The Calrec PQ2100: A Broadcast-Era Parametric EQ Worth Knowing

For decades, Calrec Audio was the quiet giant of British broadcast sound, building consoles that ran for thirty years inside radio vans, television control rooms, and outside broadcast trucks. Most recording engineers know the brand by reputation, yet few have ever sat behind a Calrec desk in anger. The PQ2100 parametric EQ module sits at the centre of that reputation, a four-band fully parametric equaliser originally developed for Calrec's broadcast consoles and offered as a window into a design philosophy shaped by live-to-air discipline rather than multi-track record-making.

Australian engineers have a long-standing familiarity with Calrec kit, from the ABC's Ultimo broadcast centre in Sydney to regional stations dotted across the country. The brand shows up in places where reliability matters more than glamour, and the PQ2100 follows that pattern. It is a workhorse equaliser, unglamorous in appearance, but deeply musical once you learn its curves and centres.

Calrec and the Engineering Mindset

Calrec Audio grew out of the post-war British broadcast boom, building consoles for the BBC, ITV, and a long list of international broadcasters. The company earned a reputation for rock-solid reliability because live broadcast has no pause button and no tolerance for failure. Engineers who learned their craft in the era of valve desks and Studer tape machines came to expect that a Calrec would still be running twenty years later, even after being bounced around in an outside broadcast van through countless footy finals and state elections.

The PQ2100 emerged from that engineering culture, where every component was sized for headroom and every switch was rated for the long haul. It was originally introduced as part of Calrec's modular broadcast console architecture, designed to drop into an otherwise fixed-format desk. Rather than treating EQ as a nicety, broadcast audio requires aggressive corrective shaping because programme material varies wildly from caller to presenter to remote feed.

For Australian readers who have only ever mixed music, it is worth pausing on what broadcast actually demands. A radio console in Sydney or Melbourne is processing speech, music beds, phone-ins, codecs, and remote contributions simultaneously, often with five or six sources open at once. The EQ on each channel has to be reach-for-and-fix, with centre frequencies chosen for the human voice first and music second. Calrec designed their modules around that daily reality, and the PQ2100 is one of the cleanest expressions of it.

Inside the PQ2100 Module

The PQ2100 is a four-band fully parametric equaliser with overlapping ranges that allow the engineer to attack almost any part of the audio spectrum. The two outer bands are switchable between peak and shelf modes, while the inner two bands operate as fully parametric peaking filters with adjustable Q. Each band offers a wide sweep window, with carefully chosen centre frequencies that align with the way broadcast audio tends to misbehave. Boost and cut ranges sit at a sensible plus or minus 15 dB, with detented knobs that make settings repeatable from shift to shift.

Under the hood, the PQ2100 uses a hybrid of discrete transistor circuitry and carefully selected passive components, drawing on the same circuit philosophy that Calrec deployed across its larger consoles. The signal handling is class-A in the EQ stages, which contributes to a particular smoothness in the upper frequencies that engineers either love or find too polite. The module is designed to be in-line at unity gain, with a hard-wire bypass that lets the engineer compare processed and unprocessed signal instantly.

Calrec's broadcast heritage shows in the physical design. The knobs are large enough to be turned while looking at the presenter through a glass window, the labels are readable under the dim lights of a control room, and the switches are positive and quiet. For an engineer working an arvo shift at a regional ABC studio, that ergonomic logic saves time and reduces fatigue in ways a studio-centric design simply ignores.

A Different Take on Parametric EQ

What separates the PQ2100 from studio-oriented parametric designs is its broadcast-flavoured centre frequencies and bandwidth choices. Where a typical studio parametric might offer sweep ranges of 20 Hz to 20 kHz with a few chosen centres, the PQ2100 dedicates much of its real estate to the bands where vocal problems actually live. The presence range around 3 kHz gets detailed attention, the lower-mid muddiness zone around 250 Hz offers plenty of pull, and the high band is positioned to deal with sibilance without choking the air out of a voice.

The Q control on the PQ2100 is wide and forgiving, which suits the corrective work broadcast EQ tends to demand. Narrow surgical cuts are possible, but the module shines when an engineer makes broad, gentle moves across multiple bands at once. The result is the kind of EQ that solves rather than sculpts. Compare this with other modular consoles like the API 1608, designed for hybrid workflows, and you start to see how differently broadcast and music console makers prioritised their circuits.

There is also a subtle matter of topology. The PQ2100 uses a parallel summing arrangement rather than the serial topology common to many studio EQs. In practice this means each band's contribution sums into the output rather than cascading through the next stage, which preserves headroom and keeps the EQ from collapsing the signal when several bands are pushed in the same direction. It is a small detail that matters enormously during a long broadcast where you are constantly tweaking.

Sound, Saturation, and the Broadcast Sweet Spot

Engineers who have sought out the PQ2100 for studio use describe a smooth, slightly forgiving top end and a creamy lower-mid range that flatters both speech and close-miked vocals. It is not a coloured EQ in the obvious sense — there is no transformer hum, no obvious iron sound, no aggressive harmonic signature — but it does have a warmth that comes from the class-A topology and the way the circuit handles transient material. Pushed hard, the high band rounds off harshness rather than amplifying it, which is a welcome trait when processing presenter mics that have been pushed through cheap preamps.

The module also behaves well when pushed into mild saturation, particularly through the input transformer that sits ahead of the EQ stages. Driven lightly, the PQ2100 adds a subtle thickening that suits rock vocals and electric guitars, although it will never deliver the obvious crunch of a dedicated saturator. Engineers who have installed PQ2100s in hybrid music rigs tend to use them as a final polish EQ, the last stage before the master bus, where they can refine tonal balance without reshaping the source.

What the PQ2100 does not do is also worth noting. It does not offer a sharp low-pass filter for cleaning up room rumble. It does not provide a sidechain input for de-essing. It does not include a high-pass filter below 40 Hz, because broadcast audio rarely contains meaningful subsonic content. These omissions reflect the brief, not a lack of design skill, and they keep the module focused on the work it was meant to do.

Use in Australian Studios and Broadcast

In Australia, Calrec consoles populated the ABC's Ultimo centre in Sydney, the network's Melbourne studios at Southbank, and a long list of regional stations that ran the same hardware for decades. Engineers at the ABC recall Calrec desks still being patched into use well into the 2000s, with PQ2100 modules turning up as replacement parts or salvage from decommissioned consoles. Independent broadcasters in Brisbane, Adelaide, and Perth followed similar patterns, and the modules occasionally surfaced on the Australian second-hand market at modest prices, which made them attractive to project studio owners and home recordists.

A handful of Australian producers have built small hybrid setups around salvaged PQ2100s, often alongside vintage Neve or API preamps and a modern DAW front end. The appeal is partly sonic, partly the romance of using broadcast gear in a music context, and partly the fair-dinkum reliability that the modules offer. An engineer working out of a small Brisbane studio described the PQ2100 as the most underrated EQ in his rack, citing its ability to settle a vocal without losing presence.

The Australian market for broadcast-grade outboard remains a small but active community, with engineers trading information through forums, Facebook groups, and audio events around the country. Stories of finding PQ2100 modules in decommissioned radio station storerooms are common enough that the modules have a quiet cult following, and engineers in Melbourne and Sydney have been known to grab a few at a time when stations upgrade. Many collectors find that off-console time matters as much as mixing time, and the chase becomes part of the hobby.

Legacy and Relevance in Modern Workflows

The PQ2100 continues to attract interest from engineers curious about broadcast-derived tools, particularly as DAW-based mixing has flattened the differences between studio and broadcast workflows. Plugins have tried to emulate the circuit, but most fall short of the real thing, partly because the parallel summing topology and the specific component choices contribute as much to the sound as the response curves. For engineers wanting to use the real module in a modern hybrid rig, rack kits are available that hold four or eight PQ2100s in a 4U chassis with proper line-level interfacing.

There is also a broader lesson in the PQ2100 for anyone interested in console recall history. Broadcast consoles could not rely on digital memory, so the physical layout of every knob, switch, and label was designed to make settings visible and repeatable across shifts. That same logic influenced SSL's computer-assisted consoles, including the SSL G Computer, which carried the broadcast sensibility into the studio world. Engineers today who use channel-strip recalls inside a DAW are working in a tradition that begins with desk layouts like the PQ2100's.

Outside the studio, the analogue world keeps finding new audiences, and collectors who celebrate broadcast outboard sit comfortably alongside those who chase rare synths and effects units. The PQ2100 has earned its quiet place among them, and chasing one is often a long, unhurried project that pays off the moment you patch it into a session.

If the PQ2100 has caught your ear, keep an eye on broadcast industry auctions, second-hand dealers, and the occasional regional station upgrade. The same warmth the module brings to broadcast audio echoes through broader live festival culture where vintage analogue gear is celebrated on stage. Grab a couple if you can. They are the sort of EQ that quietly does the work without ever drawing attention to themselves, and that is exactly the brief Calrec designed them for.