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Upsamplers, DACs, jitter, shakes and analogue withdrawals, this is it.

RE: Dacs powered by batteries - any successful story ?

" Hi, I am using an EMU1616m with a "breakout box" as my second test system. It has "120dB/192kHz" AD Converters (yes, they deliver that) and the over 60dB of gain in the microphone pre-amps are pretty useful to look at audio band noise on power supply lines.
Bandwidth limit is 96kHz of course, my AP2 goes up 108k in FFT mode, more in analogue mode.
For wide-band stuff (Radio Frequencies) the analysers build into the better modern Digital Storage Oscilloscopes (DSO) are pretty useful.
But you are likely still looking at several 1,000 Euro (my current 300MHz DSO retails for around 2.5k and is at the cheaper end of the range) to get something that is meaningful.
To cover things more accurately you can easily blow 50k Euro on a AP2 or Prism 'dscope and a wideband RF analyser... "

Hi again and thanks a lot indeed for the very interesting information.
So i serious investigation on noise is completely out of my budget ...
I have to live with that i guess.

" Split bobbin only goes so far. I avoid split bobbins and instead use a different winding structure compared to the common one that ensures minimal leakage. But you have to have transformers custom made for that. "

again i would like to stick with something off-the-shelf.
They are not all equal. Maybe they are not top but some still decent.

" Something you may find paradoxical, a decent SMPS can do an excellent job of keeping corrupted mains (noise) out of the system. It must (in order to pass EMC testing) include quite substantial RF filtering.
In any SMPS the incoming voltage is first RF filtered (both directions) and then turned into DC.
This DC is chopped up and applied as high frequency (67kHz and 132kHz are now common frequencies) to the mains transformer.
The actual mains transformer has very low inter-winding capacitance and is often actually shielded (needed to pass EMC) so very little noise can pass.
Suitable designs can minimise the value of the Y Capacitors or eliminate the Y capacitors entirely. Audio band noise depends on design, but can made very low, with enough effort. Of course, the voltage that comes out of the SMPS has a lot of noise at the switching frequency and up.
But such noise is at predictable frequencies and of predictable nature and it should NOT present a major challenge to a competent engineer to filter this sufficiently that it does not matter.
Doing all this will cost some money, but next to custom 400Hz double C-Core transformers with special winding arrangements etc. it is downright dirt cheap and all the components needed are off the shelf commodity parts.
Filtering for the switching frequency can usually be added external to a SMPS (both input and output) for anyone doing DIY. "

and this is another option i was thinking about. Adding a filter stage to a decent off-the-shelf SMPS.
Actually this is my best option now. I have only to add a DC panel socket on the unit and a filter inside the unit.
But i cannot find a suitable filter for such low V and low A.

" Hmm, it is specified as having 40uV of noise for the 3.3V part.
The old "low noise" plug-top supply which are currently replacing with a new model that is much quieter has lower levels of noise at 9V output (so much less as percentage of output voltage).
This regulator also has very poor high frequency behaviour.
At 100kHz it already has less than 40dB (100 times) noise reduction capability.
I think I would probably look at this regulator as my first target. "

the idea is not to mess with the pcb (the regulator is mounted on the pcb) and provide the regulator with the cleanest possible DC.
I cannot risk to ruin the pcb ...

" The current DIY favourite TPS7A47 from TI (used in some linear power supplies market at quite high prices and also found in a different gizmo we recently discussed) has one tenth the noise and has ten times better high frequency rejection (at 100kHz) compare to that LT part and it retains this high noise rejection out to several MHz (so it will actually kill any noise from SMPS much more effectively).
So it may be an idea to get a "kit" and instead fix that rather awful regulator, before loosing sleep on other subjects "

i will do that but upstream the regulator. So the regulator will not do actually the work. Clean DC in and out ...

" Possibly adding some LC filtering on the power input (or in line with the power cable from the external PSU) could also give a major improvement, make sure the filter cutoff is at around 1kHz or lower and 2nd order.
Then you will get around 80dB (10,000 times) extra noise filtering at 100khz and 120dB (1 million times) at 1MHz.
Ciao T "

thanks a lot again. Main problem is that i have no the money to set up a good measurement rig at all. I have no chance.
I have to rely on specifications of parts and kits.
But i will do some tests for sure ... this is sure.
Thanks a lot again, gino.
Kind regards,
bg


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