Product Review: Alternate Audio CA35 as appeared in Bound For Sound

May 1998
by Martin DeWulf

How good can this amp sound? I've been associated with audio in one form or another for the last thirty years. During that time I've heard and played with at least several hundred power amplifiers. None, not one, that I've auditioned with transistors inside has had the potential to sound as good or as bad as this one depending on the loudspeakers used.

And it's not a matter of power. The CA35 at 25 wpc is something less than a powerhouse, and it might be expected that an amp with specs like this one, would be limited in the loudspeapkers it could be used with. In this case, I have found the amplifier to be more limited than most with similar output ratings. For example, I have on hand a 25 wpc channel, class A, stereo amplifier from Monarchy. It retails for about $700. It will easily drive, and sound good doing it, loudspeakers that drove the CA35 nuts. The CA35 sounded terrible trying o drive the Gallo Reference II's. No highs, rubber bass, a bad match period. On the other hand, the Monarchy sounded fine with it. I needed a speaker that the amp liked.

Why not the Genesis APM-1? An easy to drive, extremely efficient loudspeaker capable of revealing warts and all, the Genesis seemed a likely companion for the little CA35; and seldom have I heard better. In its own way, as good as the Sunfire Signature/Gallo combo that lit a fire under my skiddle just a few weeks before. Recordings of live events were especially riveting and thrilling at the same time. Stadiums appeared at the other end of the room; fans cheered, spectators applauded, and the live sounds of a large venue came to life. Putting the APM-1 and CA35 together resulted in a sound truly hard to fault as long as the speakers weren't driven to overload the room (something the APM-1's can definitely do).

With a few weeks of audio heaven under my belt with the Genesis, I decided to try the CA35 with another easy loudspeaker to drive - the Echelon II. This speaker at 12 ohms has made many an amplifier a happy lad; it should have been good with the CA35. The results were mixed. The highs with the Echelon II were a little softer than I liked, and the bass wasn't exactly pancreas shaking. The mids were luscious though, not ultra real and accurate as they were with the APM-1, but very good nonetheless, an easy listen.

Why a sound so unpredictable? The damping factor of 80 (output impedance=0.1 ohm) isn't very high, but is high enough to control most loudspeakers. This really shouldn't be a problem. As far as I could tell, in the high-bias operational mode this amp runs almost all class A. Nothing wrong with that. So I peaked inside. Beautiful layout, a real classy job of putting things together, even nicer than the Electrocompaniet construction wise. A single-ended design to be sure from a small company, but it couldn't be nicer, even if it is a little unusual internally. One problem that I saw-couldn't we have more power supply? I lost my notes taken while looking inside, and I don't have the amp as I write this, but my memory says "little transformer, small filter section." I understand that with a design this well thought out, that Alternate probably has a reason for keeping things on the modest side, but I can't help but think that a bit more macho in the supply might tighten things up sufficiently to let the amp work with a few more loudspeakers. The amp would certainly work better into low impedance speakers if the supply contained more heft.

Two more things regarding compatibility and other components. The input impedance is a very low 18kOhms, I don't suggest the use of a tube preamp with it. Low output impedance preamps such as the BCAP from Alternate, the Diffet 5 from Audire and the Placete should be good choices. This amp worked its considerable best with power cords that I usually associate as working well with tube amplifiers, but one worked better than all the rest - the RWA. It's from Real World Audio, and it retails for $200. While the CA35 was absolutely singing in ways I can only describe as breathtaking with eyes open with the Genesis APM-1, it was fired up with the RWA power cord and nothing else. The "lightness of being" that seems to follow the RWA cord around fits absoperfectly the character of the Alternate Audio amplifier. These two worked so well together that I kept them together through almost all of my auditioning.

All other compatibility concerns aside, under optimum conditions the amp has an extremely expressive character, a character that lets the compositional heart of a creation be heard. Without a doubt, the amp tends toward the romantic and the warm. But it doesn't obliterate or mask the detail of a sound, and the highs of the amp can cut through the warmth with a sparkle. With the right speaker it has a midrange that threatens the state-o-the art, but don't ask it to do bass. As a result, it may in some systems, be the perfect amp for a person utilizing a powered subwoofer. The Genesis APM-1 has a 15" powered woofer driver on each side, and as a result, the CA35 was never called upon to supply the current and drive necessary to move a room full of air at 30 Hz. I must assume that the extreme success experienced with the APM-1 was in large part due to those powered bass drivers. To support that, I had the brief opportunity to use the amp to drive a set of satellites on top while using an M&K powered sub on the bottom. Again, superior results, though not up the level of the Genesis. I am therefore of the opinion that the CA35 is not the amp for a full range system unless its rather demanding requirements of high efficiency and benign impedance are met precisely. It is not unlike a single-ended triode in this respect. I would also match it with two-way pedestal speakers that are to be used in smallish rooms and the demand for true bass is low.

Somewhere, sometime, someone is going to put this amp with just the right speakers (Quads perhaps) and a set of powered subwoofers, and the person doing it is going to proclaim the Alternate a "perfect" power amplifier. It's good enough to do that, you just have to put it with the right company. As for me, if this amp came with more power supply, and something around 100-200 wpc with some current capabilities, it might be enough to get me to forget other amps for a while, a real long while.

- Martin DeWulf