Tube RIAA Preamps
Several topologies & tricks
Part 1 of 2

     Yet we drive. Yet records sound quite good. And records and tubes, V&V, "valves and vinyl" as the Brits say, go together well. Some have argued that the only reason tubes were resurrected was to hide or paint over the blemishes of CDs: had CDs sounded better, we would have been happy to continue down the solid-state path to perfect sound, forever. Maybe. We'll see if SACD (or DVD-A) buries the tube or (what is my guess) it only furthers bringing the tube's virtues to the forefront.

     Not too long ago, all tube phono preamps looked (topologically) the pretty much the same. Usually they held two cascading gain stages that were often followed by a unity-gain buffer (a cathode follower), which always ended in a feedback loop that actively realized the inverse RIAA equalization curve. This is the topology found in the Audible Illusion Mini-Mite, the Berning P-1, most Conrad Johnson's early preamps, Dynaco PAS-3, Lux 3300, Marantz 7 and C-22, all of the MFA preamps, the Precision Fidelity C-4, and numerous Audio Research preamps, SP-6, etc. (One notable exception to this scheme was the Leak Point One preamp, which used one pentode-based gain stage and wrapped the equalizing feedback loop around this gain stage in a plate-follower arrangement!)

     What I find amazing is not that vinyl persists, even twenty years after the introduction of the CD ("perfect sound forever"), but rather that it ever became popular in the first place.
      Imagine that records were never made and that someone today broached the proposal that the delicate nuances of a musical performance could be reproduced by dragging a rock against a piece of plastic. Madness. If nothing else, rocks are hard and plastic is soft, so shouldn't it be plastic dragging against rock?
      Of course, the same might be said if cars did not exist and someone proposes creating one-ton steel structures that could travel over one hundred miles-per-hour, controlled by anyone over the age of 16, no matter how aged, infirmed, drunk, high, or mentally unstable who could turn a key. What if he also proposes that they be placed on tracks of road 10 feet wide, what then would keep people from crashing into each other? "Painted lines on the road," he tells us. Absolute madness.
     First, psychologists would explain that the stress resulting from the constant fear of dying from an accident would render any driver mentally crippled after only a few hours spent driving, as obviously driving a car would be a hundred times more difficult than flying an airplane because of the intimate contact with the ground. Second, complex computer simulations would show that if only one driver in a hundred were slow to react by more than a few milliseconds, the whole streaming mass of cars would collide, creating a vast sheet-metal graveyard. And last, the environmentalists would point out that 70% of all land animals would die within one year of the car's introduction.

Conventional active equalization preamp

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