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Old 2nd July 2008, 01:17 PM   #1
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Default Ultrasimple MM/MC RIAA Preamp mkIII

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.
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Old 2nd July 2008, 01:23 PM   #2
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Have you checked the working points for all three JFET's? Are the JFET's capable of 12 mA Id?
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Old 2nd July 2008, 01:29 PM   #3
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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
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Old 2nd July 2008, 02:36 PM   #4
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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.
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Old 2nd July 2008, 03:08 PM   #5
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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...!

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Old 2nd July 2008, 07:42 PM   #6
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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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