Review: ZERO 24 BIT/192KHz DAC/Headphone Amp/Pre-Amp
Nov 28, 2007 at 12:23 AM Thread Starter Post #1 of 9,388


Headphoneus Supremus
Oct 31, 2006
[size=medium]Review: ZERO 24 BIT/192KHz DAC/Headphone Amp/Pre-Amp[/size]

Review equipment listing:
Digital sources used: ASUS AJS8, Sony D-EJ885, Toshiba SD-KP19, Toshiba SD-5970
Headphones used: Sennheiser HD-650, HD-580, HD-280pro, HD-212pro
Tube Headphone Amps used: LDII++, LD MKIVse
LDII++ with: Power Tubes - Sov 6C19PI, Driver Tubes - Mullard 6CQ6
MKIVse with: Power Tubes – Tung-Sol JAN 5687WB, Driver Tubes – GE 5star 408A
Stereo Amplifiers used: Sonic Super T-Amp, Pioneer SPEC4
Music used: To many to list. Just about every type, minus Hip-Hop and Punk.
ZERO 24 BIT/192KHz DAC/Headphone Amp/Pre-Amp

Out of the box:
My package from China arrived exactly 10 business days after purchasing the Zero off of eBay for $150 + shipping using BIN. I purchased it on a Monday and they did not ship until Friday the same week. The unit arrived in a standard cardboard shipping box, covered in brown paper. After opening it, I could see the Zero unit was wrapped in a protective foam sheet and cradled between two formed poly foam inserts, which kept the unit at least 1½” away from the box interior. It came with an owner’s manual, but it was written in Chinese. Even on my best days, I can’t make out a darn thing in Chinese.
A quick inspection of the unit proved it was indeed new, clean and made with more than reasonable build quality for its price range. It came with a standard power cord which fits nicely into its fused socket located in the rear of the Zero. A standard 1 meter optical cable still in its retail package was included. Optical in, Coaxial in and RCA out are all located on the rear of the unit. Even without an English owner’s manual, hooking up the Zero was simple.


Initial startup:
I knew I wanted to run the Zero for over 200 hours initially, so I looked around and the only digital source I have with that much music on it is my ASUS Notebook which has an HD audio chip and optical out. I also hooked up my Sonic Super T-Amp to the Zero, so I could test the Zeros pre-amp capabilities during burn-in. I pressed the power button in and was rewarded with a nice blue LED for power on. I pushed the select switch for Optical and got another blue LED. These are the medium brightness LEDs, which I was thankful for. The first thing I noticed was that the RCA out was at a set level and not changed by the volume knob. Great!

Verification of stated components (during initial startup):
Now I needed to verify that the pre-amp and headphone amp are on separate circuits. Unscrewing two screws on each side and two on the back and I lifted the lid. Indeed, the headphone section is built on a separate board and is not on the same circuit as the RCA output. While I had the unit open, I checked the build quality and noticed a few items of interest. First, the Zero has a toroide transformer and individual voltage regulators. I found the Opamp (OPA2604) sitting in its socket, so it could be changed out later. Everything was nice and tidy. Capacitors and other board items were upright and straight and of the quality advertised. Wires were bundled and in their place. The boards were nice and clean and there was no sloppy soldering in sight! This speaks volumes about quality control during assembly.


Specifications of the ZERO 24 BIT/192KHz DAC/Headphone Amp/Pre-Amp:
Receive chip: CS8416
Decode chip: AD1852
Analog operational amplifier chip: OPA2604
Signal to noise ratio: 120dB
Total harmonic distortion: 0.0005%
Dynamic range: 117dB
Frequency response: 20Hz - 30 kHz
Analog output level: 2V
Input interface:
One independent digital fiber input
One independent digital coaxial input
One RCA analog signal unbalanced output
One 6.3mm headphone signal output
Time delay switch for ON/OFF protection circuit
Individual PCB design for future upgrade capability
Hi End components and IC (less than 1% tolerance)
Separate and individual voltage regulators
Dual Mono Amp design
Double face PCB for reducing size
Power Usage: Only 10 Watts

Those are some impressive specifications for a $139.00 headphone DAC/amp/pre-amp! When I re-installed the “lid”, I noticed the only design flaw on the whole unit. When you get the lid in position and ready to screw in place, there is one screw on the left and one on the right on the back plate, that have too large of a head on them and this forces the rear lower outside edge to flare out about 1/8” from where it is supposed to be. It is really hard to notice, so I guess this is why a fix wasn’t implemented. You could fix it yourself by drilling a hole in the sides of the lid to let the screw heads protrude through. Seems like a picky thing to do though! The Zero has some nice plastic housed rubber feet which are screwed on, not stuck on! The top has ventilation grills cut into the surface toward the back and to the left. The lid is painted a flat black which seems to be the type that resists marks. With the lid re-installed, I plugged in my HD-650s and pressed the “phone” selector switch. I was rewarded with a nice green LED for phone on. The RCA output stopped without switching noise and the HD-650s started playing without switching noise. What a blessing. This is when I noticed the “phone” selector switch has “phone” labeled over the top of the button and “pre-amp” below the button. Sure enough, you can press that “phone/pre-amp” button and toggle between the headphones and RCA out (pre-amp mode), anytime you want without noise. It is obvious a chip controls the selections and prevents switching noise. This is great. I get to keep my amp hooked up and listen to headphones without unplugging anything or switching cables around.


First listen (during initial startup):
After booting my notebook, I took some time to verify I had Windows Media Player set to “flat” and no boost or psychedelic crap of any type was turned on. Initially, I had noise in the signal, which turned out to be my wireless talking to my router, so I plugged in my CAT6 line and turned off the wireless. With no noise being introduced, I switched the unit to “phones” and gave a quick listen. Wow! It was clear and accurate within the middle frequencies, a little shy on the highs and extreme lows, but not to the extent of displeasure. I turned on my Super T-amp and then switched the Zero to pre-amp mode. Wow again! This time, the spectrum was not lacking at all. The entire spectrum was “flat” with no accentuations I could detect. Very solid state sounding overall. In my mind, I was expecting the “pre-amp” and “headphone amp” sections to initially sound different due to the independent circuits that control and drive them.


50 Hours into the burn-in:
At this point, I simply grabbed the HD-650s and plopped them on my head and took a good listen. The bass was now tighter and deeper and the upper highs, which had been suffering, were there in a big way. I got horizontal on my couch and closed my eyes and let the music reveal itself to me. This was very enjoyable and I could sense the sound stage was changing and not done yet. Things that normally have a solid 3D position were moving slightly out and back depending on the intensity of the passage. I have heard this before in tube amps, so more burn in was obviously needed. Vocals were accurate and real. Drums were bright and detailed. This little unit is really starting to impress me MUCH more than I thought it would.

100 Hours into the burn-in:
Wait just a darn minute. Who swapped out my Zero for a tube amp? What is going on here? I picked up the HD-650s, plopped them on my head and sat straight down on the floor. I didn’t move for the next 15 minutes. I had to determine what I was hearing because it was so “not solid state” sounding. This little Zero has mutated into sounding like a nice clean tube amp!
I ran up the volume…no change. I ran down the volume…no change. I grabbed my HD-580s and swapped out the headphones and put them on for a listen. 5 minutes later I was still sitting on the floor, but with an air guitar was in my hands and I was jamming! Wow, this is a super fun amp! I swapped back and forth between the HD-650s and 580s and they were both fun to listen too. I put on Jazz, Rock, Classical and Blues trying to find a weak spot in this enjoyment. There just wasn’t any. I grabbed my HD-280 Pros from my computer and gave them a try. BASS! Huge amounts of clean blasting Bass! Good Lord! The HD-280 Pros are known for big bass once they are broke in, but I have never heard that much bass out of them. The Zero unit just kept on pumping and didn’t even breathe hard.

144 Hours, declared end of burn-in:
Today, I tried three different optical sources, four different headphones, two different interconnects and seven different categories of music. No matter what I threw at the Zero, it amplified everything wonderfully, mostly transparent with just a little bit of “tube” sound thrown in. Keep in mind that this is with the stock unit. I haven’t changed a thing in the unit, yet. What a nice Opamp it has; very well rounded and suitable for the majority of music types. The Zero has tons of power and will easily drive whatever headphones you might have.


Using the Zero as a pre-amp for dedicated amplifiers:
This testing was extremely fun! First, I tested the unit on my Sonic Super T-Amp. I used my Sony D-E885 portable CD player as source, using its optical connection. I hooked the Super T-amp up to my Cerwin-Vega S-1s. Switches on and I grabbed the volume knob on the Super T. I was able to drive the amp easily up to its maximum safe output (about 9 watts RMS). My S-1s are known for making digital sound a little bright, but this was not the case here. The Zero’s inherent “almost tube” sound came through sounding very nice. It always makes me “twitch” a little when I see those Cerwin-Vega woofers moving in and out and then look back at the small and tiny Super T-amp driving them!  Next, I hooked the Zero directly up to my Pioneer SPEC4 amplifier and hooked up the S-1s. The SPEC4 has two adjustable input level knobs, one for each channel on the front panel, so I powered everything up and grabbed both knobs. Oh yes! I was able to drive the S-1s to 100 watts RMS with room to spare. I have neighbors, so I backed it down to about 25 watts RMS and listened for a while. The SPEC4 amplifier is known for being transparent, and this trait really shows in this test. That “almost tube” sound was really showing now. Deep, deep bass and as hard as I tried the noise floor was not detectable. Very clean, dynamic and full spectrum considering the little Sony as a source!!


Using the Zero as a pre-amp for headphone amps:
First, I set the Zeros output up to my LDII++ RCA inputs. I plugged in my HD-650s into the LDII++ and let the tubes warm up a while. I used my Toshiba SD-5970 (DVD, 24bit,192KHz CD audio) player as the source, first using the coaxial and then switching to optical connections. Both type of connections work fantastic with no discernable difference between them. I popped the HD-650s on my head and pressed play. What a very interesting sound. The expected harshness of digital was not present. The sound was most definitely tube, except the bass which was tighter and powerful. Nuances in the upper frequencies were accurate and easy. Voices were smooth and detailed. The sound stage was less wide than with an analog source, but 3D positioning was right where I expected it to be using the LDII++. Very nice! Next, I swapped the LDII++ for my MKIVse and plopped the HD-650s on. Wow, this is different! The full spectrum was cleaner; bass was not so tight but powerful, the mids sounded warm and seductive, the highs were crisp and better defined. The sound stage was now wider, with positioning a little further out. This was amazing! I had not anticipated how much the higher quality MKIVse would change this listening test!


Opamp swap out, a few quick notes:
Upon installation, everything is rather harsh. The bass so tight, it almost doesn’t exist. The mids are extremely revealing. The highs are super crisp. There is a very digital sound overall and time is required to mature this Opamp. 24 Hours: Overall, far less harsh. The bass is now tight but sounding much improved. Mids have mellowed enough to fit right in with the rest of the spectrum. Highs are less crisp and more revealing. This is quite nice, especially with classical or instrumental music. A nice upgrade for non-rockers!

OPA627 x2 on Brown Dog Adaptor (See pic):
WOW!! Upon installation, everything is improved! I’m hearing a full spectrum with no deficiencies! The immediate shocker is the sound stage. Nice and wide without being too distant! Vocals are absolutely clear and the highs are clean and detailed. Bass is tight and has a proper presence to it, with punch. This was worth the money for sure! A super upgrade for all music lovers! 24 Hours: It just keeps getting better, or I should say “mature”. I’m going to leave the OPA627s in as the new default. Today I listened to a favorite CD from long ago, Pink Floyd-Animals. I have heard nuances in the music I did not know existed! I’m so happy with this setup; I’ve moved my MKIVse and have it sitting on top of the Zero unit.

This Zero unit is a monster “Bang for your Buck” unit. It is quality built with HeadFi type audiophiles in mind. Having said that, let me clarify a few things that might help those who are looking for such a unit. Inputs on the Zero are limited to optical and coaxial. No analog line-in. It is designed to take a clean digital source and convert it to really great headphone and pre-amp output. It will drive any type of headphones. It will cleanly drive a dedicated stereo amp (like my Super T-amp) or other separate amps. It is not portable, but works well with portable devices that have optical out. If you are in the market to build a desktop stereo system starting with a clean digital source, then this unit is absolutely worth investigating. It can serve as a clean bridge between portable and desktop, or as a bridge between digital and analog systems.

Last thoughts and a declaration:
This little Zero unit shows just how great solid state can be on a budget today if you hunt for it. It stands mostly alone in the market as an unknown treasure, waiting to be discovered by HeadFier’s everywhere. It is not just for newly inspired audio beginners. I’m sure it will outperform many units that demand a higher cost. This will upset some users who have already put up their hard earned cash for more expensive units. All I can say to everyone regardless of their past purchases is this; everyone deserves to have a unit like the Zero. It will compliment what you have or what you plan to have if it involves a clean digital source. In many cases, this unit will not be upgraded or replaced later on because of its excellent performance. One thing is for sure, it will never be a waste of anyone’s money. Is this low cost Zero unit really that good? Yes, indeed it is. I have to be honest and tell everyone that "your mileage may vary". I have done my best to describe what has transpired during this review and I wouldn’t want anyone to think for even a minute that this Zero unit could or should replace $600+ units with similar features. What I must get across is that this unit is worth checking out, reading about or listening too before you spend twice the money on another unit. It is a gem!

Dave McLaughlin
Zero owner and
Audiophile sense 1977

*NOTE* I have an update for all Zero users. Thanks to other Zero users, the true "pre-amp" function (a volume controlled output feature) has been found.
If you press the button for Phones and the green light comes on, this means that "IF" a headphone is plugged in, the volume knob works for the headphone amp. If you don't plug in a headphone and the green light is on, the volume knob works for the DAC output! It was discovered by accident.
If you need further clarification, don't hesitate to PM me directly. Thanks!! Penchum.

We have a banned individual named ANDREA, who has been making bad recommendations to Zero owners.
This person, comes back on under an alias and pretends to know everything about Opamps for the Zero.
Here is a link that sums this up very well, and it shows an example of someone who got a bad recommendation:
Thanks for your attention!!
Penchum 06/18/08

This addendum is for Opamps that have been tested in the Zero DAC/Amp. I'm keeping it updated so new folks can see what has worked already.

Warning: Non-unity gain stable opamps (LT1115, AD797) can not be used in the DAC section of the Zero.

Here is what we have tested so far: Note: "good" means only good. "great" means great. We recommend "great" to everyone thinking of Opamp rolling. All gradings were done with Sennheiser HD-650 headphones with over 1000hrs on them.

Dac / Amp :

LT1057 + LT1469 DAC=good, phone=good

LT1057 + LT1364 DAC=good, phone=good

LT1057 + LT1361 DAC=good, phone=good

LT1057 + LM4562 DAC=good, phone=good

LT1361 + LT1469 DAC=good, phone=good

LT1361 + LT1364 DAC=good, phone=great

LT1361 + LT1057 DAC=good, phone=good

LT1361 + LM4562 DAC=good, phone=good

LT1364 + LT1469 DAC=great, phone=great

LT1364 + LT1361 DAC=great, phone=great

LT1364 + LT1057 DAC=great, phone=good

LT1364 + LM4562 DAC=great, phone=great

LT1469 + LT1364 DAC=great, phone =good

LT1469 + LT1361 DAC=great, phone=great

LT1469 + LT1057 DAC=great, phone=great

LT1469 + LM4562 DAC=great, phone=great

LM4562 + LT1469 DAC=good, phone=good

LM4562 + LT1364 DAC=good, phone=good

LM4562 + LT1361 DAC=good, phone=good

LM4562 + LT1057 DAC=good, phone=good

AD797 + LT1469 DAC=bright, phone=odd treble

AD797 + LT1364 DAC=bright, phone=odd treble

AD797 + LT1361 DAC=bright, phone=odd treble

AD797 + LT1057 DAC=bright, phone=odd treble

AD797 + LM4562 DAC=bright, phone=odd treble

OPA2604 + LT1469 DAC=good, phone=good

OPA2604 + LT1364 DAC=good, phone=good

OPA2604 + LT1361 DAC=good, phone=good

OPA2604 + LT1057 DAC=good, phone=good

OPA627s + LT1469 DAC=great, phone=good

OPA627s + LT1364 DAC=great, phone=great

OPA627s + LT1361 DAC=great, phone=great

OPA627s + LT1057 DAC=great, phone=good

OPA627s + LM4562 DAC=great, phone=great

LT1358 + LT1469 N/A

LT1469 + LT1358 N/A

LT1469 + OPA2132 N/A

DY2000 + LT1469 N/A

AD8599 + LT1361 N/A

LT1028 + LT1361 N/A

LT1028 + LT1358 N/A

N/A means I'm missing part of the combo to test it, so someone else can take a crack at it.
If you do any of the N/A's or have an addition, PM it too me and I'll add it. THX,
Nov 28, 2007 at 1:33 AM Post #2 of 9,388
Ty for this good review.

How long you burn the LM4562 ?
I think it require something like 2 days to get almost his top potential.

For the price , I think the Zero is an interesting product.
Nov 28, 2007 at 1:46 AM Post #3 of 9,388

Originally Posted by pompon /img/forum/go_quote.gif
Ty for this good review.

How long you burn the LM4562 ?
I think it require something like 2 days to get almost his top potential.

For the price , I think the Zero is an interesting product.

I suspect not long enough. After things settle down here, I'm going to re-install it and run her for a few days and see where that goes.
Nov 28, 2007 at 1:28 PM Post #6 of 9,388

Originally Posted by TURBO /img/forum/go_quote.gif
Thanks for that great review. I knew I was not alone!. Je, je.

The Zero is amazing, isn't it? I find myself listening to it far more frequently than I intended, which really says something about its sound quality! Plus, I love a great deal when I find one!!
Nov 28, 2007 at 2:35 PM Post #7 of 9,388
Here's one more opamp for you to try: the LT1364 (a dual opamp). Overall it's alive, warm sounding, yet maybe slightly bright. A favorite of mine. Also, I would try 2x AD797. Though I'm sure that the OPA627's work great.
Nov 28, 2007 at 10:45 PM Post #10 of 9,388
The lowest phones I have are Senn HD212pro's. They are 32ohms. They have tons of bass by nature, so I tried them last night. Wow, they sound great considering the "excess bass". I could drive them right up to pain if I wanted too. So far, I'd have to say the Zero unit doesn't care what phones you use. It has plenty of power to drive any of them. No added hiss or distortions either. Have a good one!!
Nov 30, 2007 at 10:50 AM Post #11 of 9,388
For anyone interested, I'll be posting an update to the review hopefully later Friday. My disability has kept me away from the computer for a few days, but I've had some time for testing additional sources and Opamp situations.

Dave McLaughlin
Nov 30, 2007 at 11:09 AM Post #13 of 9,388

Originally Posted by arteom /img/forum/go_quote.gif
i dont mean to hijack, but how does this compare to amps 2-3 times its price, i have been thinking about getting a Eddie Current EC/SS but this has caught my eye. i would be using a denon d2000. Thanks!

I wish I had one to do a comparison against. But, that is why I did the kind of review I did. I suppose one "testimony" of quality would be when I hooked it up to my vintage Pioneer SPEC equipment. It really did sound great! Another thing I totally liked was its ability to amp any headphones. I have been enjoying my HD-580s again! I don't think you could go wrong picking one up. It sure is a bargain and another seller on eBay is selling them for 139 + 39 shipping. Not bad at all!! Good luck either way!!
Nov 30, 2007 at 11:21 AM Post #14 of 9,388

Originally Posted by Penchum /img/forum/go_quote.gif
I wish I had one to do a comparison against. But, that is why I did the kind of review I did. I suppose one "testimony" of quality would be when I hooked it up to my vintage Pioneer SPEC equipment. It really did sound great! Another thing I totally liked was its ability to amp any headphones. I have been enjoying my HD-580s again! I don't think you could go wrong picking one up. It sure is a bargain and another seller on eBay is selling them for 139 + 39 shipping. Not bad at all!! Good luck either way!!

thats odd, i am getting no results in ebay for that amp at the moment, would you happen to have a link? I do appreciate your reply, I am really considering this amp, this would be my first amp purchase.
Nov 30, 2007 at 11:30 AM Post #15 of 9,388

Originally Posted by arteom /img/forum/go_quote.gif
thats odd, i am getting no results in ebay for that amp at the moment, would you happen to have a link? I do appreciate your reply, I am really considering this amp, this would be my first amp purchase.

Pull up item # 140183988497
My internet access is freaking out, I hope you get this.

Users who are viewing this thread