GoodSoundClub - Romy the Cat's Audio Site

In the Forum: Analog Playback
In the Thread: Sensible record cleaning: vinyl piranhas and record Vaseline

Post Subject: Kerf - one cause of pops and clicksPosted by oldclassics on: 1/9/2010

After expending the better part of the day sorting through the record bins at thrift stores I came home with some finds (for me). Milstein playing Mendelssohn’s e minor on Columbia’s first LP, ML4001, and the Golden Jubilee concert given by Josef Hofmann in 1937 and released on ML 4929. Both records looked very clean despite their age and lack of inner sleeve, more important, there were no visible scratches. After giving them a couple spins with a dampened diskwasher black velvet brush I was ready to play them on a Thorens TD 160 MkII powered by a Sansui AU D9 integrated and hooked up to a pair of A/D/S 620’s. The cartridge was a Grado stereo so I knew I wasn’t optimizing the mono records to their full potential, but both records sounded good with surprisingly low levels of surface noise. Yes, there are pops and clicks but not so much as to interfere with the listening experience which is after all the goal. Incidentally, I’d recommend both of these recordings highly.

Well … then… I got the idea of cleaning them with my standard washing procedure under the kitchen faucet. I turn the nozzle to spray mode so there are many small jet streams directed down into the grooves. The disk is swirled around to cover the entire playing surface. A little water on the label isn’t a problem since all the major recording companies coat their labels after printing, so they can stand up to water briefly. The small jet stream creates microscopic bubbles that then collapse when they are deep in the groove creating a cavitation effect. The point of bubble collapse is theoretically at irregular boundaries or where the surface tension gradient is highest – i.e. dirt. Cavitational forces can be very destructive but mostly on brittle surfaces and I haven’t noticed any discernable impact on the vinyl except for removal of foreign matter. After that first spray, the disk is wiped with a very mild mixture of 95% water, 4% isopropyl, 1% windex to wet the surface and lift off organic residues and fingerprints. Then another water rinse to remove the phthalates in the windex from the grooves. Hand wipe with microfiber towel and set to dry for 30 minutes.

Except that since I was anxious to hear the records again I put them on while the records were still moist. The Thorens even has a setting to adjust skating when playing records that are wetted. I couldn’t believe what happened! The surface noise had increased so much including many more pops and clicks that I couldn’t continue playing them. I thought initially that I had ruined the records, but when they had totally dried it was another matter entirely. They were again very playable, in fact I think even quieter so the cleaning did some good. In thinking about what caused the wet records to sound so bad, I remembered that one of the problems with early pressings was that there was uneven quality control resulting in flow of vinyl out of the groove into a small microridge along the groove. I think it was called kerf and I’ve seen some pictures published on the net taken at high magnification(300x) which showed these ridges. As long as these ridges remained intact they didn’t adversely impact the path of the stylus. However with age and handling these ridges would break and parts would collapse down into the groove. When they did there was a strong possibility that the needle would scrape along the wall picking up a filament of vinyl from the partially collapsed kerf. This is one of the major causes of the pops and clicks on a record that otherwise looked clean. Of course, there are all sorts of other detritus that could be on the surface of a dirty record.

What I had feared was that these old records (the Milstein one was pressed in 1947) had gotten brittle and that the cavitation had created havoc with the kerf so that playing the records again would be impossible. Since the playability improved to even better after the washing, something altogether different had happened; namely, that the surface tension exerted between stylus and the wet groove had pulled the stylus against one wall of the groove, temporarily causing the needle to rub against the wall and the microridge or any parts of it leading to the horrendous surface noise.

One of the other posters mentioned running older records through a complete cycle with an old worn-out needle with higher than recommended tracking weight. Hopefully, if the old needle isn’t damaged in some peculiar way it would tend to drag out the dirt and break off any protruding kerf leading to less surface noise. A better approach might be to rig up a trailing laser beam on the arm to burn off the kerf. Consider this an offer to license the idea to some MIT type for the mere cost of a penny a record.

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