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digiZoid ZO1 / ZO2.3 Portable Headphone Amp Review

post #1 of 88
Thread Starter 

For my detailed review of ZO1 plus interesting SmartVektor technology info click on the spoiler tag below, otherwise continue to read about the ZO2.3


digiZoid ZO Personal Subwoofer Review (Click to show)


digiZoid ZO Personal Subwoofer Review






In an already very crowded market along headphone amps of various sizes and performances at different price figures, it's hard to experience anything new, it's mostly revamped designs merging different parts together as well as minor differences can be seen on the surface but the core construction often remain very similar. DigiZoid ZO Personal Subwoofer however doesn't belong to this category, built upon what the manufacturer calls SmartVektor™ technology, redefines the sound in a previously unheard way and it's not one of those $10 gimmicks marketed to the roofs like its name might hint about, no it actually WORKS since a lot of research and trial & error is put behind this product and one thing is for sure, DigiZoid are serious and are here to stay.


So how will this amp / sound "enhancer" with a rather modest price point of $99 fare? Read on to find out!


Technical parameters


Input                                                  Output                                                 Frequency response


connection    3.5 mm Stereo          connection   3.5 mm Stereo            20 Hz - 20 kHz ± 0.25 dB

voltage         2.0 V (max)              current        190 mA @ 3.7 V          (green contour level)

impedance    15 kΩ                      impedance   0.2 kΩ


Environmental                           Power                                                  Physical


operating temp   32 ≤ °F ≤  95       run time         14 hrs                     dimensions    2.75 x 1.5 x 0.38 in

storage temp     -4 ≤ °F 115          rapid charge     1 hr                      weight           1.2 oz     

relative humidity   5 ≤ % ≤ 95        full charge        2 hrs

                                                charge cycles   > 700






First let's take a look at the package, in the package as seen above you can find what you'd expect to see, the amplifier together with a short and a longer stereo cable as well as an USB chord for your recharging needs as well as a guide and diagram, as a little extra touch a towel to clean your ZO from the fingerprints could perhaps have been a welcomed addon as this device sure will get full of them from the glossy surface. 


I really liked the manual for it, it's small, concice, well written with no extra unnecessary or excessive technology brawl or marketing speech, only what you need to know. 




The ZO Personal Subwoofer is an amp / sound enhancing device that doesn't feature any volume control (but they have spoken about an updated version which might feature this but don't quote me on it) but adds a significant boost to the volume and DigiZoid recommends to start out with around 25% volume setting and all sound enhancing and EQ settings to flat/off. In my case it made quite a lot sense starting off with that but I also applied all my usual tweaks such as Dolby Headphone and reverb as well as my hardware EQ settings and they all sounded great (more like better than before) with the ZO device and didn't cause any issues at all.


It allows 31 different contour level settings which a light indicator changes from green (lowest setting) to red (highest setting), the first one works as a "flat" listening setting which still grants all the audible improvements of the ZO except it doesn't make the bass stronger at this setting, perfect for those who just want to listen more flat but take advantage of the device's amp/sound processing techniques. Here's an interesting manual page for you readers to check out that shows the color of the indicator light at the different levels.




It also features a bypass function so that you don't have to mess with unplugging headphones from your ZO in case you turn it off or the battery would become completely dry etc. and it's also very useful to make quick comparisions between turning it on/off to hear the difference almost instantly. However there is a fairly loud "pop" when turning on/off and I'd hope DigiZoid might try to improve this in the future. 


As nearly all portable devices it features USB recharging and one full recharge takes about 2 hrs while an 1 hr recharge will grant you roughly 80% capacity and a fully recharged battery lasts according to DigiZoid manual up to 14 hrs. A more realistic battery life is probably 8 ~ 12 hrs or so depending on contour level setting according to the homepage which is while not the worst out there but certainly leaves some room for improvement. personally bought an USB -> AC power adapter so I can simply plug it in the wall socket and forget about it as recharging via the USB port it made some static noise but that's pretty much the case with all devices, only some computers provide less static than others (some maybe not even audible).


digiZoid SmartVektor™ and subjective analyzing


Before going into further details I'd like to take the time to explain a little bit why I got interested in this little device in first place as it's very relevant to this review, you can of course skip it if you like but it'll still add valuable info to this review.


[optional, but recommended]

First I'm the kind of guy that can spend hours fiddling around with any settings found on my devices I use as I'm a tweaker and looking for that best possible subjective result I can achieve and I'm very pro-EQ enthusiast that I mainly became thanks to the very high quality hardware 10-band EQ found in the kX Audio drivers for my Audigy 2 ZS soundcard which really opened my eyes in how great of an improvement a good quality equalizer can bring, clearly beating any typical software EQ found in for example most of the music players as it doesn't distort or color the frequencies, it'll only adjust the "loudness"-curve like an EQ should be doing in best case scenario. 


At first when I started using these kX Audio drivers and the 10-band EQ especially I did some rather typical, minimalistic deviations from zero-level changes to adjust the balance of the headphone. The basshead in me during that time (we're talking probably 5+ years ago) just wasn't quite satisfied yet coming from a computer speaker 5.1 setup which I gave up in favor for listening privacy. Now I tested boosting the lows further and got very satisfied with the bass quantity however the overall balance or sound quality was less than ideal so I started boosting the rest of the range as well by various amounts and ended up with quite similar curve as previously, only the whole range took a boost but bass became boosted a little more in comparision. Eventually I started boosting the whole range even further and to my surprise the more I boosted the whole range, the more I started liking what I was hearing and then I also started realizing exactly how great this EQ was as boosting frequencies by large amounts isn't anything that common software EQs would allow without distorting, in my case the output volume just got louder at the same volume setting which forced me to lower my volume sliders to make up for it. I was puzzled, how could boosting the whole range on my EQ start sounding better than simply boosting the volume, it just didn't sound the same.


It's this more "forward" sound which I'd describe as more "dynamic" sounding which I believe is what people enjoy about this ZO device that is a bit difficult to explain in words, it's something that simply has to be experienced on your own. Whether this ZO Personal Subwoofer device uses a similar hardware EQ-technique playing around with the loudness curve and boosting the whole range or not, one thing's for sure, they DO share that similar kind of sound signature change after doing comparisions with my own ears between the hardware EQ and the ZO device. But this is certainly not the only change or benefit the ZO adds, certainly not, but more on that later!


Before moving on I'd like to show you my 2 different EQ settings I keep for XB500 for exampleone that is minimalisticly tweaked for only better balance and the other which uses this kind of EQ technique with greatly boosted range as a whole that I find providing great results that I spoke about previously making a more "forward" and dynamic experience. Also to set things into perspective of how much of a drastic bass boost capability ZO can add, to get similar kind of bass quantity out of the ZO device as the EQ setting I may only need to use around level 6 or 7 possibly (starting from level 0), whereabouts the contour level indicating light changes from yellow to orange which is roughly only 1/4 of the max capability!




On the DigiZoid website they include a sound demo of the effect ZO device adds. Of course it has to be stressed that this is merely a simulation and won't represent how it sounds like in practice but I still think it gives quite a good hint at what it does.



If further digging into the website they will also show some graphs that would strengthen my suspicions I discussed in the optional chapter, boosting the whole frequency range and depending on the setting level on the ZO it'll boost bass a little more than the rest which again is exactly the same technique I use with my hardware EQ.


Headphone: Sennheiser HD280 Pro


(Picture source)



On the http://www.digizoid.com/tech/ page you can read the following that I will try and comment with my own words and experiences how I see it and tell whether I think there's some truth to it or if it's just another attempt to advertise a product to sound better than what it really is.


The Revitalization of Sound


SmartVektor™ technology revitalizes sound to produce a sonic experience previously thought unattainable. Our patent-pending techniques deviate from current industry practices, delivering market defining performance that enables you to provide new levels of product differentiation. Put the power, balance, and refinement of SmartVektor technology in your next design and discover the true power of sound.



It certainly is a more unique implementation and differs from the competition and even goes even slightly against what many formal audiophiles would typically opt for. However theoretical aspects put aside, the subjective results heard from the ZO Personal Subwoofer is really something that has to be experienced in person to be able to appriciate. Hopefully DigiZoid might even be able to implement this technology in for example different MP3 players of various manufacturers (similar to for example BBE in Cowon MP3 players) which would pay licensing fees to DigiZoid.  




SmartVektor technology expands the audio's dynamic range in the low and high ends of the spectrum. Therefore, with loudness variation enhanced, music is revitalized with texture and clarity. Layers of sound once buried are now uncovered, and the emotional power of sound is restored.


This is very much what I experienced as well, the dynamic range is noticably enhanced but it's not only the lows and highs that are brought more forward but mids as well. However mids is the range that will start suffer the most if raising the contour level above the lowest setting but it'll still work noticably better than traditional amp bass boost controls as this doesn't only adjust the lows but the whole frequency range is altered and this also leads to a bit better instrument separation. Imagine it in the following way, as having several speakers tuned to take care of different frequency ranges. As they can each focus on their specific range you can easily boost the volume of all those speakers instead of having one speaker doing the whole range which results in more detailed and separated kind of sound where the different instruments come out more clearly without being masked by other frequencies. This is the best description I can provide of what the effect ZO provides does.


Also the people working on this has done a absolutely great job at shaping the curves optimally for each level so that there is as little bass bleed as possible comparing to how large bass boost capability we're talking about here. Of course each headphone will still require their personal EQ curves to sound optimal but they did an excellent job at where to start rolling off the bass response before it reaches the lower-mid frequencies and I can also confirm that adding your own EQing on top of ZO will work absolutely fine and won't cause any easier distortion than not using the ZO device!




Through the management of acoustic timing and power delivery, SmartVektor reveals sonic detail within the audio otherwise obscured by more dominant sounds. This "unmasking" improves the overall clarity and acoustic resolution, and provides greater spatial dimensionality regardless of the listening environment.


I can relate to this as well, every headphone I got that I plug into the ZO device I started hearing better microdetail as all my headphones started sounding a bit more balanced (muffled sounding headphones started sounding more clear and bright headphones a little less bright etc) which again I think have to do with the more "forward" sound. I can also relate to the increase in spatial dimensionality or known as "soundstage" around these parts, it expands the "borders" of the soundstage further without doing some major repositioning, sounds that are meant to sound like coming further away comes further away but due to the more forward sound, it sounds a little more "up-front" when running through the ZO device which leads to the music sounds more engaging and emotional like you'd be physically there which causes you to not being able to sit still but have to start dancing or moving along to the music!




SmartVektor technology is not a bass boost, EQ, or psychoacoustic algorithm. Instead, it maximizes the acoustic efficiency of a speaker by extending its' low frequency cutoff, and optimizing the low frequency power delivery. The result is distinct, profound bass with pure highs and unclouded crystalline detail.


The bass response is definitely improved bigtime in various aspects. I was always sceptical about reading how a headphone amp could make it stronger in deep bass but also tighter at the same time (without actually removing any significant amount midbass) while adding a more realistic "kick/punch" to it without causing any serious midrange bleed from midbass which usually stands for the punch/kick with a lot of impact to it, phew. This is exactly what ZO Personal Subwoofer does and the best is that it doesn't distort, it sounds so clean and natural, something 99% of EQs probably can't achieve when talking about the bass boost that ZO is capable of.




SmartVektor technology rebalances an audio signal to compensate for the ear's inefficiencies by normalizing the sound pressure levels of the entire audio spectrum to achieve equal loudness. Since this balancing provides more sound at less volume, the overall risk of both short- and long-term hearing damage from excessive volume level listening is reduced.


I suppose there's some truth to this as I definitely heard that the headphones sounded a little more balanced when running through the ZO. I believe the safer listening argument could probably be applied in the sense that bassheads are able to achieve the desired bass output satisfaction at lower volumes than previously so the mids and highs aren't as screaming high while still providing great detail from the more forward and more balanced sound.


Furthermore I want to add that at the lowest contour level setting you won't get any emphasized bassresponse, it'll just sound a little more balanced while sounding more forward and you'll enjoy better dynamic range as well as a bigger and more realistic soundstage with better microdetail definition while getting a much louder output volume. Between the first ("flat") level and the second there's quite a bump in bass response in my qualified guess maybe around 2.0 ~ 2.5dB or so, would probably be nice if DigiZoid added more options in between the first and 2nd level in the future (say 1.0 ~ 1.5dB or so boost), for me personally it's not an issue but I know some people would greatly appriciate a more subtle bass response boost.




It's very difficult whether you're a basshead or a balanced response listener to NOT recommend the DigiZoid ZO Personal Subwoofer for a mere $99, which I concider a steal for what it provides. Unless you need to power a very demanding highend headphone, the ZO Personal Subwoofer should be very high on everyone's "must-try" list. From increased bass response quantity as well as quality from dynamic range improvement to microdetail improvement as well as soundstage improvement along with more raw power but at the same time safer listening in the long run, the list is nearly endless. I can't imagine me listening without this ZO device after I heard it, after YOU've heard it, you quickly become an addict and listening without it, the music will sound more lifeless and boring. It's difficult to put what ZO does in words, only by trying it yourself you will fully realize what it's about and that's why it's so difficult to write a review about it, I tried my best to stay objective and calm without my emotions taking over this review and believe me, that was among the most difficult things I've dealt with in my life. :p


I really hope the effort DigiZoid has shown by having a contact here on Head-Fi co-operating with the people "in-the-know" will continue and who knows what products we will be enjoying in the future. As of now I have to excuse myself as I have to hop on the ZO-train departing for "audio Nirvana", thanks for reading and also huge thanks to DigiZoid for letting me experience all this for such an insignificant price!




- Outstanding price / performance ratio

- Vast improvement to many different aspects, bass response, dynamic range, soundstage, detail, balance

- Add as much bass as you personally prefer out of the 31 different contour levels

- Small and very portable

- Safer listening


Cons & the average


- No volume control 

- Makes fairly loud "pop" when turning on/off

- Somewhat lacking contour level steps especially in-between the first "flat" and the 2nd level

- Battery life

















digiZoid ZO2.3



IMG_0802.jpg IMG_0796.jpg



First I'd like to take the time to thank digiZoid properly for listening to users feedback and working so hard to make sure the product gets as good as possible for as many users as possible, it's certainly not an easy task to satisfy both the demanding Head-Fi crowd as well as covering both Line-Out IEM use as well as making sure it can drive a little higher impedance headphones. This was one of the main goal for ZO2 -- what ZO1 wasn't able to, to be able to use with a line-out device, bypassing the often subpar quality internal amp in portable devices for a cleaner result. This wasn't a smooth ride though like the number ZO2.3 in the title suggests, it took 3 attempts but in the end everything turned out well as digiZoid team was determined to make this happen even if it meant most of their christmas holidays time would be occupied by work. 




Technical parameters


Physical                                                                                     Sound Customization                                                                                                       Included Accessories 


Dimensions: 2.75 x 1.5 x 0.38 in.                                     Two gain modes for use with either headphone out or line-out                              Short 3.5mm stereo cable
Weight: 0.94 oz.                                                          Compatible with headphone impedances up to 300 ohms                                      Mini-USB charging cable
Designed and manufactured in the USA                            Digital volume control with 32 selectable levels                                         
Enclosure has a "soft-touch" protective coating                 LightScale with 32 distinct color changes for each sound contour profile
                                                                                Sound contour profiles tuned for equally spaced intensity changes
                                                                                Single-switch operation for all controls
                                                                                Memory feature automatically recalls last settings




High and low gain


It now features selectable high and low gain. The low gain is primarily intended for line-out use and high gain if used with headphone jack. But the low gain also offers slightly different contour level intensity so could possibly work as an alternative contour level profile in case high mode doesn't work out for you so nothing stops you from trying low gain if plugged into a headphone jack. I even possibly preferred the sound using low gain.


Volume control


There's now volume control with 32 levels that you can adjust while in low gain which is needed for LOD use. In high gain it remain fixed but it's questionable if there's any real benefits by having volume control in high gain as if you use the headphone jack it sounds perhaps best if volume on ZO2 is maxed from my testing anyway and in high gain it's too loud for LOD use.


Contour level adjustments


It features now 32-level contour level adjustment which has been tweaked, it now offers equally spaced intensity changes and the low level contour levels have been adjusted so that the lowest level offers a very transparent and neutral balance and the following 1-2 levels offer now a very fine amount of bass boost so you can more get a much smaller boost if that's desired than previously.


Low battery LED indicator


There's now a LED that will blink when the battery is low.


Coating change


The glossy plastic fingerprint magnet coating has now been changed for a "soft-touch" protective coating


Bypass/standby mode disabled


The bypass/standby functionality which made it possible to listen while the ZO has been turned off without having to unplug it first has been removed to protect the listener and equipment from excessive volume levels when ZO is used with Line-out.


LightScale LED intensity changes


Now features 32 distinct color changes for every 32 contour profile 


Battery life improvements 


It now exceeds 12 hrs, from my testing possibly around 15 ~ 18 hrs depending on mode used etc. (don't take this as an exact measurement as I haven't timed it!)


Improved on/off switching


No longer makes a popping noise and it switches on/off MUCH faster than previously and without bunch of distortion heard meanwhile


EMI/RFI filtering improvements


The ZO2.3 no longer occasionally picks up "phone-signals" now. 


Single-switch operation


High/low gain selection, volume control, contour level adjustment, on/off switching is ALL done on the same push-wheel switch. To turn on/off, you simply push down the button for aprox 2 secs, to adjust contour and volume levels you use the wheel to adjust up/down and to change between contour level and volume adjustment you only do a rapid press on the button and finally to go from low to high gain mode you first adjust to the max volume level in low gain which will make the LightScale LED turn purple and hold down the wheel button+ for aprox 4-5 secs and the LED will turn pink.



Subjective Sound Changes


What suprised me most here is the difference I'm hearing between low and high gain modes on ZO2.3. I think the SmartVektor sound has a greater effect in low gain when I'm raising the source volume to match up the high gain volume levels for some reason. As a reminder of how SmartVektor processes sounds like here's a good new comparision you can check out



There's no huge changes in sound comparing ZO1 to ZO2.3 except the contour levels are now better balanced. For me the soundstage and stereo separation on ZO2.3 is slightly better in low gain vs high and versus ZO1 it's quite similar, possibly slightly more up-front you have to listen closely to hear any differences, especially comparing ZO2.3 low gain vs ZO1 it's actually fairly the same in this regard but I think ZO1 has slight advantage if comparing against high gain. I think also the midrange is slightly better detailed and forward using low gain in ZO2.3 and the highs have ever so tiny bit better resolution for a more neutral sound. Why I'm experiencing slight differences between low and high gain is a slight mystery to me but let's say the differences is easier to notice between low/high gain than comparing ZO1 to ZO2.3. I'm guessing it probably has to do with the volume differences on the source using headphone jack and then controlling the volume on the source. In low gain using my M-Audio Q40 headphones as an example which are 64 ohm headphones I'm at like 53~54% but in high gain at 16%, so a big difference there.


The bass using low gain is not as intense as in high gain so it gives a nice alternative curve but yea the bass boost is also very drastic in low level as you up the contour levels and should be more than plenty for most people. In high gain it seems to provide slightly more "punch" to the bass compared to ZO1.


Other than I can't say for sure I'm noticing any noteworthy changes I will update this part later if I'd change my mind. But I prefer ZO2.3 sound-wise using low gain over ZO1.





Seems all the work digiZoid team has put into ZO2.3 has finally paid off, the usability now covers a greater usability range covering all the way from LOD + IEM use to headphone of up to 300 ohm use. As mentioned previously there's a number of improved features and the best is that despite all this, the digiZoid has decided to keep the price at the MSRP $99.95 price point where it's an easy recommendation from me for any one searching for a little more basic portable amp, whether you're a basshead searching for headpounding bass without ruining the overall sound which ZO2.3 is more than capable of and thanks to the further tweaked contour level adjustment anyone will find his preferred bass response. As for myself I can't even wait with what digiZoid will come up next, especially with the rumored ZO3 featuring fullrange SmartVektor adjustment which allows you to adjust the treblerange as well!


Lastly some pros & cons compared to ZO1.




- Now possible to use with line-out thanks to volume control & low gain

- Better balanced contour levels

- No longer annoying pop-sound when switching on/off and it's much faster

- No longer seems to pick up any phone signals

- Improved battery life & low battery indicator


Cons & the average


- Soundstage could probably be further improved while in high gain especially





IMG_0790.jpg IMG_0762.jpg IMG_0765.jpg

Edited by RPGWiZaRD - 1/23/12 at 1:19pm
post #2 of 88

Love the review. Finally this product gets the attention it really deserves. Any basshead needs this thing to get the most out of their headphones.

post #3 of 88
Thread Starter 
Originally Posted by slapshot30 View Post

Love the review. Finally this product gets the attention it really deserves. Any basshead needs this thing to get the most out of their headphones.

Yea it really suprised me, I was expecting to get this more "forward" sound characteristic and bass boost capability but I hadn't expected to get so many improvements too, not for this price. :p


Edited by RPGWiZaRD - 6/17/11 at 3:37pm
post #4 of 88

Wow! You finally got it! I would like to say thanks before I do the actual reading. =)

post #5 of 88

Great review and happy your are finally enjoying what some of us have easier access to =)  It truly is a gem!!!

post #6 of 88

Does this work alongside an amp/dac?

post #7 of 88
Thread Starter 
Originally Posted by Alghazanth View Post

Does this work alongside an amp/dac?

It probably works but how great it works is obviously the question, I've only got an FiiO E5 collecting dust somewhere as I've sold my other amps, testing with an E7 for example would probably give a better idea and seeing how common those are around here there's got to be at least some1 with a ZO as well as E7. Maybe some other ZO owners can comment on this?


Edited by RPGWiZaRD - 6/17/11 at 11:44pm
post #8 of 88

I think I'm going to cop one of these, just to see what it does to the bass-less AD700 I still have laying around.

post #9 of 88
Thread Starter 
Originally Posted by Alghazanth View Post

I think I'm going to cop one of these, just to see what it does to the bass-less AD700 I still have laying around.

Haha, that will be interesting, among the more common bass-less options. If it can turn this headphone bassheavy it'll be quite a feat. Somehow I still think it got the capability to do so, the bass boost of this device is just scarily strong, I barely dared going past midway on XB500 even for testing purposes and I'm a basshead lol.


EDIT: Oh wait I just remembered I should have some old Philips headphone lying around somewhere that is very very basshy and the bass sounds like "tin-can" bass. Must try it on that. 


OK So I tried it on the philips headphone which by default settings has barely even any audible bass and turned ZO to max and it made it much bassier, now it can be heard, I'd put it slightly above what I'd call neutral and it barely muddy up the overall sound at all on this particular headphone, nice.

Edited by RPGWiZaRD - 6/18/11 at 2:52am
post #10 of 88

I've tested and yes it can give it "BASS".  However too colored for my liking.  So I used my cmoybb 2.03 with bass boost on then used it with the Zo.  It reduces the amount of coloration with about 4-8 clicks to get some nice bass.  =)




And yeah...I was like WTF!?  YESSSSSSS lol

post #11 of 88

I would be sold on these, if they actually had a real volume control.  But until then, the lack of volume control is a total dealbreaker for me.  I hope that if they do, they make it a good one, since I don't want to deal with a crappy pot with bad volume imbalance.

post #12 of 88
Originally Posted by ziocomposite View Post

I've tested and yes it can give it "BASS".  However too colored for my liking.  So I used my cmoybb 2.03 with bass boost on then used it with the Zo.  It reduces the amount of coloration with about 4-8 clicks to get some nice bass.  =)




And yeah...I was like WTF!?  YESSSSSSS lol

Wait, so did you use both at once? Which of the two is superior alone?


post #13 of 88

I do use both when at home.  But if I had a choice of only one, then I would take the Zo easily.  

post #14 of 88
Thread Starter 

Here's my EQ settings for XB500 previously without and now with ZO that has the contour level setting set only one notch up from the "flat"/lowest setting: 




The bass quantity is about the same when using the new EQ setting with ZO as not using ZO and the other higher boosted bass curve. Sounds for my taste perfectly now. I guess I really must be a big fan of this "forward" sound if my EQ setting looks like it does despite even using ZO device.


Edited by RPGWiZaRD - 6/18/11 at 6:19am
post #15 of 88

You got the ZO for the XB? Is the bass not enough?

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