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Old 1st December 2009, 04:29 PM   #1
ljfont is offline ljfont  Canada
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Default JFET mu follower phono or mic pre

Has anyone tried this for a phono or mic pre?

Any thoughts on noise?

Is it better to amplify the small signal from MM/MC first before applying the RIAA eq? or buffer the input signal first then applying the RIAA, then a hi gain circuit? What's better for noise figure?


Sim of the circuit using 2sk170BL's shows THD of 0.042% and a gain of about 51.5db in the pass band with the -3db at 12Hz to 445kHz
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Old 1st December 2009, 08:26 PM   #2
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Sorry to dissapoint you but it clips at just over 4mV in and 4mV THD 0,5%.

To work with a MM you should need to have at east 50-80mV before overload.

You will not find much use for that one. Also to be a mu-follower you have to add a resistor between the lower drain and the upper source.

But the concept has a point.
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Old 2nd December 2009, 04:33 AM   #3
ljfont is offline ljfont  Canada
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Would it be enough for a MC? They are in the hundreds of microvolts.

This circuit is from National Semiconductor AN32 notes

They call it "Ultra-High Gain Audio Amplifier" or "JFET' mu amp''

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