Klark Teknik DN-3030
Two channels of ⅓-octave graphic EQ in a single rack unit. It keeps passing signal even when the power dies.
Overview
The DN30/30 - sold in some markets as the DN-3030 - is a stereo graphic equalizer with two matched, high-specification graphic channels in one chassis. Each channel gives ⅓-octave equalization across a full 30 ISO centre frequencies. That's the pitch Klark Teknik ran in the trade press. Thirty faders per channel, sixty across the front panel, at 25, 31, 40, 50, 63, 80, 100, 125, 160, 200, 250, 315, 400, 500, 630, 800 Hz, then 1K, 1.25K, 1.6K, 2K, 2.5K, 3.15K, 4K, 5K, 6.3K, 8K, 10K, 12.5K, 16K and 20KHz. Getting that resolution into a single unit was the trick, and the company's own advertising copy leaned on the phrase "breakthrough in equaliser design."
The circuit is the interesting part. Klark Teknik developed all-new circuitry for the DN30/30 using what the manual describes as ultra-stable N.I.C. minimum-phase combining filter networks. That means negative impedance convertors, rather than the conventional inductor-and-capacitor approach. The company claimed unequalled performance, and the measured numbers back up the ambition: distortion below 0.01% from 20Hz to 20KHz, and equivalent input noise better than −90dBm across the same band, unweighted. At 1KHz and +4dBm into a 600-ohm load, distortion stays under 0.01%. Push it to +18dBm and run the full 20Hz - 20KHz sweep and it holds under 0.05%. Maximum output level is +21dBm into 600 ohms. Crosstalk sits below −80dB at 1KHz. Frequency response with the controls flat is ±0.5dB, 20Hz - 20KHz.
The faders are oil-damped, and each one has a centre detent so you can find true flat by feel rather than by eye. That helps when you're thirty faders deep and trying to zero a channel in a hurry. The scale switch selects either ±6dB or ±12dB as the maximum boost and cut. The compact sliders keep fine resolution for small corrections, and the full 12dB is there when a room needs surgery. The centre position of that same switch is the bypass - a straight A-B between dry and equalized signal without touching anything else. Centre frequency accuracy is quoted as better than ±5% of nominal.
The feature list beyond the EQ is where this unit earns its keep in a working rack. A switchable 30Hz subsonic filter, 18dB/octave Butterworth, −3dB at 30Hz, handles the rumble that would otherwise eat headroom. Input and output connections are complementary 3-pin XLR sockets, with full electronic balancing on both ends as standard. The input stage is a differential amplifier with added RF filtering. The output drive circuitry is self-compensating, meaning it will drive balanced or unbalanced loads wired in any pin configuration without instability or damage, and output level stays constant between the two. For unbalanced operation the manual is emphatic that pins 1 and 2 must be tied together at the DN30/30 itself, not at the downstream equipment. Input impedance is 47K ohms nominal, electronically balanced. Output impedance is under 60 ohms source driving a 600-ohm load. Input level control gives up to 6dB of system gain fully clockwise and infinite attenuation fully anti-clockwise.
Two relays on the rear board do the work that separates a pro box from a toy. The first isolates the output sockets from the equalizer until power is switched on and all internal rails are stable. That's delayed turn-on, so no DC or power-up transient reaches the gear downstream. The second connects the inputs directly to the outputs if power is lost or a power-related failure occurs mid-operation. Total system bypass. Losing mains does not mean losing signal.
Overload monitoring is thorough. Audio levels are watched simultaneously at four points in the circuit, so the LED warns of excessive level anywhere in the equalizer rather than at one stage. Threshold is +19dBm, which leaves 3dB of headroom before clipping sets in. If it lights, the manual's advice is to pull back the input level control, unless the input stage itself is being overdriven past +19dBm, in which case the level has to come down at the preceding equipment. There's also an earth-lift switch on the rear panel that disconnects signal ground from mains and chassis earth. The manual offers it as a quick and safe answer to earth-loop problems.
Physically it's a 19-inch rack unit: 482mm wide, 133mm tall (that's 5½ inches, so three rack units), 205mm deep. Nett weight 5kg, shipping 8kg. Power requirements are 110/120/220/240V at 50-60Hz, 15vA, specified at order time, with a two-position slide switch on the rear panel for voltage changeover. Disconnect the supply before moving it, as the manual warns in bold. Mains comes in via an IEC standard 3-pin socket with the fuse accessible from the rear panel. A perspex security cover was offered as an optional accessory.
Klark Teknik's trade advertising from the period placed the DN30/30 alongside the widely acclaimed DN 22 and DN 27A graphic equalizers. The company described those units as having become standard tools for correcting room acoustics and complex equalisation problems, and framed the 30/30 as the next step in performance, packaging and cost effectiveness. The same campaign material paired it with the DN 70 Digital Delay in the company's professional line. The marketing line quoted John Donne - "No noise, nor silence, but one equal music" - and made the case that the unit offers more than a quiet ability to balance channels across the audio spectrum, citing thoughtful ergonomics and fingertip control. That's advertising copy, not a verdict. The company also leaned on process: advanced design, tough construction, stringent testing and long burn-in, claimed to exceed even Klark Teknik's previously high standards for reliability and consistent performance. Every unit, per the manual, went through a rigorous alignment and burn-in schedule before despatch.
The DN30/30 shows up in Studio-Sound (November 1982, p.59) and again in DB-Magazine (January 1983, p.22) in near-identical launch copy. It then appears repeatedly in Studio-Sound in early 1983 (January, p.57; April, p.55; May, p.63). It's the same advertisement running month after month. The record does not contain an independent measured review, a production run, or a list price.
The DN30/30 was a working tool bought by studios and touring companies, used hard, and largely not preserved as a collectible. Surviving examples are frequently rack-rashed, missing fader caps, or sitting in a warehouse because nobody wanted to scrap a functioning 60-fader EQ. The relay bypass makes it useful in a signal chain where losing audio is not an option, and the N.I.C. filter design is a different approach from the op-amp-and-cap graphic EQ that dominated the era. Buyers should check every fader for scratchiness and verify the relays still engage, since those are the two failure points that matter most. The perspex security cover, if one survives with the unit, is a nice period detail.
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