Ultrasimple MM/MC RIAA Preamp mkIII

GlidingDutchman · 2nd July 2008, 02:17 PM

A friend of mine (Ludo) tweaked the circuit by Mads K.

I a having trouble getting it to work so I thought I post it here for some discussion.

peranders · 2nd July 2008, 02:23 PM

Have you checked the working points for all three JFET's? Are the JFET's capable of 12 mA Id?

GlidingDutchman · 2nd July 2008, 02:29 PM

Quote:

Originally posted by peranders
Have you checked the working points for all three JFET's? Are the JFET's capable of 12 mA Id?

20mA max...

D

Conrad Hoffman · 2nd July 2008, 03:36 PM

You're at the mercy of whatever current flows with the gates grounded (Idss?, I forget), and this can vary. You might have to adjust the upper three resistors to get the voltage drop you want. Other than that, it looks like it should work fine. I assume the gain is rather low and another gain stage has to follow this.

GlidingDutchman · 2nd July 2008, 04:08 PM

Quote:

Originally posted by Conrad Hoffman
You're at the mercy of whatever current flows with the gates grounded (Idss?, I forget), and this can vary. You might have to adjust the upper three resistors to get the voltage drop you want. Other than that, it looks like it should work fine. I assume the gain is rather low and another gain stage has to follow this.

I guess so...

Conrad - this design stems from here: http://www.diyaudio.com/forums/showt...postid=1550522

and the unit, as designed by Mads K works just fine as it stands with my Kiseiki Purpleheart Sapphire low output MC cartridge...!

D

tschrama · 2nd July 2008, 08:42 PM

If you really want to optimize the circuit, read the optimum Voltage supply idea of Nelson in:

http://www.diyaudio.com/forums/showt...88#post1552988

and posts before there...

2nd July 2008, 02:23 PM	#2
peranders Electrons are yellow and more is better! diyAudio Member Join Date: Apr 2002 Location: Göteborg, Sweden Blog Entries: 4	Have you checked the working points for all three JFET's? Are the JFET's capable of 12 mA Id? __________________ /Per-Anders (my first name) or P-A as my friends call me

2nd July 2008, 03:36 PM	#4
Conrad Hoffman diyAudio Member Join Date: Mar 2007 Location: Canandaigua, NY USA	You're at the mercy of whatever current flows with the gates grounded (Idss?, I forget), and this can vary. You might have to adjust the upper three resistors to get the voltage drop you want. Other than that, it looks like it should work fine. I assume the gain is rather low and another gain stage has to follow this. __________________ I used to be an audiophool like you but then I took an arrow to the knee.

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2nd July 2008, 08:42 PM	#6
tschrama diyAudio Member Join Date: Jul 2001 Location: The Netherlands	If you really want to optimize the circuit, read the optimum Voltage supply idea of Nelson in: http://www.diyaudio.com/forums/showt...88#post1552988 and posts before there...

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