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Reviewer: Srajan Ebaen
Financial interests: click here
Sources: Retina 5K 27" iMac (4GHz quad-core with Turbo boost, 32GB RAM, 3TB FusionDrive, OSX Yosemite. iTunes 14.4), PureMusic 3.02, Audirvana 3, Qobuz Hifi, Tidal Hifi, Fore Audio DAISy1, COS Engineering D1, Denafrips Terminator, Soundaware D300Ref, AURALiC Vega
Preamplifier: Nagra Classic, Wyred4Sound STP-SE Stage II, Vinnie Rossi LIO (AVT module)
Power & integrated amplifiers: Pass Labs XA30.8; FirstWatt SIT1 monos, F5, F6, F7; Goldmund/Job 225; Aura Note Premier; Wyred4Sound mINT; Nord Acoustics NC500 monos; LinnenberG Audio Liszt monos
Loudspeakers: Audio Physic Codex; Cube Audio Nenuphar; Albedo Audio Aptica; EnigmAcoustics Mythology 1; Boenicke Audio W5se; Zu Audio Druid V & VI & Submission; German Physiks HRS-120; Eversound Essence
Cables: Complete loom of Allnic Audio ZL3000 and Zu Event; KingRex uArt, Zu and LightHarmonic LightSpeed double-header USB cables; Tombo Trøn S/PDIF; van den Hul AES/EBU; AudioQuest Diamond glass-fibre Toslink; Black Cat Cable redlevel Lupo; Ocellia OCC Silver
Power delivery: Vibex Granada/Alhambra on all source components, Vibex One 11R on amps/sub
Equipment rack: Artesania Audio Exoteryc double-wide 3-tier with optional glass shelves, Exoteryc Krion and glass amp stands
Sundry accessories: Acoustic System resonators
Room: 4 x 6m with high gabled beam ceiling opening into 4 x 8m kitchen and 5 x 8m living room, hence no wall behind the listening chairs
Review component retail: $30'000
Look ma. No transformers. No caps. It's Allnic's L-10000 preamplifier. And of course it runs a power transformer. How else would it come alive? But as a tube linestage with 6AN8 inputs, 12AU7 drivers and 300B outputs, it uses neither output transformers nor coupling capacitors.
These 300B—two per channel for balanced—talk without a condom to your amplifier inputs.
Whilst perhaps a crass image, the point is made. Strip away the sonic imprint of these usual intermediaries aka interpreters. What's left is the pure untainted aroma of the actual direct-heated triode. With his DHT LIO option, then the more advanced L2 preamp, Vinnie Rossi had the same idea, just single-ended. Even more radical, his spud circuit uses no other tubes, just one 300B or 2A3, 45, PX4, 101D, 205D or SV811 per side.
With stock EH Gold 300B, this nets him S/NR of 120dB, bandwidth of 2Hz-500kHz ±0.5dB; or 0.5Hz-950kHz ±3dB. Output impedance is sub 100Ω. For an amplifier meant to drive speakers not headphones, that would still be too high. For a preamp driving the stable input impedance of an amplifier, it's no issue.
As Vinnie explains about the inherent challenges of working with direct-coupled direct-heated triodes, "I learnt with LIO DHT that to make picked-up 50/60Hz AC hum essentially inaudible, the enclosure had to tie to AC ground. So did other parts of the circuit (LIO's ulta-capacitor supply floats like a battery). Even the tube shields must tie to AC ground.
"I also needed my power supply output paths as short as possible. Hence the L2's shielded power supplies are internal and their shield enclosures tied to AC ground. I now also use different voltage regulation with new OEM dedicated Belleson super regulators for heating the cathodes of each tube and for the plates of each tube; plus an all-new biasing approach."
Combating microphonics and amplified AC noise is key with tubes whose cathodes are their filaments. It's why DHT preamps are rare. I knew of Allnic, Coincident, Manley, Thomas Mayer, custom Trafomatic and Vinnie Rossi. Readers might add to this list. I suspect it'd top out below ten regardless.
Wondering about Kang-Su Park's South Korean model, I sent out an exploratory email.
"Our first stage is the 6AN8 whose triode half drives a 12AU7 which drives the 300B. The pentode half of the 6AN8 controls harmonic distortion cancellation. It also compensates the output tube grids. Because our power transformer fully floats, there's no DC at the outputs even should a 300B fail. Output impedance is 200Ω. Residual noise is 0.25mV. S/N ratio is -80dB. Ruler-flat bandwidth is 10Hz-200kHz ±0dB. Voltage gain is 18dB. The RCA inputs are separated by resistors. Only the RCA output is OTL/OCL.
"For the XLR output, we use a small isolation/matching transformer to separate signal return from ground. This transformer isn't an output transformer to function differently.
"Our 61-step constant impedance attenuator is the best version of all possible volume controls and a world premiere. Regardless of position, its input and output impedance remain unchanged. This guarantee the most stable frequency response."
Though far more complicated than Vinnie Rossi's L2, Allnic's L-10000 too offers exploded bandwidth on par with premium transistor specimens. It's not what one expects of or usually gets with 300B. In fact, Allnic's very own A-311 SET monos with typical output transformers are down 1dB at already 20kHz. To really hear a 300B unleashed means this type of preamp though of course these here are still imprinted by two preceding valves and beaucoup extra voltage gain. With Armin Bos of Dutch distributorship Live Fidelity of Utrecht making available his personal demonstrator unit plus a matching pair of A311 M PX25 monos, I learnt that "I ordered a pair of GEC 5U4G rectifiers for the monos and two 12AU7 Mullard for the preamplifier. Tube rolling can become an interesting part of your review." Allnic's choice of stock outputs for the L-10000 are the Chinese boutique TJ/Full Music 300B. For the 6AN8, they like Sylvania. The L-10000 is available in black or silver livery and costs more than we paid for our fully loaded 230HP 5-cylinder 2.5l Volvo with 9'000km on the clock. The Allnic is more of a pre-owned Maserati.
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