Integrated Amplifiers

As discussed, even without the DAC and phono stage options, the L2i-SE has a split personality. With the tubes switched out it's a J-FET/MOSFET integrated amp that offers plenty of power, low distortion and very low noise. Switch the 300B tubes in-circuit, however, and while adding an extra 8.7dB of voltage gain (32.8dB from 24.1dB) into the preamp circuit, they also bring a wealth of, well, 'colour'. Even allowing for the increased gain, the A-wtd S/N falls from 96.5dB to 82.5dB (re. 0dBW) and while there's no significant change in response the increase in distortion is typically a thousand-fold! The Graph [inset] compares distortion vs. frequency at 10W/8ohm with the triodes in [red] and out [black] of the signal path.

Tube stages can be designed for both low noise and low distortion but VR's triode implementation is single-ended (necessarily Class A) and without compensatory feedback, so THD is very high. Remember – these tubes are in the preamp, so the distortion and noise are 'created' before the (music) signal hits the solid-state power amp. As a result, while distortion increases with power output, this is just a reflection of distortion increasing with the voltage output of the tube preamp. The ability of the power amp to 'drive' the speakers has not changed. In practice, THD is already at 1% by 1.5W, reaching 2% at 8W, 3% at 20W and 5% at 78W (all 1kHz/8ohm). PM