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Threshold - SA/3.9e: upgraded version

Remark: this article is a complement of the review of the original THRESHOLD SA/3.9e; we recommend to read it   before the following article.

Another dimension

Following a lot of tests, I concluded that I needed a more powerful amplifier (than the Threshold SA/3.9e) to drive my DIVA further.
But I did not manage to get a more powerful amplifier: the Threshold SA/6e monoblocs are almost impossible to find in Europe (not easy in the States), and the SA/4e are also rare.
So I decided to make some simple modifications on my Threshold SA/3.9e.

Reminder: you must not change the circuit, because you may lose the musicality that is the exceptional quality of the SA/3.9e. You should perform at least 100 hours of burn in before going into a serious listening session and achieve any conclusion.
It is also necessary to have a deep knowledge of your system, because some parameters, such as the preamp for example, have to be adapted following the 3.9e modifications.

Here is my current configuration:
  • WADIA 850 (CD)
  • JADIS JP80MC (preamp)
  • THRESHOLD SA/3.9e modified (amp)
  • APOGEE Diva (speakers)
The beginning of the mission was complex, but patience is required to implement such a modification. Here is the list of the changes:
  • The MALLORY capacitors, 31.000 µF/75V x 4 are replaced by F & T 47.000 µF/63V
  • The 470µF/100V x 4 are replaced by their ELNA equivalent
  • 4 VISHAY capacitors of 0.47µF/630V are added in // on the F & T
  • The 10% tolerance resistors are replaced by their 1% equivalent
  • The bias has been adjusted to 1.6V as required by the manufacturer (Threshold)






The total cost of these parts is around 500€.

The original Threshold SA/3.9e is the best transistors based amplifier on the market (when used with loudspeakers that are not as "impossible to drive" as the APOGEE DIVA are). No doubt, it has a incredible beautiful mid-range, a very dynamic bass, and is simply magic in the 3D positioning. It begins to be musical after 4 hours of heat.

What about the changes.

At the begining, we simply did not understand what happened, because the entire range has changed. The bass is more present, and goes deeper of half an octave, the mid-range is less present, and the high-range is so high that we do not recognize it.
But after many hours of burn in and listening, the first tunings compensate these changes. We remind that the SA/3.9e is extremely sensitive to the preamplifier and the source used. In my case, I had to work many hours before finding the perfect balance. As I own a tube preamplifier (
JADIS JP80MC), I changed the 12AX7 tubes. Therefore, on the ELECTRO HARMONIX provide a perfect balance.
The sound is extremely dynamic, with a deep bass. The mid-range is slightly less defined but has more harmony, like if it fills more the spectrum, the highs are very very clear.
The result is surprising, but also it could be predicted. I have quite a SA/6e because with 60W and 400VA + 94000µF per channel, the power supply is huge. There is a lot of energy on the entire spectrum, and, step after step, the definition comes back to its highest original level of quality.

It is clearly another dimension, which has nothing in common with the current amplifiers, even those considered as "high quality": look at their (ridiculous) power supply, and you will understand !

If you already have a good Hi-Fi gear, go ahead and get a Threshold SA/3.9e !

Article written by Florent ("provence13").


Update by Nounours:


Everything said here before by Florent remains fully true, I just add my own feedback following the listening session that we had last week in the Florent's house.

The first thing I would like to underline is that the 4 F&T capacitors are e-nor-mous ! when they are seen inside the amplifier, they look bigger than on the photo. It is clear that FIDETECH has installed the buggest possible capacitors, compatible with the available space. The mechanical work is also impressive, and obviously required, provided that you cannot simply change the capacitors "one for one": some additional holes are necessary, and achieving a hole in the bottom plate of an SA/3.9e is something mor difficult than in a piece of butter... The bottom plate of the SA/3.9e is a few mm thick, and this explain the size of the screws used for mounting the capacitors.

When we look at these big capacitors as well as the small additional VISHAY, we immediately know that the SA/3.9e power supply has received an E.P.O. treatement...

The quality of the work made by FIDETECH is outstanding. Period.

Listening sessions:

I know very well the original SA/3.9e, so the 1st surprising thing is the quality of the mid-range/highs, the second is the quality of its bass, totally beyond what the other 60W class A amplifiers can provide.

But with the Apogee DIVA, which only have a 87dB/1W/1m in terms of efficiency, and are known to be current hungry, the story is different. The SA/3.9e, even with its 32A of current capability, has sometimes some difficulties to cope with them...

But this upgraded version completely erase this feeling: the power supply is so "incredible" that the SA/3.9e becomes able to drive the Apogee DIVA with ease, like if they were bookshielf loudspeakers... It never lacks current, nor power, and the listener feels that the Diva are correctly driven.

The 28 MOTOROLA bipolar transistors per channel (yes, there is still nothing else better on the market...), each of them being able to deliver 200W..., supported by an enormous power supply (800VA with large capacitors) have the necessary current to face the most complex situations.

The high frequencies also gain a lot of additional qualities, because of the additional VISHAY capacitors, bypassing the big F & T.

The SA/3.9e overall presentation is largely modified (understand improved) by this upgrade: it becomes close from a SA/4e, one of my favorites amp.
In addition the SA/3.9e has preserved its most important quality: its exceptional mid and high frequencies domains.

Provided the "low" price of this upgrade, this is a must have, or a must do, for any SA/3.9e owner, except maybe for those using it on high efficiency loudspeakers. The final price (original SA/3.9e + upgrade) is ridiculous compared to the cost of a new comparable amplifier in terms of musicality ! We have already lessoned to some "very famous" 20k-30k$ amplifiers, that are far from the quality of this one: they have a good reputation, a lot of magazines have said that they were the 9th world marvel, but everybody will have forgotten it after 6 months...

As a conclusion, not only the upgrade approach is financially less costly, but above all, it allows to reach a level of quality that is extremely difficult to find on new products.

So think about this: less money and much more music...

Update written by

 The 1st thing I would like to point out is the 4 F & T capacitors look really enormous: when they are seen inside the SA/3.9e case, they look bigger than on the photos. It is evident that FIDETECH has implemented the biggest possible capacitors given the available space in the case. Different holes have been made in the bottom chassis plate, and mechanically, the modification does look simple at all: the bottom plate of the SA/3.9e chassis is very thick (yes Sir, this amp was not made in Taiwan with the Financial Director deciding how many % should be saved on the case boxes…). The screws used for fixing the capacitors are bigger than the ones used for fixing the 800VA transformer, and the work done by FIDETECH was clearly not simple from a mechanical point of view…


When looking at this modified THRESHOLD SA/3.9e, I thought: this amp should have a logo "E.P.O. inside" or "Amphetamines inside"…


How does it sound ?


I know very well the SA/3.9e because I have been using it for years; the first thing I said was: "waouh, it has an incredible punch !". The original SA/3.9e is extremely pleasurable, but even with its 32A of continuous current capability and 800VA transformer, it is sometimes out of the game when it has to drive the APOGEE DIVA loudspeakers. These loudspeakers do require *a lot* of current (50A recommended) and amongst the most demanding loudspeakers in the world.

With the upgraded power supply, the SA/3.9e is another contender: it becomes close to a SA/4e (one of my preferred amp) and is now able to drive them very easily. Their 87dB/1W/1m seems to no longer exist, and the SA/3.9e has an unbelievable authority.

You will no longer feel the smallest limitation with the SA/3.9e: the 28 MOTOROLA bipolar transistors (yes sir, there is still nothing better…), 14 per channel, and the 800VA transformer, have got the energy reserve (through the 4 F&T German capacitors) that was necessary to correctly feed these so much demanding loudspeakers.



Another difference with this "E.P.O. version" is the quality of the high frequencies: they seem to go higher and more easily. It is due to the small 4 VISHAY capacitors installed in // with their 4 big German sisters F&T.


Nevertheless, the SA/3.9e seems to have kept its personality in the mid range area: this point will be fully verified with our reference D/A converter in the near future, because the WADIA 850 is not as good as our reference DAC to allow us to be absolutely sure. But believe us, the SA/3.9e has made a tremendous progress: this is the reason for which I plan to upgrade my own SA/3.9e in the same way.

I even thing about upgrading my SA/6e monoblocs similarly, but the question is not so simple: the SA/6e originally have twice the power transformer capability (because they are monoblocs), the double of transistors (28 per channel instead of 28 for the both channels) and more than twice the µF capability… So, the small VISHAY capacitors are probably more necessary than additional power supply … This will be studied deeper in the future.





One more time, the importance of the power supply in a transistor amp is verified. NelsonPASS uses to say that the power supply is so important that "you cannot put too much effort on this"… By the way, the PASS LABS amps are amongst the very few amps that are still well designed and well built from this viewpoint…


Just put a "made in Taiwan/China" amp with the same announced power (Watt) on a balance and compare with a PASS LABS or a THRESHOLD amp (or any other "serious" amp): you will understand why they do not sound the same…



Another conclusion is that you be cautious, very cautious, with the amps made today by the "well known brands" that made their good reputation in the 80s: most of these brands are now driven by Financials, or have been bought by large electronics Groups usually operating on the consumer market i.e. a market where the products are cheap and where the #1 decision driver is the manufacturing cost.

Most of the time, these brands do not offer today the same quality that they did offer in the past, simply because the money is put in the Marketing and in the look, instead of in the parts or in the technical design: the name is still there, but inside the box, it is another story…

We do not give any names, but those of you having a lot of experience with this high end HiFi gear probably recognize a few of these names very easily…


The magazines, in our opinion, do not contribute to help the HiFi user: they do not emphasize on the reduction of the products quality in favour of the look or the marketing: they do depend on the advertising earnings (we can understand this), and they less and less criticize the products they review.

As a reader, it becomes more and more difficult to identify the products being really better than the mass, and it not rare to read, each month, that the product X is better than the one reviewed the month before…and the same story occurs each month ! The review are more and more simplistic with less and less detail on the technical characteristics of the parts used, as if the look and appearance were more important than the sound and the engineering design…


Be also cautious that paying 20.000 or 30.000$­­­­­­­ is not a guarantee that you get a "close to perfect" product: sometimes the Marketing has also decided that this product should cost a fortune to be seen as a good product by the reviewers or simply by the rich people interested in the HiFi gear: but what is inside the box ?

Never believe that the last fashion amp, weighting 5kg included those so beautiful coloured leds… and this so shinny front face, will sound as good as a well engineered, weighty amp, carefully made in the U.S.A or in Europe by "fanatics" paying the highest attention to the choice of the parts…


Ask yourself only 2 questions: what is in the box, and how does it sound !


Update written by Nounours.

Creation date : 18/03/2007 @ 14:13
Last update : 09/11/2014 @ 20:13
Category : Threshold
Page read 1133 times

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Reactions to this article

Reaction #4 

by MLAS 24/04/2016 @ 19:00

Why did you had to perform the mechanical work like drilling holes in the bottomplate for repalcing the four Mallory's with the FT's?
Are the Mallory's 2.5 Inch in diameter and the FT's 3.0?

The amp does not get more powerfull with changing the large can caps with a higher capacitance to my knowledge. It only makes the powersupply a bit stiffer.
You have to put in a bigger transformator and raising the railvoltages to support a higher output in Watts.

Reaction #3 

by 1953 09/01/2008 @ 21:47

Agreed that the power supply is king!  I own several Apogee speakers including the Diva.  If you liked the sound with one amp...try using two of the SA/3.9e's.  The Diva is very easy to passively bi-amp and if the preamp will put up with the even lower input impedance of the combined Thresholds, you will be in for a real treat.


Jeff Blazey

Reaction #2 

by Nounours18200 20/11/2007 @ 18:24

Hi Jonhattan,

Sorry for my late reply: I had not seen your message...

The upgraded SA/3.9e is much better than the original regarding:
-the feeling of power, provided that the upgraded capacitors have a high enough current capability. If you replace the original capacitors by low quality ones, you may not get the feeling of having more power.
-the feeling that the amp is able to drive difficult loads.

Regarding the mids and highs, it is really bad during the burn in period (more or less 300 hours), but it continuously improves and after the burn in period, it is more or less as good as the SA/4e.
The SA/4e remains better in the power handling area and is more punchy than the upgraded SA/3.9e: this is because the SA/4e has 2 transformers instead of 1 in the upgraded SA/3.9e.
As a summary, the upgraded SA/3.9e is in the middle between the original SA/3.9e and the SA/4e. The only configuration in which the original SA/3.9e may be better than both the upgraded 3.9e and the SA/4e is in a high efficiency loudspeakers configuration (such as TAD-2001/Altec), because its wonderful midrange and trebble make the difference.

Reaction #1 

by jonathan 30/08/2007 @ 21:00

I have always been a big fan of the sa/12e threshold amps but I don't want to deal with the size of them. which is why  I am interested in the amps you are working with.

Do you feel that the moded sa/3.9e is still better in the mids then the sa/4e and the sa/3.9e is still not as good as the sa/4e in the bass?

What are your thought about moding a sa/4e?

Musicality is important to me and since I have wilson watt 5.1's speakers, bass contol is important as well.

I would like to pick up either one of the amps and was wondering which one you reccomend?

Thanks for such a great site.
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