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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
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.
ferrari
audio_ken
6 posts
 
I just got done rebuilding a later version 400a and yes, overall is a well done amp. A couple of people I have talked with complain about it blowing fuses when really pushed. I have my idea(s) as to what it could be but will refrain from speculation here. I'm currently rebuilding an early version and uncovered the problem of the lack of bass which looks to be easily corrected. Not sure why the original design falls short on this. hotrodding the amp is fun and not too terribly difficult and I'm "modding" it a bit for driving stats without blowing fuses. as usual, the sky is the limit with what can be done,..and plenty can be done. The early version can even be updated to a full fledged cascode if desired and there's plenty of room on the circuit board to get as imaginative as you want. In my mind, it's one of the few amps with all the goods to begin with to even warrant a rebuild.

After installing better parts and thermal tracking, I was told it warmed up in an hour instead of the usual 4-8 hours.
ferrari OP
617 posts
 
For those of you that have the talent to work on these amps check out.

http://www.diyaudio.com/

A wealth of information there, plus from time to time Nelson Pass contributes to those threads and certainly the 400A is one of his favorites.

In my opinion the early Threshold amps and preamps are true genius from the mind of Nelson Pass and readily accept upgrades. The 400A as well as the 4000 and Stasis 1,2 and 3 were cutting edge,over the top designs, that have withstood the test of time, and continue to deliver the promise some 25 plus years since new.

Nelson Pass was trained as a Physicist, as opposed to an Electrical Engineer and I believe this is one of the reasons his designs and products have that certain sonic signature a vast majority of us seek. Plus his designs have been ripped off more times than I can remember.But remember a forged Picasso will never be a true Picasso. So why even bother with a ripoff.

Although Threshold under Nelson Pass continued to deliver one break through design after another and continues to this day with Pass Labs. The main drive has always been the music and accurate reproduction thereof. And to this day Nelson Pass has remained totally dedicated to two channel audio.

The build quality of the early Threshold products set a bench mark that to this day has not been surpassed. These are true lifetime products of the highest caliber. No doubt, this is why these have survived all these years and will continue to do so. Plus the craftmanship of these products are a tour de force seldom found.
audio_ken
6 posts
 
Ferrari, ... you sure you're not N.P. in disguise..lol?? (JK!!!) Yes, I agree that the early amps are truly a breakthrough, monster heatsinks, power supply and all. And they no doubt can be updated with new parts and tweaked to not play second fiddle to any amp. Someone mentioned a Dynaco 416 earlier and did you know that this amp has the same "stacked" output stage as the 400a and 4000 and also has fewer components to muck up the sound? Also, there are circuit similarities too, which sort of makes me wonder if some ideas were not taken from the Dynaco to make the Thresholds. I'm no patent expert or anything, but I can't help but make the observation and have to speak up for the Dynaco and say it's not nearly as bad as some who have slammed it before would have you believe. As far as comparing the amps to each other, it's pretty much a joke as they all have cheap parts which limit the sound. Hotrod each amp and the differences become less I believe. Too bad it's a fact of life that good parts are not used in manufacturing most amps as they are so incredibly vital to good sound. But it is true the Thresholds took it all to another level and made us realize that we need amps like this to get the job done. I got my 400a and 4000 and feel complete with not much need to look further. I look at most other amp's power supplies and heatsinks and just chuckle! Amps like this are a rare breed indeed.
ferrari OP
617 posts
 
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.
lngbruno
210 posts
 
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
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