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Trying to find a resistor value for JFET RIAA Phono Preamplifier schematic
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MasterT:

--- Quote from: Adinol on December 05, 2017, 02:22:28 am ---
--- Quote from: MasterT on December 04, 2017, 10:40:21 pm ---...I discovered an error in R5 value, it has to be 22 k. Definitely not a 28k...

--- End quote ---

Good catch...!

I think this is one of the things they addressed in rev.3 of this schematic. They changed that R5 to a value of 22.1k. I believe you were probably still looking at the rev.2 schematic (which is the first one I posed) when you caught that error. In one of my subsequent posts I posted rev.3, which I discovered at a later point.

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What I was trying to say, that even R5 = 22k value is not correct. Mathematically R5 + Zout = 22k, though to estimate R5 correctly you need to know an output impedance of the first amplifier. Roughly it's about 1.5k, you may try to simulate its in CAD or find an online some-kind calculator. Though R5 = 22 - 1.5 = 20.5k .  Point is you don't need a C3, and 1% tolerance in audio circuitry,  in most circumstances 10% is o'k. I also would change 221k - R10 (Rev. 3) to 1-2 MOHm, since it's loading RC filter.
floobydust:
I think R10/C4 set a LF corner 16Hz, probably for rumble or warped LP's.
R10 needs to be low for low noise, and needs to be high to minimize loading on the passive EQ.
TimFox:
Magnetic cartridges are velocity-responding, and the normal RIAA preamplifier equalization as used in the OP's circuit is designed accordingly.  Piezoelectric cartridges (crystal or ceramic) are displacement-responding, and need a different equalization circuit.
Magnetic cartridges are either moving-magnet or moving-coil.  The moving-magnet cartridges are more common and put out much higher voltage than the moving-coil units.  47 k is the usual terminating resistor for moving-magnet units, and the Shure cartridges work better into their specified capacitance in parallel with that resistor (better frequency response).  Moving-coil units usually use a lower load resistance, either through a step-up transformer or into a special low-voltage-noise preamplifier (often with paralleled bipolar transistors).
Frankentronics:
Thank you all, once again, for taking the time to share your expertise.

I also discovered that those JFETs 2SK170 must be obsolete and I only found them on Amazon. Hopefully they are not fakes.

Thanks...
Brumby:

--- Quote from: Adinol on December 05, 2017, 05:39:22 am ---I'm ordering 1% resistors. 1/4 W should be OK, right?

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Perfectly.

In fact, the 1/4 W rating is going to be far more useful in handling (component size) than any power dissipation requirement in that circuit.
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