Digizoid zO2 Personal Subwoofer in Review – who let the dogs out?

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 zO2, which floored me.

I’ve been mopping up ever since.

Care to discuss this in our forums? Go ahead!

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 zO2 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$, you get a tiny little plastic box with anti-slip coating, decently spaced in/out ports, and a little nob that does everything. Oh yes, the front lights up, too! Yippee! But, to be honest, the zO2 looks like a sub 100$ 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 zO2 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 zO2 is a breeze. If you hold it in your right hand with the zO2 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 zO2. A long inward push turns the zO2 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 zO2 makes it seem harder than it is. Trust me, even an early-thirty something can figure it out.

Unlike a GoVibe product that hides all the goodies under the chassis and even buries its dual Wolfson DACs like it’s embarrassed, the zO2 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 zO2 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 pink, low gain is blue. To get to pink, nudge and hold the toggle switch for 6-8 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 zO2.

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 zO2 allows. Bright red is as woofish as it will get. And that’s a bloody wolf pack.

Here is where the zO2 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 zO2, 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 zO2.

Subwoofing power
Flick it to yellow, or if you dare, to red, and the zO2 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 zO2.

In terms of raw data, the zO2 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 zO2 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 zO2 that aren’t present in other, more expensive audio devices. For instance, noise levels are on par with many amps that cost many times the zO2’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 zO2 does.

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

prodigious bass is off the charts!

Then, there is distortion. Quite a bit, to be exact. Driving the SM2, the zO2 outputs up to 2dB of averaged noise and intermodulation distortion, mostly, you guessed it, in the bass. That is when the zO2’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 zO2’s are. In the high frequencies, however, that number reverses, and the zO2 has the upper hand. Again, the zO2 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 zO2 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 zO2 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 zO2 to sound a bit more muffled than a stock iPod. There is slightly less ‘sparkle’ in the stereo image, and of course, the zO2 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 mask the perception of high frequencies. The quantitative effect is that even though the zO2 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.

Digizoid note: add a little treble to you player’s EQ and voila! you have that sparkle back!

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 zO2 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 zO2 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 zO2 delivers all of that, but just in case you need to validate your purchase, take a look at the graph below and remember, the zO2 is under load. Incredible.

Charts Disclaimer
This review’s RMAA measurements reflect the performance differences between the naked iPod touch 4G and the same iPod when paired with the zO2 and Twisted Cables line out dock. Since these measurements are taken with my equipment, they should not directly be compared measurement-to-measurement to other technical data taken with different equipment. The data represent the ability of the amplification circuit to drive headphones and speakers.

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 zO2 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 zO2 has.

I have only two niggles with the zO2. 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 zO2 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 zO2 could be better shielded.

Sound Conclusion
The zO2 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 zO2 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. (And believe me, something incredible is in the works!)

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 if you want more than a traditional headphone amp; i.e., you want bass for gutless speakers and headphones, and loads and loads of fun to boot, the zO2 represents the cheapest and best way to make every single headphone, speaker, stereo you own into a bass powerhouse. Audiophiles, too, should take note as the zO2 delivers top performance in key areas. Fun included!

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

Kiss It Rating - 5/5

App Summary
Title: Digizoid z02 Personal Subwoofer Developer: Digizoid
Reviewed Ver: z02 type: headphone/speaker/stereo amp/preamp and subwoofer
Price: 120-140$
  • Light and tiny
  • Extremely powerful sound
  • Top-level sound
  • 32-levels of bass adjustment
  • Lowest volume level in low gain mode is too loud
  • Radio interference

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