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Threshold - SA/3.9e


Edit, 14th october 2007: this review of the original THRESHOLD SA/3.9e has been followed by an article on its upgrade and optimization, which can be found here
. We recommand you to read the upgrade and optimization article only after having read the following review.


The THRESHOLD SA 3.9e amplifier was built from 1990 to 1994. It was a commercial success in the USA, but it remained confidential in Europe (particularly in France) because of a too high price due to the French importer.



The THRESHOLD SA-3.9e, front view.


Therefore, it is extremely difficult to find in Europe, whereas it is easy in the States: there is only 1 piece presented for sale on the European forums every 3 years...(average).

It is a 2 x 60 W amplifier in pure class A operation, designed by Nelson PASS who founded
PASS LABORATORIES when THRESHOLD went to bankrupt and then moved its production to the professional amplifiers, too far away from the Nelson PASS interests and passion.
The SA 3.9e is considered by Nelson PASS as being the best THRESHOLD amplifier (I read that a few years ago in a U.S. forum), regardless price or output power. The Threshold appearance was styled by Rene BESNE.
As all the THRESHOLD amps made during this period, it is as robust as a military tank, and most of them are still in use.



The THRESHOLD SA-3.9e, back view.

There is almost no maintenance, only the 2 power supply capacitors may require to be changed after 15 years, but our 2 SA 3.9e (with their original P.S. capacitors) are as good as their 1st day,...17 years after ! There is no capacitors at all in the signal path.


The THRESHOLD SA-3.9e, top view.


You can get a review (in French for the time being) in the download area. The only English review I found is a Stereophile review that relates to the SA-3, (which is not as good as the SA-3.9e, by a large margin, in my opinion); If some of you as an English review of the SA-3.9e, please send it to me, and I will put it online (Thanks).

This amplifier has an excellent musicality, and is able to drive the very demanding speakers such as the THIEL or the APOGEE DIVA with ease ans an exceptional sense of rythm.

For me, these exceptional qualities are typical of the Nelson PASS designs: there is no doubt that the THRESHOLD SA series and the current PASS LABS amplifiers have the same father... In addition, I have found that THRESHOLD SA-3.9e and the THRESHOLD SA-6e monoblocks have the same "signature". I mean that they are both extremely musical, they have a "velvet" side, a lot of elegance and refinement.... (but of course, in terms of power and bass authority, the SA-6e do not play in the same category).

The SA/3.9e is equipped with 28 bipolar transistors (14 per channel), referenced MJ-15011 and MJ-15012, rated 10 A / 250V / 200 Watt for each of them...


Systems used for the review:

System 1: CD source: COUNTERPOINT DA-11 + COUNTERPOINT DA-10 new version (look at the complete review on this site), Preamp THRESHOLD T2, Speakers THIEL CS-2, modulation cable by SIGNAL CABLE Silver Reference XLR Neutrik, speaker cable MIT T2.

System 2: CD source: idem system 1 + WADIA 850, Preamp JADIS JP 80 MC, Amplifiers JADIS JA 80, speakers APOGEE DIVAs (new ribbons), modulation cable by SILTECH 4-80S silver, speaker cable by SILTECH LS2-090.



How to get the best from your Threshold SA-3.9e:

1-.The choice of the preamplifier is of the highest importance: a 3.9e will not be musical if the preamplifier is not at the same level of quality than it, I mean "state of the art". So, avoid to link the 3.9e directly to the variable output of CD (worst case) or to a "just good" preamp...

2-.After having tested many preamps, the quality of the SA 3.9e is so high that it will transmit any difference related to the preamp or to the source: any improvement will go throughout the speakers.

3-.The best results we have got have always been obtained with solid state preamp (no tube), maybe (?) because the input impedance of the SA 3.9e is a bit low (?):

3-a-.the association with the THRESHOLD T2 amplifier is extremely good: no grain at all, wonderful bass and sense of slam, a lot of elegance in the sound reproduction with the feeling of an excellent signal/noise ratio.

3-b-.the association with the Audio-Research SP6-B is not that good: it does not transmit enough details to the SA 3.9e and does not reach the same level than the T2 by a very large margin.

3-c-.the association with a PERREAUX SM3A provides better results than with the ARC SP6B: more detail particularly on the complex signals. But not as good as the T2 or the JADIS JP80 which has proven to be also an excellent preamp with the SA-3.9e.

3-d-.the "cheap" preamps such as NAD or ROTEL should be avoided: they are not good enough for the task...

3-e-.The JADIS JP80 is currently under evaluation: it seems that the results strongly depends on what tubes are used. A coming test with our "reference source" will be performed shortly in order to have a better viewpoint on this association.
Update: the Jadis JP80 has been deeply auditioned with the SA-3.9e, in combination with an excellent source and with a totally renewed pair of APOGEE DIVA speakers. There is no doubt that the JP80 does an excellent work in association with the 3.9e. The musicality is "state of the art", extremely refined and a lot of elegance. Of course, the 3.9e is not powerful enough for the DIVAs, but it never becomes agressive and never loses its musicality ! the DIVA just need more power, but the final result clearly shows that the JP80/SA-3.9e is an excellent combination.


4-.The 3.9e is not sensible on the type of connection (RCA vs XLR): it performs extremely well in the both configurations as long as the quality of the source and preamp is at the correct (i.e. best) level.
After al ot of tests, we believe that Silver based cables are the best. We also believe that the XLR connection is (maybe) a little better, going a litle further is the rightness, but by a very small margin.

5-.The 3.9e is very sensitive to the AC power cable: you can improve it even further by changing the AC cable with a better one. The following tips are useful, *but not recommanded as they can be dangerous*, so it is your own responsibility if you test them: not connect the 3.9e to the Ground: this will increase the clarity of the signal, but this is a risky option, so it is only under your own responsibility.

5-b-.replace the original AC power cable by a bigger (AWG 12, Teflon insulation is recommended) and better one.

5-c-.if your 3.9e comes from a country using different AC plugs, then replace the AC plug with the appropriate one: do not use an adaptor because it significantly decreases the musicality of the amplifier.


6-.The 3.9e is very sensitive to the support on which it resides on: use granit (3 cm of heigh), with 3 metal cones, one of them being under the power transformer. You MUST avoid to put the 3.9e on a carpet at ground: this is the worst basement for a THRESHOLD, which absolutely needs a solid and heavy basement.

7-.Turn it on, wait 1 hour, play an entire CD, let it in peace 45mn, and ... ENJOY ! it will reach its best after 4 hours.


The THRESHOLD SA/3.9e is an exceptional amplifier with most of speakers; it has an extremely refined sound: there are only a few amplifiers in the world having so many qualities in terms of musical reproduction and coherence:


Warning: the previous version, named SA/3, do not reach the same level of excellence...

Article written by Nounours ("Nounours18200" on the Forum).

Creation date : 01/06/2009 @ 11:58
Last update : 09/11/2014 @ 20:02
Category : Threshold
Page read 1665 times

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