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hochopeper

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  1. At the moment acg and I are working through details for a linear psu for part/all of his PC so I've done some research recently. Since the OP was asking a more general question and thread is not specific to the John S Mac mini supply I'll add a few comments of my own. I have done almost no research on smps as my supplies for acg will also be used for a few other applications where smps just isn't an option, my comments are focused on linear supplies. Regarding kelvin sense wiring, not sure if it has been mentioned already but the 3.3V rail in ATX standard has option for a 3 terminal version of this config. Some fixed voltage regulator ICs offer this and some of the newer regulator ICs for wide bandwidth and low noise offer this and adjustible output too, though these are mostly limited to 1A. The fixed voltage ICs can be found that offer 3.3V at up to 3A, though become rarer for higher voltages at this sort of current (I havent found any IC 'chip regulators' that do more than 1A and offer this with higher than 3.3V output). Traditionally kelvin sense seems to be used for voltage drop over cable for what would seem to be low freq variations in voltage at the load terminals. The presence of this functionality in wide bandwidth focused ICs does make me wonder about the feedback loop and it's effect on higher freq noise (provided the wiring allows this to be carried reliably). I have no real data to back that claim / idea but it's something I'd like to look into and why I'm building (diy) measurement preamp and measurement focused ADC(s) to better understand the interaction. In terms of filtering before the regulator I will be using a snubber across the bridge rectifier and a pre-reg before each of the final low noise IC regulator. Noise for higher than 100kHz would seem to be dominated by sources on board the PC rather than the power supply so IC regulator PSRR is mostly important for lower freq. I hope that is more helpful than confusing! Chris
  2. That's me Might want to think about more than 10x gain ... I'm building a design that's by a gent on a diy forum that has a low noise 80dB amp and a thermal RMS noise measurement device and Samuel Groner published a design of another LNA in Linear Audio 'zine' both of which are designed with measurement of low level noise in mind to ensure that their noise contribution does not dominate the measurements. The input referenced noise contribution of the amplifier needs some careful consideration when looking at linear regulators that have single digit uV RMS noise...
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