Threshold Stasis SA/12e power amplifier

"Tomorrow we'll go over to Larry Archibald's house and pick up the Threshold amplifiers."

It seemed like an intimidating project to me, but Danny Sandoval, Stereophile's intrepid chief of Shipping and Receiving, didn't bat an eye. But then, anyone who'd schlepped the Thiel CS-5s out to the desert in the predawn hours—to be photographed for Stereophile's June 1990 cover—wasn't likely to be defeated by a pair of measly 130-pound amplifiers.

As for me, well, I've been known to go into training at the prospect of moving loudspeakers half that weight. Still, the anticipation of reviewing a pair of monoblock amplifiers which (to my knowledge) would break the Stereophile review record for size, weight, and (not coincidentally) cost, made the effort seem tolerable. LA had been using Threshold's flagships on and off for a few weeks while I was enmeshed in other reviews. But the time had come for me to give them a listen. I'd prepared the way by building a pair of support bases (footnote 1) to elevate them off the carpet and provide proper ventilation.

Danny and I managed to move the Thresholds without major incident, despite my trepidations. Handles are provided front and rear for "easy" two-man carriage. But I recommend against trying to handle these amplifiers by yourself unless your health insurance is paid up and you can afford a long-term relationship with your chiropractor. When I mentioned all of this to J. Gordon Holt, he suggested that it was time for some enterprising manufacturer to market an "Ampli-Hoist."

The Stasis SA/12es appeared even larger when moved from LA's wide-open spaces to the more typical 15' by 20' (Stereophile) listening room that DO and I currently share. Placing them between the loudspeakers—the only practical location—made me feel as if I were in a CES exhibit. I felt like putting out brochures and brewing coffee. I had to turn the SA/12es sideways to allow room for DO to set up other amplifiers for his listening sessions, obscuring Threshold's striking front-panel cosmetics but providing easy access to the rear input and output terminals. No one ever claimed high-end audio was easy.

Aside from its sheer bulk and obvious quality construction, there's not much to say about the outside of the SA/12e. The large meters of earlier generations of Threshold amplifiers are conspicuous by their absence—but then, meters in general appear to be disappearing from high-end amps (they were never of much practical use). A massive on/off switch (which, backing up the line fuse, also acts as a circuit breaker that trips if a significant fault occurs) is the only front-panel control. On the rear are the sockets for the four power-supply rail fuses, balanced and unbalanced inputs (and a switch to disable the latter), and heavy-duty output terminals.

The latter are not five-way binding posts, but are designed to be used with spade lugs. I initially had mixed feelings about these terminals. They are, as I understand it, custom-made for Threshold and are certainly impressive-looking. But they require a wrench to fasten down tightly (I know of no nut-driver large enough). To use the wrench without obstructions requires that you do the tightening before connecting the input and power leads. And the spade lugs provided on most audiophile brands of loudspeaker cable are just not large enough to make the best use of Threshold's terminals (though they'll work well enough). But despite these disadvantages, I really appreciated these terminals when I looked at them from inside the amplifier and saw their long, solid, rear shanks and the heavy output-stage to output-terminal leads soldered onto large, metal plates firmly attached to them. Anyone who's seen the skimpy rear solder lug on the amplifier end of conventional five-way binding posts would be similarly impressed. The lugs on ordinary posts simply don't permit the attachment of internal leads comparable in size to the loudspeaker cables currently used by many audiophiles. Threshold's do.

The huge heatsinks of the SA/12e hint more than subtly at the works inside. All circuit boards are military-grade glass epoxy; the front-end boards have gold-over-nickel paths and gold plated-through holes. There are no capacitors in the signal path, making the Thresholds DC-coupled. (As with all such amplifiers, the user should insure that his or her preamp or other source does not feed DC into the amplifier (footnote 2). Outside the signal path, capacitors are film and silver mica. Resistors are metal-film and wire-wound, depending on application.

The output stage of each amplifier consists of 64 (footnote 3) transistors, each rated at 200V, 250W, and 20 amperes—with peak-rated amperage and wattage at twice those values. This represents a power-dissipation margin of about 50W of output device for each output watt. Sort of a conservative design, no? Because of this seeming "engineering overkill," neither protective circuitry (other than thermal shutdown protection for overheating, which is incorporated) nor fusing between output transistors and loudspeaker load is provided for or required. The power-supply fuses provide the only protection needed. No amplifier is unsinkable, but Threshold clearly feels that they have made the risk low enough to justify elimination of circuitry which has a reputation for degrading sound quality.

The power supply of the SA/12e consists of twin 1200VA toroidal transformers (with a short-term capability of twice that value) and 250,000µF of total filter capacitance. You can get some feeling for the sheer size of this power supply from the caution in the owner's manual to position "hum-sensitive" equipment at least 18" away to guard against possible noise generation. The quality of the supply is also indicated, perhaps surprisingly, by Threshold's 0dB dynamic-headroom rating for the amplifier. They argue that headroom specs provide a measure of the difference between an amplifier's continuous and short-term capabilities. That distinction blurs in an amplifier such as this, with its extremely rugged, stiff power supply. And in an amplifier this powerful, who's concerned about "dynamic headroom" anyway? One could argue, with some justification, that this is, again, "overkill," that music is a dynamic phenomenon in any event, and that a less "brute-force" approach is perfectly adequate. Threshold clearly is not shooting here at a target of "perfectly adequate."

Footnote 1: A fancy name for two painted sheets of ¾" plywood with feet made of eye-bolts anchored in T-nuts.

Footnote 2: If using other than a Threshold preamp, check with the maker of your preamp or other source, such as a CD player which is fed direct or via a passive preamp or attenuator.

Footnote 3: That's not a misprint. 64. As in 8 by 8.

Threshold Audio, Inc.
PO Box 41736
Houston, TX 77241
(713) 466-1411