YBA 2 HC power amplifier Page 2

Naturellement, there's no output inductor to define the ultimate high-frequency rolloff with highly capacitive loads, meaning that Yves-Bernard has either designed a circuit with plenty of ultrasonic phase margin, or he just likes living dangerously. (Optional air-cored coils are available for those with problem loudspeakers; the coil is placed between the output terminal and the positive speaker lead.) Negative feedback (said to be less than 20dB) is taken from the emitter resistors' common junction—the fuse therefore doesn't appear to be in the feedback path—and fed to the non-inverting pair of the input differential pairs' bases. A small transistor glued to one of the output devices ensures efficient thermal bias tracking—the amplifier runs quite hot. The circuit's HF rolloff seems to be defined by a shunt capacitor on the input, shunting TIM-inducing signals safely to ground.

A closer look at the 2 HC reveals signs of lateral thinking. Each pair of reservoir caps is shunted by a high-power resistor to give a constant 50mA drain, said to stabilize the power supply's loading. The input caps are wedged between blocks of felt to minimize microphony. The two differential pairs and their associated resistors are damped with felt and covered with a copper-foil shield. Rather than conventional mica washers insulating the power transistors from the heatsinks, these are copper-plated and connected to the positive supply rail. The idea, explains Yves-Bernard, is to eliminate the parasitic capacitances that usually exist between the transistor collectors and the grounded heatsink. Such capacitances are highly non-linear and, he feels, contribute heavily to "transistor" sound.

The 2 HC comprises high-quality parts: the resistors look like Holcos; the circuit capacitors are polypropylene, polycarbonate, and polystyrene; and a long-crystal copper conductor developed by Yves-Bernard is used for all internal wiring. If this is over-engineering, then you can call me Alain Prost (le Professeur, en français).

Listening
I find tubes seductive. There's a recognizable "rightness" to the sound of a big tube amplifier that, once heard, is hard to forget. The Jadis JA 200 monoblocks that DO reviewed last November come to mind. I had my most recent experience with them in Jonathan Scull's room—instrumental images sounded tangibly real; the music was projected at me with robust vigor. The Audio Research Classic 150s that Jack English uses to drive his ProAc Fours had a similar effortlessly powerful presentation, while the smaller Audio Research Classic 120s have provided the most consistently enjoyable sounds in my system.

But a big tube amplifier requires more of a relationship with the hardware than I—and perhaps many other audiophiles—am prepared for. (Men aren't over-renowned for commitment anyhow.) I want the virtues of solid-state. I don't want expensive output devices that wear out as fast as I do, even if they can be replaced. I don't want an amplifier that forces me to choose between leaving it on all the time because turn-on transients with cold cathodes reduce tube life, and turning it on and off because leaving it on all the time wears out the tubes faster. I may have been brought up a Catholic, but I can't handle that much vacuum-packed guilt.

I also want foot-stomping, funky-butt, shake-a-tail-feather, solid-state lows. I want the bass line on Michael Jackson's "Billy Jean" to fall from the speaker cones, shimmy across the floor, and lift me to my dancin'-fool feet. Tubes just don't do enough of that, no matter how real they make Mr. Jackson seem as he lays into the song's "the chair is not my son" refrain. (Those who logically insist the lyric proclaims that the kid or child is not the fruit of the ex-Pepsi promoter's loins need either more system transparency or more imagination.)

The YBA 2 HC therefore faced a tough challenge. Its bass was a little soft-sounding compared with that of the expensive, fully regulated Mark Levinson No.20.6es, and lacked a little extension and weight. But hey, what doesn't? The YBA did score in its low frequencies' articulate character. Whether it was Willie Weeks's big ol' fatback Fender bass on the live Donny Hathaway album (Chad Kassem's Acoustic Sounds might still have stocks of European vinyl, if you're interested), Mark King's finger'n'thumb ultrafunk on Level 42's World Machine, or Nathan East's tight-fingered triplets in his "Old Love" solo on Eric Clapton's 24 Nights, there was not a bit of boom, no hint of overhang, no trace of treacle. I could clearly characterize every note of that famous bass on Paul Simon's "You Can Call Me Al."

COMPANY INFO
YBA
Audio Plus Services
P.O. Box 3047
Plattsburg, NY 12901
(800) 663-9352
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