Country of Origin


Activ Audio EMI filter

Reviewer: Srajan Ebaen
Financial interests: click here
Main system: Sources: Retina 5K 27" iMac (i5, 256GB SSD, 40GB RAM, Sonoma 14), 4TB external SSD with Thunderbolt 3, Audirvana Studio, Qobuz Sublime, Singxer SU-6 USB bridge, LHY Audio SW-8 & SW-6 switch, Laiv Audio Harmony and Sonnet Pasithea; Active filter: Lifesaver Audio Gradient Box 2; Power amplifiers: Kinki Studio EX-B7 monos & Gold Note monoa on subwoofer; Headamp: Kinki Studio THR-1; Phones: HifiMan Susvara, Meze 109 Pro; Loudspeakers: Qualio IQ [on loan] Cables: Kinki Studio Earth, Furutech; Power delivery: Vibex Granada/Alhambra on all source components, Vibex One 11R on amps, Furutech DPS-4.1 between wall and conditioners; Equipment rack: Artesanía Audio Exoteryc double-wide 3-tier with optional glass shelves, Exoteryc amp stands; Sundry accessories: Acoustic System resonators, LessLoss Firewall for loudspeakers, Furutech NCF Signal Boosters; Room: 6 x 8m with open door behind listening seat
2nd system: Source: FiiO R7 into Soundaware D300Ref SD transport to Cen.Grand DSDAC 1.0 Deluxe; Preamp/filter: Lifesaver Audio Gradient Box 2; Amplifier: Kinki Studio EX-M7; Headamp: Cen.Grand Silver Fox Loudspeakers: MonAcoustic SuperMon Mini + Dynaudio S18 sub; Power delivery: Furutech GTO 2D NCF, Akiko Audio Corelli; Equipment rack: Hifistay Mythology Transform X-Frame [on extended loan]; Sundry accessories: Audioquest Fog Lifters; Furutech NFC Clear Lines; Room: ~3.5 x 8m
Desktop system: Source: HP Z230 work station Win10/64; USB bridge: Singxer SU-2; DAC: iFi Pro iDSD Signature; Head/speaker amp: Enleum AMP-23R; Speakers: Acelec Model One
Headphones: Final D-8000 & Sonorous X, Audeze LCD-XC, Raal-Requisite SR1a on Schiit Jotunheim R
Upstairs headfi system: FiiO R7; Headphones: Meze 109 Pro, Fiio FT3

2-channel video system: Source: Oppo BDP-105; All-in-One: Gold Note IS-1000 Deluxe; Loudspeakers: Zu Soul VI; Subwoofer: Zu Submission; Power delivery: Furutech eTP-8, Room: ~6x4m

Review component retail: $1'950

"We make electromagnetic interference filters for the RF shielding industry. After several inquiries, years ago we adapted one filter designed for shielded enclosures—sometimes called faraday cages like MRI rooms or military secure rooms—for use with streaming audio. That $550 GigaFoilv4-Inline had a couple of complimentary reviews and was fairly well received by the audiophile community. [Former contributor Michael Lavorgna wrote about it and enjoyed it – Ed.]  Recently we developed new EMI filter tech so again made a version for streaming audio enthusiasts. We just released the Activ Audio EMI filter and I'm curious whether you'd be interested to try it." The email was signed Steve McNally of DJM Electronics. It's not often that military suppliers find our niche audiophile community then adapt an industrial product for our use. Caelin Gabriel of Shunyata did make this transition fully after a stint at the Defense Advanced Research Projects Agency. Since then he's also made the return trek to the medical sector. Equipment for military and medical industries demands 24/7 stability and extreme immunity from interference. We'd not want a switch-mode power supply or diagnostic kit to give out during surgery or whilst on life support. Compared to life-or-death scenarios in hospitals or national defence, our communal quest for better sound is a trifle. Just so, many of us get very intense about it and often spend enormous sums on a pursuit which to Jill next door is OCD behaviour and a serious misallocation of domestic funds. Costing nearly four times more than DJM's earlier GigaFoil filter, I imagine that Jill will eye today's AA with suspicion whilst Joe already likes it better just for being priced more 'serious' and finished more upscale.

Its insertion loss aka noise rejection spans 50Hz-40GHz at a claimed 100dB+. This dirt-cleaning deed applies proprietary DSP "without disturbing the fast rise times required by digital square-wave signals". It auto configures itself from 10Mbps to 10Gbps speeds to cover 10Base-T to 10GBase-T protocols. It's hot pluggable. It automatically relinks to the network after a lock loss. It runs off an external 12V/2A power adapter and in typical inline manner sports just one RJ45 input and output. We obviously keep the Ethernet link between it and our final destination as short as possible to minimize downstream aerial noise collection. A red LED confirms power, two color-coded LED show i/o speed. The lot fits into a compact 5.8 x 3 x 0.9" nickel-plated aluminium case. Given DJM's background, the device conforms to all international safety and regulatory standards whilst their no-frills website is all facts and zero audiophile puffery. Warranty is 2 years.

"So what is this?" If you're still more crusty than crystal, it's an active inline noise filter for Ethernet aka a LAN decrapifier. The difference is that it comes to us from far outside the usual audiophile sector. To our ilk secure military rooms are proper spook stuff. It makes AA far more hardboiled utilitarian than most product aimed at high-performance sound worshippers of deeper pockets. Its genetics are more Humvee than Bugatti. How much it can do for us should depend on our general exposure to EMI; how much or little our present hifi hardware including cabling already does about it; how high our overall system resolution is; and just how attentive we listen.

As I see it, there's one way to know. Try the DJM whilst being mindful that we still can't extrapolate universal results from our experience, be that positive or 'couldn't tell a difference' neutral. As a curious cat of six lives left, I responded to Steve's solicitation with yes. The worst that could happen was nothing. In which case I might blame living too rural for EMI to be problematic enough, my cable loom too effectively shielded or perhaps me too civilian so insufficiently spooky.

In terms of product category, I certainly expected to play in the shadow realms of the subtle. With two LAN distributors aka reclockers in series at the end of a 20m CAT8 spur from router to iMac, I might have to remove my slaved Ethernet switches before AA could do its thing. That was my raw scenario: router ⇒ iMac. My full-bore chain was router ⇒ LHY 1 ⇒ LHY 2 ⇒ iMac. AA would add to either. In that game of musical thrones, my switch combo gets $594 + $794 = $1'388. That's significantly less than the DJM for more functionality. Would DJM's 'military-grade' expertise eclipse that of engineers working in consumer audio? Would their Activ Audio do a noticeably better job as LAN noise blocker?

Next comes the front end of my main system. The DJM was destined for right behind the iMac.