system.  It is uses Dr. Chesky’s binaural recording process.  The Spring delivered an excellent sense of realism; especially from the double bass.
The entry level Spring DAC works well, but in a narrow capacity.  The consensus of Spring owners here on HeadFi is that the NOS mode sounds best.  After a few weeks with my Spring and plenty of my own critical listening, I completely agree.  It’s the only mode that I use now.
If the Holo Spring won an Oscar for best actor, then the Singxer SU-1 would surely win the award for best supporting actor.  I found that the SU-1 helped take the Holo’s performance up a notch to reveal its true capabilities.
Do I feel like I “left something on the table” by choosing the entry level Spring over the fully pimped out level 3 DAC?  In a word, “no”.  In my particular system, I found that I got a significant performance boost by improving the quality of the USB signal path.  I do not think that the upgraded capacitors and hand wound silver transformer in the level 3 would have made anywhere near as much difference as cleaning up my USB signal path.  The $900 cost “savings” of the level 1 vs level 3 provided the budget for a DDC convertor, USB filtering and new cabling.  Had I “sprung” for costlier Spring (I purposely saved that bad pun for the end of the review), I would have had the same experience with sub-optimal USB performance and still found myself in need of a better source.
My personal recommendation is that one should have everything “in front of and behind the DAC” completely locked down before investing in a level 3 Holo Spring.  The level 1 DAC is an admirable performer.  I found that I could wring a lot more performance out of the entry level Holo Spring DAC by tweaking my USB signal path.  
T Bone
T Bone
*** UPDATE *** 
I've had a chance to do a direct comparison of the  I2S input and the AES/EBU inputs.  
The I2S input has a small edge over AES in detail.  
I've posted a little more detail HERE
Out of interest, as I've seen a number of people do this for various products: With there being significant cons, such as the USB input, could you explain your reasoning for giving it 5 stars?
T Bone
T Bone
Thanks for the question, @Currawong. I think that's fair feedback.  I wish we had the option to award stars for different characteristics such sound, value, usability, etc.  I chose to give it 5 stars because of sound quality and value.  The NOS mode sounds amazing at a comparably attractive price.  Granted, it didn't sound amazing via straight USB, but this DAC performs admirably when fed an I2S signal.  This is the way that I would dare say "most" Holo owners use their DAC.  With a more granular rating system, I might have docked  the Spring a point on usability.