Simplistic NJFET RIAA

diyAudio Chief Moderator
Joined 2002
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@ lohk

Here is what I came up with, regarding your request. The challenge is the second stage JFET to have some Vgs that can afford a bit of swing. I actually breadboarded a BF245C Fairchild and reconstructed its sim model to be sure. Since higher Vgs JFETs are short for gain most work is done by first stage and that dominates the noise spec to a good measure. With 47R degeneration there is enough Vgs to take 100mVpk-pk input before asymmetrical compression and clip eventually. Soft knee. With that degeneration being 3 times lower than a 150 Ohm capsule, the mic still sets the noise spec, so no real addition there beyond the ~1nVsqrt of K170's. It could marginally reach 40dB gain in that config which is what I saw in Jensen mic trafo specs for the active part along with 15K secondary termination in FET interface trafos. Some BF245s may show a bit more Yfs even but it won't change the gain drastically. Watch the channels gain to match if using X-Y mics anyway.
 

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Ok, no, that wont work. With a transformer it is even worse.
The crucial thing with mic-pres is the undistorted headroom, this is my experience. Some of the better mics can put out up to 1V peak, so I have been told, but I did not measure that yet.
Well, I do have the parts (maybe not with the very sophisticated psu) in my box, so I should just try it. Thanks for the effort.
 
After posting elsewere about the qualities of another riaa preamp I could not resist to leave my other opinion here.

Some say the Simplistic has special staging qualities. I did find it to be true and never heard anything aproaching the Simplistic in this area (not even the best jfet EB implementations that I had the oportunity to evaluate). Off course this can only be obtained with a very carefull layout implementation and carefull choice of components. IMO the type of shunt used is determinant.

Apart from staging, the Simplistic can have the sweetest mid/trebble causing a magical transe state on the listener....

Off course it might be difficult to get all this at first start (it took me a while to get here) but diy difficulties should never stop those who are really determined.

This post serves to remove all doubts about my subjective evaluation of this superlative design by Salas.

+1