icOn 4Pro SE

Reviewer: Srajan Ebaen
Financial interests: click here
Main system: Sources: Retina 5K 27" iMac (4GHz quad-core with Turbo, 32GB RAM, 3TB FusionDrive, OSX Yosemite. iTunes 14.4), PureMusic 3.02, Audirvana 3, Qobuz, Tidal, Denafrips Terminator+ clock-synced to Soundaware D300Ref SD transport/USB reclocker; Preamp: Vinnie Rossi L2 Signature with WE VT52/300B or Elrog 50/300B; Power amps: LinnenberG Liszt monos; Headamps: Questyle CMA-800r monos; Phones: HifiMan Susvara; Loudspeakers: Audio Physic Codex; Cube Audio Nenuphar; Aurai Audio M1 [on loan]; Cables: Complete loom of Allnic Audio ZL; Power delivery: Vibex Granada/Alhambra on all source components, Vibex One 11R on amps, LessLoss C-MARC Entropic cords between wall and conditioners; Equipment rack: Artesanía Audio Exoteryc double-wide 3-tier with optional glass shelves, Exoteryc Krion and glass amp stands; Sundry accessories: Acoustic System resonators, LessLoss Firewall for loudspeakers, Furutech NCF Signal Boosters; Room: 4 x 6m with high gabled beam ceiling opening into 4 x 8m kitchen and 5 x 8m living room so no wall behind the listening chairs
2nd system: Source: Soundaware D100Pro SD transport; DAC/pre: Denafrips Terminator or COS Engineering D1; Amplifier: Bakoon AMP-13R or Crayon CFA-1.2; Loudspeakers: Acelec Model 1 w. Franck Tchang magnesium super tweeters, sound|kaos Vox 3awf, Zu Submission subwoofer; Power delivery: Furutech GTO 2D NCF; Equipment rack: Hifistay Mythology Transform X-Frame [on extended loan]; Sundry accessories: Audioquest Fog Lifters; Furutech NFC Clear Lines; Room: ~4x6m
Desktop system: Source: HP Z230 work station Win7/64; USB bridge: Audiobyte Hydra X+; Headamp: Kinki Studio Vision THR-1; Phones: Audeze LCD-XC on Forza Audio Lab cable; Powered speakers: Fram Audio Midi 120
Upstairs headfi system: Source: Soundaware A280 SD transport; Integrated amplifiers: Schiit Jotunheim R or Bakoon AMP-13R; Phones: Raal-Requisite SR1a, Audeze LCD-2, Final Sonorous X & D8000, HifiMan HE-1000
2-channel video system: Source: Oppo BDP-105; DAC: Kinki Studio; Preamp: Wyred4Sound STP-SE II; Power amp: Pass Labs XA-30.8; Loudspeakers: German Physiks HRS-120; Room: ~6x4m
Review component retail: £2'799 as reviewed [with active xover, firmware switcher, firmware upload interface and extra aluminium remote with extra A/B test features]

Older but still optional display. I ordered the current 7-segment orange version.

The morning after. I'd put the icOn 4Pro review to bed and slept with dreams of forbidden desires. Then an email: "Nice review on that new autoformer passive. It reads like a TAP-X in a different form factor with extra features. Quite the find. Kudos for sniffing out novelties that some of us can still afford. I especially like all the custom order options including true balanced from an AVC. I sensed that you were close to getting one for yourself? It must have smarted to realize how close it came to your big tube preamp!" Signed not the devil but Patrick Croyden. Had this reader manipulated my dreams from afar? The real trouble was, our Vinnie Rossi Lio with Slageformers already covers the same ground. I couldn't justify a virtual duplicate. But wherever there's a will, there's a way.

Ask me and ye shall receive. I remembered this from the apocryphal writings of Pál the pacifist. As one of the forgotten preamp apostles, he's too passive to be much quoted. But there's also the populist encouragement of asking never hurts. So I did. To appreciate my question, first some background. In my upstairs system's front left corner sits a very tall Zu Submission subwoofer. I like to sneak it in below various monitor speakers which are good to about 40Hz then fall off. Without running them through a quality active high-pass filter, all I really want from the sub is the bottom octave of 20-40Hz. In reality not wishful thinking, that would require a virtual brick-wall filter.

Zu's Hypex plate amp has a continuously variable 4th-order Linkwitz/Riley low-pass filter. It can be set anywhere from 10Hz-110Hz. Yet even at 10Hz, there's too much bleed well past 80Hz. My way of cheating had been to use PEQ gain at 20Hz, then very subdued sub fill for just a bit of low-bass reinforcement. It works quite well but not as clean as I'd like. Knowing that Pál Nagy listens to big Linkwitz 4-way open baffles to have experience building active filters, here was my question to him: