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RE: OT comment on Silvaweld phono stage

First, I sort of disconnected the high-gain FET-based input section, because I only wanted it for MM and MI cartridges. So the input goes right to the grid of the first tube. In the 550, he used two SRPP topologies, one at the input that adds gain for the RIAA, based on the two halves of a 12AY7/6072. I did not want to change that topology at the input, because it would change the output impedance of that gain stage and I would have had to re-design the RIAA network, which is above my job description. This first SRPP had a resistor from cathode to ground bypassed by an electrolytic. I removed both parts and replaced them with a pair of Schottky diodes in series, ground to cathode. This biases that tube at about -1.7V. Then I changed the topology of the second SRPP so it is now a plate-loaded common cathode stage. (In other words, I take the output off the plate of the lower tube, instead of the cathode of the upper tube.) Here too, I replaced the cathode resistor and bypass cap with a Schottky. The change from SRPP to plate-loaded gives a higher output impedance but it sounds better. Since this stage feeds a CF, it is no problem to raise its output Z a bit. Thus the plate of the lower tube is now direct coupled to the CF output stage. There I disconnected the feedback loop between the cathode of the CF and wherever it went and instead installed a solid state constant current source between cathode of CF and ground, using a kit supplied by K&K Audio. I also replaced the tube used for CF from (I think it was) a 12AY7 to ECC99, which has a much lower Rp, and gives a lower output Z for the whole circuit. (ECC99 is completely compatible with 12AY7 socket.) I am using Mundorf silver/oil output coupling capacitors. Gosh, it's goooood.

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