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There are in fact still more powerful tube amps such as the 800-watt VTL Siegfried monos, the older 1.250-watt VTL Wotan or the 450-watt VAC Statement. Those are cost-no-object realizations sold at indecent prices. For example the VAC 450 monos demand $80.000 dollars whilst the Siegfrieds were introduced at $65.000. In this context the new kid in town seems quite affordable at €23.500. Of course the new KT150 significantly boosts the Orthos XS power from 250 watts (KT88) and 300 watts (KT120) to finally 400 watts in maximal pentode mode. But the Ayon, acclaimed by its designer as "one of the absolutely best-sounding KT88 power amplifier in the world", also would seem to gather most of the refinement of the aforementioned monsters. This XS reference amplifier should thus provide unsurpassed sound quality and drive a truly wide range of speaker types to optimal and consistent performance under all conditions. As usual chef Gerhard applied his personal touch to this KT flagship with very short signal paths even for the PCB copper traces, 0dB negative feedback, no solid-state device in the signal path and a high-current/low-impedance design which operates its tubes in the sweet spot of their load lines with a dual-grounding system.
The Orthoss XS are shipped in two robust raw wooden boxes for a good level of protection during transportation. However no crazy amount of money was spent on these boxes. Gerhard Hirt focused exclusively on the quality of the product itself. His high-grade aluminum anodized and brushed anti-vibration chassis are hand assembled for the best level of craftsmanship. The previous XS chassis was improved for better heat ventilation. Its four aluminum feet are resonance-absorbing types to banish most mechanical interferences. All front and rear panel descriptions are engraved. On the front panel a backlit 'Ayon' logo blinks during thermal stabilization.


All fourteen valves of each monaural amplifier are numbered to indicate careful prior testing/matching and should be placed in their dedicated sockets. The new KT150 bottle looks very pretty compared to its KT88 grandpa and the amps look refined and modern, matching the cosmetics of Ayon's complete line The Orthos XS has an automatic bias circuit with a twist as Hirt has designed a new automatic fixed bias circuit to control the operating conditions of his power tubes reliably without a negative sonic influence. This intelligent auto-fixed bias system thus must not be mistaken for a semi-automatic or fully automatic bias which won't achieve comparable results. Ayon's circuit does not operate during actual playback. The Orthos XS auto-fixed bias circuit also adds a sophisticated electronic two-way protection circuit which kicks in during the tube test program and switch-on period. In case of excessive bias current or a defective tube, the high voltage switches off immediately either via the opto-coupler controlled comparator circuit or an A/D converter. These protection circuits are transparent and outside the signal path.

After the amplifier has run for more than 45 minutes to reach optimal tube operating temperature, an additional bias reference control happens after power-down confirmed with the rear display. The measured bias values are stored and used as reference value for the next session to always provide the best possible working points accounting for wear and aging. Logic-controlled automatic biasing of all tubes means constant optimal performance. Should the reference control detect that a tube can no longer attain its optimal value or that its perfect working status is no longer guaranteed (bias current showing too high a value), the high voltage switches off, the logo blinks and the respective tube is indicated by its display digit on the backside of the amp.

On the top plate an analog bias meter provides direct control of the bias value for each tube thanks to the bias selector switch on the rear panel. Above the meter a mode switch allows easy change between triode and pentode modes. As the relationship between circuitry, output transformers and speaker crossover network can be very complex, the manufacturer advises us to try both modes and see which one works best. With my Vivid speakers not being extremely demanding, triode mode was more convincing. Considering the specifications, the power level in triode mode is certainly high enough to drive almost any load whilst delivering a level of delicacy and sweetness that seems commonly unattainable with big pentodes.

From the rear panel there are a few details typical for Ayon gear: a ground switch useful to increase noise rejection; and an AC power polarity indicator that lights up under incorrect electrical phase. Ayon's output transformers are rather impressive. The biggest challenge with designing such big iron is that it needs to be maximally large for bass current which makes it harder and harder to maintain top-end finesse. If the coupling is not watched carefully, capacitance and leakage inductance will roll off the high frequencies. Technically the design of the new super-wide bandwidth output transformer is a substantial increase in the number of interleaved sections, "significantly improving the coupling between primary and the secondary windings (even the individual wires) and increasing the efficiency of the transformer by lowering the insertion loss." The output transformers are sealed in an anti-resonance potting compound.