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Common-Mode Rejection Ratio for miniDSP Balanced 12 years 1 month ago #1918

  • sjsobanski4
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I would like to include a miniDSP unit in a preamp I'm designing for an audio design class of mine. I want it to have balanced in's and out's, but inside, the signal will go bal -> unbal and unbal -> bal as the gain stage will work with the unbalanced signal. My main question is, what is the actual CMRR specification of the miniDSP Balanced? This is if you run it with balanced inputs and unbalanced outputs. Would it compare to that of a quality transformer such as a Jensen or Lundahl? My professors make a big deal about the superiority of balanced signals and good transformers. I'm aware of this thread balanced input , but it was regarding the unbalanced miniDSP kit.

Also, how does the miniDSP Balanced handle the balanced input? Does it convert it to a single-ended one before the AD conversion and differentiate it later on? Or does it individually process the positive and return signals?

I have two options regarding the input stage of this preamp:
1) Balanced inputs into miniDSP with unbalanced outputs.
2) Balanced inputs into miniDSP with balanced outputs; then a transformer.

Option 1 would be the most cost-effective, and I will probably go that route. But, I'm still curious about the MiniDSP's transformer-like capability. :huh: Could any common-mode noise exist in the balanced outputs of the miniDSP that a transformer could eliminate?



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Last edit: by sjsobanski4.

Re:Common-Mode Rejection Ratio for miniDSP Balanced 12 years 1 month ago #1932

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In answer to your main question: how does the miniDSP compares to a transformer like Jehnsen? it's a pretty simple one to answer: Transformers achieve the best CMRR as you may already know..
- miniDSP balanced achieves 75dB CMRR which is not a bad spec at all.
- A transformer like Jensen could achieve 100 to 120dB.

There is a very good app note if you haven't read it already by Bill Whitlock. You can find it here

Another great link by the same author can be found here .

On the miniDSP the balanced input is indeed first converted to an unbalanced input before AD. For the Output, it goes Unbalanced to balanced.

Hoping this information helps, have fun with your project!

miniDSP, building a DSP community one board at a time.

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