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Marantz discrete op amp (line stage or headphone amp)

Posted 10th November 2013 at 12:00 PM by rjm
Updated 10th November 2013 at 02:11 PM by rjm

Last one for today.

I was having problems getting this to work, the key seems to be adjusting R6 to null the voltage offset. Works fine now, but this is just a rough reverse engineer of the diagram, the parts values and the type of transistors are essentially placeholders.

The input jFET is shown as a dual package. The output bias current is most likely much lower than the 100 mA I configured, so the class A output power is proportionately smaller. For the rest of the currents and the types of transistors used, your guess is as good as mine.

edit: R7 should most likely be closer to 47 ohms, while another 5p capacitor should go in parallel with the feedback resistor, R17.
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Posted in The Lab
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Total Comments 3


  1. Old Comment
    You might have to adjust R6 a lot less if you substitute a diode connected BC547c for D1. As is you get uneven contributions from each side of the diff pair.
    Posted 11th November 2013 at 05:48 AM by mirlo mirlo is offline
  2. Old Comment
    rjm's Avatar
    I'll look into that. Thanks!
    Posted 11th November 2013 at 01:00 PM by rjm rjm is offline
  3. Old Comment
    Why are R4 and R6 such drastically differently values? Shouldn't they be the same?
    Posted 21st January 2014 at 12:08 PM by FoMoCo FoMoCo is offline

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