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Octave Audio – core convictions
 Herr Hoffmann has long nursed very specific convictions relative to valve amplification. Let’s put it this way. If you’re after audiophile fireside romance and automatically equate glowing glass with class A single-ended zero NFB operation, you’ll not find your bearings in Octave’s universe. To Andreas Hoffmann, a tube is primarily an electronic part with useful traits such as drive parameters and clipping behavior, period. That certain valves look pretty is nice but utterly irrelevant. Whenever transistors are superior such as in power supplies or the output stage of the HP300, that's what gets used. There’s no silly just-tubes dogma. Rather, one prefers hybrid technique in the sense that at junctures vital to sonics, valves are employed but at the periphery, modern semiconductors appear which support the sonic potential of the valves (if not make it outright possible).


Hoffmann is in fact convinced that technical progress in amplifier development now occurs at the periphery. Basic tube circuitry as such has long since been perfected. Be that as it may, I found it interesting and amusing that what to most reeks of exotica—SETs without feedback—here is considered the mainstream: "When they talk of bass, I talk of midrange", quipped Hoffmann acerbically.


All Octave power and integrated amps work a/ with pentodes, b/ in push/pull and c/ in class AB. Relative to parts and circuitry employed, this yields higher output power than the ‘mainstream approach’. While power isn’t everything, to the self-professed Wagner fan Hoffmann it certainly isn't irrelevant.

More important than raw power in the Octave canon is load stability however. It’s precisely here that one departs from the competition. Delivering stable rated power into speaker loads in flux isn’t exactly what valves in general are known for. Absolutely vital for that purpose are powerful and particularly low-impedance power supplies which eliminates chokes by design. Such parts increase the resistance of the power supply which then collapses when serious bass transients draw on it. This not only weakens and softens the lower octaves but compromises the entire audible band due to power supply modulations. Stability then is a very important design goal for Hoffmann and not merely for his top Jubilee model—its Coca-Cola can Epcos capacitors above are admittedly extreme eye candy—but each player in the line benefits from this approach which is merely scaled to suit a given budget. Then it’s perfectly logical that the optional power supply reinforcements called Black Box and Super Black Box should exist to offer a plug’n’play upgrade path in the load invariance sweepstakes.

Octave Audio: Stability, control, music
 Since he considers his amps stable, a side effect for speaker control is reduced reliance on high damping factors. Put differently, the relatively high output impedances of his amps are not synonymous with a loss of control. Hoffmann calls it a fallacious conclusion to believe that high damping factors alone guarantee powerful well-defined bass. Quite the contrary, a very low output impedance implies that the counter-inductive back EMF of the speaker hits the power supply even harder. If the latter is insufficient for the task, the presumed higher damping is for naught. While the nominal damping factor of Octave amps is middling—into a 4-ohm load, it’s ca. 5 which equates to an output Z of about 0.8Ω— it’s mostly test-bench fetishism that would raise concerns, never mind that higher damping is liable to induce ultrasonic instability.


In the end and under dynamic—rather than steady-state test tone—conditions, his combination of sonically optimized damping factor and stable low-impedance power supplies beats the majority of his tubed competitors. Or so believes a rather confident Octave boss. That the majority of his competition will likely disagree with it goes without saying. Which wasn’t the end of the coffee/cake discussions. It included sense and nonsense over zero feedback (Hoffmann suspects ideology); full dual-differential architectures (theoretically ideal but in practice sonically compromised due to difficulties with implementing volume control); and multiple output taps (“impossible to optimize”). Octave clearly pursues its own path which they articulate clearly and at length, the latter beyond the scope of this article.


In the end all of that is less interesting than the audible results. So where was the auditorium? And what speakers would a Wagner fan embrace? Time for the basement which, besides warehousing, packing, shipping and transformer prototype machines, houses Octave’s listening room.

It’s here in the cellar where prototype amps have to prove their mettle. To suit this purpose—"I want to hear the amps, not the room"—the space is dry and sports an RT60 of less than 0.3 seconds all the way into the bass. The photos showing an Isophon Vertigo 4-way bandpass speaker with seven drivers suggest a certain addiction to full-range reproduction. There’s also a JMlab Utopia—"that baby can be fun"—and other speakers which don’t conform to common 'valve friendliness' precepts. Forget high-sensitivity knaves and hornspeakers altogether.


Hoffmann doesn’t just shun technical but also musical dogma. He of course cued up Wagner and the finale of Rheingold over the Jubilee/Isophon combo was rather impressive. But no less exciting was Gypsy brass band Fanfare Ciocărlia I’d not heard before, a kind of dirty, fast and out-there Roma Punk formation. To keep up with 12 crazy East-Romanians at 200kmh breakneck speed over such a system was quite the treat. I reckon I better follow up in a local record shop to learn how this album does over my resident rig. Thanks for that music tip. And the cake!

redaktion @ fairaudio.de
Octave Audio website