Leak Stereo 30 Plus amplifier

摘要

It's not unusual for a successful hi-fi product to be updated with mild revisions during its lifetime. Often the changes are minimal: a tidied-up fascia to match a new model added elsewhere in the range, or an extra function or minor circuit redesign. This was certainly not the case with the Leak Stereo 30 Plus amplifier of 1969, which replaced the Stereo 30 [HFN Oct '10] first seen in 1963. Side by side the two looked much the same, but inside the 30 Plus was all new in order to take advantage of improved technology. The Stereo 30 was Leak's first transistor amplifier. The number '30' equated to the sum of the outputs of both channels when measured under the most favourable conditions. Two lots of 15W easily trumped the outgoing Stereo 20 valve model, even before the improvements in reliability and performance due to the elimination of the output transformer (both key claims by Leak at the time) were taken into account. The Stereo 30 used germanium transistors because that was all that was available at the time. They worked but were noisy and prone to thermal runaway, making it a challenge to design practical hi-fi amplifier circuits using them. Nevertheless, the Stereo 30 was well regarded and sold successfully until the appearance of silicon transistors in the middle of the decade signalled a step change in amplifier performance. Quieter and more stable, silicon made it possible to build high-gain, high-power circuits with relative ease. The Stereo 30 Plus was essentially the original concept built around a complete lineup of silicon devices. It was the same, only better.