British manufacturer Audio Note (UK) has celebrated the 35th anniversary of its Oto amplifier with the introduction of the Oto SE 35, which it claims is the most significant design revision and improvement in decades. First introduced in 1991, the Oto holds a unique place in Audio Note (UK) history.
The design, conceived by founder Peter Qvortrup and engineered by Andy Grove, was the first amplifier to be developed and manufactured entirely in-house. While Audio Note (UK) was already known for the Ongaku, the Oto proved that the philosophy of single-ended tube amplifiers could be realized at a more accessible level, without compromising the company's focus on musical experience.
Peter Qvortrup says the amplifier's longevity reflects Audio Note's (UK) broader design philosophy: “When I gave Andy the challenge of designing a single-ended pentode version of the Oto in the early 1990s, single-ended amplifiers were still the exception. The Oto and now the Oto SE 35 are emblematic of our philosophy of timeless, high-quality audio design. We still service and repair our customers' Otos to ensure they last for years. This is what true longevity means, and it will never change.”
For Andy Grove, the initial Oto SE design emerged unusually quickly. Instead of resulting from extensive modeling or iteration, the circuit topology fell into place almost immediately, through careful calculations and consultation of the tube datasheets rather than lengthy simulations. “Anyone involved in creative work like design, architecture, composition, and songwriting knows when what you have in front of you fits together harmoniously. It looks good, feels good, and you know it's really good.”
Grove recalls designing the amplifier in 1991 at his parents' kitchen table in Suffolk, before the first prototype was built with fellow engineer Claus Molgaard and demonstrated shortly thereafter. The listening session, he admits, was a tense moment, but ultimately confirmed the design's soundness.
While the Oto has undergone a gradual evolution over the years, the Oto SE 35 represents a more fundamental overhaul. Following a special request from a customer and inspired by recent work on Audio Note's (UK) Meishu amplifier, Grove decided it was time for a more thorough overhaul. “I decided it was time to give the Oto SE a complete makeover. The result is an amplifier with a more realistic ‘bass thump,' that physical presence you feel when you're in the same room as a kick drum or bass guitar.”
The anniversary edition introduces a new, in-house designed output transformer, a revised power supply with a choke featuring optimized time constants, and targeted updates to the power amplifier circuit board. The phono input has also been revised, with increased sensitivity, eliminating the line preamplifier required in previous phono versions. According to Grove, this improves phase integrity and reduces noise, while revised internal wiring, shielding, and a new, in-house developed mains transformer further enhance the amplifier.
