In its day it offered large amounts of clean power at a very reasonable price -- mine still does today, more than twenty years after I bought it. It's never needed a repair.
If you find a old one in good working order, don't hesitate to buy it for purity of sound even if you don't really need 200 watts RMS per channel, (400 @ 4 ohms).

For me, none. I'm told of you drive it hard you'd better use a cooling fan.

I bought my 400 in about 1978. In those days I owned a pair of Ohn F's - an exotic speaker by any standard - that required huge power to be driven properly, so I was looking for a high-power amp. By then the 400 was no longer a new model. Also, it had established a bit of a bad reputation, mainly among sound professional and others who constantly drove it very hard.
I picked up a copy of a then-new audiophile magazine (whose name I don't recall, unfortunately) that had done double-blind listening tests of over twenty high-power amps. Surprisingly to me (and many others no doubt), Phase Linear 400 came out on top. On the strength of that review, and because it was less costly than most others, I bought mine and have never regretted it.
Today my 400 is matched with an APT Holman preamp which I bought in about 1979 -- also a great component by the way. I unloaded the Ohm F's in about 1982 for a pair of B&W DM7 (Mk.I)'s, a smoother, more accurate speaker, but also notably inefficient. The 400, the APT, the DM7's have been together almost twenty years: after all this time I'm looking to replace the DM7's, but if I get my wish, the 400 will be here for a long while yet.

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I haven't used any other amplifier of comparable power.

Lots of good clean power. Mucho headroom.

Required lots of ventilation to prevent overheating.

This is an excellent amplifier. I would love to find one today for my home theatre system. I gave mine to a friend in the 1979 to 1980 time frame after purchase of a model 700. I used the Phase Linear model 400 amp to drive a pair of Bose 901 series III loudspeakers. I popped two drivers in the Bose. This was not from square waving the amp but from the excellent headroom and power it had. We bench tested it a 370w per channel at 4 ohms load with both channels driven.

This amplifier is for a serious audiophile that wants a touch of class in his system and these amps are true classics. I have a model 300 in my living room today and some day would love another 400 to join it.

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Phase Linear model 700 amplifiers, Phase Linear model 300 amplifiers.

Power, smooth and warm sound

None tho' look dated

Great amp. Used it now for more than 10 years and always a joy to listen to with my equally excellent Magnepan.
Sad that they are so rare now!

Not a 95 model but had to fill in the field. 1977 in fact.
This Amp beats my Naim 250. What a classic.

Speaker connections to shallow. Have drilled mine deeper

This classic amplifier has amazing depth and resolution
when used with decent pre-amp.I have trialed this aquisition
for over a year and although I am a Naim 250 owner as well
the Phase Linear wins hands down, long term listening etc.
No fatigue, never to loud or course. whatever happened to the Company because this product, today could command $3K+

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Used with Naim NAC82 and Audiolab 8000Q

Clean, powerful, cheep to purchase and repair.

Loves to eat drivers and predrivers. A bit unstable is an understatement.

I collect Phase Linear amplifiers and as long as the metal work is flawless, I snatch them up. Repairing the units is a breeze, and parts aren’t a problem as long as you understand the design changes that where made over time. The Audio PCB had many solder problems from the factory and many changes over the production time line. Once you have that complete history understood you have the knowledge of how to cope with rebuilding these units
Without getting into too much design details the 400 original and the B and then became the series II series used two different power transistor configurations and design criteria’s. The power transistors changed from a quasi-complimentary to a full complimentary design and with that the make and models of the devices also changed. Beware that the models of the amp stayed the same for a short time before it became a 400B. In fact there where two models of the basic 400. Even the heat sinks changed several times in design. If you need information on these amplifiers I have the original technical shop manuals and supplement printings on technical changes. E-mail a reply and I may be able to help on rebuilding amps not working into stronger more reliable units. Hey it’s a classic and worth the meager price most will sell it for.

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Crown DC300 Marantz 500

Superb headroom power, awesome openness, clarity and definition

expensive to re-tool if you blow it!

Was blessed to hear my bro'-in-law was going to pitch his Phase 400amp, 2000 preamp and 5000 tuner when he got hissony "ES" series surround receiver. Offered to "take them off his hands" and obtained the finest amp imaginable to drive my very cantankerous double set of stacked Dahlquist DQ-10 speakers.

With a separate dedicated amp/subwoofer combo to take some of the lower register stress off the DQ's - the Phase 400 has driven them to a degree of bredth, depth, clarity and accuracy that I had not imagined possible in sound reproduction.

Unfortunately I was too eager to show it off a few weeks ago and failed to wait for it to properly warm up, blowing one side and requiring the replacement of all the solid state pieces [on both sides so they'd still match up.]

Before that, the 400 drove the touch 1.8-3ohm load without fail or fault for over ten years. I hope it will sound as good or better next week as it has over the years.


Chris Fisher

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Citation, Nikko 550, Hafler, Mac, Crown

Clean and well-defined at all volume levels.

Blows up occasionally (twice since 1976)

I am the original owner, having bought it on my brother's recommendation when I was just out of high school. I run it into Yamaha NS-690's, also bought in 1976, which were the cheaper cousins to the reference monitor, the NS-1000.

As a casual musician, I believe I have a decent ear for tonal characteristics, transparency, and what folks like to call the "sound stage." In 25 years, I have rarely heard anything that comes close. I once ran a Denon integrated amp into the Yamaha's for a while, and they lacked much of the depth and clarity they reached with the Phase.

It's been in constant use since 1976, and it's still running strong, although the VU meters are no longer lit. It got fried twice but seemed to come back stronger with new gear in it. Great amp, looking forward to the next 25 years of use!

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None

AWESOME POWER FOR THE MONEY HUGEHEADROOM DAMPING FACTOR HIGHER THAN VIRTUALLY ANY AMP OUT THERE

WILL BLOW OUTPUT CAPS BUT EASILY REPLACED WITH NEWER READILY AVAILABLE ONES

THESE AMPS ARE A LITTLE FINICKY BUT ARE WELL WORTH IT ,IVE BEEN USING THEM FOR YEARS SINCE THE EARLY 70S,THE DYNAMIC RANGE DISTORTION AND POWER 201 @8OHMS CONT POWER SEEMS NOT MUCH BY TODAYS STANDARD ,BUT ONE LISTEN WILL SHOW YOUR EARS WHAT ITS ALL ABOUT,IM SURE THERES SOME HIGH END SNOB OUT THERE THAT WILL SAY PHASE LINEAR IS GARBAGE BUT IVE BEEN LISTENING TO HIGH END FOR MOST OF MY LIFE AND YOU NEED TO GO DEEP INTO THOSE POCKETS TO COME CLOSE.FOR THOSE OF YOU OUT THERE THINKING ABOUT A GOOD USED ONE THEY ARE AVAILABLE
WITH A LITTLE SEARCHING,EBAY USUALLY A FEW A MONTH,PRICES RANGE FROM 200.00 TO 300.00 FOR A PRESTINE UNIT YOUR COMMON TROUBLE IN OLDER SERIES 1 MODELS WILL BE OUTPUT TRANSISTORS
THE OLD XPL909 SHOULD BE REPLACED WITH MOTOROLA MJ15024 THEY HAVE A MUCH HIGHER RATING AND STILL BEING MADE.IF YOU WANT TO TEST ALL YOUR GOODS I SUGGEST THE 700B 350 WPC MIN @
8OHMS CONT BOTH ARE GREAT,I LOVE THESE AMPS,IF YOU HAVE THE PPATIENCE TO FIND AND MAYBE DO SOME MINOR MODS IT WILL BE WELL WORTH IT

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CARVER,DYNACO,CROWN,AUDIO RESEARCH,

Sound, power, looks, versatility

Runs hot, needs a fan

I first owned one of these amps in the late 70s. I loaned it to some bands who used it as a PA at club shows and ruined it (long story). Unfortunately for me, I waited until 2000 to replace it. Perhaps I just do not fit the definition of audiophile (I said audio enthusiast), but this amp sounds better than any amp I have listened to, period. It sounds more natural. I listen to all types of music (except rap or techno), and it just sounds better. There is depth and space...it does not sound like so many other pieces of solid state costly junk. When my fiance heard it, she admitted that she thought I had to be full of myself when I had been telling her how much difference it would make...then she said...."it sounds like we have a whole new CD collection"
Put on Little Feat's "Waiting For Columbus" and turn up "Fat Man In The Bathtub." Listen to the cowbell, the wood block, the cymbals, the bass, the drums, the keyboards and finally the guitars as they kick in one by one. Listen to Lowell George's growl and sweetness. Damn, I missed this thing for all those years.
I bought my unit from someone I found on the web who is a partner with a technician who worked at Phase Linear for years. The tech checks out the amps and brings them to factory spec. Email me if you want to find those guys.
By the way, a great inexpensive pair is the Phase with a Carver C-4000. You can buy them for maybe $600 total. I have never posted and know I seem like a shill, but I just love this sound and the price is absurd.

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Various

Low Distortion at low to medium volume ranges. Channel output control for direct input connections and Balance correction (If no pre-amp is to be used).

VU meters don't respond accurately (well on mine anyway). May "Thump" speakers with a low level transient, possible to dammage amp and/or speakers if amp is switched on and off quickly.

My 400 was Originally owned by my father, purchaced in 1975. Used for many years to power a pair of Heil AMT-3A Rock Monitors with decent sound quality.

We recently used it in a Home Theater Application with good results. It was paired with it's AC-4000 pre-amp and an Adcom Surround processor. With the old AMT-3a's having two 10" drivers and this amplifier no Sub was required. Especially with low-range noise effects (explosions etc...). This amp is no slouch when driven hard! Watch your speakers however.

Also Great for Low-Budget beginning Audiophile Applications like my system. Amp has low distortion and great imaging and soundstaging qualites. Quite a step up from most reciever units. We have an Aragon 2200 Amplifer and most recently a wonderful Mark Levinson No336 Power Amp. The AC-400 has been paired with equipment driven by these amps. While not as good the two latter, the results were quite good for 1970's technology.

The system I have it currently set up with is:

-B&W DM-302 Loudspeakers on 24" Spiked stands...connected with some vintage Kimber 4-Wire Cable.
-Sony CDP-ES15D 10-Disc Player. Variable output connected directly to the 400 via LAT Interconnects.

If you are looking for a good amp under the $1000 price range for good Listening quality or Home Theater application I beleive that the 400 would be a good one.

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Phase Linear AC-4000 Pre-Amp.