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Page 7
1.2 Basic Operation of the Amplifier
ANK Audio Kits is proud to present the Interstage Monoblock 300B SET Amplifier. As anyone who has
ever heard the transcendent musicality of a single-ended amplifier will tell you, there is something
very special about the music that flows from (relatively) simple, classic Class A triode circuits.
Perhaps it's the absence of crossover distortion, perhaps it's the gorgeous midband reproduction,
perhaps it's the zero feedback design, perhaps it's the organic (even desirable) expressiveness of the
second harmonic; more likely it's all of this and more.
ANK Audio Kits and SET amplifiers go a long way back, right to the beginning in fact, with our Kit1
300B, which has had successive and successful anniversary editions. It's no surprise then that these
300B single and parallel SET monoblocks are simply awesome! A pair of these power amplifiers are a
perfect mate for the Mentor pre-amplifier and a path to truly exceptional audio enjoyment.
Design Elements
The Interstage Monoblock 300B SET Amplifier is a uniquely different amplifier —it is our highest and
most extreme expression of single-ended amplification, reserved for the true connoisseur audiophile.
The interstage transformer design style is currently used on Audio Note (UK)'s top of the line Ongaku
211 amplifiers. Importantly, rather than an additional tube driver stage, the interstage transformer
takes over this task, for ultimate authority, providing a level of realism and detail that you may not
have experienced and driving the 300B triode in single-ended mode. The triode then drives the
output transformer (OP-300).
Audio Note (UK)'s Peter Qvortrup has underscored the significance of interstage transformers:
"It is becoming increasingly obvious that applying transformers at every stage of an
amplifier yields a great benefit in sound quality, provided of course that the transformer in
question is of an appropriate quality and design. Replacing any coupling capacitors with a
well designed and correctly matched driver or interstage transformer yields an almost
shocking improvement in sound and should be tried to fully understand what a good wide
band transformer has to offer."
It's also interesting to read what Audio Note (UK)'s design engineer Andy Grove has to say about the
theory behind the key concepts of this amplifier:
"I explained in the interstage transformer article about the virtues of transformer coupling
to the output valves, and here the bifilar interstage transformer is used to full advantage.
The extremely high impedance AC load to the 6SH7 means that you get more or less the full
gain of the valve, and the loadline is horizontal, which means because the 6SH7 is so linear
the distortion produced by the driver stage is very low, and predominantly even order. It’s
an innate characteristic that a good triode has a constant mu over a wide range of operating
