Company Address: 7325 Roseville Rd., Sacramento, Cal. 95842.
The Threshold SA/4e is the kind of product that makes me feel sorry for those audiophiles who believe that all amplifiers sound alike, or that they can be chosen solely on the basis of measurement or through the results of a survey. This is the kind of product, like a fine wine, that deserves to be celebrated for its differences. In saying this, I don't mean that the Threshold SA/4e is necessarily better than other top high-end amplifiers; virtually all top manufacturers and top designers have now reached the point where the issue is never one of overall quality or dramatic differences in sound quality but rather the particular mix of sonic qualities presented in a given product.
This makes choosing between top-of-the-line amplifiers from firms including Audio Research, Cello, Classe Audio, conrad-johnson, Counterpoint, Krell, Mark Levinson, Jeff Rowland Design Group, Spectral Audio, Threshold, and VTL increasingly a matter of taste.
You also have to blend an amp into a given system and listening environment, and tune your system to get the maximum possible synergy. The sport of audio no longer consists of deciding which product is best (if it ever did). It consists of combining affordable equipment to reach the best possible level of audio reproduction.
The Threshold SA/4e provides a unique blend of top- to bottom-octave power, extraordinary detail, and the ability to provide the full range of dynamic contrasts in music without be coming exaggerated or unrealistic. It also offers remarkable compatibility with a very wide range of speakers and preamps. Unlike some otherwise excellent high-end amplifiers, it can cope with very complex speaker systems without losing its quality or distinctive personality.
Some of these performance characteristics almost certainly owe some thing to the dollars lavished on it. The SA/4e is a $6,300 amplifier. It does not provide the no-holds-barred performance of the Threshold SA/12e, which costs about $900 more, but even a casual look at its construction reveals that cost has not been a significant limit in its design. In fact, you get a pretty good idea of its quality the first time you lift it. The amplifier weighs 97 pounds and measures 19 inches wide, 83/4 inches high, and 23 3/4 inches deep.
Once you open up the SA/4e, you find a pair of 800-watt toroidal transformers, 186,000 uF of power-supply capacitance, top-quality resistors and capacitors, and 28 transistors per channel, each of which is a 250-watt, 200-V, 20-ampere device. The wiring, heat-sinks, and panels have the same "feel" of quality, and there are a number of special touches; for example, it has the first set of binding posts I have seen that can really clamp a speaker cable lead to the amplifier without any fear of a poor contact. Also, its balanced and unbalanced connectors are exceptionally easy to use.
I make no claim to be able to assess the sonic impact of a given circuit topology. In fact, I am continuously amazed at the differences in sound that similar circuit topologies produce and how similar even amplifiers operating in Class A and Class AB can sound. There can be no doubt, how ever, that the circuitry of this Threshold uses a number of sophisticated proprietary design features. The front-end of the Threshold SA/4e employs FETs in a noninverting, complementary-symmetry, d.c.-coupled design. It employs dual optical bias technology to control the current flow within the amplifier and to keep the gain devices at an optimum operating state under a wide range of conditions. Optical coupling is used to achieve outstanding isolation from internal interactions, and the bias circuitry is intended to keep the gain devices at an exceptionally uniform operating temperature.
The pure Class-A output stages do not have an overall feedback loop and include the latest refinement of the Stasis circuit that Threshold has used for many years. It operates both the voltage and current sections in pure Class A, and the term "Stasis" refers to the use of a binary topology in which the voltage amplifier, operating without with a high-amperage voltage mirror, with out voltage change. The 28 output de vices provide an exceptional amount of power reserves, and the large twin 800-watt toroidal power transformers and high power-supply capacitance provide exceptional current-dissipation reserves.
Like the technical specifications of virtually all top amplifiers, those of the Threshold SA/4e say relatively little about its distinctive sonic performance. However, few products in this price range are rated as having such high current capability. Output current capability is 35 amperes continuous and 120 amperes peak. The SA/4e is rated at 100 watts per channel in pure Class A with less than 0.15% distortion into 8 ohms of resistive or reactive impedance. Bandwidth is flat from d.c. to -3 dB at 100 kHz. Slew rate is 50 V/µS.
Noise is rated at -100 dB, and the gain factor is + 26.6 dB. The input impedance is 600 ohms balanced or 50 kilohms unbalanced, and the output impedance is less than 0.1 ohm from 20 Hz to 20 kHz.
I am not immune to technical glitz, but it is the taste of the wine that counts, not how well it was made or how attractively it was bottled and labeled. Similarly, the key test of an amplifier is its ability to provide every possible nuance of a given performance in a musically convincing manner.
Whereas you might not insist that a wine taste equally good with every course of every meal, a great amplifier should provide outstanding and consistent performance with every possible speaker and system. The Thresh old SA/4e passes this test in every way I can think of. Further, it does so regardless of whether it is operating in a simple two-channel system, in a complex multi-amped system, in the balanced or unbalanced mode, or with a tube or transistor preamplifier.
I used the Threshold with very low-impedance ribbons, complex electro static speakers, complex hybrid cone and planar systems, and troublesome mini-monitor loads. I used it with tube preamps that irk some other high-end transistor amps and with a wide range of interconnects and speaker cables. I cannot say that it will perform equally well in every possible system, but I can say that it provided excellent performance with a representative range of the most demanding loads any audiophile is likely to encounter.
As for its unique sound characteristics, the Threshold SA/4e is striking for its extended apparent bandwidth. It does not favor any particular part of the frequency range or appear to emphasize any group of instruments over any other. While some high-end amplifiers seem to try to optimize performance in the midrange, this Threshold amplifier provides very transparent midrange performance along with very extended bass and treble. It also did not change in apparent spectral balance at very low listening levels or at sonic peaks.
A number of otherwise good amplifiers seem to lose part of their transparency and neutrality with very soft pas sages, or when you need to hear a great deal of low-level musical detail.
Others lose deep bass energy, mid range and treble sweetness, or resolving capability when they are asked to deliver high power levels, and this appears to alter their spectral balance.
This unit did not exhibit any of these inadequacies. It provided the same open sound and extended treble and bass at every level and at any reason able power level and provided far cleaner high-powered dynamics than I am used to hearing with mid-fi amplifiers rated at well over 200 watts per channel.
The SA/4e delivers strong deep bass by any standard. When really deep bass is present, and the speakers can reproduce it, the SA/4e can provide visceral power. This is not, however, an amplifier that seems to extend the bass of virtually all music.
The bass power is only delivered when it is really in the music, and it is very controlled and accurate. There is exceptional resolution of detail and minor frequency differences in the deep bass.
The mid-bass to lower midrange transition is smooth and open. There is no touch of discontinuity and no added warmth. This amp is, however, clearly a transistor design. There is none of the upper bass warmth that some tube amplifiers add to the sound. The Threshold SA/4e is the kind of amp you want to use with a speaker system good enough not to need help in this area, although I should note that the SA/4e provides exceptional control of several speakers whose loads often cause problems in this region with other amplifiers.
The midrange is very neutral and detailed. I could not detect any exaggeration of voice or instruments, and the resolving power of the SA/4e was excellent. Midrange dynamics were very natural. The extended bass and treble does, however, mean the mid range has less focus and apparent impact than with some competing amplifiers. Again, this amp will work best with very neutral and transparent speakers that also have extended bass and treble.
The upper octaves of the SA/4e are exceptionally detailed, extended, and open. With good source material, there is no trace of inherent harshness at any power level-even with very complex musical dynamics. But this Threshold is not a forgiving amplifier. If the recorded material has too much treble energy, or problems in the upper mid range, the SA/4e will reproduce these flaws with great accuracy.
This kind of upper octave performance requires careful attention in choosing a cartridge, adjusting VTA, and selecting a CD player. Quite frankly, it would be foolish to use this amplifier with inferior associated components or to assume that the Threshold SA/4e will fail to reveal any problems in a poor recording. I also would advise the use of a speaker with a very ex tended, fast, and detailed upper octave response. Amplifiers with this kind of performance capability can some times be a bit merciless in revealing the problems in a bad tweeter or a speaker that provides extended treble without providing extended bass.
The musical dynamics of the SA/4e are truly exceptional. They combine excellent power and control at every music level and do so throughout the full range of audible frequencies. Musical contrasts are very natural, and there is no exaggeration or surprise. At the same time, the kind of musical dynamics that are stunning in a live performance, whether symphonic or rock, come through in a way very few of even the best high-end amplifiers can match. I don't spend much time listening to sonic spectaculars, but this is an amplifier that gives them real life. More importantly, when you hear a sudden powerful drum shot, or bowing sound from the bass viol, this amp delivers the dynamics you should really hear.
I have stressed the resolving capability of this amplifier so often that I risk repeating myself, but it is remarkably transparent without losing musicality or exaggerating any special aspect of the music. There is no etching of the treble, and there are no surprises in terms of added musical detail where such detail does not seem natural. Once again, however, the extended deep bass and treble mean that there is no special focus on the midrange and no forgiveness of problems in the source material or associated components.
The SA/4e provides a neutral soundstage, which is very wide and just a touch recessed. The sound is dynamic but not forward. There is very good depth, but it is not the kind of extended depth that is provided by some competing products.
Imaging is excellent. It combines outstanding detail with outstanding stability and does so without any apparent tendency towards a hole in the middle, a lack of left-to-right extension, or a lack of depth. Some competing amplifiers do a somewhat better job o' resolving the layers of depth you can hear from the very best recordings, but this Threshold still provides very good imaging in this respect. I found it to cope better with the imaging in complex percussion than virtually any other amplifier I have heard.
As I have mentioned, the Threshold is likely to provide outstanding and predictable performance in a wide range of systems. This also makes it unusually easy to audition. What you hear in a really good dealer setup is very likely to be what you hear at home. The SA/4e does require extended break-in with music to deliver its best performance. I would allow sever al days after taking a new unit out of its box. It also benefits from several hours' warm up, even after it is broken in, although it provides 90% of its best sound after 20 minutes of warm-up.
I also have noted that it is a bit silly to use an amplifier this revealing with poor associated components or a speaker whose overall balance emphasizes either the treble or bass, or one that does not provide extended deep bass and treble. At the risk of revealing my prejudices that cables really do sound radically different, I also would strongly suggest the use of interconnects with a flat and neutral sound rather than the kind of cables that try to add something to the music.
Speaker cables should have the same sound characteristics and be able to handle truly powerful bass.
As I have said from the start, the best high-end amplifiers have evolved to the point where attempts to rank them are largely meaningless. High-end designers and manufacturers have reached the point where the choice of a given amplifier has to be made on the basis of extended listening and personal taste. The special advantages of the Threshold SA/4e are its excellent dynamics, extended bass and treble, transparency, and ability to resolve musical contrasts. Its limitations lie only in its reproduction of depth and lack of emphasis on the richness of the lower midrange and upper bass.
All in all, the Threshold SA/4e is a "reviewer's amplifier" in the sense that it is extraordinarily compatible and revealing without losing any aspect of musicality. If you are serious about trying to build a great high-end system, or if you just want to hear how much better one of the best available high-end amplifiers can sound, this is a product that I would strongly recommend you audition.
-Anthony H. Cordesman
(Source: Audio magazine, Jan. 1991)
Threshold Stasis 3 Power Amplifier (Dec. 1980)
Yamaha M-70 Power Amplifier (Jan. 1984)
McIntosh Model C-27 Stereo Preamplifier (Sept. 1978)
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