“The BHK Signature features a classic dual-triode vacuum tube in a modern configuration. Hand-matched pairs of Russian Gold Lion 6922s are self-biased with constant current and high voltage, through a MOSFET current source and MOSFET-regulated plate supplies. The input stage zero negative feedback design achieves low timing and phase distortion errors, allied with fast step response. The balanced-input vacuum tube stage runs in Class A configuration, and is coupled to the following balanced-configuration current amplifier stage by way of REL film capacitors.
“Hybrid amplifiers are not new (as evidenced by the 36-year-old Infinity HCA), and most incorporate a low-loss input interface, voltage amplification through vacuum tubes, and high power/low-distortion current amplification and delivery through MOSFET outputs. While these basic elements are present in the BHK Signature Amplifiers, it is King’s utilization of a new topology of MOSFET amplification that makes the BHK Signature Amplifiers not just possible, but far superior to ordinary designs.
“To maximize the benefits of the two different amplification devices (vacuum tube and MOSFET) inside the amplifier, King felt the amplifier should be built as if it contained two separate, independent systems, each with a power supply tailored to fit. Thus, the BHK Signature has two power transformers, one for the vacuum tube input stage, the other for the MOSFET power output stage.
“Regulation of the power supply for the input stage is important. Separate and discrete MOSFET regulators are used throughout to preserve details found in the music and keep noise levels to a minimum. The path music takes through the amplifier must be pure and without a polluting sonic signature. Each passive component is hand-selected to provide the cleanest path possible. PRP resistors, film and foil Rel caps, and the finest-sounding parts possible are hand-soldered onto BHKs circuit boards. King insisted that no surface-mount parts be used in the signal path; assembly is by classical through-hole means.”
You don’t produce a superb-sounding amplifier by choosing the wrong circuit. At the same time, I believe Paul’s comments do more to reflect how much a search for the best possible sound, the experience of the design team, and a deep commitment to creating the best product contribute to an amplifier’s success. The way products evolve are a critical part of its design, and often a part that explains a great deal more about their character and performance than any technical data.
In practice, high-end audio is not shaped by finding a singular solution. It is the result of the work of dedicated audiophiles who make what they listen to, and who become the equivalent of auteurs in sound.
The Music and Sound Quality
In any case, the end result is outstanding, so I think you will quickly find that this is a superb-sounding amplifier, and one with some unique sonic qualities. I’ve already provided a summary description of its merits, but when it comes down to the details, as I’ve stated, the BHK Signature 300 provides exceptional imaging and depth. You will need equally good components, wires, and speaker placement to hear this. You will also need source recordings that are recorded naturally and simply enough so you can get a real-world soundstage.
These are scarcely demanding conditions for any real audiophile system, however, and once they are met, the BHK Signature 300 makes the soundstage come truly alive. The sound presentation is somewhat more forward in character than many of the BHK Signature 300’s best rivals. For example, the Pass Labs 160.8 monoblocks I use as one of my references provide an excellent soundstage with the same degree of realism, but one whose sonic perspective is more mid-hall.
But both types of soundstage are musically realistic, and I have not heard another power amp that does as well in providing the same kind of detail in a musically natural, concert-hall way, or one that provides the same kind of slightly forward imaging and soundstage width and depth without slightly exaggerating the upper octaves.
The Signature 300’s soundstage performance is particularly striking with some older recordings such as the best of those from RCA Red Seal label and Mercury, chamber music made on the Accent label, and the top Smithsonian Jazz pressings. These were produced at a time when the focus was on providing a natural soundstage with minimal analog or digital editing, extra mikes, or other production tweaks.
Some of the current focus on the sound quality of LPs and analog tape almost certainly comes from the fact that they were originally recorded at a time when the processes were more natural; there was less emphasis on close miking and on detail over natural timbre, and it was far harder to “assemble” the music by joining different parts of multiple takes into a single performance. Better small human flaws than robotic, post-performance production perfection.