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.
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.