Leak Stereo 30 Plus amplifier Lab Report

Lab Report

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


Dynamic power output vs. distortion up to 1% THD into 8ohm (black trace), 4ohm (red), 2ohm (cyan) and 1ohm (green) speaker loads. Max current is 5.6A


Distortion vs. extended frequency from 20Hz-40kHz (1W/8ohm, black; 10W/8ohm, red)

Power output (<1% THD, 8/4ohm) 20W / 23W
Dynamic power (<2% THD, 8/4/2/1ohm) 27W / 37W / 43W / 31W
Output imp. (20Hz–20kHz/100kHz) 0.28–0.64ohm / 4.2ohm
Freq. resp. (20Hz–20kHz/100kHz, 0dBW) –4.3dB to –1.9dB/–23.8dB
Input sensitivity (for 0dBW/15W) 93mV / 375mV (Low Gain in)
A-wtd S/N ratio (re. 0dBW/15W) 87.7dB / 99.5dB
Distortion (20Hz-20kHz, 10W/8ohm) 0.048–0.14%
Power consumption (Idle/rated output) 19W / 65W
Dimensions (WHD) / Weight 343x122x228mm / 6.1kg