Differential MC preamplifier and RIAA corrector

Created on Jul 12, 2017 | 8:05 am / Last Updated 2 years 10 months ago

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In reply to by anonymous_stub

  • Balanced connection to the head
  • First stage of the amplifier is in the head shell
  • The head can be replaced by a MM/MI type together with its input stage (47 kohm version)
  • Each head can be fine-tuned by its own input stage
  • Balanced signal on the tonearm cable too
  • Extremely high radio-frequency immunity (including mobile-phone radio signals)


The q8 and q9 are placed in the headshell. They must be extremely low noise type (with very small internal Rb' resistance). Unfortunately, such transistor are high-frequency (microwave) types, triggering other problems (such as oscillation). The additional RC parts are necessary to prevent microwave oscillation.


The MM/MI input stage (with 47 kohm input) is not displayed here. It contains a double jFET device (U404), that's why it cannot be tested here (lack of jFET model).


The main amplifier starts with q4 aqnd q5. They also provide power for the input stage via the headshell cable.


The opamps op1 and op3 only for setting up the operating point of the input current mirror (eliminating the current differences produced by the input stage).


The op2 makes the correction.


I would like to approach the 0 dB noise figure this way as much as possible. This design helps me to analyze the possible noise sources.

As you say, the main noise source is the base resistance of the input transistors. A trick that I remember from 30 years ago is to use a power transistor instead. Even better: put a number of (those) transistors in parallel. 

To see the improvement you will need to use the real SPICE models as SV apparently does not model base resistance.

In reply to by anonymous_stub

Hi György,

Thanks for sharing this!  I had to look up the meaning of RIAA.

Did you know that you can use SPICE models in SystemVision?  I found a Spice JFET library online that Gunthard Kraus put together.  I created a simple test circuit for it here:

JFET U404 model


You can reuse this model in your own design by adding it to "My Favorites" using the RMB.


JFET U404 Model

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