I need help diagnosing a sibilant problem on vinyl

You can add inadequate PS filtration in the Phono Pre and the rest of the chain to the list. I have become aware of this over the last year or so. My DIY gear (all K%K Audio fully differential designs) use active constant current sources in series with the B+. A resistor shunts a small amount of that current to ground establishing the B+ voltage (V=I*R, ohms law). These active CCSs have a very high AC impedance. One would think that very little crud would get through. However, replacing the shunt resistors with active shunt regulators made for a huge difference in clarity and yes, a reduction in apparent sibilance. The first shunt regulators used a simple JFET in series with a resistor to set the reference voltage for the shunt device. A second generation shunt reg. used a LM-334 current reg. wired as a zero temperature coefficient current source cascoded with a MOSFET (cascode current sources almost always perform better than single devices). Again, more transparency and less sibilance.

Recently I upgraded an early but fully modded K&K Maxed Out SE phono pre for a friend. This unit has active constant current plate loads on all the tubes. One might think that adding a current source fed active shunt to the B+ supply would not make a huge difference. It did, by a large amount.

I guess the take home here is this: no matter how much filtering you have in your power supplies, crud can get though and muck up the signal. I'm not a big fan AC power line filters as I think this should be addressed in the design of the equipment itself; but if all else fails you might try it. I would suggest you borrow the clean up filter first and try before any purchase.

David256, the " high frequency spike" when a MM cart. "plays through a defect" is not inherent to the cartridge. It's the result of improper loading. Typical MM carts have a rather high inductance compared to the usual MCs. This makes them much more sensitive to the amount of shunt capacitance loading them. Too much results in an electrical resonance at the high end of the audible range. Any defect in the record that causes an ultrasonic pulse will excite this resonance and cause it to ring, resulting in a "high frequency spike". Please refer to Jim Hagerman's white paper on cartridge loading for more information on this subject.

IMO, excessive sibilance is a different animal than high frequency ringing. My experience has been that distortion in the payback chain can cause issues with excess sibilance and all the monkeying with cartridge set-up in the world won't cure it if the problem lies elsewhere. That's not to say that a badly set-up cartridge won't cause problems, it will. But it's not the end all, be all, cause of the problem. In my experience distortion is the problem. Whether it's caused by the stylus profile (think elliptical and inner grooves), improper set-up (imperfect azimuth leads to excessive IM distortion for example) or lack of transparency in the playback chain of electronics. Every link in the chain has to be addressed or the problem will persist.