JFET mu follower phono or mic pre

ljfont · 1st December 2009, 04:29 PM

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?

Thanks.

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

revintage · 1st December 2009, 08:26 PM

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.

ljfont · 2nd December 2009, 04:33 AM

Ok,

Would it be enough for a MC? They are in the hundreds of microvolts.

This circuit is from National Semiconductor AN32 notes
http://www.national.com/an/AN/AN-32.pdf

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

Thanks

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1st December 2009, 08:26 PM	#2
revintage diyAudio Member Join Date: May 2007	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.

2nd December 2009, 04:33 AM	#3
ljfont diyAudio Member Join Date: Feb 2008 Location: Vancouver, British Columbia	Ok, Would it be enough for a MC? They are in the hundreds of microvolts. This circuit is from National Semiconductor AN32 notes http://www.national.com/an/AN/AN-32.pdf They call it "Ultra-High Gain Audio Amplifier" or "JFET' mu amp'' Thanks