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TAC Scorpion

Mixing Desk

Not quite a desk in a million - studio owner Gareth Stuart gets to grips with one of TAC's 73 possible variations in their Scorpion mixer range, the 16-8-2+16.

Total Audio Concepts manufacture an extensive range of frame sizes and modules for their Scorpion mixer (73 variations in all), and the version we chose to review comes under the heading of 'S model' (small frame) and comprised sixteen S1000 input channels, two S2000 auxiliary send/return channels, eight S3100 monitor modules, and one S4000 master module. In this category, there are seven possible layout variants.

For the purpose of this review I unwired my Soundcraft Series II 16-8-2+8, now umpteen years old and a bit tatty, and hid it in a corner of my studio behind a Marshall stack (hoping the vibrations would shake the dust out of it!) and took great delight in fooling all unsuspecting clients what a neat, stylish, up-to-date setup I had. The impression the new desk made on regular clients was marked - they reckoned the Scorpion desk raised the image of the studio. Can't be bad if simply having a new desk creates work! The Scorpion's 19" rack-mountable power supply is an impressive rack filler, occupying 3U of space (a little more tasteful than matt black blanking panels). And both it and the desk are extremely well-built, sturdy pieces of equipment.

The 56-page ringbound manual at first approach comes across as another epic in the Yamaha/Roland vein, but makes surprisingly good reading. It is certainly useful as a friendly reference book on day to day usage of the mixer. It covers all possible TAC Scorpion variations, and in the end there are only 11 pages to read that specifically deal with this model. Or rather, the modules that this model is made up of.

One thing that immediately struck me whilst installing the desk is that the Scorpion works almost exclusively on stereo jacks: line inputs, inserts, direct outputs - wherever a jack socket, as opposed to an XLR, is applicable (excepting the Left/Right monitor outputs). All connection details are clearly printed in the manual and in table form on the rear of the chassis, beneath the microphone inputs. A nice touch when you're crouching behind the desk, trying to avoid burning yourself with a scorching hot soldering iron. Here it reminds you to 'only use stereo jack plugs.'

Taking note of this for the first time was a little disturbing. My usual desk works entirely on mono jacks and, since I'd recently heard that on D&R desks inserting a mono jack into a stereo socket shorted the input, I was a little concerned as to how I was to wire in enough channels to review the TAC Scorpion in a realistic working environment. Anyway it turned out that, apart from one occasion, it wasn't strictly necessary to use stereo jack plugs.

TAC's intention behind using stereo jacks is to allow for many more options when wiring in the desk, as the tip, ring, and sleeve of the stereo jack are used to their greatest potential to enable different operating levels and phase selection.


Time now to run through the functions of the various modules. The S1000 Mic/Line Input module offers mic/line input, insert, and direct output jacks. The mic input is via an electronically balanced XLR socket. As mentioned, it's possible to use mono jacks in these sockets. On the face of it, this would appear to limit the options open to you regarding choice of operating levels and phase but this isn't in fact the case. Let me explain...

With mono jacks fully inserted, the line input receives a positive phase signal; the insert jack sends a post-EQ, post-gain, pre-fader signal (but no return signal) - I'll cover this in more detail when I talk about the insert point; and the direct output sends out a 0dB signal. Pulled half-way out (ie. making contact with signals which would normally feed the ring of a stereo jack), the line input receives a negative phase; the insert has a signal returned (pre-gain, pre-EQ, post-fader); and the direct output sends out a -12dB signal. Both mic and line inputs are electronically balanced. When using a balanced line input you must use a stereo jack plug. Incidentally, just in case you are wondering if I actually used stereo jack plugs as TAC recommend, the answer is yes.

Returning to the practical aspects of the insert points; there's good and bad news depending on the sophistication of your outboard gear, and your methods of working. The good news is that because an effect is returned to the same channel it's sent from, you save on channel space. The bad news is that on inserting a stereo jack into the insert socket, the direct signal is muted, allowing you to monitor only that signal being returned from the effects unit.

As Richard Swettenham points out in the APRS handbook, 'Sound Recording Practice', "preferably there will be a switch in the channel, allowing the effect of the inserted device to be compared with the straight through signal." Between the Scorpion and your outboard gear, you can either use a volume pot in the monitor section corresponding to the insert channel - switched to tape return mode to allow you to mix together or compare the unequalised signal from the tape machine (the dry signal) with the fader on the appropriate channel controlling the level of the equalised and effected signal; or switch your effects unit into bypass mode.

In case you have ever wondered why some mixers have channel inserts as well as auxiliary sends, the manual explains: "Whereas auxiliary sends are used to feed effects devices which may be used on more than one signal, eg. reverb or echo (delay), and which only require slow or occasional changes in input level, inserts are principally used for introducing fast gain control devices (eg. compressors, limiters, expanders, gates) into the channel circuit."

The channel insert comes after the equalisation and is terminated in a stereo jack. The tip of the jack is the insert send, whilst the ring is the return to the input of the fader. What this means in practice is that a signal being output to an effects unit via the insert, has its output level governed by the gain pot and EQ. The fader only controls the level of the signal being returned to the channel.

I can understand why the gain should be used to control the send level but having EQ effective in this part of the chain seems crazy to me, and seems to go against the grain when it comes to putting a mix together. For example, let's say you decide to gate your snare drum. So you set up a suitable threshold level on your gate so that you effectively remove all unwanted sounds apart from the snare itself. However, the moment you add EQ to the snare extraneous sounds are introduced as the increased output from the channel insert renders the gate threshold too low.

I swapped between the inserts and the aux sends in order to compare the results in each case of adding EQ before the gate and after the gate - and really, there's no question that EQ'ing after the gate is the easier to work with and produces the most pleasing results.

I spoke to TAC's technical staff about this, and whilst they agreed with me that post-EQ was a pest for gating, they considered it was fine for compression. Well, I think post-EQ is a pain for setting up all sorts of effects but it seems to be the norm in mixer manufacture. TAC were very helpful in clearing up several points I raised, and on this particular issue suggested that if somebody desperately wanted pre-EQ sends on the inserts, it could be arranged... but it would be an "inelegant" job, as TAC put it.

A final point about the insert regarding wiring it into an external jackfield (I say 'external' because on the larger framed Scorpions it's possible to have the desk fitted with an internal jackfield). When using the inserts 'casually', that is to say leaning over the desk and plugging in a stereo jack when necessary, you effectively mute the 'straight through' signal. On wiring them into a jackfield it would be necessary to normalise the send and return contacts, in order to create a loop, and thus avoid muting the channel when inserts weren't being used.

Before talking of the need for different operating levels I'll clarify the application of the mixer's direct output. On this particular Scorpion desk, because it only has eight buss outputs but is intended for use with either an 8-or 16-track tape machine, the direct outs on channels 9-16 become substitute buss outputs.

It's not possible to route several channels to any one direct output, so, in the event of having to record on more than eight tape tracks simultaneously, you'll have to exercise a degree of organisation in choosing which track to record a particular signal on as the input to Channel 9 (say) will be directly output to Track 9.

Leaving aside the dual operating level setting for a moment, the level recorded on tape is controlled by the gain fader and EQ, which I think is daft. I would suggest that the recording level on tape should be gauged solely with the gain control, ie. it should be post-gain, pre-EQ, and pre-fader. My reasons for this are simply that when constructing a mix while recording, it would be a whole lot easier. As it is, in order to monitor and change the audio level of signals being recorded via the direct outputs (channels 9-16), it's necessary to switch them out of the routing system (disengaging all routing options) and monitor a flat (ie. unequalised) signal on the appropriate volume pots on the upper monitor section (switched to bass mode). Any alteration made to gain, EQ or fader position on channels 9-16 during the recording process will directly alter the recording level.

Using a mono jack on the direct out is no problem: with it fully inserted a 0dB signal is sent out (to your multitrack) and with it plugged half-way in a -12dB signal is sent out. I checked this using a conventional PPM meter - in fully inserted mode the signal peak was +6, half pulled out the result was +3.

So why have two different operating levels? Well, if your multitrack is a Fostex E16 which operates at -10dB, a 0dB feed will register in the red on the E16's meters before the Scorpion has had a chance to flash its buss LEDs at you. Since you're likely to be viewing levels on the desk rather than on the multitrack (which might even be in another room), it's a little frustrating not to be able to see the desk working. In which case you opt for the lower operating level.

Apart from that somewhat cosmetic justification for dual operating levels, it's not a bad idea to have your entire system working at one level in order that a fixed audio level is maintained throughout as you switch between various sound sources - that way, what goes in comes out.


On the front of the Scorpion, the S1000 module divides into five main areas. At the top are four buttons for selecting the appropriate input - 48-volt phantom power for mics, a pad button which attenuates a mic input by 20dB, line/mic switch, and a phase control. After these comes the gain pot. Used not only for balancing input signal within a mix so as to leave sufficient headroom on the fader, but also to feed outboard gear patched in via the insert point.

Next, the equaliser (switchable in/out) - a 4-band device with swept frequency midrange controls. The high and low frequency controls are both shelving devices with selectable turnover points at 6kHz and 12kHz for HF and 60Hz and 120Hz for LF. If you're at all unfamiliar with this type of control, basically what you are presented with in each case is a set point in the frequency spectrum after which you can either decide to boost or dip frequencies at a rate of 14dB per octave.

For instance, with HF shelving on a rhythm guitar part, selecting the turnover point at 12kHz and boosting the signal tends to enhance the sound in a similar way to an aural exciter. All frequencies below 12kHz are left unaffected. Whereas switching in the turnover point at 6kHz and excessively boosting the frequencies has the effect of sharpening the sound to the point of harshness. At both turnover points, dipping the frequencies makes the sound duller, but with the 12kHz shelving more of the original sound is left unaffected. The low frequency control works in exactly the same way - rolling off or boosting bass frequencies below either 120Hz or 60Hz.

Because the midrange EQ is sweepable, you have tremendous tonal control over the sound being equalised. The MF1 (mid frequency) control allows you to boost or dip (again by +/-14dB) any frequencies between 500Hz and 18kHz, enabling an exact frequency band to be located for boosting or cutting. As TAC point out in their manual, "your ears should quickly tell you how to adjust the frequency band centres to make the sound fit your requirements."

Below the EQ section are four auxiliary sends, which are switchable pre- or post-fader as pairs 1+2, 3+4. They have two possible functions: (1) to feed outboard equipment such as reverbs or delays, and/or (2) to provide foldback for musicians. In the first instance I'm sure you will be au fait with the normal use of an auxiliary to send signal to an effects unit, but the aux sends are also particularly useful to feed foldback amps/headphones. With auxiliaries 3+4 switched to 'pre-fader' it's possible to create an independent headphone mix; independent that is of fader positions and therefore independent of the mix being heard over the monitors in the control room. The pre-fader auxiliary send is post-EQ and postgain, so variations to gain and EQ settings in the control room will influence the foldback mix. Incidentally, that's not a criticism. On the S2000 Aux Master Send/Return module, which I'm coming to, you're not only able to control the level of the sends but also change EQ settings pre-effects/foldback.

Below the aux sends are the subgroup/buss, 1-8/buss stereo selectors and a pan pot allowing you to route a signal to any one of the eight buss outputs (level controlled by the subgroup faders) or direct to the stereo buss output. If you're at all unsure of the possibilities open to you here, the manual comes in very handy, explaining that routing signals to a subgroup "enables you to control the level of a number of input channels using one or two group faders. For example, suppose your drum kit occupied five tracks on the multitrack tape and were being fed back into the console through channels 1-5, the signals being bass drum, snare, hi-hat, and overheads (left and right). To control the overall level of the kit, it would be easier to form a stereo subgroup using subgroup faders 1 and 2." The manual continues to explain exactly how to route input channels to subgroups in eight steps...

As this particular Scorpion model has only eight buss outputs, you can't subgroup any of channels 9-16 using the master routing button on the channel. This particular button is only fully operational on 16 buss models.

Below the pan pot are two buttons Mute and PFL (Pre-Fade Listen). A red LED indicates if mute is on and the muted channel is silenced. The Pre-Fade Listen button lets you check (listen to) the channel signal with a fader closed (pre-fader) and set up the correct gain structure through the channel circuit before the signal is fed to any of the outputs that are post-fader. You are able to vary the level at which you hear the PFL signal using the PFL volume control on the S4000 master module.

Finally, the channel fader - I think it's widely understood that the fader is used for fine level adjustments required during recording.


The rear of the S2000 module is an all-XLR affair, where the pins on the send XLR relate to the dual operating levels and the return XLR assumes your effects units are unity gain. I say that because the wiring of the return XLR is pins 1&3 screen, pin 2 signal. You wouldn't really want two different input levels, would you?

This may not be too important to you but I wondered why the effects sends and returns merited XLR connectors when most other sockets didn't. TAC to the reply - quite simply, all main outputs are XLR. I know that the direct outs aren't XLR but, in terms of PA use where direct outs as buss outs wouldn't merit 'main output' status, all main outputs in PA application are traditionally XLR. Anyway, the S2000 rear panel is laid out with four XLR aux sends and two sockets for returns, with your other effects to be returned to either channels or monitors.

Looking at the front of this module there's the EQ on the master aux sends, comprising two 2-band shelving equalisers: HF +/-14dB; LF +/-14dB. I found EQ on fold back to be particularly useful.

In order that you should have maximum flexibility over aux returns 1+2, you are able to subgroup as well as send them direct to the stereo buss. You'd make the most use of this facility if you wanted to record effects on your multitrack.


The rear panel of the Scorpion's S3100 Subgroup/Dual Monitor input module comprises eight XLR buss outs (pins govern level), eight tape/effects returns (stereo jacks), and eight insert points (stereo jack). Now here, if you're using a 16-track recorder, you can't get away with using mono jacks.

To get tape returns to both sections of the dual monitor module it's necessary to solder two leads onto one stereo jack. The tip carries the lower monitor section signals (channels 1-8), the ring carries the upper monitor section (channels 9-16). If it's not already clear, what you have to do here is solder the leads 1+9, 2+10, 3+11, 4+12 etc, from your multitrack outputs onto the same stereo jack. The obvious drawback of having to wire two leads onto one jack plug is that screwing the plug cover back on becomes pretty difficult - depending on what diameter of cable you're using.

In reply to a query on this point TAC said that, in the first instance, there's not enough room on the rear panel to fit in two sets of returns (1-8), (9-16), and secondly, regarding the wiring of two leads onto one stereo jack (which is in no way meant to be a criticism of this design), there's not really another way of doing this. Best to use narrow gauge cable.

On the front of the S3100 modules you're presented with 16 monitor pots, each with four auxiliary sends. The lower bank of monitors may be switched to receive tape/effects return signals (from inserts), line input (channels 1-8) or buss (1-8) information. The lower monitor may only be used as an additional effects return when the subgroup fader is not in use or when it is not being used for playback monitoring. The upper bank of monitors, even though labelled 'buss/tape/effects', will only receive two sets of information - signals coming off tape (channels 9-16) or signals coming from the direct output of channels 9-16.

On mixing with the desk for the first time (and by the way this is still relevant to the S3100 module), I was very aware that LEDs 1-16 on the meter bridge weren't registering any signal even though the stereo output looked very healthy. This is because they only read information that has been routed through buss outputs 1-16. The reason why the stereo LEDs light up is because the signal is routed to the stereo output, ie. the stereo buss, in subgrouping any channels to busses 1-8, so LEDs 1-8 on the meter bridge register the level of the buss output. (Remember that the tape/effects/buss switch must be in the buss position. If it's not, you'll hear tracks 1 and 2 from your multitrack).

On both the S2000 and S3100 modules, AFL (After-Fade Listen) as opposed to PFL buttons are present. Whereas the PFL is useful in establishing the levels of inputs into channels 1-16 in the pre-mix stage, the AFL allows you to listen to signals post-fader and therefore at a level proportional to their final level in the sound mix.


Next along is the S4000 Master Monitor/Stereo Buss output module. In the Scorpion console, all monitoring and mixing is done through the stereo mix buss, which is used at all times. During recording on the multitrack tape machine, the monitor mix sections of the S3100 modules will feed the stereo buss with a combination of 'buss' and 'tape/effects' signals. During mixdown, all signals will go to the stereo buss either directly from the S1000 input modules or via the subgroups to the stereo buss, which is summed in the S4000 module.

On the rear panel there are several different outputs from the S4000 module - the stereo buss out XLR and mono jack. Here the XLR pins relate to operating level. The stereo buss outputs feed the inputs of your 2-track machine. I noted with interest that the stereo buss outputs weren't balanced. Strange, I thought... balanced inputs, but unbalanced outputs. I spoke to TAC about this. They confirmed that the outputs were not balanced. If you need balanced outputs, they're available as an option at about £35 per output.

So why have balanced inputs? Well, for PA applications mainly. But in some studio situations, where long runs of cable are used, a balanced line is essential to maintain the quality of the signal. As the output stage is likely to pass into a power amplifier positioned at close quarters (for ease of operation), a balanced feed is not seen to be essential.

Above the buss outputs are two insert points, which I can see being used for compression of a complete mix for instance. (Incidentally, this is the only time that I would condone using post-EQ at the insert point.) Above that are two monitor outputs, feeding the control room amplifier. The level is governed by a pot on the front of the panel. Aux monitor output - a fixed level output similar to the stereo bus out. Suggested uses in the manual for this output are driving a second set of speakers or cassette player. If you weren't intending to use auxiliary sends 3&4 to feed foldback headphones, this output could be used instead - feeding the foldback amplifier(s) with a control monitor mix.

After that you have two sets of tape inputs, Tape 1 LR and Tape 2 LR, an oscillator, and talkback output. Apart from playing back tapes via these inputs, one use might be to monitor the mix off tape from your master 2-track recorder. A switch on the front module governs which source you send out of the buss, monitors, and aux monitors, be it Tape 1, 2 or stereo (the current mix on the desk).

TAC suggested that the oscillator would most likely be used to calibrate meters. However, in the cases of both the single oscillator and talkback jack on the rear panel, the idea is that they're there for the sake of flexibility and ready for any use you care to imagine.

The S4000 module's front panel is split into seven sections, which actually perform five functions. First up is talkback, a female XLR socket suitable for microphones not needing a phantom power feed. Talkback may be fed to the aux sends (ie. talk to foldback) or to slate (ie. 16 subgroups and stereo buss out). When the talk switch is operated, the monitor outputs will drop (dim) by 20dB. This is to avoid feedback if you happen to talk to an output which you are simultaneously monitoring. For example, you may be listening to aux buss master outputs 2 or 4 in PFL mode to check the musicians' foldback mix and need to talk to them at the same time.

Below the talkback input is a button labelled VU/Peak, allowing you to change the response of the stereo LED meters, depending on which you feel more comfortable with. The VU meter registers an average reading, lulling the unexperienced or unwary user into a false state of security, whereas the Peak meter registers all the (potentially damaging) signal peaks. It has a much faster rise time, or 'ballistic' if you prefer to talk technical, and consequently gives a more accurate reading of the actual level being output from the desk.

From time to time you may decide to run routine maintenance checks on the mixing desk. Below the VU/Peak selector, three trim pots allow you to adjust the meters' response. An auxiliary monitor level pot allows you to feed an extra power amp/pair of speakers, or could equally be used for foldback or as a stereo aux send.

The PFL monitor allows you to adjust the level of PFL and AFL signals relative to their levels in the mix. This is particularly useful in checking that the signal passing through the desk is doing so at a consistent level.

Because the PFL and AFL share the same LED indicator light on the meter bridge, making immediate checks on input and output levels is extremely easy. The monitor pot controls the level on the control room speaker. Here, you may listen to tape 1, tape 2, or the stereo buss by depressing one of three buttons. Below this monitor pot are a mute and dim button. In case of feedback (howlround) or when you simply want to have a chat about the mix or whatever, being able to either temporarily dim or mute the control room monitors and then return to the exact same monitoring level is very useful, for continuity's sake. That, as they say, just about covers everything on the TAC Scorpion.


I had a great time working with this mixing desk. I've criticised some operational features - the fact that inserts send post-EQ signal, the direct output level being controlled by the fader, etc - but really they're the only criticisms. The pros for this desk certainly outweigh any cons and make quite a list:

  • Beautifully clear, quiet sound.
  • Great equalisation.
  • Handsome appearance.
  • Solid construction - all-steel chassis.
  • Extremely flexible (with enough variations of input and output jacks to boggle your mind and dual operating levels for compatibility with any system).
  • Fully modular - allowing you to carry on mixing in the event of a single module needing repair...
  • Straightforward to install.
  • Comprehensive and well-written manual.

Price 16-8-2+16 £4443 inc VAT.

Contact Total Audio Concepts, (Contact Details).

Also featuring gear in this article

Previous Article in this issue

Sony Portable DAT Recorder

Next article in this issue

Roland MT32 Update & Editors

Sound On Sound - Copyright: SOS Publications Ltd.
The contents of this magazine are re-published here with the kind permission of SOS Publications Ltd.


Sound On Sound - Jul 1988

Gear in this article:

Mixer > TAC > Scorpion 16-8-2+16

Review by Gareth Stuart

Previous article in this issue:

> Sony Portable DAT Recorder

Next article in this issue:

> Roland MT32 Update & Editors...

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