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  Review: Threshold 400a Amplifier
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
Click to view my Virtual System

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.

by Ferrari on 10-04-05 

 Threshold 400a

 Threshold 400a Back
  Follow ups
Click title to read one, or click date to read all below it.

10-04-05   I own the threshold 4000 the 200watt/channel bigger bro ...   55dok

10-05-05   That is a great review - thank you. it seems like ther ...   Peter_s

10-05-05   I've had a love/hate relationship with the threshold 40 ...   Jvogt

10-05-05   Thanks to ferrari for another nice review! i hav ...   Harhau

10-05-05   Many thanks for the review, ferrari. i'm in the ...   Dr_joe

10-06-05   Dr. joe: yes the threshold sa 3.9e would certain ...   Ferrari

10-10-05   Found some technical data of the threshold 400a for the ...   Ferrari

Review: Threshold 400a Amplifier
I've been using a Threshold 4000 (the follow up to the 400A) to drive a pair of Beveridge Model 3 electrostats for the last 25 years. I've actually bi-amped with two 4000's upgraded by Jon Soderberg for the last two years. They continue to drive the Bev's tough load without issue and have plenty of power to overcome their relatively low efficency. As you point out, Nelson's known how to do it right for a long time. 11-12-05

11-17-05   Not many amps will drive those speakers past or present ...   Ferrari

11-24-05   I purchased a 400a about a year ago from a local hi-fi ...   joe@

12-01-05   I just got done rebuilding a later version 400a and yes ...   Audio_ken

12-01-05   For those of you that have the talent to work on these ...   Ferrari

12-01-05   Ferrari, ... you sure you're not n.p. in ...   Audio_ken

12-01-05   From np on longevity of his amps: (quote) br ...   Ferrari

12-01-05   Not a 400a response but a tilt of the hat to jon sonder ...   Lngbruno

12-15-05   I have the big brother to this amp the 800a. it has bee ...   utazfan@

12-15-05   From what i remember on this unit. it is 200 per side c ...   Ferrari

03-17-07   Absolutely fantastic review from a guy that fnally was ...   rlock79@

03-24-07   Hi rlock i didn't quite understand what you meant by ...   Noams

04-17-07   First off, where does it say the reviewer has a japanes ...   Centaurus3200

07-06-08   Thanks for review. i was trying to remember the specs ...   Charles_peterson

08-29-09   Thanks for the great dialogue on the threshold 400a. ...   Zjmeyer

10-08-09   The 400a was certainly a groundbreaking product for its ...   Madisonears

11-15-09   How did your upgrade go? i am in process of restoring o ...   Kshallenbeck

07-04-11   Great review, except for some of the placebic statement ...   Sound_bites

07-09-11   Sound bites is quite correct in regards to thermal stab ...   Ferrari

07-17-11   Just saw this review and really enjoyed it. i owned a 4 ...   Dogmcd

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