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Mackie U420 & U420d

Analogue Firewire Mixers By Martin Walker
Published January 2009

These compact, lightweight mixers are designed with live DJ‑style performance in mind, but with an audio interface on board, there's plenty of flexibility when it comes to recording too.

Mackie U420 & U420d

For many years, buying an analogue mixer meant acquiring a host of mono input channels. Some mixer manufacturers then added a couple of stereo input channels to make it easier to plug in keyboards and synths. However, even when manufacturers started to combine mixing desks and audio interfaces a few years ago, they still gave us largely traditional mixer designs with a Firewire or USB audio interface bolted on.

Until recently, few manufacturers catered for the new breed of musician who wants to plug in and mix a small but eclectic selection of sound sources — including mics, instruments, synths, and decks — and then record the results onto a computer with the minimum of fuss; or those using laptop computers, who want a lightweight and compact live setup.

Enter Mackie's new U‑series mixers ('U' stands for 'Universal'), which comprises the U420 and U420d models and provides an impressively flexible selection of input options. These two mixers differ from the norm in the EQ department, since instead of the normal boost/cut at various frequency bands you get boost/kill (similar to the 'EQ Kill' switches on DJ mixers, but offering more control), while the U420d pushes this DJ crossover still further, with two deck inputs and a crossfader for creative cutting and scratching. They also act as monitor controllers, incorporate a Firewire stereo in/out audio interface, and are both small and tough enough to stand the rigours of regular live performance.

Tiny But Tough

In the flesh, these mixers are very compact and 'bijou' — not much bigger than a couple of paperbacks side by side, but several times as thick. However, despite their small size there's still sufficient space between all the knobs to cope with the fat‑fingered among us, while the non‑slip rubber feet prevent them sliding about on the desktop.

The design of the grey moulded cases cleverly incorporates a 'U' shape, with half of the input channel strips on each of the two vertical 'upstrokes'. The black rubberised handrest forms the bottom curve, and a central, inset control‑section in black contains the output knobs and meters. The U420d model is slightly wider than the U420, at 9.4 instead of 8.8 inches, largely to fit in extra sockets across the rear panel. It's also deeper, at 10 instead of 8.6 inches, in order to accommodate the extra couple of controls per input channel.

The control layout and many of the controls are common to both models, but unlike most mixer families, where cheaper models have less of everything (input channels, output channels, and so on), the two models are intended for different users, so there are also some fundamental differences between them.

Keyboard Control

Horses for courses: both these small mixers include a Firewire interface, but which is right for you will depend on your needs. The U420 (top) gives you four stereo line inputs but no mic inputs, whereas the slightly larger U420d provides only two stereo input channels but also features two 'combi' jack/XLR mono inputs.Horses for courses: both these small mixers include a Firewire interface, but which is right for you will depend on your needs. The U420 (top) gives you four stereo line inputs but no mic inputs, whereas the slightly larger U420d provides only two stereo input channels but also features two 'combi' jack/XLR mono inputs.

Let's start with the simpler U420, which is designed for small home studios, 'producers', keyboard submixing, portable live performance, and as the audio nerve‑centre of a computer/video/game system. It offers four stereo line‑level inputs with six sets of largely identical front‑panel rotary controls. The first is Gain, with a useful 'unity gain' centre‑detent position, and I found the associated level LED very handy when finding the optimum gain setting between the twin perils of distortion and excessive background noise.

Next up is a three‑band EQ offering high shelving at 4kHz, mid‑range peaking at 1kHz, and low shelving at 300Hz. Each band provides up to 15dB of boost, but in the cut direction it can reduce the contribution of each band to almost total silence. This 'EQ Killing' is widely used by DJs to deconstruct live tracks, by completely removing the kick drum and bass line, for example, making it far easier to mix in a new track without the beats clashing too much (which rather explains the relatively high turnover frequency of 300Hz). Although having adjustable crossover frequencies would have been more helpful for working with a range of programme material, I nevertheless found it very effective.

Each channel has a stereo Aux send control, and the combined output from these could be sent via the rear‑panel stereo Aux output to feed another mixing desk, stage monitors, or a hardware effects unit (you'd need to use more or more input channels to get the return back into the mixer though). Finally, there's a channel output level control, which, in the case of the U420, is another slightly larger rotary knob. Unusually, this also has a centre‑detent setting marked for unity gain.

Now for the extras. Stereo input‑channel one has an Instrument button to convert it to a mono high‑impedance input, suitable for electric guitars. Surprisingly, while many audio interfaces incorporate such line/instrument switches, very few mixing desks do, so many guitar‑owning musicians will appreciate this feature, especially as the alternative is finding a mixer with a mic input and then buying a separate DI box to plug into it.

Stereo input‑channel four also features a phono RIAA‑equalised preamp so you can connect a turntable, and there's an associated ground terminal on the rear panel. Plugging anything into channel four's line‑level inputs automatically disconnects the phono preamp, so it's an either/or scenario, but, like the guitar input, this is a handy option that's rarely seen on mixing desks.

The outputs of all channel strips are combined into a single stereo signal that's sent to the Firewire audio interface input, a powerful headphone output via a rotary level control, and to the main output via a larger rotary level control and an eight‑segment output level meter.

All the I/O sockets are on the rear panel, which makes it easier to keep your cables tidy and out of the way, and apart from the phono sockets for the turntable input they're all stereo quarter‑inch jacks. Another feature that's very commendable at this price‑point is that all line inputs and outputs are balanced, which can help a great deal in avoiding the hums and digital noises of ground‑loop problems.

DJ Heaven

Mackie U420 & U420d

The U420d model is rather a different beast and is aimed at a range of users including DJs, small bands, and those producing podcasts, or radio interviews. To this end, channels one and two are rather more sophisticated mono channels incorporating Mackie's famed mic preamps (with a 48V globally switchable phantom power option), which sounded both crisp and extended, to my ears.

There's also a more traditional ±15dB three‑band EQ, this time with a variable‑frequency mid‑range over the remarkably wide band of 100Hz to 8kHz, and with more widely spread low and high shelving EQ bands at 80Hz and 12kHz respectively — just as in Mackie's more traditional desk EQ designs, and just as effective. Both channels connect via 'combi' jack/XLR input sockets, and as on the U420, Input one offers a switched high‑impedance guitar option.

Input channels three and four are both stereo, and are largely the same as those on the U420, except that this time both offer phono preamps, so you can connect two decks instead of two line‑level signals and really get stuck in during live performance with the three‑band kill EQ.

Channels one and two are equipped with short faders for output level, while channels three and four have their own rotary level controls, but with an additional horizontal 30mm 'crossfader' between the two, so you can smoothly fade from one source to another.

Associated with the crossfader is a Curve button. With the button in its 'Slow' position, the fade will be performed linearly across the entire fader range, for a classic constant‑power crossfade from one song to another. In the 'Fast' position, a so‑called sharp taper allows you to quickly cut in beats and scratches without losing the energy of the main track, by concentrating the fade of each channel towards the two ends of the slider. I found the Fast setting particularly creative, and the rubberised handrest came into its own at this point, providing a non‑slip base while I rapidly cut in beats.

To help those doing interviews and DJ performances, the U420d model also provides a latchable Cue button for each channel, which lets you hear one or more channels in the headphone output without them reaching the main output — so you could, for example, cue up some new vinyl contribution before the audience hears it, or a music clip that you're about to play back during an interview. There's also a large, flashing, red LED in the central control section to alert you if any Cue buttons are engaged.

Final Thoughts

Both of these U‑series models provide a comprehensive array of inputs that will please plenty of potential users. They sound very clean, offering preamps and EQ up to Mackie's usual high standard, and have headphone outputs that could provide more than enough welly for live performance use.

I missed having pan controls for U420d channels one and two, which are simply fed to both output channels equally so they appear in the centre of the stereo image. While this will be fine for many applications, I can certainly think of situations where being able to send one to the extreme left and the other to the extreme right would be very useful — in an interview situation, for example, so you get the interviewer and interviewee's contributions recorded on separate audio channels, and of course for band recordings when you might want to simultaneously record two completely different mono instruments and add different software effects to them later on.

Also, with my pernickity hat on, while all the jack sockets maintained a commendably firm grip on their plugs, the power connectors seemed rather a wobbly fit, and all U420d outputs exhibited a nasty DC offset that caused large thumps whenever I plugged them into other gear — although I'm willing to declare this a one‑off rogue unit, because the U420 was, in contrast, very well behaved. Other than that, I was impressed.

At nearly £200$300 , the U420 has been seen by some as on the expensive side for a four‑channel mixer, but they forget that it actually has four stereo channels (which is equivalent to eight of the more usual mono channels), and that it also incorporates an RIAA‑equalised phono preamp, a DI box and a stereo in/out, 24‑bit/96kHz Firewire audio interface. In my book, that makes it very good value. Meanwhile, for an extra £50$60 the U420d offers six input channels in total, but two of those channels include mic preamps and more flexible swept‑mid EQ, and you get a second phono preamp, cue buttons for each channel strip, and, of course, the crossfade functions. Once again, I feel this is excellent value for money.

With the 'U' series, Mackie have adopted a fresh approach to small mixers, and I can see both units proving very popular with a wide range of potential users who have never before found everything they needed in a single box.


There are plenty of Firewire and USB mixers available, such as the Alesis MultiMix16, Edirol M16DX, M Audio's NRV10, the Phonic Helix Board 18, and Mackie's own Onyx series. However, most of these offer lots of input channels and separate feeds from each channel to your computer, and are priced at £300‑500a little more expensive than the U‑series mixers. For those with a smaller budget who require a smaller number of simultaneous channels and are content with a single stereo feed to the computer, there's less choice. There are several models at bargain prices with a built‑in 16‑bit/48kHz USB interface, but for those who aspire to the better audio quality of 24‑bit/96kHz the options reduce. One model to consider is the Alesis MultiMix 8, with eight channels, four mic preamps and 10‑in/2‑out USB 2.0 audio interfacing. However, apart from this there's little to compete with the versatility of Mackie's 'U' series.

Firewire Audio Interfacing

Both mixers have a built‑in, stereo in/out, 24‑bit/96kHz Firewire audio interface, and include a CD‑ROM containing drivers for Mac OSX (10.3.9 or higher) and Windows XP SP2, as well as a bundled copy of Mackie's simple‑to‑use Tracktion 3 sequencer. On my PC, driver installation proved simplicity itself, although I found the supplied metre‑long Firewire cable too short to reach my floor‑mounted tower PC (it would be perfect for most mobile rigs, though).

The interface receives the combined stereo mix from all input channels: there's no way to record an individual channel contribution other than reducing the output levels of all the others to zero, and both mixers also include a dedicated 'Firewire In' level control, so you can monitor the stereo output from your sequencer software. You also get true zero‑latency hardware monitoring, because you can listen via the headphone output to both your live performance and previously recorded tracks.

You can optionally combine the stereo output from the Firewire audio interface with the signal that's sent back to the interface input by pressing the FW Loop Out button. This mode is handy when you want to capture everything you can hear coming through the mixer into a single stereo recording, while with the button in the 'up' position you can record fresh tracks containing the combined channel‑strip contributions, but without including any previously recorded tracks that you're playing along with.

Using the Rightmark Audio Analyser with the FW Loop Out button engaged (to bypass the mixer and test the interface alone), dynamic range is a reasonably good 98dBA, distortion levels (THD) are very low, at 0.002 percent, and frequency response is ‑0.3dB down at a good 8Hz and 20kHz (but with no extra HF extension at the 96kHz sample rate). My hardware comparator tests of audio performance showed good subjective audio performance as well, and although it was easily outclassed by the extra clarity and imaging of my benchmark Emu 1820M (as you'd expect, given the price difference), it's on a par with many well‑respected budget '2496' interfaces.


  • Innovative 'U' design incorporates lots of features in a compact size.
  • Very flexible input options.
  • Creative 'kill' EQ.
  • All line‑level inputs and outputs are balanced.
  • Very few mixers offer high‑impedance guitar input options.


  • No pan controls for U420d mono input channels.


Mackie's U‑series mixers manage to cram in more input options than any similar design I've seen to date, while not skimping on any aspect of performance, and should sell by the bucketload to those needing a compact mixer to complement an eclectic range of sources.


U420 £199; U420d £249. Prices include VAT.

Mackie UK +44 (0)1494 557398.

U420 $299.99; U420d $359.99.

Mackie US +1 425 487 4333.