Leben RS-30EQ phono preamplifier Measurements
Sidebar 3: Measurements
To measure the Leben, I used Stereophile's loaner Audio Precision SYS2722 system (see www.ap.com and the January 2008 "As We See It").
The RS-30EQ phono preamplifier offered a voltage gain of 37.1dB, which is very much higher than the specified 23.5dB but is appropriate for moving-magnet cartridges. The preamp preserved absolute polarity (ie, was non-inverting), and its input impedance was 46k ohms at 1kHz, this dropping slightly, to 41k ohms, at the frequency extremes. The low-frequency output impedance was ridiculously high, at 28k ohms at 20Hz, and was still an extremely high 14k ohms at 1kHz and 6k ohms at 20kHz. The RS-30EQ needs to be used with a preamp having an input impedance of at least 100k ohms. (The CS300 just about meets that need.)
Fig.1 shows the RS-30EQ's RIAA error. The channels are quite well matched, though there is a slight but broad lack of energy evident in the lower midrange. The rolloff below 20Hz is well managed, but the top-octave output is down by 4dB at 20kHz, which will soften the treble somewhat. Channel separation was good, at >70dB below 2kHz, and decreased only slightly at the top of the audioband. The wideband, unweighted signal/noise ratio, taken with the input shorted and ref. 1kHz at 5mV, was modest, at 40.3dB left and 43.9dB right, mainly due to some residual hum components. These ratios improved to 65 and 67.7dB, respectively, when A-weighted.
Fig.1 Leben RS-30EQ, RIAA error (left channel blue, right red; 0.25dB/vertical div.).
Overload margins at low and middle frequencies were excellent, at 24dB, and were still 17.6dB at 20kHz. Fig.2, taken with a 1kHz input signal at 5mV, shows that the only distortion component present is the subjectively innocuous second harmonic, at 64dB (0.06%), though the noise floor is contaminated with low-level supply-related components. High-frequency intermodulation was less good, the RIAA equalization increasing to 46dB (0.5%) the level of the second-order product with an equal mix of 19 and 20kHz tones (fig.3).
Fig.2 Leben RS-30EQ, spectrum of 1kHz sinewave, DC10kHz, at 5mV input (left channel blue, right red; linear frequency scale).
Fig.3 Leben RS-30EQ, HF intermodulation spectrum, DC24kHz, 19+20kHz at 5mV peak input (left channel blue, right red; linear frequency scale).
The Leben CS300 measures as well as can be expected from its retro design and use of a pair of EL84 tubes for its output stage. I am less impressed by the RS-30EQ phono preamplifier, mainly because of its very high output impedance.John Atkinson