Ray H
12-29-2004, 09:08 PM
Dunno 'bout y'all, but an accurate strobe disc is a very useful diagnostic for me. I've been relying on a copy of the disc lable of a Shure Audio Obstacle Course test record that I got "free" just for buying one of the company's cartridges way back when. Butt-ugly scan, but, it seemed to work. For Christmas I treated myself to a nice 10" (more or less) plastic VPI strobe disc that was to be my remaining lifetime reference. Except for one thing. It didn't reflect my turntable's (Rega Planar 3) speed as "verified" by the home-scanning of the Shure test record label. Yet, the Shure was spot on. Two established companies with reputations for "truth" and reliability in disagreement over something as basic as turntable speed? On a TT from a company whose TT speed is known to be "off" more often than not? (doesn't help that Rega's founder is somewhat of an opinionated iconoclast whose philosphy often runs counter to mainstream audiophile thinking either...) GHAHHHH! So, I was intrigued by the prospect of downloading printable image files of strobe discs to print and compare to, as well as a DOS executable to roll my own to boot from this site (http://www.enjoythemusic.com/freestuff.htm). I immediately set about downloading the 120Hz (an even multiple of 60Hz) 33 rpm PDF file and printed it out. After trimming and punching a hole, I eagerly placed the "disc" on my platter and spun 'er up. Gag me with a spoon! - it was WAY off! (somewhere around at least 1% slow if I was interpolating correctly from my still mounted VPI strobe disc - like, Children, can you say 33 rpm, perhaps?) Well, nothing to do but download the DOS program and have at rolling my own rather than rely on some stranger (Matthias Brennwald) to do the job right. The program (Strobe.exe) is run from the DOS prompt. A BMP image file is created nearly instantly which can then be loaded into your favorite graphics program and printed out. Easy, but does require consulting a chart to verify the number of "bands" according to desired reference speed and mains frequency. The chart's posted on the website. (for anyone contemplating rolling your own, the band number for 60Hz 33 1/3 rpm is 216 and for 60Hz 45 rpm, 160 The printed strobe is even worse looking than my beloved Shure scanned copy. But, surprise, Surprise, SURPRISE - it works deceptively well when rotating despite the "fuzzy" appearing bands when viewed statically. (you'll likely think your printer is dying when you see the result initially) And it agrees spot on with the copied Shure disc! I have no way of knowing whose strobe disc is really "accurate" and there may well be honest difference of opinion on the means to reference "truth" in this matter (May have something to do with "33 1/3" - there's NO exact decimal equivalent! Who was the whacko who decided on 33 1/3, anyway!?). But, at least I now have two discs (a copied Shure test disc label and a home-rolled disc from a DOS program) that not only agree with each other, but Roy Gandy's notion of rotational speed truth to boot.