Opportunity, creativity, and experience must each play a role in the creation of a great power amplifier. Paul McGowan, head of PS Audio, created an opportunity in 2014 when he wanted his company, based in Boulder, Colorado, to develop “one of the top five power amplifiers in the world, regardless of price.” Creativity arrived when longtime reviewer and audio designer Bascom H. King -- who measures audio components for the SoundStage! Network -- agreed to lead the project, provided he’d be able to design the amplifier without restriction. Together, McGowan, King, and Arnie Nudell -- founder of Infinity Systems, who collaborated with King on the first hybrid tubes-and-solid-state amplifier -- brought more than 150 years’ worth of experience to the voicing of the final designs.

PS Audio BHK Signature 300

Their two-year collaboration resulted in PS Audio producing three BHK Signature (for Bascom H. King) models: the BHK Signature preamplifier ($5999 USD), the BHK Signature 250 Stereo amplifier ($7499), and the BHK Signature 300 Mono amplifier ($14,998/pair). PSA sent me a pair of BHK Signature 300s, along with a BHK Signature preamp, which I reviewed in December 2016.


Measuring 17.1”W x 8.7”H x 14”D and weighing 83 pounds, the BHK Signature 300 Mono is a big, heavy amp -- and I needed two of them. Refusing to take the sensible route, I unpacked and moved them on my own, but fortunately sustained no injuries. The black review samples (the amp is also available in silver) made a huge visual impact against the natural finish of my listening room’s red oak floor.

The Signature 300’s styling is staid: two grooves run across the faceplate and around the corners, and the top and bottom edges are beveled. The 0.5”-thick front, corner, and rear panels are all powder coated in a matte finish. The side panels are actually massive, 2”-deep heatsinks, their inner edges flush with the top panel of gloss-black wood. Each vertical heatsink fin is notched at top and bottom to continue the subtle bevels of the front and rear panels.

The front panels are not mirror-imaged; at the top left of each is a backlit blue power button for the tubed circuitry -- the only control on that otherwise empty expanse. I’d prefer to see this button in the left corner of one amp and in the right corner of the other -- or both at the center -- for a more balanced look when they’re placed side by side.

PS Audio BHK Signature 300

On each rear panel are one unbalanced (RCA) and one balanced (XLR) input jack; I used the latter. Near the outer left and right edges are two pairs of custom-made binding posts of gold-plated copper, each pair with its own fuse. Power enters via an IEC mains inlet at bottom center, next to a large rocker power switch and two more fuses. Just above the power inlet are two Trigger In ports for remote-control systems. At the top center of the rear panel is the easily removed access panel for the input tubes. A red LED inside the case goes dark a short time after the amp is unplugged, helpfully indicating that it’s safe to put your hands inside to change the preinstalled tubes. Each of my review samples contained two hand-matched, self-biasing Gold Lion E88CC (6922) twin-triode tubes, made in Russia by Genalex.

The tubes are the active devices in the zero-loss input stage of the Signature 300’s fully parallel hybrid design. PS Audio’s technical description indicates that the huge numbers of free electrons in a vacuum tube provide the optimal sensitivity for the highly nuanced audio signals entering the amplifier, and that the tubes used in this amp use constant-current, high-voltage levels to maximize control in passing the signal to the “high bias differentially balanced MOSFET output.” Bascom King chose to use only N-type MOSFETs for the output, for their inherently lower levels of distortion over P types.

PS Audio BHK Signature 300

Each Signature 300’s power output is specified as 300W into 8 ohms, 600W into 4 ohms, or more than 1000W into 2 ohms. The claimed total harmonic distortion (THD) is less than 0.1% from 20Hz to 20kHz at the rated power output. The damping factor of 100 is not all that high compared to some solid-state amps, but was high enough to provide good control of my speakers. The circuits are hand-assembled on custom dual-layer fiberglass boards, using only through-hole installation: the parts’ wire leads go all the way through the circuit board, and are typically soldered in from the bottom. From what I could see, all electronic components appear to be of high quality; PS Audio says that they select them for superior sound quality -- e.g., resisters from Precision Resistive Products (PRP), and film and foil capacitors from Reliable Capacitors (RelCap).


I used the BHK Signature 300 Monos in the same system with which I’d reviewed PS Audio’s BHK Signature preamplifier: iTunes and Tidal streaming services ran on an iMac fed to a Benchmark Media Systems DAC2 HGC D/A converter via a Nordost Blue Heaven USB cable. Because, for maximal sound quality, PS Audio recommends balanced connection for all BHK Signature models, I did so for all connections between preamp and amp and between DAC and preamp, using Dynamique Audio Shadow interconnects all around. Transparent Audio’s MusicWave Ultra speaker cables linked the BHKs to my KEF R900 speakers.

The power consumption of each amp is specified as 175W at idle, or 850W at full power into 8 ohms. At idle, the heatsinks were warm to the touch; when playing music, they were quite hot. These big, massive amplifiers need room to breathe. After hooking them up to my system, I powered up the Signature 300s with their rear rocker switches and left them on for the rest of their time here. Day-to-day listening required turning on the tube circuits by pressing the front-panel button.


Before beginning my critical listening, I checked out the BHK Signature 300 Monos’ impressively low noise-floor spec with the preamplifier’s output muted. My KEF R900s’ coaxial tweeter-midrange drivers emitted so little noise that I had to place my ear inside each speaker’s midrange cone before I could hear any sort of buzz. Most amplifiers I’ve had here have been at least a little noisier than that. I heard nothing from the woofers.

Listening more critically, I was consistently amazed by just how prodigiously big were the BHK Signature 300s’ soundstages. A convincing soundstage is more than just wide -- most amps can put up a reasonably convincing but flat plane of sound between my speakers. Instead, the 300s put up a tangible, fleshed-out, holographic space comprising large volumes of my room, between, behind, before, and to the outer sides of the speakers themselves -- at times even past the walls of my midsize room. That’s a lot of space to fill with sound.

Those supersize soundstages were valuable when I played Jean-Michel Jarre’s 2015 album of collaborations, Electronica, Vol.1: The Time Machine (16-bit/44.1kHz ALAC, Sin/Sony Music). In “The Train & The River,” recorded with Lang Lang, parts of the performance seem to have been recorded with the microphones inside Lang Lang’s piano, his runs up and down the keyboard extending past the speakers’ outer side panels. The Signature 300s reproduced the piano’s sound with great accuracy -- it sounded exceptionally realistic -- but it was the size of the presentation that most interested me. This recording presents parts of the instrument as if you’re listening from the center of the keyboard, just behind the bottom of the music rack. Lang Lang’s right hand played up to the right speaker, his left hand down to the left. In my room, the result was an enormous soundstage -- it was very easy for me to “see” this collage of sound from the vantage of Lang Lang as he sat at the keyboard -- it was as if I were sitting at the piano, rather than at some distance away.

PS Audio BHK Signature 300

Lang Lang’s solo is supported by a driving bass line that travels laterally from the centrally placed piano. I could easily follow the supporting sounds as they flowed smoothly from side to side across the soundstage. Throughout, I heard an aural image in which the piano strings were at the center, with musical impressions of the sounds of trains and water moving all around them. The most important part of all of this was that the PS Audio monoblocks were projecting what the recording contained, and not making things sound bigger than they should.

Richard Strauss’s tone poem Eine Alpensinfonie is scored for a huge orchestra, and includes both high-volume passages for massed brasses as well as small, delicately played solos. I have the 1980 recording by Herbert von Karajan and the Berlin Philharmonic (16/44.1 AIFF, Deutsche Grammophon 439017). About midway through the work, the listener reaches the summit of the Alps in the section titled Gefahrvolle Augenblicke -- Auf dem Gipfel (Perilous Moment -- At the Summit). A solo oboe just to the right of the orchestra’s center carries the listener up the last few steps up the mountain and over the top, where the roar of the entire orchestra represents the beauty of the vista spread out beyond and below. And yet, a single trumpet -- and then, a moment later, a French horn -- reach out in brief solos above the rest of the orchestra. Through the Signature 300s these solos imaged fabulously, the sounds of these two brasses extremely clear and not wavering in space, despite the enormity of sound around them. The image of a full orchestra arrayed in front of me was solid and never varied in position, from the quietest passages to the loudest. With such excellent imaging and superb soundstaging, I could easily envision the orchestra’s various players and sections.

The 300 Monos’ sound was wonderfully neutral -- from the lowest bass through the highest highs, no part of the audioband was too pronounced or relaxed. The music I listened to was reproduced exactly as I believe it was recorded. “Mein Teil,” from Rammstein’s Reise, Reise (16/44.1 AIFF, Island), is as forward a recording as you’d expect from a German heavy-metal band that uses copious amounts of fire and explosions in their shows. Richard Z. Kruspe’s progressions of short, rapid, distorted chords on strident lead guitar were pushy and in my face, and the 300s held none of that back. Lead singer Till Lindemann’s deep, guttural voice reached across the room to assertively articulate precisely what he had to say. The 300 Monos also let distant-sounding tracks such as “Sometimes (Extended Mix),” from Erasure’s The Circus (16/44.1 AIFF, Sire), sound spacious and deep. In this case, Andy Bell’s voice sounded as if he was standing some way behind the speakers, and I was listening from the middle of a gymnasium -- very deep into the stage -- with Vince Clarke’s keyboards even farther away.

PS Audio BHK Signature 300

The 300 exhibited none of the midrange fatness or warm sound I expect from a tubed amplifier. That didn’t mean it could be mistaken for a purely solid-state design -- it did have a sweetness in the highs that could have been an artifact of the tubes in its input stage. In Itzhak Perlman’s 1976 recording of Brahms’s Violin Concerto, with Carlo Maria Giulini conducting the Chicago Symphony (16/44.1 AIFF, Warner Classics), at a few points when his violin is supported by a piccolo, both instruments are played in their highest registers -- but through the BHK 300s, neither sounded harsh or shrill, and the piccolo notes were positively round and emboldened. The 300’s sound was fleshed out, never thin or threadbare. And as Perlman’s violin went higher and higher, it never turned irritating or harsh -- the top end of this amp always sounded sweet, and I never suffered listening fatigue.

The BHK Signature 300s also excelled at bass reproduction. Strong, deep notes were firm and had appropriate support without bloom, and my KEFs were entirely controlled by the amps, no matter what I played. Timpani, bass drum, double bass, and the basses of the Boys’ Choir of Harlem all play roles in “Closing Credits,” from James Horner’s score for the 1989 film Glory (16/44.1 AIFF, Virgin). The basses in the choir were tight as a singing group, and their transients at the beginnings and ends of words were razor sharp. The double bass, bass drum, and timpani were all fully developed in size, voluminous in space, and unwavering in strength -- the slam of the bass drum was satisfyingly perfect as it ended the track.

In fact, this track from Glory presents an amplifier with many challenges: heavy deep bass, complicated choral passages, brief trumpet and trombone solos, cymbal crashes, delicate sections with triangle solos, varying pacing, and more. And as it goes on, it dares you to increase the volume. As I took that dare, all that happened was that the volume kept increasing -- there was no bloating of bass, no sharpening of treble, no glazing of the midrange, no loss of resolution. The BHK Signature 300 Monos were equally comfortable playing at low or high volumes, and never sounded stressed or lost their composure. I tried, but I couldn’t make them behave badly at any time during their stay here.


Simaudio’s Moon Neo 330A amplifier costs $4300 and can be bridged to operate as a monoblock (I had only one of them). But used as a stereo amp, it costs $10,698 less than a pair of PS Audio BHK Signature 300 Monos -- a big difference.

The Simaudio and PS Audios are similar in being class-AB power amps that are fully balanced from input to output. From there, they quickly diverge. The Simaudio is purely solid-state, the PSA a hybrid. The Moon Neo 330A’s footprint is similar in size to that of one BHK Signature 300, but it’s only about one-third the height -- the Neo 330A looked small beside one 300, and beside two it looked tiny. Similarly, the Moon Neo weighs 33 pounds, compared to a single Signature 300’s 83 pounds. All told, the Simaudio is well built for its price, but doesn’t begin to approach the substantial feel of the PS Audio.

The Moon Neo 330A is claimed to output 125Wpc into 8 ohms or 250Wpc into 4 ohms -- so much less power than the BHK Signature 300’s respective 300W and 600W outputs. Mind you, the Neo 330A’s THD at full power is 0.05% -- precisely half that of the PS Audio’s 0.1%. That’s a big difference, considering the big difference in price. One advantage of a pair of Signature 300s is that they operate in true dual-mono mode, sharing no parts and thus offering total channel separation. Most stereo amps, like the Moon Neo 330A, are claimed to have dual-mono construction, but nonetheless, the two channels do share some parts, such as the power cord, case, and often the main transformer.

PS Audio BHK Signature 300

When I reviewed it in July 2016, I described the Moon Neo 330A as throwing out “palatial” soundstages. The PS Audio BHK Signature 300 Monos’ soundstages were more spacious and more three-dimensional -- higher, wider, deeper -- and in comparison made the Sim’s stages sound surprisingly average in size.

The Moon Neo 330A’s strengths are its extraordinary neutrality and its lack of tonal colorations. The BHK Signature 300 Monos didn’t sound quite as neutral with a sound that definitely had a slight warmth -- not a full tube-like warmth, but music played through them had a subtle, smooth feel that probably had to do with their tubed input stages. The clarity of musical images presented by the PSA amps was superior as well -- everything I played through them sounded more tangible and holographic than through the Simaudio. Most notably, the Moon Neo played recordings like an analytical instrument used to measure the recordings themselves; the BHK Signature 300s created a tangible embodiment of the music. While I could respect the Neo 330A’s more clinical, analytical sound, particularly for its much lower price, I better liked what I heard through the Signature 300s.


PS Audio’s BHK Signature 300 Mono amplifiers produced wonderfully clear sound in my room, yet with a tangible, 3D quality that gave the music emerging from my speakers a bit more body -- which I really enjoyed. Their soundstaging was exceptional, and they proved unflappable throughout the listening period, despite being challenged with complex music and punishing volume levels. Their treble response was clean without sounding edgy, allowing me to enjoy longer listening sessions than I have with any other amp. I also appreciated the BHK Signatures’ tight-fisted bass reproduction, which delivered plenty of slam when the music called for it. While their looks may be bland, their build quality and tolerances of fit and finish were superb. The BHK Signature 300 Monos are expensive, but nothing in their build quality or sound makes me doubt that they’re worth every penny PS Audio asks for them -- or that they’re great amps.

. . . Erich Wetzel

Associated Equipment

  • Loudspeakers -- KEF R900
  • Preamplifiers -- Hegel Music Systems P20, PS Audio BHK Signature, Simaudio Moon Neo 350P
  • Amplifiers -- Audio Research D300, Simaudio Moon Neo 330A
  • Source -- Apple iMac running Mac OS 10.11.6, iTunes, and Tidal HiFi
  • Digital-to-analog converter -- Benchmark Media Systems DAC2 HGC
  • Speaker cables -- Transparent Audio MusicWave Ultra
  • Interconnects -- Dynamique Audio Shadow XLR
  • USB link -- Nordost Blue Heaven

PS Audio BHK Signature 300 Mono Amplifiers
Price: $14,998 USD per pair.
Warranty: Three years parts and labor; one year, tubes.

PS Audio
4826 Sterling Drive
Boulder, CO 80301
Phone: (720) 406-8946

Website: www.psaudio.com