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Lazarus Cascade Deluxe preamplifier Measurements
Sidebar 2: Measurements
Intrigued by Dick's description of the Lazarus preamp's phono stage as having "zippy" treble transients, I ran a low-level 1kHz squarewave through the magazine's inverse RIAA network into the Cascade Deluxe's phono input (set to 47k ohms impedance). Fig.1 shows the result at the tape output sockets: excessive leading-edge overshoot which will certainly lend an "etched" quality to the sound in the treble, as well as exaggerate the audibility of disc surface noise. Note also the slight uptilt to the plateau of the waveform, implying too much upper-bass energy. The relatively "square" shape to the 1kHz waveform, however, indicates that if the Cascade preamp does have phase problems, as postulated by Dick, they will be much lower in frequency.
To confirm these findings, I ran a conventional response curve, again measuring the output from the tape-out sockets: fig.2 shows that the entire treble hinges up both above 1kHz, where it rises by 2.7dB at 50kHz, and below, with a maximum of 1dB boost in the low bass. In practice, the phono input brightness will be ameliorated a little by the fact that the Lazarus's line input starts to roll off above 10kHz, reaching 0.6dB down at 20kHz, but the fact remains that this preamplifier has a decidedly non-flat response through its disc input, something that in my opinion just shouldn't happen in a 1989-vintage, $1200 preamplifier. As many MC cartridges already have a depressed midrange, the Cascade Deluxe will add to this tonal idiosyncracy, exaggerating the degree of cartridge-sourced coloration.
I also checked the disc-input overload margins, to make sure that added distortion wasn't exaggerating the bright sound. These were all pretty good, however, at 13.5mV, 156.3mV, and 447mV at 20Hz, 1kHz, and 20kHz respectively (all figures true RMS). As with the Conrad-Johnson PV9 also reviewed in this issue, the 20kHz figure is approximate as the sinewave could be seen to triangulateie, suffer from slew-rate limiting problemsbefore severe clipping was noticeable.John Atkinson
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