LCR phono stages we know about

Yes, that's one problem with designing a tube-based LCR; the needed 600-ohm impedance on the input side is hard to achieve with tubes. There are many interesting threads on that subject. One such claimed that you only need 600 ohms on one side of the LCR, not on both input and output side; I am not sure about that. Some use a transformer to achieve the needed impedances. But another approach is to build an LCR that can be driven by a higher impedance, 10K ohms being another more recent standard. A very smart DIY guy I know in Australia has built a high-gain LCR RIAA using ~20K ohm LCR, built from parts supplied by Dave Slagle. I have the schematic. I actually have no idea how or why 600 ohms was ever adopted as a standard or why it is anathema (to some) to deviate from that value. It could merely be that the original LCR modules, made by Silk and/or Tango, in Asia, were set at 600 ohms, and everyone jumped on that bandwagon when those were the only LCR modules available. I welcome input from others who may know more about this.

Perhaps the 600 ohm "standard" stems from the pro side when making records in applying RIAA EQ, which was made using LCR network, inverse curve of course.

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One difficulty in using higher impedance LCR is that the inductance of the choke will be higher accordingly which is harder to wind. You gain some you lose some.

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Good point. That's where Dave Slagle jumped in, to design and build chokes that will work well in "high-impedance" LCR designs. Dave can create very precise modules.

One of our readers has done a little digging into the Emia phono stage. Apparently it is NOT an LCR type. Rather, it is a novel CR type wherein the high value resistor(s) in the signal path have been eliminated. In fact, my correspondent says he was told that there are NO R's or C's in the series signal path between the input stage and the output stage; All Rs and Cs are shunted to ground. (I am only the messenger here.) Thus the plate of the input tube is direct-coupled to the grid of the output tube, with all the filter components shunting to ground. I can only say it sounds great, no matter what the topology. But I really do not know how one can avoid having either an R or a C in the series signal path and still get to proper RIAA equalization. On the other hand, the two designers are smarter than I.

Hi Lewm,

Nearly a year back, we did a phono shootout, including a Thomas Mayer LCR phono, please see some of the write up in the following thread (mainly in the 2nd and 3rd page from the most recent)

http://www.1pekingroad.com/zaspx/replies.aspx?PageNo=2&topicsno=4&subjectno=1849&uppersubjectno=1849&sortby=updatedate&orderby=desc