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solid yellow line = 19Ω
Thinking of the Iridium 20 as a SEPster (single-ended pentode) might in fact be the closest conceptual approximation shy of hearing one in the flesh. Zu Druid V owners keen on maximizing tone density and harmonic richness might want the lushness of a bona fide SET outfitted with chunky Elrog 845/211. Those who prefer to lean out and accelerate Zu's naturally meaty presentation could want a Tellurium Q I figured. To test this seemingly fair hypothesis, my ivory Druid V took pride of place. Or shame as it happened.


That's because this combo was far from happy. Whilst the presence region did benefit from the added illumination the amp's lit-up personality predicted, the Zu's strongest suit—big-time whomp factor in the upper bass—had completely unraveled. In stark anti-Zu protest, the sound had gone anaemic. It was bereft of real bass and showed little sense of that tight drive these boxes excel at so naturally. In the sub 150Hz range where the speaker's quasi-ported saddle response hits 50Ω at 75Hz, drops to 12Ω at 40Hz then rises again, it sounded very much as though the amp's power response had gone limp. The sound didn't just miss greatness by a hair. It was as piss poor as that very bad haircut my former Laiki Bank of Cyprus had just suffered as part of an EU bailout. It was academic to speculate. I'd simply say that contrary to certain propaganda, a nominal 16Ω load is no universal panacea when the actual impedance plot is all over the place. Nothing beats actual experimentation. Back it was to the soundkaos Wave 40 for a day'n'night difference and a tête à tête with the stereo SIT and F5 amps.


F5 versus Iridium 20: The F5 is a simple push/pull Mosfet circuit making 25/40wpc into 8/4Ω. It went for $3.000 when available new—occasionally used samples still pop up on Reno Hifi—and arguably is the most DIY'd amp of the wild bunch at the FirstWatt corral. Sonically the Brit now behaved like a super F5. It had more spice, focus and separation. Certain of Anoushka Shankar's sympathetic sitar strings showed more glinting. Stage depth was more specific, sharpness of articulation keener in general. This made the F5 comparatively diffuse and genteel. Those familiar with the Californian would never describe it in those terms. And that's the point. The Iridium 20 was more 3rd-order p/p than a real push/pull amp but added to that single-ended suchness. As such it also was the even more ruthless about revealing compressing on 320kps MP3 tracks I'd bought from Spotify Plus until I could hunt down full-rez versions.


These descriptions were harnessed with my new Nagra Jazz valve preamp in the loop. With the Bent Audio Tap-X TVC passive instead, the Iridium 20 went the full Monty to become offputtingly pornographic. That's shorthand for strident, glassy and lean as an overabundance of transient speed and cutting power against insufficient fluidity and body.


SIT2 vs. Iridium 20: Moving in the 10/8wpc into 8/4Ω power Jfet amp retained the Tellurium Q's transient speed but introduced a different gestalt of elasticity. Textures became more fluidic and stage depth expanded further. This shift removed both the stinger and upfront posture from the equation. Everything settled back and relaxed without altering the acuteness of micro-detail visibility. In tech terms this was a goodly dose of sweeter gentler zero NFB triode flavor which the Iridium 20 swapped for a very firm pentode aroma with feedback. A recent review which mined the same difference in the line-level milieu had compared the Nagra Jazz and Octave HP300SE valve preamps. The latter's high feedback and transistor output buffer occupied the sonic polarity now taken up by the Tellurium Q. Both preamps had very comparable noise specs and output impedance just as I presume was the case between today's amps. Yet the preamp presentations had reflected two quite different aural schools and likely also very different distribution of remaining THD.

Expressing this difference in output device terms, the Iridium 20 sounded more like bipolars than Mosfets. If with the latter one should associate Sam Tellig's famous Mosfet mist, one must now utterly exorcize that warmish minorly fuzzy image from any mention of the British amp. It might be using Mosfets but similar to the Bakoon AMP-11R doesn't exhibit their usually highlighted qualities. Here it diverges from expectations once more.


In the context of widebanders, as speaker sensitivities rise to hit 100dB and above—multi-way hornspeakers like Avantgarde Acoustic models are a different matter—it's become quasi consensus that single-ended tube amps are best. Transistor equivalents have likely been excluded due to their extreme rarity. But there also might be a tie-in with their greater top-end bandwidth and steeper rise times. Those could negatively interact with extreme dynamic reflexes and minor tonal brightness centered in the presence region as is routinely the case for widebanders. Rethm designer Jacob George who offers a pure valve plus a hybrid amp with transistor outputs still prefers pure valves. He and I both thus were curious how his 100dB Saadhana would get along with my SITs. Having the Iridium 20 on hand made for additional data points though the above suggested that it might be too much of a cold shower. And so it was.


Every listener has his or her golden mean. That's a sonic ideal or feel of rightness. One can meet or approach it by all manner of different means and gear combinations. Back in the happy context of the Wave 40 speakers and vis-à-vis my customary SIT1 monos, I found such a personal equalizer in AURALiC's Vega processor. As captured in its review, "three key phrases are vibrancy, minor sweetness and saturated tone. Where the Metrum Hex majors on timing and associated easefulness—two subversive qualities which don't produce quick 'wowie' responses during brief auditions but dominate the longer haul—Vega's tuning creates an immediate Whoa! reaction. Color temperatures are very high. So is an associated sense of ebullience. Like a dollop of cream atop that timbral ardor hovers the type of sweetness which distinguishes good DSD but here also applies to PCM. You might even say that PCM sounds as though it had been doused in DSD."


Like the Hex, the Iridium 20 majors on timing precision and incisive beat keeping. Did it not stand to reason that replacing the Dutch DAC with the Hong Kong challenger would move things yet closer to my own golden mean? Indeed. Icing on that cake was replacing PureMusic 1.89g in 176.4kHz NOS upsampled mode with Audirvana 1.4.6 in integer mode 1 and 352.2kHz upsampling. The sweeter quasi-triode/DSD flavor of the Vega I'd called "a whiff of the voluptuous" made for my kind of sound with the Tellurium Q. The only two complaints I now had were purely functional. One, the pronounced turn on/off gun shot was most annoying. On the 100dB Rethms in fact I didn't dare connect their speakers cables to the amp until after it was on and also disconnected the same cables before powering it down. Similarly annoying were the three red LEDs. Those remain lit when the amp is off. Who really needs to know that it's still connected to AC? Seeing green in operation is expected even if doing so in triplicate seems excessive. Seeing bright red in a room dimmed for late evenings when the entire system is off is neither expected nor welcome. Those two operational items should get fixed.


Conclusion. Clear as a bell, sharp as a whistle, penetrating like a search light in the fog, Tellurium Q's Iridium 20 amp is a massive antidote to sonic congestion and indecisiveness. Speakers copasetic with its power rating which perhaps suffer a bit from energy-robbing network filters will get the proverbial kick in the arse. Aficionados of completely lit ultra-specific and well-sorted soundstages will be in love. So should be fans of close-to-stage proximity and heightened beat precision. Here the former doesn't mean a foreshortened perspective or lap dance. It simply means uncut transient energy as one hears it close to a drum kit. Except for the 16Ω Druid V which was an obvious electrical mismatch—and to a lesser degree the 100dB Rethm Saadhana which electrically was just fine but became sonically too forward—I had no speaker beyond the amp's ken or sonically unhappy. Even the 88dB sealed Aries Cerat Stentor with its complex 30-part crossover played louder than I'd ever want without indicating deficiencies in bass control. And yes, in keeping with its pure class A bias, the amp runs very hot. That's simply part of this recipe. It's called hot stuff in at least three ways I can think of...
 
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