I origianlly owned a Phase Linear 400 when I was in college, back in the early 1970's. In the day it was a wonderful sounding amp with tons of power and was affordable. The problem was that the amp was very unstable, and mine would blow, taking my speakers with it. This happened on so many occasions, I finally traded the amp for a Luxman M-2000. About a year ago, I found that there had been a lot of wok going on refining the Phase Linear amplifier line. White Oak Audio had SPICE modeled the amplifier and had discovered many of the original design problems which made the amp unstable, and had created a new PCB driver board which addressed the problems with the design. Another individual had designed a DC protection circuit which turned the amp off if it sensed any DC current in the output signal of the amp. Also there had been a new LED light board for the meters developed and a new kit for replacing the storage capacitors with three times the storage capacity. With all these improvements, the Phase Linear 400 (as well as the 700, 700B and all Phase Linear amps using PL14-20 PCB boards) were back in my sights. This amp lives again! And it is not the same amp you might remember. The frequency response is now ruler flat to below 20 hz, and to abover 40 khz. Distortion is lower than the original amp. I think it could compete with any amplifier on the market today. The new production driver and output transistors recommended for this amp, combined with the new PCB now give this amp the ability to produce about 550 watts RMS into an 8 ohm load. I see a resurgance of popularity and renewed interest in this venerable old road warrior. With all the fixes incorporated into the newly designed parts, I think this amp is ready for another 40 years of producing music. Over the years I have owned many different brands of amplifiers, most of them come and go, but this amplifier has been reborn. If you want a powerhouse of an amp, cloaked in a vintage wrapper, this is the amp for you. If you need more than 500 watts you might want to consider the Phase Linear 700B. This amp is now capable of producing over 1,000 very clean and thunderous watts. My rack now houses two Phase Linear 700B and four Phase Linear 400 Series I amplifiers.I can listen in stereo, or 7.1. These amps are hard to beat. I could use all the audio phrases to describe the sound of these amps, but suffice it to say they sound GREAT. It is not the same amp I owned in the 70's.
The first quality of the Phase Linear 400 are, of course and as reported by others, the low frequencies reproduction. These, however, it is better to say right away, are not particularly profound, say not much below 30Hz and the 400 does not present the typical grip of a big Krell but it is appreciated for the roundness and an unexpected sense of rhythm, at least with my setup (Ensemble speaker cables and Gale GS401A loudspeaker).
Listening to some of my reference discs in both analogue and digital format I was surprised by the sense of the reproduction speed of low frequencies, so much so that I checked that there was some variation in the motion of both the turntable (Roksan Xerxes) and the CD player (Meridian 203) such that I think to an increase of rotational speed, which of course has not been found.
However, I must observe that the notes referred above have emerged listening to an average volume because the sample under test can not play recordings at full live levels due to a premature and continuing intervention of the protection that disconnects the speakers for a fraction of a second and if conditions persist, for longer periods such that to force me to lower the volume. It is true that the speaker, the Gale GS401A, may induce into crisis many power amplifier of my knowledge, but I think this is a lack of some internal amplifier adjustments that should be corrected in order to appreciate a live playback levels in the area of 0db (VU meters) or slightly more why not. Furthermore it should be noted that in these near extreme working conditions, the light coming from the bulb of the VU meters was not constant, but danced with the music.
Unexpectedly, the 400 is sufficiently refined to reproduce musical details such as reflections captured in the recording studio and various noises coming from the stage when playing discs recorded live. These details, fortunately, are not thrown in your face hurting your ears but it offers such details with the right proportions, emerging them with the right playback level from the rest of the music. This is a further demonstration of design skills by Bob Carver, as well as his taste in music I would say, because we do not must forget that the 400 was placed on the market when the common thought was that if the amplifiers measured in the same way then they play the same way and compared to some beasts of the time, the 400 is preferable, at least as far as my taste of music playback is concerned, to his other contemporaries such as the Crown DC300A.
Of course the 400 does not have the bloom trait of a good tube amplifier when it comes to reproduce the voice and other acoustic instruments within the midrange. Nevertheless, its presentation in this range of frequencies is good and valuable, and far superior to that proposed by other amplifiers as previously highlighted. In some circumstances it seems to hear a good MOS FET power amplifier à la Accuphase so to speak, and again it is amazing how this was obtained by Bob Carver with bipolar devices and during the prehistory of solid state audio. Sometimes we forget this detail but I think it is very important because today it is like to treat an infection with penicillin, but it would be much more difficult at times when this drug was not available.
Thanks to its power reserve and listening unfortunately at medium to low SPL level for the problem mentioned above, the 400 is appreciated for a good reproduction of the stage that still is not huge but nicely extended and clear. Another solid state power amplifier of my knowledge, the Classé DR9, was much better in this regard, but connecting it to speakers which provide both plasticity and three-dimensionality of the reproduced sound their workhorse, such that offered by the beautiful Dahlquist DQ-10, this amplifier ended up playing in an overly diffuse way, losing both outline definition and tactile sense, subtracting pleasure from reproduced music.
The 400 let you allow to listen to the music for long periods of time without causing headaches or other aches and this is, in my opinion, a sign of ultra low distortion especially in the extreme high frequencies of the audio spectrum. The 400 is also smooth enough in this range of frequencies even though I've heard better in the past as in for example the Ensemble B50 Tiger (but this one, more than a tiger was a kitten when it came to reproducing low frequencies) which was also appreciated for the midrange but they are very different kind of equipment (the Ensemble has tubes in the front end and transistors in the power section while the Phase Linear is completely solid state) and a direct comparison between these twos becomes more difficult to do.
Back to the low frequencies reproduction, the workhorse of the 400, I must emphasize that the Spectral DMA50 first series was even more accurate than the 400 and much more brutal when it came to bestow that energy blasts to the hapless speaker woofers but I think that the 400 in this range of frequencies is more pleasant, because the magnificent Spectral’s reproduction of bass frequencies is offered in a way to capture and grab your attention always during the reproduction and this does not allow you to relax, almost never.
In conclusion, the Phase Linear 400 was a great discovery for me, especially considering that you can get it at prices not exorbitant, but we must borrow attention, with new filter caps and such other care necessary for a machine of this age. He will repay you with an excellent and enjoyable sound so do not trust the evil tongues that emerge from time to time (and spit) over the internet, the 400 sounds very good and definitely does not catch fire, as long as it is well maintained and lovingly cared for.
I own a Phase Linear 400 power amp, matched with a Phase Linear 4000 pre-amp and 5000 tuner. I purchased them all in 1975, and have been using them ever since then. They are awesome, and make my Infinity Reference Standard IIIb speakers sing. Whether it be classical, jazz, rock, pop, funk, blues, or country--the 400 (being the foundation), is amazing. I feel I have received more than my $450 investment in this power amp. Throughout the years, I considered switching to tubes, but did not because of problems I had with my musical instrument tube amps (300 watts with 6550 tubes)--I am a bass player. The 400 never fails, never disappoints. The 4000 and 5000 have also been bullet-proof. Thank you Bob Carver for designing and building such a great classic amplifier.
I'm no audiophile and I don't play my music very loud anymore. I seen this amp sitting on a shelf in a used lp store about 15 years ago with a hundred dollar price tag on it and couldn't hardly believe my eyes. I took it home and have been using it ever since without so much as a hiccup. I use an old Maratz 2238 that I picked up at a garage sale for $10 as a pre-amp and have had several pairs of speakers hooked up to it, and I simply love it. I also have a pioneer spec-2 amp (500watt) that I got at a pawn shop for $100. The owner told me that I was getting a pretty good deal on that 100watt amp as I was walking out the door with a big smile on my face. I did have to take in the shop once, they said all it needed was cleaning. I have the phase linear and the spec-2 hooked up side by side in my living room and my girlfriend thought I was nuts when she first came over, now she just loves coming over and listening to my collection of L.P.'s