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BL2 Input Controller: The BL2 had a very high input impedance of 1.14M ohms, a little lower than the specified 1.5M. At these high impedances, however, an accurate measurement is difficult to obtain. Output impedance was a very low 55 ohms across the band.

The BL2's gain into a 100k load was 5.93dB, fractionally under the 6dB to be expected from converting a single-ended signal into a balanced signal. DC offset levels were quite low, measuring 4.3mV (left channel) and 1.5mV (right channel). The input overload point was greater than 13V RMS.

The…

LS5 preamplifier: Fully balanced, pure vacuum-tubed line-stage preamplifier. Tube complement: six 6922 dual triodes, six 12BH7 dual triodes. Frequency response: 1Hz–100kHz ±0.5dB (–3dB points below 0.1Hz and above 250kHz). Distortion: <0.01% at 2V RMS output (typically <0.005% in midband). Gain: 30dB/12dB switchable. Input impedance: 200k ohms balanced. Output impedance: 400 ohms balanced. Maximum input level: 20V. Controls: Gain, Input Selector, Power On/Off, 30dB/12dB Gain, Monitor/Source, Mute/Operate. Noise: 40;uV RMS residual IHF weighted balanced…

I don't want to give the impression that the VT-150s sounded soft, rolled-off, overly lush, or "tubey"—they didn't. The midrange and treble magic I've…

The VT-150s drove Thiel CS3.6es—a moderately difficult load, and a loudspeaker that tends to be amplifier-sensitive. Loudspeaker cable was primarily AudioQuest Sterling. Interconnect was Expressive Technologies IC-1 or AudioQuest Lapis.

Source components included a variety of digital processors and transports, but most of the critical evaluation of the VT-150s was done with a Sonic Frontiers SFD-2 driven by Theta Data Basic or Mark Levinson No.31 transports via AES/EBU interface (the excellent Wonder Link). Interconnects between the SFD-2 and Audio Research LS5…

I measured a voltage gain of 10 (20dB) from the VT-150's 4 ohm output tap, 14 (22.9dB) from its 8 ohm tap, and 18.6 (25.4) from the 16 ohm tap. This increase in voltage gain at different output transformer taps occurs because the taps have different turns ratios (the number of turns of wire on the secondary winding in relation to the transformer primary winding). Input sensitivity (the input voltage required to drive the amplifier to clipping) was 2.4V RMS (balanced), which is ideal for the high-gain LS5. Input impedance measured a high 215k ohms across the band…

Description: Vacuum-tube monoblock power amplifier. Tube complement: two matched 6550 pairs (output), two 6550 regulators, one 12AX7 regulator, four 12BH7A driver, two 6922 input. Power output: 130W continuous into 16 ohms (24.2dBW), 20Hz–20kHz, with <1% THD (typically !x0.05% at 1W). Approximate power available at clipping: 145W at 1kHz (24.6dBW). Power bandwidth (–3dB): 12Hz–80kHz. Input sensitivity: 2.3V RMS balanced for rated output. Input impedance: 200k ohms. Hum and noise: <0.5mV RMS (98dB below rated output, IHF weighted, input shorted). Power-…

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If you've followed our coverage, you know that prime time has arrived for current-mode phono preamps. Over the last year, Stereophile has reviewed, in columns or regular reviews, The Loco ($8200) and Little Loco ($3400), both from Sutherland Engineering; the Lino C 2.0 from…