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The lay of hybrid land. With pure valve machines a full half of their catalogue, Pathos' Italian colleagues at Unison Research offer similar hybrids in their Unico range. Meanwhile George Kaye's Moscode hybrid is an American sample of the breed. When Dan Wright of ModWright bowed his first integrated, many expected it to be another. Instead it went all transistor. Enter a former Sonic Frontiers designer now working in Serbia under the cunning Beyond Frontiers Audio banner. Their very big Tulip A hybrid sports a novel wrinkle. Its tube linestage is DC coupled to avoid all capacitors and interstage transformers. That's a breakthrough if you believe transformers to limit bandwidth and introduce phase shift; and signal-path caps to be plain bad for sound.
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* The Tulip and their monos of course do get huge 4 x 47000µF Mundorf electrolytics in their power supplies.
Bob Backert of Backert Labs does think particularly electrolytics bad. Hence his patented GreenForce supply runs on just ~0.5% of the capacitance of conventional tube power supplies. This massive reduction cancels electrolytics to adopt the very best small film-foil VCap Teflons instead. As he put it for his Rhythm 1.1 preamp, "there are no aluminium electrolytics. This gives serious clarity and none of the congestion, bass bloat, damped-down sound or compression effects that lead to warmth but reduced dynamic accuracy."

Conventional hybrids must use electrolytics in their valve power supplies and better types (or transformers) for their interstage coupling. BK Butler's Tube Driver Blue circuit combines small-signal triodes and bipolar Sanken transistors with output-load mirroring circuitry whilst his Monad version loads 300B power triodes with transistor followers and backs it with a 2'000'000µF power supply. Frank Blöhbaum's breakout Thorens amp combines balanced tube drivers with ultra-power single output transistors per Circlotronic phase. Alex Peychev combines a DHT input stage—45, 2A3, 300B or other—with monaural transistor current buffers in his new APL Hifi Reference HA-Master. Burson Audio had a transistor amp whose voltage-gain stage could be bypassed to strap to a traditional low-power transformer-coupled valve amp as a pure current buffer.


Nelson Pass' FirstWatt F4 with negative voltage gain could be exploited in the same way. And there are even 'inverted' hybrids from KR Audio which perform the voltage gain with solid-state whilst the final speaker-drive stage runs on power triodes. Inverting such inverted hybrids again finally gets us at Rogue Audio's Hypex UcD amps which combine valved input stages with class D output stages; and similar efforts from Arion Audio.

But the most common hybrids—and you already realize that the general breed is quite rare in fact—combine small-signal tubes with Mosfets which are viewed as most similar to tubes. The implied promise is that just like a mutt often combines the best attributes of its mixed parentage whilst the pure-bred dog with the fancy lineage suffers hip dysplasia and other overbred ailments, hifi hybrids extract the best from their respective gain devices and eliminate or downplay their weaknesses. One thing we can say about it all without being engineers? If it were simple, we'd see far more hybrids. In reality the closest most people ever come to playing in hybrid land is leashing a tube preamp to a transistor power amp. Or the reverse.


Whether that way or in a single hybrid box, the basic concept is the same. Use tubes for voltage gain where their linearity excels; and transistors for current gain which nets higher direct-coupled power at far lower output impedance and noise to offer superior control over reactive loudspeakers. The purist advantage of the true hybrid rather than mix'n'match pre/power scheme is that it can avoid redundant gain and buffer stages. Ideally it'd be a simple two-stage affair. In the real world things simply get more complex again.

 
Luca Zanini
  Back to the Logos MkII, it comes with this svelte wooden wand to handle volume, mute, input selection and LCD brightness. Under the hood things go dual mono with dedicated supplies for the pre and power stages and dedicated power transformers per channel. The snazzy heat sinks are home to 3 pairs of Mosfets per side which are biased in class AB. The class A tube stage is fully balanced to lower self noise (a claimed >90dB signal-to-noise ratio at the output with <0.05% THD). That this gets by with two rather than four tubes is due to these being dual triodes, i.e. two complete valves in one glass envelope.


The 100-step Burr Brown volume control reflects in the two-digit alpha-numerical central display and can also be turned mechanically with the spring-loaded chrome cylinder surrounding the display. The input selector also triggers the display and "hi-tech miniaturized relays, originally developed for very high frequency telecom applications."

In the company's words, "after almost two years of design, prototypes, testing and listening, the new Logos integrated amplifier finally came as close as possible to the peerless quality of our proprietary INPOL technology [used in their TT, InPower and InControl top models and short for Inseguitore a Pompa Lineare or Linear Pump Tracker - Ed]."

For a quickie down memory lane, the company's launch dates back to 1994 already. With Andrea Palladio's famous architectural monuments in their home town of Vicenza which today is focused on metal production, jewelry and fashion, it's no surprise that Pathos sees itself as making "hifi jewelry; small monuments". Co-founder Gaetano Zanini operates a local high-end shop for plenty of benchmark testing. Paolo Andriolo is responsible for their industrial designs. Together the team calls theirs "the unorthodox approach". All their products are handcrafted on site which in 10 years changed location twice to scale up with internal growth. A subsequent relocation increased the previous space by five times again.