Variability of RIAA eq with tube characteristics?

[leadbelly]

OK, I think I answered my own question, I found an online passive eq calculator, punched in the numbers from the eBay schematic, and they were pretty close. So it looks like the position of the blocking cap does not make a difference.

 

[Sheldon]

Geez, that's a problem. What my plan actually is, is to build a preamp with cheap PCB's I got on eBay. The schematic for those PCB's is the upper half of the file I attached. I am thinking I would like to build it as a hybrid, with a JFET replacing the first triode stage, a Russian 6922 for the 2nd stage, and a Russian 6N6P for the CF. So the blocking cap needs to be before the RIAA section.

You can do it as shown in your schematic, but you have to have a large enough value so that its reactance, compared to the following resistor, is small at 50Hz. The one advantage of having it before the RIAA compensation, is that you can then use low voltage RIAA caps. You will have to recompute r108 either way, to account for the change in Rp of the 6922, as compare to the x7.

Sheldon