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Trying to find a resistor value for JFET RIAA Phono Preamplifier schematic
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Frankentronics:
Hello,

I've searched the web before posting here, but can't find the answer.

I would like to build a JFET RIAA Phono Preamplifier described here:

http://diyaudioprojects.com/Solid/JFET-Phono-Preamplifier-Kit/

Here is the schematic.



Everything is clear to me, except the value for the R2.

Does anyone have any idea what that value might be?

The other 2 components that are not specified are the C6 and C7 caps. I've been able to determine that they must be 220uF, 50V. Does that sound right?

Thanks...
Paul Moir:
I'm only just acquainted with this end of electronics, but R2 should depend on the phono cartridge you're using.  It provides the recommended load impedance.
220uF for the power supply bypass caps should be plenty.  Half that would be plenty too.  50V seems a little unnecessary but I don't know what the power supply is.

MasterT:
I 'd set R2 = R10.
Frankentronics:
Thank you, both.

I guess I can just put a 100K trim pot and adjust the value, depending on the cartridge (I'm planning on using a Moving Magnet cartridge). Not sure how exactly I would set it, though. Perhaps I would listen for distortion, as I'm setting it?

Regarding C6 and C7, I just zoomed in on the image of the parts and I figured out those were 220uF, 50V caps. The recommended power supply is 18VDC. I'll start with 2x9V batteries and if it performs well I'll build a power supply later.

Thanks again...
Frankentronics:
Well, here's an update...

After some more Googling I found this schematic...



...which is different from the schematic I posted initially. The initial schematic appears in this assembly manual...



..some other resistors also have different values in the new schematic and it looks like the new schematic is rev. 3, while the one I first posted is rev. 2.

But I guess I got my answer.

Thanks...
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