McCormack DNA-225 power amplifier By Kalman Rubinson   •   November, 2000 Back in 1992, Robert Harley's Stereophile review of the McCormack DNA-1 and Parasound HCA-2200 amplifiers (April 1992, Vol.15 No.4) and the accompanying technical measurements piqued my interest. So, with great curiosity, I arranged to borrow a DNA-1 to audition, along with competitive amps from Aragon, Bryston, and PS Audio. They were all a leap ahead of my Adcom GFA-555, but it took an act of great courage to accept that, despite its less-than-stellar measured performance, the DNA-1 was my favorite. The bottom line was that the DNA-1 excelled at driving my Apogee Duettas to make lively and harmonically pure sounds. I bought my McCormack DNA-1 amplifier before I began reviewing equipment for Stereophile, and it still occupies an honored place in my system.

My choice was confirmed by the long-term popularity of the DNA-1 and its sibling, the DNA-0.5. It was a sad day when their manufacturer, the California-based McCormack Audio, née The Mod Squad, went out of business and these wonderful amps became orphans.

But there was a happy ending. A new company, McCormack Audio Corporation of Virginia, owned by Bill Conrad and Lew Johnson of Conrad-Johnson fame, is offering handsomely updated versions of the DNA-series amps as well as the new RLD-1 preamp/controller, and will service older McCormack amplifiers. Steve McCormack's SMc Audio also offers upgrades to the original DNA amps, and Steve is still the guiding spirit behind these new models, which incorporate aspects of the original designs, much of the SMc upgrades, and some new wrinkles. I quickly put in my bid for a test sample of the DNA-225.

DNA Evidence
The eponymous feature common to all DNA amps is the Distributed Node Amplifier concept, described as the distribution of the total power-supply capacitance as a series of smaller capacitors, located as close as possible to individual output transistors. This proximity permits the stored charge to be available to the active device with no intervening circuitry. Because each capacitor is, of necessity, smaller than would be a single device comprising their total storage capacity, sonically superior types can be used.

The DNA-225 and the smaller DNA-125 carry on this tradition while forgoing the original series' complex DC-servo amplifier, needed to control DC offset and drift. To accomplish this, the DC gain is reduced significantly but not all the way to zero (unity gain); to do so, says Steve McCormack, would affect the perceived bass performance. However, because of the low DC gain, static DC trim is sufficient to control offset. The low DC gain also allows McCormack to take advantage of newly available capacitors with outstanding sonic performance to complete the DC-blocking task.

The curious might consider substituting their favorite hotshot caps. The truly adventurous might experiment by eliminating the series input caps completely, although this could expose the speakers to any DC that might be passed through the amp. Either effort will change the sound and will probably violate the warranty. (Did someone say tweak?)

The DNA-225 also sports revised topology in the J-FET/MOSFET driver stage, as well as refined output-stage biasing. The former is particularly critical; this stage is designed to clip before the output stage, giving the amp a more graceful overload characteristic than it would from a misbehaving bipolar output stage. Of course, the DNA-225's high power output makes such an event unlikely. Like the original DNA, the DNA-225 is a no-nonsense amp.

The front panel has a power switch and indicator LED, the rear panel a pair of RCA input jacks and two pairs of speaker binding posts. An IEC power cord and connector and a line fuse complete the external features. In place of the retiring gray of the older series, the DNA-225 has a matte-silver front panel with a large McCormack logo above the power switch—sort of like a DNA-1 with a new suit.

The big surprise was when I flipped the power switch and got...music! Having lived so long with the DNA-1, whose DC servo mutes the output for about 10 seconds as the amp stabilizes, I was taken aback by the instant gratification afforded by the DNA-225. The manual says that there's a break-in period of 50 hours, and that optimal operation requires a 30-minute warmup thereafter, but I can't vouch for that. The amp seemed a bit hard initially, but that perception faded rapidly and didn't recur. My practice soon became to leave the amp on most of the week, give it a rest on weekends, and jump right in on my return; even the precautionary warmup wasn't really necessary.

At turn-off it was the other way around: The servos in the original DNA-1 take over immediately to mute the output; the DNA-225's output fades slowly as the power-supply caps discharge.

The Trial
Before settling in with the DNA-225, I considered another recommendation, one not mentioned in the instructions: Steve McCormack insists that a beefy aftermarket power cord is needed to get the best out of the amp.

I was skeptical, but tried the stock IEC and Audio Power PL313-6 cords that I use with my Rev.A DNA-1. The DNA-225 sounded okay with both. However, when the Harmonic Technology Pro-AC11 AC cord connected the amp to the wall, it was evident that Steve was right. I can't fathom why a 6' AC cable should so smooth and soften the tonal balance of a power amplifier, but the DNA-225 was a much better amp with the Harmonic Tech AC cord, and all of my listening comments are based on its use.