Counterpoint SA-4 monoblock power amplifier

Some audio products deliver truly superb sound of a kind that really makes all the frustrations of building a high-end system worthwhile; they also require exceptional attention and care. The Counterpoint SA-4 is a case in point. With the right speakers, it competes for the title of "Most Transparent Amplifier Available at Any Price." On the other hand, this amplifier steadily loses output power as speaker impedance drops; it must be carefully matched to the right speaker. Then, and only then, can it produce one of the finest musical experiences available.

Technical Description
The SA-4 eliminates both the usual output transformer and the output coupling capacitors. It is not only an OTL (output-transformerless) amplifier; it's about as close to a straight wire with tubes as anyone can get. The only problem is that there is no way to maintain power into low impedances, and the amplifier has trouble with some difficult loads (especially those with dynamic impedances below 4 ohms). In a word, amplifier-speaker interaction effects are especially unpredictable.

This form of OTL design carries the Futterman designs pioneered by New York Audio Labs one step forward. The lack of an output coupling capacitor extends bass response to less than 0.1Hz, although a second input is available which rolls the bass off at 16Hz. The drive stages use one 12AX7 as a "long-tailed" differential amplifier, and two 6FS5s as phase splitter and gain stage. Direct coupling is used throughout.

The output stages use eight heavily regulated high-current 6FL6 pentodes in a "totem pole" configuration. They normally operate in the class-AB mode, but can be biased close to class-A. This high biasing is recommended; it shortens tube life but makes the sound even sweeter. Even with such biasing you should get six months of tube life; more moderate biasing may yield as much as two years.

To avoid any risk of dumping DC voltage into the speakers, DC offset is continually monitored by a TL-082 op-amp, with a time constant of 12 seconds. In addition, the amp is monitored by an op amp-based comparator. If the offset exceeds a fixed limit, a set of relay contacts in series with the speaker terminals opens, removing the risk of damaging voltages delivered to the speakers. Signal distortion from relay contact rectification is minimized by an 8µF polypropylene capacitor in parallel with the relay contacts.

The amp is superbly built: it has a massive power transformer, epoxy circuit boards, and a modular construction allowing (in most cases) rapid repair without having to send the amp back to the manufacturer. The resistors and capacitors all seem to be very high grade, and there is a massive bank of power-supply capacitors. The Counterpoint SA-4, visually excellent, is available in black or silver: it looks like a superb piece of high-end gear.

Above all, the SA-4 has excellent protection, exhibiting the careful control of high voltages needed in an OTL design to guard against internal shorts or critical part failures. It performed with great reliability right out of the box. It can also be biased quickly from the front panel, and even the fuses are on the front panel—a design feature which should be compulsory for any large amplifier.

The Sound
Transparency is getting to be an overworked adjective, but the Counterpoint SA-4 achieves it to an extraordinary degree. Sweet and airy, yet convincingly close to the Audio Research D-250-II Servo in its ability to pass on every bit of the music and soundstage, the SA-4 provides a tremendous amount of detail and information in a musically natural way.

The SA-4 is also capable of exquisite dynamic contrasts. You hear what you pay for in the naturalness with which the softest and loudest passages are handled, and the way in which sudden dynamic changes in the music seem convincing and right.

The highs and most of the midrange, with even the most demanding voice, strings, percussions, and woodwinds, are excellent into virtually any load. The bass and lower midrange are highly speaker-dependent: they can be excellent into compatible loads, but lose all extension, dynamics, and lower midrange warmth with incompatible speakers.

Unlike the New York Audio Labs OTLs, the overall sound character of the SA-4 is not rich and romantic; it is, instead, rather extended and flat. If the NYAL amps have a touch of the 19th century above their sound character, the Counterpoint SA-4 is the perfect amplifier for the 17th and 18th centuries. Telemann, Mozart, and Bach might well have rushed down to their local high-end store to buy one had the SA-4 been available (footnote 1). (Salieri, on the other hand, bought all of his stereo systems off department-store racks.)

The soundstage is open, has convincing imaging without etching or exaggeration, and has excellent depth. Like many really good amplifiers, it opens up electrostatics and the Magnepan MG-IIIBs, and makes the music far more live. If you have blamed your electrostatic for sounding musical but a bit closed-in, try the SA-4. It not only improves the soundstage of the Quads, but of the Acoustats and Sound Labs as well. It is also excellent in this respect with such demanding cone speakers as Thiels, Vandersteen 2Cs, Syntheses, and Fuseliers.

The Counterpoint SA-4 is definitely a new contestant for Best Amplifier Around, joining the select circle of manufacturers—Audio Research, Classé, Conrad Johnson, Jadis, and Krell—who define the limits of the art. In fact, the Counterpoint SA-4 is as good an amplifier for the Quad ESLs and Magnepan IIIbs as exists anywhere.

There is no doubt, however, that the SA-4 is load-sensitive, which shows up in many subtle ways. It has virtually no damping factor, and is very definitely not for speakers that need amplifier help in providing control. It will produce 140 watts into 8 ohms and drive relatively simple 4-ohm cone speakers at 80 watts with no trouble, but there is a tremendous loss of power and dynamics, and at least some clouding of its transparency, when driving speakers at less than 4 ohms.

The SA-4 is definitely not the amplifier for complex ribbon systems that drop much below 6 ohms (such as the Apogees), or a difficult load (the EMIMs and EMITs in the high frequency and midrange panels of the Infinity RS-1Bs). Try the Counterpoint SA-20 in those cases; it's supposed to produce over 1000 watts into 2 ohms.

The practical problem in making a decision to buy is how to match the proper speaker to one of the sweetest and most transparent amplifiers ever built. The SA-4 is an amplifier you must audition with the given type and model of speaker you intend to use, and preferably in your own home. Find a dealer who knows and loves the amplifier, and let him demonstrate it.

I'd want good dealer support for a high-end amplifier of this price and class in any case, but you can't simply plug in the Counterpoint SA-4 and expect to hear it at its best. You may also need help choosing the speaker, speaker cables, preamplifier, and front end which can live up to such an amplifier. With a good partner, however, the SA-4 can be made a key part of a truly superb and musically enjoyable system.

Footnote 1: Are you kidding? They would have been making their own—or writing for high-end journals, with opportunities for "extended loan."—Larry Archibald
Counterpoint Electronic Systems
Company no longer in existence (2018)

Bogolu Haranath's picture

Atma-Sphere still makes OTL vacuum-tube amps these days ............ Any Stereophile reviewers are willing to review one of those Atma-Sphere amps? :-) .......... May be their Novacron mono-bocks?:-) ..........

volvic's picture

Fond memories of listening to these components in the 80's. Who can forget their great DAC from the mid 90's DA-10? Good times sadly gone.

Bogolu Haranath's picture

True .......... Some of the Stereophile reviewers were young and energetic in the 80's ............. Now they are old and worn out :-) ...........

Roger A Modjeski's picture

Hey, Thanks for running this review on my very first power amp design. I almost merged Music Reference with Counterpoint, but glad I didn't, for I am still here and they are not!