Posted on: 2014-01-26 15:44:00 -0500
Our stereo included both an Adcom GFP-750, a two-channel audiophile classic, and a Denon AVD-2000, a digital-only unit, with the latter providing a stereo downmix of the Dolby Digital audio signal from our TV. Our amplifier, a Bryston 4B-ST, can switch between RCA and XLR inputs, so the Denon connected to the RCAs and the Adcom to the XLRs. The problem was that neither worked well at night-time listening levels. With the Adcom, pushing "up" on the remove control when it was too quiet would result in too high a volume and vice versa. You had to (horrors!) get up and carefully adjust the knob to hit the Goldilocks zone. The Denon wouldn't get quiet enough—the sound got fairly quiet at the lowest level of -40 dB, but the next step down muted the output.
The Adcom uses a motorized potentiometer for volume control, which seems a poor choice for precise adjustment due to mechanical engineering realities in mid-priced gear. The Denon's digital approach with discrete steps seemed an inherently better idea but didn't go low enough. Sound quality on the Denon also seemed marginal.
Cambridge Audio conveniently announced their 851E preamp at CES 2014, which looked like just the ticket. The volume went down to -90 dB, more than quiet enough, and the marketing material touted:
While the volume is controlled digitally, but the volume control is analogue. This innovative, solid state solution delivers absolutely precise and linear control and retains channel balance perfectly at low levels while ensuring the audio signal is left untouched.
Sign me up! Other handy features included an adjustable gain for each input for matching levels between components and the ability to name inputs. I called up HiDEF Lifestyle, an authorized Cambridge Audio dealer, and they said that the were expecting their first batch in a few days and could ship one my way the same day they received their shipment.
The preamp arrived less than a week later. A quick test after unpacking showed that it solved the volume control problem, with the minimum volume setting proving virtually inaudible and the 1 dB steps providing subtle changes. This preamp would match nicely even with extremely sensitive horn speakers. We watched an episode of Fringe that evening, and the dynamics and bass extension in the effects seemed improved, but I didn't think much of it at the time.
The real surprise came when spinning a variety of CDs a few days later. The texture of instrumental timbres, air around the performers, and rhythmic drive of the bass line all improved markedly over the Adcom. Standouts included the percussion in Dead Can Dance’s Children of the Sun, the sense of space in Peter Murphy’s Huuvola, and everything about Pink Martini’s Amado Mío. The level of difference was on par with upgrading loudspeakers. The Adcom was no slouch, and I wasn’t expecting an improvement in sound quality, but the 851E clearly bested it.