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Dangerous Music 2-BUS-XT

16-channel Analogue Summing Mixer By Matt Houghton
Published March 2023

Dangerous Music 2-BUS-XT

This classy analogue device boasts some impressive specs and has applications that extend way beyond summing.

Launched in 1999, the 2‑BUS was, according to Dangerous Music, the world’s first standalone summing mixer. Back then, the music production world’s migration from consoles and tape machines/digital multitrackers to DAWs and audio interfaces was nascent, and in the ensuing decades things have changed considerably. We have access to computers that can run many plug‑ins, and those plug‑ins can do more and sound better. What’s more, the digital summing in our floating‑point DAWs is pretty darned good. If you wish to mix inside the box, it’s perfectly possible.

But lots of us still see (and hear) plenty of value in a hybrid setup, recording to the computer but coming out of the box to use high‑quality analogue processors. I tend to mix with a lot of subgroups and often run them and the master bus through outboard compressors, EQs and saturation boxes. When working with outboard, there’s potentially a role for a good analogue summing mixer. With everything on a patchbay it’s easier to create different signal paths than when you set things up as ‘external plug‑ins’, and this approach bypasses unnecessary converter stages too. A high‑quality summing box with plenty of headroom also means you needn’t think too hard about the levels at each stage: just tweak controls until things sounds right, keep a loose eye on your gear’s meters, and you only have the level at the final A‑D stage to think about. I’ve used the eight‑channel summing of my Dangerous Music D‑BOX for a number of years, but have often wondered about a setup with more channels, so I was keen to check out the company’s new 2‑BUS‑XT.

Dangerous Conversation

If you wish to perform summing in the analogue domain without a console, you have a broad choice of active or passive summing boxes. The latter can be tempting, as they offer reasonable performance for very little outlay, but you need amplification and if you demand the best performance they cannot match a well‑designed active summing amp. For example, there’s no common‑mode rejection and no isolation of the D‑A converter’s ground from the audio ground of the summing mixer, two factors which will limit how low the noise and crosstalk can be made.

Dangerous Music have long offered some of the best active summing devices, in terms both of specs and build quality. They also have a wonderful habit of moving with the times, and were quick to see that engineers wanted more from such devices than the summing alone. My first‑generation Dangerous D‑BOX, for example, now 14 years old, combined an eight‑channel summing amp with a range of other facilities (source selection, great D‑A conversion and monitor‑control facilities). Even today, it holds its own: it presents a lovely clean and detailed sound stage, with distortion well below audible levels, crosstalk below the noise floor and generous headroom.

Good as the D‑BOX and other early products were, Dangerous have gradually been refreshing their range, developing new facilities and refining existing ones, as well as further improving the technical performance. Alongside a range of other high‑quality gear, including monitor controllers, mastering routers, A‑D and D‑A converters, a compressor and an EQ, there are now three second‑generation summing devices. In SOS April 2016, Frederick Norén reviewed the 2‑BUS+ and in August 2019 Hugh Robjohns looked at the D‑BOX+. The noise floor, distortion and crosstalk of these devices is even lower than on their predecessors. As Frederick explained, one factor which made this possible was the availability of smaller components, which allowed designer Chris Muth more freedom in laying out the circuit: think shorter, straighter lines and six‑layer PCBs.

Ins & Outs

The 2‑BUS‑XT appears nominally to have replaced the 2‑BUS‑LT, yet draws just as heavily on the 2‑BUS+. As you’d expect, it boasts class‑leading technical specs, and the build quality is nothing short of exemplary. The signal path is entirely analogue, but digital control is involved and, as with my trusty D‑BOX, some buttons perform different functions in response to short and long presses. Unlike the D‑BOX, there’s an internal power supply which receives mains AC through a rear‑panel IEC inlet. This caters for US and European voltages, though you must fit the appropriate fuse if moving from one region to the other.

At the heart of the 2‑BUS‑XT is a 16‑channel active summing mixer, whose balanced inputs are presented on two rear‑panel AES/Tascam standard DB25 D‑sub connectors. On the front, every channel has a green Signal Present light, and they’re demarcated as stereo pairs. For each DB25’s first pair (1+2 and 9+10) a dedicated Mono button routes both channels to the left and right mix busses, placing both signals in the centre (there’s no pan facility). The 2‑BUS‑LT had this facility for every pair and some might miss that, but it’s not often you’ll need more than four mono channels right down the centre. One thing to watch out for is that if you send a stereo signal to the channel pair and hit mono, the balance between centre and hard‑panned sounds will change; I noticed this when trying to ‘collapse’ a stereo drum and bass bus to mono.

The Exp input is designed to accept the output from another Dangerous summing mixer to create a larger analogue summing system — but you could use it simply as another stereo input, taking the total at mixdown to 18 channels.The Exp input is designed to accept the output from another Dangerous summing mixer to create a larger analogue summing system — but you could use it simply as another stereo input, taking the total at mixdown to 18 channels.

On the rear, two balanced XLR pairs provide stereo outputs Main Out and Mon Out, which are identical. Their level is determined by the Sum Level Trim pot on the front panel, and this can be set anywhere from full attenuation (anticlockwise), through unity (a shade past 1 o’clock) to a considerable amount of gain when fully clockwise. This allows you to set an appropriate level for your recording device or, potentially, to ‘drive’ a master bus processor that lacks its own input gain control. There’s no facility to monitor the effect of any external stereo‑bus processing, though to be fair Dangerous do point out that the 2‑BUS‑XT is really designed to be used with other gear (eg. routers, monitor controllers) that make that possible, and other summing devices in their range possess master‑bus inserts.

A third XLR pair, Exp In, is intended to receive the output from another Dangerous Music summing mixer, to increase the number of inputs. During my tests, I fed the output of my D‑BOX’s eight‑channel summer to this Exp In, giving me 24 channels of summing in total, and then routed the 2‑BUS‑XT’s Mon(itor) output to the D‑BOX’s Analog In XLRs, while routing the Main Out to my A‑D converters. In practice, you could patch in the main out from a mixing console or a feed from your DAW/converters, or just use them as two extra inputs.

A Little Sum Thing Extra

The 2‑BUS‑XT also incorporates two switchable ‘analogue coloration’ circuits, which can be applied to channels 15+16 or to the stereo mix bus (or neither). These were not present on the 2‑BUS‑LT and they’re most welcome additions!

The X‑Former and Coherence effects, the latter a parallel processor with its own level knob, are available for the stereo bus or channels 15+16.The X‑Former and Coherence effects, the latter a parallel processor with its own level knob, are available for the stereo bus or channels 15+16.

The first, labelled X‑former, runs the signal pair through output transformers (a model they’ve not used previously, and which I’m told was made after yet more listening tests). Unlike on the higher‑priced 2‑BUS+, this effect is simply switched on or off: there’s no gain control to ‘drive’ the transformers harder. But that can still be achieved by running hotter levels into the 2‑BUS‑XT. Essentially, what this processor does is add a pleasing blend of odd‑ and even‑order harmonics, which means it has a bigger subjective impact on some sounds than others. The effect is always pretty subtle, as befits a processor intended for master‑bus or subgroup processing, but it’s noticeable nonetheless, often manifesting itself as a pleasing thickening of the sound that adds a little ‘weight’. Interestingly, I found myself wanting to use it not only for processing mixes but also for printing the effect on individual sounds in the mix; vocals and electric guitars, for example. It’s a nice bonus that a ‘summing mixer’ can do other jobs in a studio!

I loved using Coherence on an electric guitar bus in a thickly layered rock mix; it was perfect for injecting a little life and presence into the wall of rhythm and lead guitar parts.

The contribution of the other effect, mysteriously labelled Coherence, is much easier to discern. It’s a parallel processor, with a button engaging the effect for the desired channels and a pot in the Mix Bus section determining how much of the effect is mixed in. Dangerous say it “injects dimensional asymmetry” and can “subtly tighten up the source by pulling down spiky transients, gently widening and tilting the track forward without any phase skulduggery”. Make of that what you will! Again, it seems to introduce harmonics, though a different blend than the transformer effect. Subjectively, it serves to pull things into focus, brightening them in a fairly relaxed, natural sort of way. I loved using Coherence on an electric guitar bus in a thickly layered rock mix; it was perfect for injecting a little life and presence into the wall of rhythm and lead guitar parts, without treading on the toes of the lead and backing vocals. And on a picked electric bass it was easy to shift the emphasis toward the pick and ‘twang’. It’s nicely judged, though if applying it to individual sources (again, a lovely effect to print) you should be careful when making comparisons, since it inherently adds level. That’s less of an issue when processing subgroups or the mix bus at final mixdown, where it’s much more a case of “if it sounds good...”

Switching of these effects is achieved with two pairs of buttons, one for each processor on channels 15+16 and another for the stereo bus. With a simple short press of the processor’s button, the effect is engaged for that channel pair (when not engaged, it’s a true hard‑wired bypass). A longer press will apply the effect only while the button is pressed; when you let go it reverts to the previous state. So you could long‑press to audition the difference between applying the transformer to the full mix or, say, only the drum bus. Again, a nice touch that makes life easy.

Adding It All Up

I’ve loved working with the 2‑BUS‑XT. On a technical level, there may not be much wrong with in‑the‑box summing today, but there’s something effortless and forgiving about working out of the box, and I still hear a benefit when using good outboard. Once I’m there, it’s great to have the option of ultra‑clean, quiet summing, and it doesn’t get cleaner and quieter than this. With 16 channels available I was able to do much more than I’ve been doing with my eight‑input D‑BOX, and the two worked really well in tandem. But this is so much more than a summer: it’s a very capable sonic sweetener too, and I love the dual‑function buttons.

Is there anything I’d change? Not much. In fact, the only thing I really longed for was a master‑bus insert send/return, so I could audition the effect of any master bus processing via the Mon Out from the front panel. But if that bothers you, Dangerous offer precisely this facility in the 2‑BUS+ already! In short, then, if you’re in the market for a simple yet very high‑quality 16‑channel summing mixer, and the tonal bells and whistles appeal, this one’s very hard to beat.

Talking Crosstalk

The published specifications are impressive. The whopping +27dBu maximum input level means the 2‑BUS‑XT can accommodate the signal from pretty much any D‑A converter. The frequency response is within 0.1dB of flat, way beyond the audible band (10Hz to 50kHz). And total harmonic distortion (THD), intermodulation distortion (IMD) and noise are commendably low.

Dangerous seem particularly proud, though, of the vanishingly low levels of crosstalk: rejection is given as >109dB at 1kHz. To put that figure in context, at the same frequency SPL’s MixDream achieves 97dB and Rupert Neve Designs’ Orbit 103dB. But crosstalk usually rises considerably as you move higher up the frequency spectrum. I didn’t have the opportunity to measure this myself, but Dangerous kindly shared their own Audio Precision plots with me, which compared this device with a top‑performing competitor, and showed the 2‑BUS‑XT achieving ≥100dB right through the audible band. Could this be a reason it sounds so good? Perhaps. It’s hard to be sure, but it’s the best performance I’ve seen and such figures aren’t achievable without a huge amount of care and effort going into every aspect of the design and build.


High‑quality active summing mixers with 16 or more channels are also available from A‑Designs, Neve, Rupert Neve Designs, Heritage Audio, Speck Electronics, Tonelux, Looptrotter Audio and SPL, amongst others. But none outperform those in Dangerous Music’s portfolio.


  • Superb build quality.
  • Much more than a summing mixer!
  • Impressive on‑paper specifications.
  • Equally impressive subjective sound quality.


  • Master bus insert might be nice.


Dangerous Music have updated the final summing amp in their range to a very impressive ‘second‑gen’ spec, and some very appealing tone‑shaping facilities have been added in the process.


£2499 including VAT.

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