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API The Box

Analogue Console By Hugh Robjohns
Published January 2014

How much of API's legendary large-console technology and sound have they managed to pack into this smaller sibling?

When API were formed, at the very end of the 1960s, there was enormous competition in the analogue console market. The ensuing two decades were the age of 'transistorised' equipment, in which the diminutive silicon transistor allowed enormous circuit complexity to be accommodated in very small spaces. The primary benefit for mixing consoles was the ability to cram far more facilities into the design than was possible in the preceding valve era. Hence the emergence of the big multi-channel, feature-packed consoles that we associate with the '70s and '80s. API's approach to audio circuit design revolved around a concept called the 'discrete operational amplifier' module, or 'DOA'. This simple but elegant transistorised gain stage was known as the 2520 (see box), and it formed a basic building block for API's studio consoles. The 2520 DOA is still used to this day in 'API discrete products', and it undoubtedly forms a key part of the legendary sound character for which API have become known.

The Box

Most of the traditional big-console manufacturers now offer digital consoles, but API remain resolutely analogue. They have several large-format analogue consoles in their current product range, including the Vision, the Legacy Plus, and the 1608. The market for big, expensive, analogue consoles is not what it once was, though, and the smaller DAW-based project studios that now dominate the industry have very different requirements. Recognising and addressing this potential market, API have borrowed some ideas and technology from their versatile 1608 console to form a new DAW-optimised mixing desk called 'The Box'.

The Box is designed specifically for well-heeled project studios that want to integrate a DAW with a fully-specified, high-end console — but a console which has an appropriate scale and format to suit a project studio's requirements. To that end The Box provides four API mic/line/instrument input channels as the front end; enough for recording solo artists or small ensembles, or for overdubbing. For the 'back end' The Box is equipped with a separate 16-channel summing section, with faders for mixing to the main stereo program bus (it's actually possible to mix 22 channels simultaneously, or 28 with some thoughtful patching). The third important element of the console is the inclusion of a complete monitoring section with comprehensive cue and talkback facilities. All inputs have balanced insert points, and both input and summing sections can access four aux or two artist cue sends, so integrating analogue outboard and effects is very simple. The Box also includes a dual-channel API 527 compressor (see box), which can be assigned either to the stereo mix bus or two of the four input channels, while the first two input channels feature built-in 550A three-band EQ sections. The second two input channels are provided with 500-series module slots, allowing the user to install any desired preamp or processor that comes in single-width 500-series format directly into either of those channels.

Although The Box has a relatively small channel count, especially on the input side, it's still a fully specified console that matches the high technical standards we've come to expect of API. It features the same transformer-coupled 548B multi-input preamps as the 1608, and has a similar, but simplified, console architecture. The four input-channel insert sends and direct outputs, as well as the main stereo-bus inserts and outputs, and the aux and cue outputs, are all transformer balanced, too. The build quality is exemplary; it's no wonder it weighs over 36kg! But before you get too excited, I should tell you this desk's price reflects both this quality and the reputation of the API brand.

Studio Rig

Given the raison d'être of The Box, we decided to try it out on a real-world recording session. The console had been installed in a studio at the University of Westminster, alongside their Amek Angela II console, and I used it to track an interesting live drum & bass group called Imperium, with the help of my SOS colleague Matt Houghton and two staff technicians, Rich Evatt and Sebastian Torres. The band's line-up was unusual, comprising a Roland SPD-S electronic drum pad with real cymbals and additional drum samples triggered from a laptop, electric bass and guitar (both with DAW processing), a stereo backing track, stereo keyboards, another mono sampler, and a female vocalist. The band wanted to get a good recording of them playing this material live, so we agreed to record the whole lot at the same time, though in the end captured a separate vocal overdub to overcome the inherent problem of cymbal spill on the vocal mic — just to keep options open on mixdown.

We used the four mic inputs on the API console for two cymbal overheads (miked with AKG C451s) the vocal (a Microtech Gefell M92.1), and the bass (via a Radial J48 active DI box). The preamp direct outputs were patched into a Pro Tools rig via Prism Sound ADA 8XR converters.

All of the other sources were DI'd using more J48s, and brought up to line level via the preamps in the control room's Amek Angela II console. In theory we could have routed these line sources directly into the API's summing channel inputs, taking PT recording feeds from the inserts, but the studio's wiring infrastructure made it more practical to work as described. So the line-level direct outputs from the Amek console were patched directly into the ADA 8XRs for tracking.

Different stages in the signal chain have their own patchable I/O — and this means that if you have any 500-series preamps, you can record up to six mic sources at once, as we did on the test sessions.Different stages in the signal chain have their own patchable I/O — and this means that if you have any 500-series preamps, you can record up to six mic sources at once, as we did on the test sessions.All of the Pro Tools source tracks were routed back via the Prism converters and into the API's 16 summing channels for monitoring and to throw a rough mix together, the latter also being recorded back into PT as a guide. We also set up a washy reverb (via Waves' Trueverb plug-in), fed from the vocal track, and sent the wet output back to the API for the monitor mix and for the artist headphones. Artist foldback was derived using the console's aux sends, with aux 1/2 providing a 'band mix' and 3/4 providing the vocal and reverb, and these signals were patched into the studio's own headphone monitoring system, which allowed each musician to adjust their own headphone balance.

Input Channels

All four input channels in The Box are equipped with API's 548B preamp, which was debuted in the 1608. This is similar to the company's 212L preamp (which traces its roots right back to the 2488 series console), and uses the same 1:10 input and 1:1 output transformers, as well as the ubiquitous 2520 DOA. This gain stage offers +10 to +45 dB of gain, while the input transformer provides another 20dB. However, whereas the 212L only has a mic input, the 548B also includes a high-impedance instrument input and a balanced line input. Rear-panel connections accept an XLR for the mic input, and TS and TRS plugs for the instrument and line inputs respectively.

User controls comprise four buttons to select phantom power on the mic input, polarity inversion (on mic and line inputs), input pad (-20dB for mic and -6dB for line), and a mic/line selector. The mic input is replaced by the DI input automatically when an instrument is plugged in, but it would have been more convenient had this been switched from the front panel, to avoid having to grub around the back of the desk when wanting to record a guitar DI instead of a mic source. The gain control range is unmarked on the panel, but actually spans +30 to +65 dB in mic mode, +5 to +40 dB for the DI, and unity gain for the line input.

A transformer-coupled channel direct output, accessed via an AES59 (Tascam standard) 25-pin D-sub connector, can be fed straight from the preamp's output, or from after the channel fader if preferred, as selected by a push button on the channel strip. Each channel is provided with an eight-LED bar-graph meter, which can be switched to show the level either at the preamp output or after the fader.

As I mentioned earlier, the first two input channels are equipped with built-in (and slightly re-packaged) 550A EQ modules. These are three-band semi-parametric equalisers with an overall bypass button, and the top and bottom sections are switchable between bell and shelf modes. The proportional-Q design means that the EQ responses narrow as the cut/boost is increased, making them progressively more selective. All three bands are provided with seven centre-frequency options, and ±12dB boost/cut range. A band-pass filter (-3dB at 50Hz and 15kHz) can also be switched in to help control unwanted out-of-band signals.

API The BoxThe signal path gets a little convoluted after the preamp stage, but the benefit is considerable flexibility. The output from the EQ module goes to a transformer-balanced insert send connector (TRS socket), and the signal is normalled through a corresponding TRS balanced return socket, with an 'Insert In' button to switch external devices into circuit as desired. The insert sends from all four input channels are presented alongside the direct outputs on the D-sub connector.

When assigned to a channel, some elaborate switching allows the 527 compressor module to be connected either pre or post the channel insert. This allows the compressor to be patched in to form two possible signal paths: preamp, compressor, EQ, insert send, insert return, fader; or preamp, EQ, insert send, insert return, compressor, fader.

Input channels three and four are fundamentally the same as one and two, except that, instead of the built-in 550A equalisers, they feature 500-series module slots and the insert arrangements are slightly different. The inclusion of two 500-series slots is a feature borrowed from the 1608 and enables the user to install EQ, dynamics, alternative preamps or any other compatible devices to suit their requirements or preferences.

16 channels take a feed from your DAW via the ubiquitous Tascam-format D-sub connectors. Each of these channels has a balanced send and balanced return socket, making it possible to patch in outboard processors or, if you wished, further mic preamps.16 channels take a feed from your DAW via the ubiquitous Tascam-format D-sub connectors. Each of these channels has a balanced send and balanced return socket, making it possible to patch in outboard processors or, if you wished, further mic preamps.To maximise the flexibility of the 500-series slots, the transformer-balanced preamp output appears on a back-panel TRS socket labelled, reassuringly, 'preamp out'. This is normalled to another TRS socket labelled 'EQ In', which connects directly with the corresponding channel's 500-series slot input. The slot output is routed back to the insert-send socket, which is normalled to both the D-sub and corresponding insert return. The rest of the signal path is the same as the first two channels, but with this alternative arrangement the compressor switching options create the signal paths: preamp, compressor, pre out, EQ in, 500 slot, insert send, insert return, fader; or preamp, pre out, EQ in, 500 slot, insert send, insert return, compressor, fader. This may seem complicated in print but it makes perfect sense in practice, and everything is clearly labelled and explained in the manual.

Although the 500-series slots are intended primarily for EQ or dynamics modules, we decided to install alternative preamps in the slots for this session (a Focusrite Red 1 and an Electrodyne 501), both to test the slots were working as intended, and as a point of comparison with the onboard preamps. We connected the mic signals directly to the 'EQ In' TRS sockets, bypassing the desk's own preamps completely, and recorded the replacement preamps via the post-fader direct outputs, alongside channels one and two. We didn't require more mic preamps for this session, but it struck me later that the console's channel-patching flexibility makes it perfectly possible to record six mic sources simultaneously, if desired. The internal preamp outputs from channels 3/4 can be patched straight to their insert returns to restore the normal channel path, and the 500-series slot inputs and outputs can be accessed directly from the EQ In and Insert Send sockets. Intriguing!


Following the compressor and insert switching, the channel signal path continues to the conductive plastic fader (which has 12dB gain in hand), a switchable high-pass filter (50Hz, first order), a mute switch (above the fader), pan control, and a program bus routing button. Illustrating the high calibre of this console, all of the mix buses are impedance balanced, to minimise crosstalk and noise. The usual pre-/post-fader signals are derived to feed the aux and cue sends, and the pre-fader signal source can be configured via internal links for pre- or post-EQ (The factory setting is post-EQ and post-insert).

For a console of this size, the solo facilities are impressive — and not only because of the easily visible solo/mute indicators!For a console of this size, the solo facilities are impressive — and not only because of the easily visible solo/mute indicators!Unusually for such a compact console, The Box is very well equipped in its channel monitoring facilities, with channel 'Solo' buttons that can be switched between non-destructive PFL or stereo AFL modes, as well as a destructive solo-in-place (SIP) option. Each channel can access two mono aux sends (1/2) with independent level controls but shared pre/post and on/off switching. Aux sends 3/4 are configured as a stereo send, with a single level control and pan-pot. Again, the pre/post and on/off switching are shared, but a third button routes the output onto a stereo cue bus instead of the aux 3/4 buses.

Considering the entire channel signal path, it's worth noting that a mic input signal passes through four transformers, four 2520s, a 2501 and two 2510 gain blocks as it travels between the input XLR and the stereo mix-bus console output. If routed as we did, using the preamp direct outputs to feed a Pro Tools rig and returning via the summing inputs, the count goes up to five transformers, five 2520s, a 2501 and three 2510 gain stages. That's clearly where the characteristically rich, punchy, unmistakably analogue API sound comes from!

Monitor Mixing

Having established sensible recording levels into Pro Tools from the four input channels' post-fader direct outputs, our attention turned to building a rough mix from the Pro Tools returns that were patched into the 16 summing channels. These balanced line-level inputs are connected via two more AES59 D-subs, which are wired straight into the corresponding inputs' balanced insert-send sockets. In installations where there's no requirement to patch outboard equipment, the insert return socket can be used as an alternative TRS line input, and switched in place of the D-sub input via the 'Insert In' button.

The summing channels' signal path is very simple compared with that of the recording channels. A 2510 gain stage receives the balanced input (post-insert), and passes the signal to the fader (with 12dB of gain in hand, again). A 2520 DOA block then drives the pan control and program bus routing. Usefully, a push button at the top of the channel strip allows the fader to be bypassed, if preferred, for accurate unity-gain mixing. The same aux/cue routing and PFL/AFL/SIP monitoring facilities are provided as the four recording channels. Surprisingly, there are no meters on the individual summing channels — not even simple signal present/overload LEDs. I imagine the assumption is that the levels will have already been optimised in the DAW software.

The summing section layout groups the faders as eight stereo pairs, with the two corresponding sets of channel controls arranged one above the other in line with the faders. The channel allocation follows API's usual practice of locating channel one's controls as close to the user as possible, which means the odd-numbered channels are directly above the faders, and the even-numbered channels above them at the top of the panel. I struggled with this layout at first — my small brain expected the odd channels to be on the top row, which seems to be the 'British way' — but I gradually became used to this configuration and found myself reaching for the right knobs by the end of the session!

In normal mixing applications, the provision of 'destructive' solo-in-place monitoring is very useful. In this mode the stereo mix-bus is monitored at all times, and pressing the solo button on a channel actually leaves that channel alone and mutes all the other channels instead (hence being 'destructive'). Pressing multiple solo buttons allows multiple channels to be auditioned together, of course. Making this function even more useful, all of the summing input and recording channels on The Box are equipped with 'Safe' buttons (alongside the program bus routing buttons). Pressing a Safe button prevents that channel from being muted when channels are soloed in SIP mode. As an application example, reverb return channels would be made 'safe' so that the associated reverb remains audible when soloing contributing channels.

In our session, since we were recording the stereo bus as a guide mix, we didn't want any source checking to affect the recorded mix — so we used the 'non-destructive' mono PFL and stereo AFL modes instead. Pressing the Solo buttons in these configurations routes the channel signal onto dedicated monitoring buses and simultaneously switches the monitor section to audition those buses, thus ensuring the stereo mix-bus remains unaffected (hence 'non-destructive').

The stereo mix-bus section of the desk uses 2520 DOAs as summing amps, the outputs of which drive the insert sends via balancing transformers. The 527 compressor can be switched into the mix-bus path prior to the insert point if required. More 2510 gain blocks receive the balanced insert returns and feed the master stereo fader (calibrated for 0dB at the top of its travel), with more 2520 DOAs driving the transformer-balanced main outputs. Usefully, an external stereo mix-bus input is also provided, with a dedicated 'Sum In' button, to permit additional external sources to be incorporated, if required. With 16 summing inputs and four recording channels all routable to the programme stereo mix-bus, plus an external stereo mix-bus input, The Box can accommodate a total of 22 simultaneous mix inputs with ease.