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Electronics |
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E.L.A.D. 2-Channel Line-Level Preamplifier"...as close to a "a straight wire with gain" as we are likely to get."The following text is the complete review written in The Audio Critic magazine, issue no. 27.
"This amazingly perfect little preamp, the best we have ever measured, was reviewed in depth in Issue No. 25. Meanwhile the unit has undergone some minor changes and improvements, hence this follow-up. (Of course, a mediocre preamp that has been made a little less mediocre would not call for a second look.) For those, who did not read the original review, here is a brief description of the Morrison E.L.A.D. The most important thing about it is that it's circuitry is designed around the Analog Devices AD797, a highly advanced op-amp made with a fully complementary IC process. This complex device, consisting of 60 transistors, settles to a full 16-bit resolution in under a microsecond, has a noise spec equivalent to a 50-ohm resistor from 10 Hz to 1 MHz, and achieves lower THD + N levels than any discrete audio circuit that has come our way. The preamp consists of two AD797's with associated circuitry- including separate volume controls for each channel- in one metal box and a fairly elaborate power supply in another. In early versions the preamp circuitry was potted (to keep it safe from the soldering irons of untutored tweako "modifiers"); in the current version this has been eliminated and an improved board substituted (the danger being less now that the unit has a solid high-end reputation). The gain can now be switched from 6 dB to unity by means of DIP switches on the board. In addition, an input coupling capacitor has been added, partly on the advice of David Rich in Issue No. 25. Slight cosmetic improvements complete the changes. I measured the preamp all over again to see whether the already astonishing specs have been further improved. They have. Frequency response at 1 V output is -0.05 dB at 10 Hz and -0.11 dB at 200 kHz. Between 15 Hz and 40 kHz it's +/- 0.00 dB. Channel separation at 1V output is 100 dB or better at all frequencies below 20 kHz; at most frequencies it hovers around 102 dB. Noise floor, with inputs shorted and gain at maximum, is 0.1 to 0.2 uV below 1 kHz, 0.7 uV at 20 kHz, and 2.3 uV at 200 kHz. THD +N now bottoms out at 2.3 to 2.4 V instead of 10 V, a most sensible change in view of the maximum of power amplifiers; and (get this!) the bottom is now -106 to -105 dB, except at 20 kHz, where it is a mere -102 dB. This is as close to a "a straight wire with gain" as we are likely to get. Don't for a moment misunderstand me and think that this level of performance is audible- it could be 40 dB worse and you still wouldn't hear a diffrence. It's nice to know, however, that the heart of your stereo system is utterly transparent- and at a cost of only $790, not $10,000."
- Peter Aczel
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