McCormack Power Drive DNA-1 power amplifier SMc modifications for the DNA-1

Kalman Rubinson wrote about the SMc modifications for the DNA-1 in November 2000 (Vol.23 No.11):

As a public devotee of the DNA-1, I have been besieged with e-mail from dedicated McCormack fans asking about Steve McCormack's SMc Audio modifications to the original DNA-1, DNA-0.5, and DNA HT-1 amplifiers (footnote 1). But, being a seasoned but reforming tweaker, I take a dim view of most aftermarket modifications. Sure, most of them will make a difference; but lacking a reference or A/B comparison, how can you know the difference is a positive one? In this case, the original designer himself says so; moreover, I had an original DNA-1 and a new DNA-225 on hand to compare to my SMc-modified DNA-1.

The basic Rev.C DNA-1 mod ($375), the essential core of all the mods, eliminates the DC servo by reducing the DC gain to near zero so that a simple offset trim keeps the amp from welding your woofer's voice-coils into solid metal. Along with some other improvements, this is similar to the DNA-225's topology, except that SMc does not use DC blocking caps in the signal path. The Rev.B mod ($450-$700) adds Cardas binding posts, Kimber RCA jacks, Cardas board-to-board wiring, and heavy-gauge van den Hul output wiring. Because Rev.B also includes an upgrading of signal-path components similar to that in McCormack Audio's well-received Deluxe Edition amplifiers, the cost of Rev.B (and Rev.A) is lower for Deluxe Edition amps than for the plain-vanilla ones.

Rev.A ($850-$1200) is, as SMc calls it, "the Full Monty!" Every single part affecting the signal, including output-stage caps and emitter resistors, is replaced with what he feels to be the best available, resulting in a complete rebuild of the amp. My DNA-1 is a Rev.A with a plus: switched balanced XLR inputs via studio-quality Jensen transformers (a $450 add-on).

Run from the Sonic Frontiers Line 3 via a balanced JPS Super-Conductor 2 interconnect, my Rev.A+ amp seemed noticeably quieter, less ripe in the midbass, and decidedly smoother in the HF than the original DNA-1 via single-conductor Cardas Cross. Fair comparison? Of course not, but the Rev.A+ DNA-1 was still superior with the Cardas cable, although the balanced connection made the distinction clearer. Compared to the SF Power 3, the Rev.A+ DNA-1 had a bit more bounce and dynamics but lacked the tube amp's achingly delicate detail and tonal integrity. That said, I switch between them for many reasons and never feel deprived.

This raises the obvious question of whether the current owner of a DNA amp should go for the mod or trade up to a DNA-225. The DNA-225 already includes much of the Rev.C mod (and more). The new amp has greater power, much more than is suggested by comparing the quoted numbers, and the DC blocking caps make it bulletproof. In addition, the new amp comes with a three-year warranty. As for sound, it's a toss-up; the Rev.A+ DNA-1 mated well with the Revel Ultima Studio loudspeaker, while the DNA-225 made a happier union with the Kharma Ceramique.

If you own a DNA-1 and wish it were smoother and less assertive, you should go, at the minimum, with the Rev.C mod, which frees you from the DC servo. But whether that buys you enough to trump the DNA-225, I can't say. I'll be keeping my Rev.A+ after the DNA-225 goes back—the Rev.A's balance is more appropriate for my system and room, and besides...I already own it! On the other hand, if you want to keep the DNA-1's irrepressible vitality but want more power and resolution, sell it and get a DNA-225. The resale price of a DNA-1 will get you nearly halfway.

But is a used DNA-1 plus mod a better deal than a new DNA-225 for someone just building a new system? Even my full-bore Rev.A+ isn't better than the DNA-225; it's just different. Unless there's some basic incompatibility with your intended setup, go with the DNA-225. It's a great amp right out of the box.—Kalman Rubinson

Footnote 1: SMc Audio, 929 El Pajoda Place, Vista, CA 92084. Tel: (760) 732-0352. Fax: (760) 732-3209. E-mail: