Boulder 2050 monoblock amplifier:
Page 2 Around back are more surprises. The amps are supplied with a bright blue, industrial-looking mains connector that's keyed to the electricity in your part of the world. If you like, the 2050s can be operated on a 220V circuit. The custom-engineered speaker terminals are gold-plated and robust beyond description, and are said to offer a good, low-impedance connection. Only one input is available on the rear panel, and that's balanced XLR, pin 2 hot. Just above it sits a male XLR marked Loop Out for passing signal to a second amplifier in a passive biamp setup. And Boulder provides beautifully machined and fine-sounding adapters to allow the amplifier to be driven by an unbalanced source.

The 2050 is a direct-coupled design with a servo eliminating any DC voltage offset passed along by the preamplifier or other front-end sources. An offset of 3V or more engages a speaker-protection circuit that mutes the output. In addition, a thermal-protection circuit signals when the transistor cases reach 75 degrees C.

The amplifier is a two-stage design using one pair per channel of discrete amplifier modules called 993 gain blocks. These provide input buffering, voltage gain, and fully balanced operation. According to Boulder, the 993 modules offer a high slew rate, wide bandwidth, high output current, and low distortion and output impedance. The output stage uses 80 (!) output devices and 48 filter capacitors per chassis for a stable, high-power output into any load, even those below 1 ohm. Internal switches allow for 19 or 26dB of voltage gain, making the 2050 an easy match for any preamp, single-ended or balanced.

When I inquired about negative feedback, I hit a brick wall—or a boulder. Here's what Jeff allowed: "A hallmark of Boulder designs is the proper use of feedback. Decades ago, feedback got a bad name because designers were asking the circuit to do something it couldn't do, and the amplifier's cry of 'I can't do it!' resulted in horrible distortions. Other designers who didn't know how to solve the problem simply tried to remove the feedback, which resulted in a compromised sound. The Boulder 500AE showed the audiophile community, perhaps for the first time, that proper use of feedback results in an improved sound. Using feedback, the gain of the output stage can be reduced and its bandwidth increased. The resulting design has lower distortion than any single-stage design."

As in all Boulder products, the amplification stages use nothing but bipolar transistors. Jeff: "Bipolars are inherently more reliable and aren't prone to static-related damage. More important, the circuit topologies required for FETs are awkward, with high levels of pre-distortion required to drive the outputs. I haven't yet seen one that I liked."

Low distortion is Rule #1 at Boulder. Jeff: "We must compare two similar phenomena—musical overtones and electronic harmonics. Overtones are the notes added to a fundamental that give it a recognizable character, making an oboe sound different from a violin, for example. And these overtones follow a certain numerical sequence. Harmonics are also notes, but electronically added to a fundamental frequency. These harmonics will follow the same numerical sequence as do the overtones. An amplifier adding these harmonics can, upon first listening, be deemed musically pleasing. For a fundamental note of C, the second harmonic is the C an octave above it; and the third harmonic is the G above that. These added 'notes' are on pitch for 90% of all music, so the deception is complete. That's how triodephiles get away with it!

"The sound of electronically added notes is like putting a sugar coating on everything you eat. You lose the different tastes. The individuality of recordings is coated over, and the maximum musical enjoyment is reduced. It's simply 'too many notes.' To our way of thinking, electronic harmonics are still distortion, and we work hard to design them out. We don't tweak for the best sound, but for the elimination of distortion, which we feel is the best sound."

Sound
The Boulder 2050 monoblocks sounded huge, powerful, and commanding. Their sheer grip and control throughout the frequency range was astonishing. Transparency and speed were of the very highest order: a sense of pace and timing without peer. Imaging was crisp, highly focused, and palpable. Retrieval of detail was extraordinary. The soundstage itself was wide, deep, and layered—the big Utopias well and truly disappeared in the 2050s' encompassing electronic embrace.

As regards tonal color and harmonic development, that depended largely on which components drove the big monoblocks. The way the 2050s allowed upstream components to "speak" while themselves remaining totally neutral was almost uncanny. The YBA 6 Chassis preamplifier sounded cool and elegant, slightly removed and cerebral—as I know it to be. The Nagra PL-P was more crisp and dynamic, more rhythmic, precise, and on time than the YBA. The low-feedback, plate-loaded triodes of the B.A.T. VK-5i made a wonderful companion for the 2050s, making music that was liquid, sweet, round, palpable, and entirely engaging.