Simplistic NJFET RIAA - Page 798 - diyAudio
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Old 11th September 2012, 06:13 PM   #7971
RCruz is offline RCruz  Switzerland
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Splendid
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Old 11th September 2012, 07:05 PM   #7972
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Now that I thought of it, why not a single 369 for 0.5mV carts, 63dB was for LMC, 57dB is MC classic. Less input capacitance more headroom for MC. And it dawned on me, since varying the PSU can have analogous effect like varying R13 why not use a trimmer for R12 instead that shows less drop and less mW ta-da!
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Old 11th September 2012, 07:19 PM   #7973
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Can we use a k170 instead of the k369 for the input ?
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Old 11th September 2012, 07:22 PM   #7974
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Not much gain or same noise in this same config, wait I will set one for double 2SK170 so we will have an ''equivalent'' like for the 4XK170 LMC example a few pages back.
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Old 11th September 2012, 07:27 PM   #7975
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Thanks

So you mean k369 might be lower noise for that gain and config ?
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Old 11th September 2012, 07:42 PM   #7976
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K369 for noise is as using 2 K170 roughly. Yfs and Ciss go up together, so no free lunch, it shows some advantage in lower frequencies for a special kind of noise named generation recombination as Scott W. explained. Here you are, another toy attached.
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Old 12th September 2012, 01:32 AM   #7977
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Meantime the folded thingy goes for 8 hours without moving bias or gain. I think it passes as a gain cell to be evaluated. Not bad 20kHz square wave for a high capacitance JFET and 50 Ohm source also. Carts will be lower Zo. There is the cascoding BJT, but no loop feedback, or substantial local to speak of, plus 40dB gain and all that remaining Crss Miller Jazz. -3dB is @ 500kHz BTW.
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Old 12th September 2012, 08:19 AM   #7978
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What about output impedance of the cascode?
Will that affect the response of the passive filtering?
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Old 12th September 2012, 10:27 AM   #7979
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The telescopic cascodes in the standard PDF guide configs had 3.3K or 2K4 load resistors, i.e. even bigger. The difference will be the BJT's bias current which has to be lower here and the slew when charging the same value filter capacitors. Does not give any limitation hint in the sim, but no mod will go universally recommended if not built in full phono by hands and approved by ear(s) first.
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Old 12th September 2012, 11:57 AM   #7980
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My sim shows an almost perfect fit... I would only use 6k8 // 1M4 instead of 6k8 // 2M2.

The output impedance of the cascode beeing ~ 2k2, it adds to the 47k in the riaa... very good.
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