Digizoid zO2 personal subwoofer in review - who let the dogs out?

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Go here for the front page z02 review.

Indeed. Digizoid dub this diminutive piece of plastic a ‘personal subwoofer’. I’d dub it a personal wolf pack – that is, if wolfs were known for barking. They probably growl, so maybe the metaphor stands. Which is more than I could do the first time I heard the z02, which floored me.

I’ve been mopping up ever since.

Specifications
32-step digital potentiometer
Class-A headphone amplifier
Uses ultra-low noise pre-amp
Compatible with output impedances from:
High Gain: 16 – 250 ohms
Low Gain: 16 – 80 ohms
Gold-plated, four-layer PCB, with high-grade SMT components
Input impedance: 16.7k ohms
Output impedance: 1.4 ohms
Max input voltage:
Low Gain – 2.8 Vpp
High Gain – 1.47 Vpp
THD + N: 0.05% (x dB, FS, 1kHz)

It retails for 119,95$ USD from Digizoid and ships worldwide. It’s popular though, so from time to time, it may be out of stock. Snatch it up when you see it.

Digizoid reckon the z02 packs ‘jaw dropping sound’. It does. And it does so for a price that will floor even the most stalwartly thrifty of audiophiles. We can come back to that. Let’s get on with the template, shall we?

Build Quality
There’s not much to say here. For 120$, you get a tiny little plastic box with anti-slip coating, decently spaced in/out ports, and a little nob that does everything. Oh yes, the front lights up, too! Yippee! But, to be honest, the z02 looks like a sub 100$ item. The seams are rough, the paint job is reminiscent of pre-teen model-building, and the anti-slip coating feels like an iPhone case.

The upside to what at first blush looks kitchy, is a well-built device that can stand the rigours of a pocket full of change, that hole in the car where you throw all your wrappers, lids, and old CD’s of Amy Grant, and even a place of honour next to horrible bedroom speakers.

Also, the upside to a plastic housing is that it bounces. It doesn’t scratch as easily or noticeably as metal does. The best thing about plastic, however is that it’s weightless.

Ergonomics and polish
A small piece of two-sided cell tape would hold the z02 to a wall or a speaker for its life. It floats on poorly-made jello and Swedish coffee. Metal wouldn’t do that. Please don’t try either.

In use, the z02 is a breeze. If you hold it in your right hand with the z02 logo smirking up at you, the LightBar (a multicoloured pillar of flame or moss) winks at you like a cat’s eye. Above it on the top edge are the speaker/headphone output and input ports. Your thumb rests firmly on the toggle switch which adjusts volume, bass contour, and triples as a power switch.

As long as you can get the hang of punching it long and short, you will get on well with the z02. A long inward push turns the z02 on or off. A short inward push switches it between contour and volume mode. If you nudge it up or down, it cycles various settings such as volume and intensity in either mode. The literature included with the z02 makes it seem harder than it is. Trust me, even an early-thirty something can figure it out.

Features
Unlike a GoVibe product that hides all the goodies under the chassis and even buries its dual Wolfson DACs like it’s embarrassed, the z02 wears its features proudly.

There are two gain modes that you need to be aware of. Low gain mode is for when you make use of line out ports and docks from your CD player, computer, DAT player, crocodile vinyl player, or iDevice. It allows you to adjust volume on the z02 itself. High gain is for when you use variable outputs such as the headphone output of all the above devices. The volume in high gain mode must be controlled via your device. High gain is purple, low gain is blue. To get to purple, nudge and hold the toggle switch for a few seconds when the LightBar is blue. Voila! Purple. To get back, do the same, but in reverse order.

I tend to use line out docks, so I use low gain mode in order to directly control volume on the z02.

As soon as you have managed low and high gain modes, you can move onto the fun part: contours. Push in the toggle switch. The LightBar will turn orange or green. Nudge and hold the switch up or down and the LightBar will change colours. Green is as neutral as the z02 allows. Bright red is as woofish as it will get. And that’s a bloody wolf pack.

Continued

Sound
Here is where the z02 differs from a traditional amp. It DOES have a good amp circuit included. And yes, that amp can drive even very difficult earphones such as the Earsonics SM2 with little to no effort. Yes, it is a powerful machine, even a good standalone amp.

But, if you’re interested in the z02, it’s possibly because you’ve had enough of amps and DAC’s that make your music sound the way the recording artists intended. You just want to have fun and enjoy your music. I understand completely. So do Digizoid.

They reckon that the bright red contour setting is good for movies. I reckon it is good for anything. In fact, the amp is at its best in terms of dynamic range and noise levels when its circuitry is clubbed out. That’s great news for me. I’ve been known to vacillate between earphones on a daily basis, but I always come back to the Audio Technica CK10, an earphone that could do with a bit of clubbing. My recent love affair with the DBA-02 MKII describes a similar outcome. Both earphones are considered by some as stark, boring, and metallic. Of course, fit is of grand importance with these earphones, but even with perfect fit, you won’t get heaps of bass out of either one.

Unless you have the z02.

Subwoofing power
Flick it to yellow, or if you dare, to red, and the z02 will give you club-level bass. Honestly. With a good seal, even bass-neutral earphones will rattle in your ears and you will swear your chest is pounding from 1-meter subs and that Paul van Dyk is on stage. That bass is clean, comparatively artefact free, and detailed. It is the best bass enhancement I’ve ever heard, even trumping Graham Slee’s Voyager headphone amp, a device that costs more than three times the z02.

In terms of raw data, the z02 can push around 15 decibels of difference between low and high frequencies, and focuses on the frequencies between 10Hz and 300Hz. It’s incredible.

Unlike traditional amps that have ‘EQ’ settings, the z02 allows you thirty-two levels of customisation. In other words, you don’t have to succumb to one company’s interpretation of enhanced bass. The power is completely in your hands.

There are no drawbacks to the z02 that aren’t present in other, more expensive audio devices. For instance, noise levels are on par with many amps that cost even give times the z02’s meagre sum. Yes, with sensitive earphones, you will hear white noise in the background, but it could hardly be called stentorian. To be honest, ALO’s wonderful The National headphone amplifier has as much background noise as the z02 does.

It’s a small price to pay for such lovely bass.

Distortion
Then, there is distortion. Quite a bit, to be exact. Driving the SM2, the z02 outputs up to 2dB of averaged noise and intermodulation distortion, mostly, you guessed it, in the bass. That is when the z02’s contour settings are orange or yellow settings, and again, under load. GoVibe’s VestAmp+, a fine-sounding piece of equipment has similar peak levels of IMD and noise under load, though its base levels of distortion in the low frequencies are lower by about 20dB lower than the z02’s are. In the high frequencies, however, that number reverses, and the z02 has the upper hand. Again, the z02 is much cheaper, smaller, and bounces when dropped.

Stereo image
Onto stereo separation. Phenomenal. This tiny piece of plastic, aimed at bass heads, sustains -73 dB (averaged) of stereo separation under load. It handles that separation well in the midrange, loaded or unloaded, but low and high frequency separation gets squashed as soon as the z02 is under load. It comes quite shy of my reference amp, ALO’s Rx, and in well under the GoVibe VestAmp+, but then again, the z02 costs less than a third of the cheapest of those? I will. And it does.

However, higher levels of distortion in the midrange and bass cause the z02 to sound a bit more muffled than a stock iPod. There is slightly less ‘sparkle’ in the stereo image, and of course, the z02 spends no energy in emphasising high frequencies which helps to paint a bright, separated sound picture. This is a subwoofer and emphasised bass tends to dull the perception of high frequencies. The quantitative effect is that even though the z02 sustains great stereo separation, it will sound sound more closed, more intimate than your most audio sources will for headphone use. As a subwoofer, I’d expect nothing less.

Dynamic range
I feel funny even bringing up dynamic range here, but I’ll do it. Why? Well, by nature, a subwoofer overpowers the perception of dynamic range, tipping everything to the floor and beyond. Still, the z02 is probably capable of exceeding the bounds of 16-bit audio, which is 96dB. I say probably because my equipment, while decent, isn’t professional, and introduces a bit of its own distortion into the signal. Still, feeding the Edirol FA-66, the z02 manages to push 94,6dB of dynamic range. Not bad.

But et’s be honest: if you are in the market for a subwoofer for your portable device or your living room, you are probably not worried about dynamic range. You want power, volume, and fun. The z02 delivers all of that, but just in case you need to validate your purchase, take a look at the graph below and remember, the z02 is under load. Incredible.

Volume
Finally, let’s talk volume. With earphones, you will get more than enough volume for any use, ever. For large headphones such as the Beyerdynamic DT880 600Ω, you will get enough, but won’t be able to pierce your eardrums. Bugger. When hooked up to speaker systems, I suggest using the z02 as a preamp. It won’t give enough juice to smaller powered speakers unless in small rooms. Remember, this is a palm-sized device. It has its limits. But those limits are feeble in comparison to the myriad plusses the z02 has.

Niggles
I have only two niggles with the z02. The first is that in low gain mode, and with sensitive earphones such as the Sleek Audio CT7, even the lowest volume setting nears uncomfortably loud levels. The overall gain should be lowered even further, preferably to near zero levels so that users can comfortably adjust their music for any headphone or speaker. The second is that if you use the z02 near a phone or other radio-toting device, you will get beeps and boops from time to time. Those beeps and boops are radio interference. The z02 could be better shielded.

Sound Conclusion
The z02 is a good headphone amplifier that sustains relatively high quality signals even under difficult loads. In similar price categories there are few amps that can trump it across the board. The iBasso T3D is the only one I can think of off the top of my head that actually does. But that isn’t the only way the z02 defines itself. It is also a portable subwoofer that can be attached directly to headphones, powered speakers, car stereo’s, and powered microphones (yes, but I don’t suggest it). Don’t expect anything like it to hit market at any price until Digizoid’s push out the next z0.

Conclusion
Get one. That’s it. If you have been looking for a small portable headphone amp, there are few better options in the price category. And iff you want more than a traditional headphone amp; i.e., you want bass for gutless speakers and headphones and loads and loads of fun, the z02 represents the cheapest and best way to make every single headphone, speaker, stereo you own into a bass powerhouse. Fun included!

There is nothing like it. I’m howling-proud of this device. Bow wow wow.

Thank you for review. You spelled zO2 wrong, it is zO2 or ZO2 not z02. But very thorough and good information.

Hey Dimitri, thanks for coming out. I know I spelled it wrong, but oh well. I've noticed that some of my reviews are better than others. I could chalk it up to excitement. The zO2 (the right spelling of course) is the most exciting palm-sized audio device I've ever used, so I really worked on this. Thank you for the loan. Now I want one!