Allen & Heath WZ320S

Photo: Mike Cameron

A robust and unusually flexible mixer with lots of stereo inputs.

Allen & Heath have built an enviable reputation for fine-sounding, affordable, and flexible mixers, and with the Mix Wizard series especially. The latest addition to the range is the third-generation WZ³20S console, a version with four mono mic/line channels, and eight stereo channels contributing to the stereo output. However, this configuration is much more flexible than the name suggests since the stereo channels all have two inputs (Input A and Input B) which can be used at the same time, and there are two separate stereo returns. The console is intended to serve equally well for live-sound mixing, simple broadcast, or home-studio applications. The copious number of stereo channels in particular makes it ideal for musicians using a lot of stereo keyboards and samplers.

The original WZ20S was reviewed in SOS February 2000, and the differences between that version and the current model are few but significant. They include a completely new mic preamp design and a better internal grounding scheme; slightly revised EQ characteristics; enhanced output options such as a dedicated mono output fader configurable as a mono sum output or as the Aux 6 master; and a separate AB stereo output. There are also some changes to the stereo channels, with separate routing options for the two inputs, and balanced XLRs for Input B's connections.

Like that first model, the current version can be rackmounted, occupying 10U of space, or it can sit on a desktop. In his review of the original model, Martin Walker complained of skinning his arms on sharp rack edges, but I'm pleased to report that the new model has chamfered corners with plastic edge protectors, so there is no risk of damaged arms at all. Also as on the original model, the connector pod at the rear can be re-mounted to sit under the console (for rackmounting) instead of forming the rear upstand which raises the rear of the console when it is resting on a table.

The WZ³20S features a built-in mains power supply with the IEC inlet socket and power switch on the rear panel. There is also a socket here to connect an optional backup DC power supply, while a four-pin XLR on the front panel provides a power feed for a suitable plug-in gooseneck lamp.

Mono Channel Facilities

The four mic/line channels are each equipped with an XLR for microphone input and a TRS jack socket for balanced line input. Buttons at the top of each channel strip apply phantom power to the corresponding XLR socket, and select the line input. A slightly unusual arrangement is that the XLR socket is also connected to the normalling contacts on the TRS socket, so that if nothing is connected to the line inputs, selecting the line input effectively inserts a 20dB pad onto the microphone signal.

The channel gain control provides a 50dB range from +10dB to +60dB for the mic input and -10dB to +40dB for the line input. Following the input amp is a fixed high-pass filter (12dB/octave from 80Hz) activated with a button, and then the signal is routed to the unbalanced insert TRS socket on the rear panel (with a nominal 0dBu operating level). The insert return feeds a four-band semiparametric EQ section which is engaged with an EQ In button. This is identical in specification to the original Mix Wizard, so it's clearly an EQ design that works and is liked by the users. The top and bottom bands are fixed-frequency shelving filters turning over at 12kHz and 80Hz respectively, with up to ±15dB of gain adjustment and a detent at the unity-gain position. The two swept mid-bands share the same gain range, with the high mid-band centre peak being tuneable between 500Hz and 15kHz. The low mid-band spans 35Hz to 1kHz, and both sections have a Q value of 1.8 (about 0.8 octaves) with a constant bell-shaped response in both boost and cut.

Following the EQ section, the signal feeds the fader, the channel mute button, a post-fade amplifier, and the stereo mix buss pan control. The pre-fade signal also feeds two LEDs, with a green light to register the presence of a signal above -12dBu and a red Peak light to show when the signal gets within 5dB of clipping. The latter also illuminates when the channel PFL button is pressed.

Each channel can access six aux sends, all with individual level controls. The unity-gain position is marked at three o'clock, and a further 6dB of gain is available. As standard, the auxes can be switched with buttons between pre/post feeds in two groups: Aux 1-4 as one group and Aux 5+6 as the other. An internal jumper link on each channel card allows the pre-fade selection to be changed by the user from the factory default of pre-insert and pre-EQ, to post-EQ. The pre-insert mode is ideal for live-sound applications, since if the pre-fade auxes are used for sends to stage monitors, they are unaffected by any channel EQ or compressors inserted into the channel.

However, Allen & Heath also provide some further internal jumper options for the aux sends. Instead of following the pre/post selector, the auxes can be hard-wired to a particular send. Aux 1-4 can be fixed pre-fade in pairs, while Aux 5+6 can be independently hard-wired as post-fade. It sounds complicated, but provides a lot of flexibility. You could, for example, arrange Aux 1+2 as fixed pre-fade monitor sends, Aux 3+4 as switchable, Aux 5 as switchable, and Aux 6 fixed as post-fade for effects.

Returning briefly to the rear panel, in addition to the channel insert point there is also a direct output TRS socket. This is configured for impedance-balanced operation and operates at a nominal 0dBu. The signal feeding the output can be changed with internal jumpers from the factory default of pre-fade to a post-fade feed. The pre-fade selection follows that used for the aux sends (pre-insert and pre-EQ, or post-EQ.)

At the bottom of each mono channel strip is a smooth long-throw fader with 10dB of gain in hand, plus a large mute button (with red LED) and a PFL button. Any number of channels can be PFL'd at the same time, their signals being combined and routed to the headphones (and possibly the AB output, of which more in a moment). As an option, the standard fader can be replaced with an Alps K-Fader with built-in micro-switch to drive mic-open lights, studio-speaker muting, or equipment-start switching. An optional 25-pin D-Sub socket can be fitted to the rear panel to provide convenient access to the micro-switch contacts (if installed), and to enable remote control of some of the desk's internal switching functions.

Stereo Channels & Returns

The stereo channels have slightly simpler EQ facilities, but are otherwise similar to the mono channels. Each channel has two sets of inputs: Input A is via a pair of unbalanced quarter-inch sockets, with the left channel normalled through the right socket to make connection of a mono source easy. Input B is via balanced XLRs. There are no inserts or direct outputs associated with these channels, but each input pair has its own level control (from fully off to +16dB) and an On button.

The factory default condition is that both Input A and Input B are mixed together before feeding the channel EQ and fader, allowing up to 16 stereo inputs to be routed to the mix buss. However, Input A has a recessed button on the top panel (which can be operated with a pen or other small pointed implement) and this deselects it from the channel, routing it directly to the stereo mix buss instead. This facility is useful for accommodating MIDI-controlled sources that do not require EQ or manual fader control, or for effects returns.

The equaliser features four fixed bands, all with ±15dB gain range. The top and bottom bands have shelf responses turning over at 12kHz and 80Hz, while the mid-bands have bell curves centred at 2.5kHz and 250Hz (with a Q value of 1.8 again). The same arrangement of six aux sends is provided, but with the pre-fade position being fixed post-EQ. The stereo channel signal is normally summed to mono to feed the aux sends, but more internal jumpers allow the left channel to feed auxes one, three, and five, and the right channel auxes two, four, and six. Furthermore, this function can be configured separately for the pre- and post-fader sends, so that pre-fade feeds can be mono sums, while post-fade feeds can be in stereo, for example.

At the bottom of the channel strip are a centre-detented balance control, a mute button, and a PFL button. The same signal and overload lights are provided above each fader, and the switched faders can be installed if required for automatic machine starts and so on.

There are two more stereo inputs, called Ext1 and Ext2. The latter is the simpler of the two, accepting unbalanced inputs on quarter-inch sockets — although balanced inputs can also be accommodated, since the ring contact is grounded. Ext1 handles balanced sources properly via TRS sockets. In both cases, connecting only the left channel provides a mono signal. The Ext2 input is equipped with only a level control (off to 0dB) and an On button which routes the signal to the main stereo mix buss. The input signal is also routed from before the level control through to the monitoring section of the desk, allowing it to be used as a tape return for monitoring a recording. The Ext1 input is more fully equipped, with fixed pre-fade send controls for Aux 1-4, and a short fader (with 10dB of gain in hand) to control the level going to the stereo mix buss.

Aux Masters & Outputs

Each of the six auxes has its own master level control with up to +4dB of gain, and the outputs are presented on a row of six TRS sockets. These can be configured for one of two possible output configurations. The factory default provides impedance-balanced outputs operating at a nominal -2dBu and with a +21dBu peak level. However, if there is a need to drive very long cables, true balanced operation can be obtained for any or all aux outputs by installing additional op amps. This will provide a nominal +4dBu output level (+26dB peak) and all that is required is to cut two links and press an appropriate op amp IC into the provided socket for each aux master. The handbook provides clear instructions and diagrams for this process, as well as for re-configuring all of the internal jumper options.

Photo: Mike CameronThe main stereo output buss is controlled by a single long-throw fader with 10dB of gain in hand, and the fully balanced outputs are provided on XLRs with a nominal +4dB level. A pair of TRS sockets are also provided for pre-fade unbalanced mix-buss inserts operating at a nominal -2dBu. The post-fade stereo output is also summed to mono and routed to the adjacent mono output fader, and then on to another fully balanced +4dBu XLR output. This mono output could be used for a centre PA cluster, for example. Alternatively, a recessed button above the mono output fader re-configures its source to be the Aux 6 signal (taken from before the master level control) instead of the post-fade stereo signal. This arrangement allows the Aux 6 output to be controlled more easily, and could be used for a variety of purposes. For example, it could manage a dedicated mix of sources feeding a separate speaker array — perhaps a group of radio mics in a theatre production, or a mix of bass-heavy signals to feed the subwoofers.

The secondary AB stereo output is provided on impedance-balanced TRS sockets and is normally fed from the post-fade stereo output via a rotary level control with up to 10dB of additional gain available. This facility might be used to feed a backstage monitor speaker, for example, or maybe a stereo recorder — although in that case it would make sense to take advantage of yet another set of internal jumpers to obtain a pre-fader stereo buss signal.

Another recessed front-panel switch allows this secondary AB output to be fed from the desk's monitoring section instead of from the main outputs. Normally, the monitoring section only feeds the stereo headphone socket (via a level control), but by pressing this button you can gain a dedicated control-room monitoring facility. What's more, there is a muting relay built into the secondary output which can be configured, for example, to mute the monitoring feed if a mic-channel fader is opened (assuming a micro-switch-fitted fader has been installed) — the perfect feature for a self-operated DJ setup.

The monitoring section on this console is as comprehensive as the rest of its facilities. A column of buttons provides access to all the key signals. The six aux-send feeds can be auditioned individually or in pairs (in which case the odd channels are routed to the left and the even channels to the right). There are also buttons to monitor the two stereo external inputs (pre-fade) and the mono output (post-fade). With no buttons selected, the monitoring signal is the post-fade stereo buss output. If any channel PFL button is pressed, the PFL signal overrides the current monitoring selection. A pair of compact but very readable LED bar-graph meters show the monitored signal level.

Mixer Magic

The WZ³20S is an impressively specified and equipped mixer, built to high standards and with a commendable sound quality. The semiparametric EQ is very versatile and musical, and the simpler version on the stereo channels performs almost as well. All the controls feel solid and reliable, although I would have liked a few more LEDs to indicate some key functions — such as when the channel EQ is switched in.

The technical specifications are very good, with outputs of up to +26dBu into 600 Ohms from the actively balanced outputs, and +21dBu into 2kOhms from the impedance-balanced outputs. The system frequency response is flat to 50kHz, with noise and distortion below 0.004 percent. The new mic preamp EIN figure is given as -128dB and I found it performed very well indeed, being clean, essentially neutral, and quiet — which is exactly what is required.

The real strength of the WZ³20S, though, is its immense flexibility, allowing it to be used in a wide variety of applications with the absolute minimum of operational compromise. It may appear expensive compared to some budget consoles, but I know of no other unit that can match this level of flexibility, build quality, and sonic competence.