C-280

Reviewer: Srajan Ebaen
Financial interests: click here
Main system: Sources: Retina 5K 27" November 2020 iMac (i5, 256GB SSD, Ventura 13.3, 40GB RAM), 4TB external SSD with Thunderbolt 3, Audirvana Origin, Qobuz Sublime, Singxer SU-6 USB bridge, LHY Audio SW-8 switch, Cen.Grand DSDAC 1.0 Deluxe, Sonnet Pasithea DAC; Active filter: icOn Gradient Box 2; Power amplifiers: Kinki Studio EX-B7 monos, Goldmund/Job 225 on subwoofer; Headamp: Cen.Grand Silver Fox; Phones: HifiMan Susvara, Meze 109 Pro; Loudspeakers: sound|kaos Vox 3awf + sound|kaos DSUB15 on Carbide Audio footers, Audio Physic Codex, Qualio IQ [on loan] Cables: Complete loom of Allnic Audio ZL; 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: Shanling M3 Ultra into Soundaware D300Ref SD transport to COS Engineering D1, iFi iDSD Pro Signature or Denafrips Terminator Plus 12th Anniversary firmware; Preamp/filter: Vinnie Rossie L2 Signature or icOn 4Pro, icOn 4th-order/80Hz active filter; Amplifier: Crayon CFA-1.2; Loudspeakers: MonAcoustic SuperMon Mini or Acelec Model One + 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: legacy Auralic Vega; Head/speaker amp: Enleum AMP-23R; Speakers: EnigmAcoustics Mythology M1;  Headphones: Final D-8000
Upstairs headfi system: Source: Shanling M3 Ultra, Soundaware D300Ref; DAC/headamp: iFi iDSD Pro Signature; Headphones: Meze 109 Pro
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: €12'000 without filter, €16'000 with filter

C for vitamin, control or both?

2 years ago, darko.audio polled 13'000 people on using stand-mounted x floorstanding speakers.

1) Just over half of all respondents run stand-mounts.
2) Of those, 20% augment them with at least one subwoofer.
3) Roughly 40% of those polled use floorstanders.
4) 1/3rd of them run at least one subwoofer.
5) 1/3rd of all voters run at least one subwoofer.

The majority of our hifi mainstream press still plays dumb of course. It's readers who wised up. The addition of an active sub (or two) is often the smarter 2-channel play. For the system and its owner, it means two more, two less. More are performance in bandwidth, control and quality; plus new functionality like adaptive bass, placement options and room correction/EQ. Less are size requirements for the mains and their amp; and coin dropped versus what a bigger amp with bigger passive towers will cost that could compete even though active bass usually beats passive bass regardless.

To deliver fully, there's just one critical condition. The sub must integrate via active low and high pass. Otherwise neither the speakers nor the amp driving them are relieved of bass signal nor its demands on current and excursion plus their impact on rising voice coil heat, resultant dynamic compression and distortion in general. How to accomplish the necessary active high pass which precedes the speaker signal to filter out their low bass by just the right amount? Home-theater pre/pros already have all the answers. High-zoot stereo preamps rarely do. Now one looks at external crossovers from German Physic, icOn, JL, Magico, Manunta, Marchand, spl or Wilson which start at €3K and can well eclipse €10K; the $499 Sublime with affordable plug-in cards to set turnover frequencies; digital equivalents in DACs from Bel Canto, Linn and TotalDAC; or power DACs like Lyngdorf's which build in smart bass management via app control. Adding itself now to the pure analog side of our limited choices are Aavik of Denmark. Whilst I'd penned a version of this intro by November 2021, it wasn't until late July 2023 that an actual sample beckoned:

"Last time we had the pleasure of hosting Dawid in Aalborg, we talked about a review for our active analog dual-slope crossover. Dawid mentioned you as the ideal choice. Knowing from some of your reviews how you integrate subwoofers in your systems, we agree. If interested, we'd send you one of our models available with this filter option, the C-280 preamp. Please be aware that we're specifically interested in an article that investigates the filter's many advantages. [Focus on the filter. I dug that – Ed.] Allow me to explain. It's an analog dual-slope filter without DSP so zero latency. Both slopes adjust individually. This can pull them apart or overlap them more. The low pass also has its own level control. These features can be exploited in a number of scenarios:

• If you run the Aavik C-280 plus filter with a set of speakers and active subwoofer with analog line input, you avoid digital time delay, adjust the subwoofer precisely and shield the speakers from low bass. Moving bass to an active sub improves its quality. Relieving the main speakers of bass has them play more freely and seriously improves their power handling and dynamics.

• You can 'filter out' your primary room resonance. Simply pull the two slopes apart in the area of that resonance. By sending lower SPL into the room's self resonance, you can limit or avoid its boom.

• Even without a subwoofer the filter has potential. You can use it to 'adjust' your speakers. If you have small monitors that always struggle with low bass, it really improves their performance when they don't even see bass frequencies they can't handle. Conversely, if a big pair of speakers overloads the room with bass, you can filter out the lowest problem area and have those speakers better play a smaller space.

"I hope I managed to explain some advantages of this one-of-a-kind active analog dual-slope filter. We see a great future for Michael's new take on active crossovers. At present they may be fitted to our C-280/C-580 preamps and come standard with the C-880 and I-880. What's more, this filter is a great upgrade for our newest flagship M3 and M6 Børresen speakers, both 2.5-way designs with biwire terminals. Their internal passive crossovers are designed to take full advantage of our active filter. With a C-880 preamp and two P-880 power amps for example, one can very precisely dial in these speakers from the listening position by remote."