Review: Threshold 400a Amplifier


Category: Amplifiers

This is the amp that started high end as we now know it. Volumes upon volumes of reviews, and lavish praise have been heaped upon this classic Threshold 400A amp,delivering 100 watts rms per side in Class A output.

This is the amp that forever established not only Threshold but Nelson Pass as well, as one of the most gifted of audio designers. A true visionary product from the mind of Nelson Pass.

To say that the 400A caught the audio world by complete surprise is a major league understatement. Solid state prior to this time was not held in to high regard, except the power amps from CM Labs. But here for once was a major technical break through in solid state running in Class A and at that time an unheard of 100 Watts RMS per side. The sonics were to die for and the control and musicality this amp put on speakers were nothing less than a tour de force, that one does not often experience in life in any medium. I remember sitting for hours in a dealers show room listening to the 400A and playing damn near every musical genre I could find, jazz,classical,rock and just sat mesmerized by what I was hearing. Just one jaw dropping experience after another!

I was already 20 years into this hobby when the 400A came out and was becoming rather jaded at the time and about to abandon the hobby when the 400A made its debut. Without question for me this is the product that totally renewed my interest in hi-fi. Plus this amp has opened more eyes and ears to the possibilty of high end like no other before it and to this day remains one of the most sought after amps in the secondary market place, a true timeless classic.

Since then have had many power amps in and out of various systems over the years, most of them Threshold or Forte power amps with some others as well. But for me, have for the most part remained firmly entrenched in the Nelson Pass camp. I just like the way his products perform and the sonics, plus the build quality is way above repproach and set a standard the industry had not seen before and continues to this day with his Pass Labs gear.

Recenly had the opportunity to acquire a very pristine example of a 400A complete with box,owners manual and the supporting documentation. This had apparently been put away for sometime as it does not look used at all, in fact it looks like new out of the box. Just splendid condition as is rarely seen today.

Once home installed into my system and powered the 400A and let it have about 90 minutes of warm up time before auditioning the 400A. The 400A will remained powered 24/7 except for when I am away for long periods of time. Class A amps do need to be powered 24/7 for best possible sonic siganture and thermal stability. Key word is thermal stability as switching Class A amps on/off puts additional strain on the amp as opposed to leaving it on. A good surge protector or power conditioner is strongly recommended for any Class A amp.

Would it have the same magic for me as it did in 1978? or has time and technology pushed it aside? For me as soon as I dropped the tone arm on the LP, it still retained that same magic I had experienced so long ago, at once I was transported back to a time when the music really mattered and I could not wait to get home to indulge my senses in a pure musical experience each day. A time when I enjoyed visiting the record store and finding gems of music to be played by the 400A. This was like lost innocence revisited and a time when above all the music mattered the most, as it should. After all this endeavour is about the music and the reproduction thereof.

The 400A retains its ability to handle speakers with aplomb and reproduce music with a solid verve, not often found today at any price, a musical amplifier that totally involves one with the music, that one can easily get lost in and forget about equipment. It is very easy to get lost in the sonics of the 400A.

So as far as I am concerned here is a classic Nelson Pass product that has truly withstood the test of time and continues to deliver the promise and has done so since its inception. Very few products can lay claim some 27 years down the road. While in some aspects perhaps time and technology may have surpassed the venerable 400A, but for me and most likely for a vast majority of us the 400A will remain a benchmark that others will be judged against. And with updates available from Jon Soderberg at Vintage Amp,I can clearly see the 400A delivering the promise well into the 21st century. In my opinion this offering from the then fledgling Threshold Corp has in years since become somewhat of an icon in power amps. Prices continue to rise on pristine examples of this amp and now command about an
average of $800.00. Each year the prices continue to rise on the 400A as more audiophiles aquaint themselves with this legend.

Lastly the 400A is not everybodys cup of tea, although in your search for a power amp, one can do seriously worse than the 400A and few if any will every have the outright longevity of this timeless classic.

As I contemplate plans to relocate to Costa Rica next year,I will no doubt bring along the 400A. For me it is that good.

Yes I do have more modern amplfiers that the 400A, but the 400 A for me is just magical and I just don't grow tired of listening to it. For me the magic of long ago is back.

Associated gear
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Similar products
Threshold,Forte,Spectral,CM Labs,Classe,Marsh,Levinson,Coda, in 47 years name a amp,probably have had it at one time or another.
ferrari
Thanks ferrari for a great review.
It puts even more life and certainty of the Threshold 400A.
I bought mine in March 1981, almost 39 years ago.
I went into the shop Best Sound in Stockholm, listened to its sound through other components. Finally I bought it. It was there in the closet for 2 years before I bought more parts in the stereo system. I was a student and couldn't afford more after I bought the Threshold. I never regretted that purchase ))
It still delivers, it still lives, it still performs magic sound.
It will last surely through 40 years.
Many other components failed throughout the years; preamp, cassette deck, CD-player etc. Still the Threshold amp stands tall.

I have a pristine re-capped 400A, a later model with an ICE input, that is part of my collection of Threshold gear.

A good friend who loves tube amps, builds his own and their are quite good, burrowed the 400A just for fun to see how it would sound in his system.  He was some what shocked how good it was!  He said as far as timbres/colors it sounded just like his tube gear and had a lot more bass power/control on his speakers then his EL-34 based amplifier.  Now he is only in his early thirties, therefore he knew about these legendary Threshold pieces, but had never heard one before.  He chuckled that an amp that's older then him, particularly a SS design could sound this good now.  

I have also a pristine SA-4e and a 550e that compete with most amps on today's market and actually out perform many of them.  Yes, the 400A is not quite as transparent as the later Threshold amps, but it still has magical timbres and tonality and overall musicality even today.  Nelson was and still is a genius at building musical devices.  For me the wonderful XA-25, which I reviewed professionally and bought the review amp, is a modern version of the Threshold 400A. 
I am an original owner of the 4000, bought new in the early 80s....I sent it off the Jon Soderberg around 2000, and continue to use it, w/o problems, to this day....I have had several preamps over the years, currently using LTA MicroZotl and Herron Phono stage, and things sound real nice.  I suspect my low end has gradually lost a little, but as it is gradual, I cant be sure.  Am getting ready to send it back to Soderberg, but wonder how it  sounds compared to current Pass Labs amps?  Anyone have any experience?  If the change is substantive, I would consider a switch and selling my beloved 4000.(any interest?)......


I will answer my own question, posted just above.  My Threshold 4000 was sold to a wonderful new home( it was actually emotional to let it go after all these years of wonderful sound).  I replaced it w Pass Labs X250.8. Let me say, briefly, the improvement is quite noticeable In the bass, midrange tone, air, soundstage depth and separation.  In a word, amazing!
Kudos to Nelson Pass!

Old thread, but I recently purchased a later model 400A re-capped, upgraded and including XLRs in place of the RCAs. My local highend shop convinced me that I would not be disappointed and boy were they right! My daily driver is a Mark Levinson 585 integrated, and it sounds a little cold and sterile in comparison, which I didn't really think until the Threshold was put in place. I have had many Amps over my 50+ yrs and I can't remember one being this 'listenable'. It is not the last word in resolution and blackness of background, but it is soooo smooth and vocals are as good as I think I've heard (in my system). It is also not the most neutral Amp especially by todays standards, but is as musical as one can reasonably ask for from a $1500 investment. Now I'm wondering what a Stasis model would sound like in comparison?.....