Phono Stage - The great analog tragedy

I'm whish share my journey with external phono stages and the significant improvements I've experienced.

My first external phono stage was a Croft Micro tube preamplifier with a passive RC RIAA circuit and a cathode follower preamplifier output stage, which I acquired in 2002. Later, I purchased a used EAR 834p. Despite their different RIAA designs (active and passive), both the Croft and EAR offered similar sound quality, though I slightly preferred the EAR.

My next project was inspired by Romy The Cat's "End of Life" (EOL) phonostage, which is based on the EAR 834p schematics. The EOL design features a superior power supply (with a parallel stabilizer and LCLC filter) and air RIAA capacitors, which are improvements over the original 834p. I built this into a single box unit, and it was a significant upgrade from the original 834p. Over the years, I continued to refine it with further upgrades, including a larger and better power supply, as well as improved cathode and output capacitors.

More recently, I rebuilt the EOL into a two-box system, and the resulting difference in sound quality has exceeded my expectations. 

This experience has reinforced that while the RIAA schematic is crucial, the implementation truly makes a huge difference. My current EAR 834p version sounds vastly different from the original.

While what you wrote, and what I am about to write, has absolutely nothing to do with the "topic", such as it is a topic, I will add that I too have found that upgrading the capacitors used in the RC type RIAA network makes a tremendous difference, BUT one must be certain to use exactly the same values of C as was used by the designer, else the RIAA will be inaccurate. (Even high quality capacitors are only specified to be within a few percent of the marked value; you have to measure each one individually to reproduce the curve.) This really means you need an accurate capacitance meter first to read the values used in the original, and then you need the meter to select from among the replacement capacitors, to find exact values. It's very worthwhile if you have the patience. And of course, PS upgrades almost always help if done right.

(I kind of wonder how you got away with air capacitors since I understand that they can be unstable in value due to humidity, etc.)

In my phonostage are only two small air capacitors 330pf and 110pf are important for RIAA equalization accuracy. All other - interstage, output, cathode filament PS and B+ PS capacitors values are not important in this schematics.

I setted up RIAA air capacitors with capacitor meter. But I don't take into account air humidity. Air capacitor advantage: the dielectric is not sensitive to polarity changes.

Air capacitor advantage: the dielectric is not sensitive to polarity changes.

Neither is mylar, polypropylene, polystyrene or Teflon. 

Or ceramic