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
From NP on longevity of his amps:

(quote)

In fifteen years the electrolytic power supply capacitors will get old. Depending on
usage, you will begin to have semiconductor and other failures between 10 and 50 years after
date of manufacture. Later, the sun will cool to a white dwarf, and after that the universe will
experience heat death.(end)

In my experience with Threshold amps and preamps, it is about at the 25 year mark, where service should be done.But it all depends on usage and how used as to when service should be done.

Just had Jon Soderberg go through the 400A and NS10 I have and should be good to near heat death - LOL.

After 47 years in this hobby and other than Threshold gear, there is precious little else that warrants service,or modding. And where else can you get help and advice from the man that started it all.
Not a 400a response but a tilt of the hat to Jon Sonderberg for his amazing mod skills. He just moded my Threshold s450e amp and Forte 44F preamp. A truely nice update and they should last me the rest of my natural life too.

Oh yeah, I am the orginal owner of the s450e (1990) and Jon stated when he removed the mail caps one of them had a little leak happening (material damage to cap but no where else). Even though I was just doing some preventive maintenance/life extention by asking him to replace them in the first place, I'm even happier after I learned what he found. A leaking main cap is not a good thing.

L
I have the big brother to this amp the 800A. It has been, and continues to be a pleasure to own. What can you tell me about it?
Az Ed
From what I remember on this unit. It is 200 per side Class A output and the only Threshold amp made with a cooling fan in the back of the unit. Very short production run. I believe only 168 of these were produced. This was the first power amp from Threshold, produced from 1975 to 1977,under the leadership of Nelson Pass. Very impressive with its large VU meters and would drive the hardest of speakers loads with ease.

If it were mine I would ship off to Jon Soderberg at vintage amp, for a complete check up and upgrade of the Caps. This is by far to rare of a Threshold piece to let something happen to it. If it hasn't been serviced recently,it would be very wise to do so, before it needs a major rebuild.

Got a great one, enjoy it.
Absolutely fantastic review from a guy that fnally was able to purchase a 400A 20 year after introduction. With depreciatin of the Amp itself and 20 years of increased dollar value all contributing to putting an "extremely" high end esoteric class A amp into the hands of a pioneer reciever guy like the reviewer.
Unfortunately high end amplifiers are not like 250 GTO Ferrari's in that the car was impossible to buy 20 years ago and now thirty years later is "beyond" possibility for ownership combiming the resourses of the reviewer and "everyone" he knows or has ever been aquainted with " to consider purchasing used now!
It's really sad when thresholds become low-fi equipment and attract reviews from the integrated sanyo japanese audio crowd.
Best leave the reviews to audiophiles who purchased and "used" these Amps "decades " ago rather than reviewers who consider themselves on the cusp of high end because the amp came "boxed with instructions!
It's impossible to live in 1980 no mattter how hard you try!!!!!!
Regards Robert Lock Threshold-Ampzilla- Bryston