Pre/Power Amplifiers

While Boulder remains resolutely tight-lipped about the detail of its proprietary gain stages, we were able to tease some insights from Founder, President and Chief Designer Jeff Nelson. 'Boulder's near 40-year history designing analogue circuits is based primarily on my work in pro audio. Back in the heyday of the '70s and '80s there were some very talented engineers and technicians who were dedicated to making it better, and I was fortunate to have many of them as mentors. That understanding of how an audio signal travels through electronics became, and still is, the basis of all Boulder Amplifiers' products.'

From the outset, Boulder has been committed to fully balanced circuit design. 'Certainly', says Jeff, 'starting with the signal coming into either the preamplifier or power amplifier, there is a high impedance buffer stage for each of the balanced inputs' plus and minus signals. These are matched for all parameters necessary for yielding good CMR (common mode rejection) of hum and other unwanted electrical noise.

'A following stage performs the differential function to recover the audio signal. In both the 1110 and 1160, the bandwidth of each gain stage is more than necessary to pass audio but not so high as to attract "alien" signals. These multiple stages deliver low distortion and uniform group delay in the audio band.'

Ever tempted by FETs? 'We use bipolar junction transistors for the simplified topology and improved thermal performance. Their inherent ruggedness contributes to the value of Boulder's products.' PM