max@trinity.uucp (Max Hauser) (04/18/88)
In article <4301@batcomputer.tn.cornell.edu> rtaylor@tcgould.tn.cornell.edu (Russ Taylor) writes: >Hi - I was wondering if people could give me recommendations as to >what the best op-amp to use for preamp and active-crossover applications >is. ... Not to be overlooked in this quest are the venerable K2-W series from George A. Philbrick Researches (later Philbrick-Nexus, later Teledyne Philbrick, now I-don't-know). Besides decent specs (open-loop gain 50,000; output swing +- 50 volts; slew rate, if memory serves, 20 V/us), they also use vacuum tubes and for that reason alone should be of special interest to rec.audio readers (each has a pair of selected 12A?7-series dual triodes in a remarkably 741-like topology with a differential pair, bootstrapped common-cathode-common-plate gain/buffer stage, minor-loop compensation, and +-300V power supply). DC stability is poor without optional chopper module but hey, you don't need DC in a preamp. I can't speak for noise: thermionic cathode hath its liabilities. Note that the later members of the family are available in several configurations, such as the SK2 series in all-metal ventilated cases, besides the original K2 octal-plugin package. I am surprised not to have heard mention of these devices earlier on rec.audio, killing as they do two birds with one stone, and also allowing one virtually to have one's cake and eat it too. As one who has designed a few integrated-circuit op amps and dozens of discrete versions, I cannot but admire the K2-W. It is not, of course, the only vacuum-tube op amp; but it was the first mass-marketed op amp in history, and produced in the greatest number. Max Hauser / max@eros.berkeley.edu / ...{!decvax}!ucbvax!eros!max