Vintage

Five years and over 40,000 Stereo 30 amplifiers later, Leak's original germanium integrated [HFN Oct '10] was replaced with the silicon transistor 'Plus' version we have here, and the uplift in performance was/is significant. Where the Stereo 30 was rated at 15W/4ohm the Plus was boosted to 15W/8ohm and 20W/4ohm, a promise exceeded to the tune of 2x20W/8ohm and 2x23W/4ohm with a little extra – 27W, 37W, 43W and 31W – under dynamic conditions into 8, 4, 2 and 1ohm loads, respectively [see Graph 1, below]. The overall gain (Low, +29.8dB and High, 42.4dB) is broadly unchanged but noise is reduced and the S/N improved from 76dB (Stereo 30) to 87.7dB (Plus). Similarly, with a full 60dB negative feedback operating across the Stereo 30 Plus, distortion is reduced by, typically, a factor of 3x down to 0.025%/1W, increasing gently to 0.04%/5W, 0.06%/10W and 0.075%/15W (all 1kHz/8ohm). Distortion increases at high treble frequencies, as expected, from 0.045%/20kHz/1W to 0.14%/20kHz/10W [see black vs. red traces, Graph 2 below].

Leak also took the opportunity to better engineer the Stereo 30's frequency response in the Plus model. A new subsonic filter was included, operating a third-order slope below 17Hz, and this resolves to ±0.0dB/35Hz, –4.3dB/20Hz and –22dB/10Hz. There's less change at the top-end of the frequency spectrum where the response rolls off above 10kHz to –1.7dB/20kHz, –12.5dB/50kHz and –24dB/100kHz. Switching-in the 'Treble Filter' brings a +1.4dB boost at 3.5kHz before the HF roll-off kicks-in at –3dB/6.5kHz down to –27dB/20kHz. Stereo separation was adequate for the tape, radio and phono sources of the day at 50dB/1kHz and just 30dB/20kHz. PM