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Old 17th September 2013
  #23
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Quote:
Originally Posted by Oli View Post
Would it be possible to put an inductor on the supply to the charge pump, to reduce noise coming back from it to the supply rails?
Very possibly. I tend to avoid using inductors simply because of their price and bulkiness. But I'm not that familiar with this style of one chip charge pump so I'm unsure what affect driving one through an inductor would have. I'd need to read up more about them.

The 10R 3W resistor and 220uF cap works very well. But although this does remove the unwanted perturbations on the +12V supply it doesn't work as well as filtering the DAC reference voltage directly. A combination of the two would be best as, right now, the 80kHz noise is having to be worked out of the audio path by the op-amps' PSRR and feedback mechanisms. I'll be looking into this at some point in the future when I get some free time.

The Mopho generates the +5V digital line from the +12V regulated supply. Personally, I would have driven the +5V regulator from the 13V wallwart directly with some additional RC filtering. That would have kept the +12V line clearer of any of the +5V noise.

Quote:
Originally Posted by Oli View Post
... do you see a lot of 'interesting features' like this?
Let's put it this way; I have never owned a synth, except the Virus KC, that I haven't modified in some way.

Tony