LCR phono stages we know about

Lewm --

Sorry I missed your post from last week. The 'Kahn' in Kahn phono stage refers to the metalworker who implemented the design of the box -- very steampunk!

As to the performance...spectacular. I have experimented with tube rolling and am very pleased with where things ended up. These pieces (phono and line stages) are very special, bespoke pieces. And yes, Dave Slagle's handiwork is integral to the implementation. The EMIA product offers a large measure of the Kahn for much less money.

Best part: both Jeffrey and Dave are first class music geeks who are extremely fun to work with.

Jazdoc, Now that we know the Emia is not an LCR type, do you know anything more about the topology of the RIAA that you could reveal without violating any confidentiality agreement with the two designers? I am still wondering how they effect direct coupling and whether the accuracy of the RIAA equalization would be affected as the gain stage tube ages, and its output Z drifts accordingly. I think Hiho said it first; the virtue of the high value resistor at the output of the gain stage in typical RC RIAA networks is that it ameliorates the negative effect of tube aging. No matter; the Emia sounds excellent in the home of my neighbor, and he is thrilled with it.

I thought more about the Allen Wright RTP. As Hiho mentioned, the RIAA equalization depends upon the constancy of the input impedance of that 50K attenuator seen in the schematic. But at the same time, the signal must pass through a 2.2uF capacitor between the plate of the gain stage and the input of the attenuator. Those are at least minor drawbacks. My MP1 has a second gain stage downstream from the dual-differential cascode input stage. THAT second gain stage then drives the attenuator, thus isolating RIAA equalization from the attenuator. However, there's no free lunch; you still need a largish coupling capacitor between the output of the second gain stage and the attenuator. I use a smaller value capacitor (0.68uF) and an attenuator with a higher input Z, 100K ohms, to achieve roughly the same low frequency cut-off.

Wise statement Lewm. I think the same but can't break my addiction. Oh well.

Lewm --

I certainly do not have the technical background to comment intelligently on your question...all I know is it sounds good! :-)

If you load the input stage cascode with an active current source you can effectively achieve an infinite output impedance. This allows you switch the RIAA series resistor from a series connection to a shunt connection. No issue with RIAA response changing as the tube ages. The excess current from the plate load CCS is shunted across this resistor to ground and sets the plate voltage. Neat trick. To maintain the set plate voltage the cascode pair needs to be biased with a cathode/source (tube or tube/SS hybrid cascode) CCS.