I am currently using a Signet TK7e. No distortion is detectable.
I am running the phonostage thru a Numark EQ, which sends it to a P.S. Audio IV-H (used as a passive source selector), then into either my single ended triode headphone amp, or my BGW 250D.
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So then we have to conclude that the Shure M55E is be faulty,since it does not connect directly to J1 in the schematic you shown, right?
I'm not sure I understand what you're concerned about here. T1A's grid is at 0V, so it won't put any DC on the cartridge, and the cartridge obviously isn't going to put any DC on the preamp input...
The vast majority of tube RIAA circuits, old and new, have not used an input coupling capacitor to the first grid.
The only exception that comes to mind immediately is the HK Citation I preamp. Oddly enough, the easiest way
to improve the sound of that preamp is to short out that very 0.47uF 10V ceramic Z5U input coupling capacitor.
The only exception that comes to mind immediately is the HK Citation I preamp. Oddly enough, the easiest way
to improve the sound of that preamp is to short out that very 0.47uF 10V ceramic Z5U input coupling capacitor.
I will have to take your word for that, I made an observation. I don't simulate anything. What is the purpose of R15, not to bias the grid? Maybe it is because my textbook knowledge from the 60s is very rusted. I apologize for spreading misinformation.
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Just to point out that these measurements by Stereophile I found are consistent with my simulation above, 49.2 dB gain for MM and even the same slight bump around 1 kHz in the frequency response, so it looks like my 12AX7 model is reliable. If anyone is interested, I can post the model and simulation file for you guys to play with.
Although I never simulate, yes why not post it. It is not important, but would be interesting to compare standard models that is offered in MicroCAP12 with a confirmed working model.
Here it is. I include the sim file, mytubes.txt (which contains the 12AX7 model as well as an ECC88) and the .lib and .sym files for the RIAA subcircuit, which is an inverse RIAA filter (without IEC pole) so you get a flat response at the output and can check RIAA accuracy more easily. If you're familiar with LTSpice you probably know this but, just in case, put mytubes.txt and RIAA2.lib in ..\lib\sub, RIAA2.sym in ..\lib\sym and you're good to go.
My Chinese clone is a different circuit, which has been documented on this very forum.