Simplistic NJFET RIAA

Starting a new one gentlemen.

Hope this one will be even better than the previous builds 🙂

As usual, I will keep posting here my reasonings hoping for feedback that I know I will get from many of you.

My first approach starts with the riaa filter and due to the limited means I only have two options Following Salas Folded pdf schematic:

First:
R14 = 46600 // 2.4mega
R4 = 2190
R7 = 1mega
R5 = 6760
R6 = 390kohm
C2 = 15.01nF // 363pF = 15.37nF
(second stage miller = 1.034nF so total C2 is 16.407nF)
C1 = 47.8nF // 60pF = 47.86nF

With these values I get near perfect riaa curve.

Now second option:
R14 = 46600 // 20 mega
R4 = 2190
R7 = 1mega
R5 = 6760
R6 = 5.6 mega ohm
C2 = 15.01nF // 11pF = 15.12nF
(second stage miller = 1.034nF so total C2 is 16.154nF)
C1 = 47.1nF

With this option I also get near perfect riaa curve...... Now my question is:

What would you suggest, for C2 ?

C2 = 15.01nF // 363pF = 15.37nF
or
C2 = 15.01nF // 11pF = 15.12nF

The main cap is the same but the bypass is much smaller in the second option so I believe second option would be better because there would be less bypass "signature"... or am I wrong ?
 
No tweaks yet - much better today. Very clear and defined with very good bass. The sound is warm - something that lacked both of my LOMC's. They were quite a bit more analythical but don't get me wrong - I love them to but maybe my C2 + C2Y should be measured in my 63dB build...

Regards
 
Whatever will sound most balanced to you in total, not sure 275pF is written in stone, but you can note down the correct total after adding the JFET's own. Just don't bias yourself towards a recommended total, experiment, this is not a BJT or OPAMP pre with loop negative feedback so you may end up balancing Cx bit differently than the norm.
 
Whatever will sound most balanced to you in total, not sure 275pF is written in stone, but you can note down the correct total after adding the JFET's own. Just don't bias yourself towards a recommended total, experiment, this is not a BJT or OPAMP pre with loop negative feedback so you may end up balancing Cx bit differently than the norm.

How would one check total capacitance from the cart pins to amp? Can one measure the JFET's capacitance just as that? Doesn't it change with voltage upon it?

Or 75pF it is?

Will test the Sonus Blue Gold next, eager to sample it's sound through the fsp...

Regards
 
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There is a Ciss - VDS chart for the Toshiba and its input capacitance is indeed 70-75pF with the VDS we use here. Maybe by applying the LCR meter on disconnected from cart arm wiring pins ending to the preamp you can measure total pF but I haven't done it. It will surely overdrive the preamp hard though bcs the meter uses a highish sinewave gen for MM level.
 
There is a Ciss - VDS chart for the Toshiba and its input capacitance is indeed 70-75pF with the VDS we use here. Maybe by applying the LCR meter on disconnected from cart arm wiring pins ending to the preamp you can measure total pF but I haven't done it. It will surely overdrive the preamp hard though bcs the meter uses a highish sinewave gen for MM level.

Hmmm, I'll rather take this by the ear 🙂. As long as I'm pleased with the sound (as I am 😀).

Close enough seems to be good enough.

Thanks for your thoughts Salas.

Regards