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In Reply to: RE: Dacs powered by batteries - any successful story ? posted by beppe61 on June 15, 2015 at 04:20:16
Hi,
> 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.
You will have to calculate the filter (there are many on-line calculator options) and then purchase the correct inductors and capacitors. There are no ready-made "filter modules" I know,there is little point for any manufacturer to make such.
> 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 ...
You give this regulator perfect DC. No noise at all. You still have 40uV noise fromthe regulator. Nomatter what you do, this is what you got.
> i will do that but upstream the regulator.
That would be pointless. It is like buying pure evian (or whatever you like) mineral water and then pee in it and insist the result is pure water because the source is pure.
> 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.
LCfilters are quite primitive. You can probably get something towork well enough without much stuff.
Take a high ESR Electrolytic Cap as part of the filter, set the filter impedance to the ESR of this cap (say we use a 100uF/6.3V part with 1 Ohm ESR - this makes the filter impedance 1 Ohm) set frequency to 1 kHz, let the calculator work out L & C and then buy suitable L & C.
As the ESR of the cap and the filter impedance becomes lower the required capacitance goes up inductance down. All a tradeoff of size and cost.
Ciao T
At 20 bits, you are on the verge of dynamic range covering fly-farts-at-20-feet to untolerable pain. Really, what more could we need?
Follow Ups:
" Hi, You will have to calculate the filter (there are many on-line calculator options) and then purchase the correct inductors and capacitors. There are no ready-made "filter modules" I know,there is little point for any manufacturer to make such. "
Hi and thanks for the advice. I will look for them.
I am interested a lot. That solution would make things much easier.
" You give this regulator perfect DC. No noise at all.
You still have 40uV noise from the regulator. Nomatter what you do, this is what you got. "
well ... i could live with that very well.
Now i think that the actual noise is much higher than 40uV.
A lot of garbage reaches the regulator.
" That would be pointless. It is like buying pure evian (or whatever you like) mineral water and then pee in it and insist the result is pure water because the source is pure "
if i understand you mean that whatever there is upstream the regulator the outcome will be always a 40uV of noise ? really ?
This is a very fundamental point to understand for me.
If this is the case i will leave also the ps untouched.
I can bear 40uV of noise ... for me is nothing.
" LCfilters are quite primitive. You can probably get something towork well enough without much stuff.
Take a high ESR Electrolytic Cap as part of the filter, set the filter impedance to the ESR of this cap (say we use a 100uF/6.3V part with 1 Ohm ESR - this makes the filter impedance 1 Ohm) set frequency to 1 kHz, let the calculator work out L & C and then buy suitable L & C.
As the ESR of the cap and the filter impedance becomes lower the required capacitance goes up inductance down.
All a tradeoff of size and cost.
Ciao T "
thanks a lot again for the very precious advice
I have to understand well that any mod upstream the regulator will have no effect on the actual noise at its output.
If this is confirmed this changes completely my plans.
I will just solder again some caps that i took out and stop.
I should have added that after the main regulator lt1963 other local regulators follow. I cannot spot them but someone more expert than me has spotted them.
But as i said i will avoid messing with the ps.
Thanks a lot.
Kind regards,
bg
Hi,
> well ... i could live with that very well.
But this regulator makes so much noise, batteries or even our "next generation" plugtop supplies would be wasted, just as the pure water in my rather graphic example.
> Now i think that the actual noise is much higher than 40uV.
This is possible. It is almost impossible to say without suitble test ger.
> if i understand you mean that whatever there is upstream the
> regulator the outcome will be always a 40uV of noise ? really ?
Of course. All electronic circuits generate noise. The specific one you mentioned is specified as adding this much noise under ideal conditions.
> I can bear 40uV of noise ... for me is nothing.
Well, 40uV of noise might be expressed as 93dB (forgive if I am a little out) below 2V. If driving a clock, this may matter. On a single gate it will likely add around 1pS of jitter. Many modern circuits have 100's of gates. SO these 40uV can very quickly become several 100 times 1ps jitter...
> I have to understand well that any mod upstream the regulator will
> have no effect on the actual noise at its output.
It will, especially in this case. The regulator you mention does not do much to reduce noise past appx 1kHz. So giving it a passive filter in front will add the passive filters effect to the regulator.
Of course, you cannot go lower than the regulators self noise, but you can minimise the noise that gets to the regulator and past. Just there is a point where further improvements no longer help, due to build in limitations.
For fun, I can routinely make something that offers around 0.4uV of self-noise using less than one USD in parts for two channels (in 1KU), if all we need is 3.3...5V at 0.5...1A per channel and using quite generic parts. We can go as low as 0.15uV if we spend more money. Walt Jung is a good source.
> I should have added that after the main regulator lt1963
> other local regulators follow.
And if you are unlucky, they produce 400uV of noise... ;-)
Ciao T
At 20 bits, you are on the verge of dynamic range covering fly-farts-at-20-feet to untolerable pain. Really, what more could we need?
Good morning Mr. Thorsten
" But this regulator makes so much noise, batteries or even our "next generation" plugtop supplies would be wasted, just as the pure water in my rather graphic example "
actually i saw the datasheet and was surprised to see a poor performance on the higher Hz.
Clearly some kind of additional filtering is mandatory to keep noise down.
" This is possible. It is almost impossible to say without suitble test ger "
and this is my main regret because i understand that good testing rig are both complex and very very expensive. And this also normal.
" Of course. All electronic circuits generate noise. The specific one you mentioned is specified as adding this much noise under ideal conditions "
unfortunately i have no chance to test it but i trust you completely
In the end is a cheap product.
" Well, 40uV of noise might be expressed as 93dB (forgive if I am a little out) below 2V. If driving a clock, this may matter. On a single gate it will likely add around 1pS of jitter. Many modern circuits have 100's of gates. SO these 40uV can very quickly become several 100 times 1ps jitter... "
I see. However i see also very expensive master clock generators powered by what look like off-the-shelf SMPS.
Maybe there is also some kind of filterin, actually i am sure of that.
" It will, especially in this case. The regulator you mention does not do much to reduce noise past appx 1kHz. So giving it a passive filter in front will add the passive filters effect to the regulator "
and this exactly one of the reason to replace the toroidal.
I understand that a same effect of a split bobbin transformer (that i see used on high end units) can be achieved with passive filtering before the toroidal, but if space were not a constraint that toroidal will fly in the garbage bin immediately.
My approach is simple. Look what is inside the best unit and try to use it. Unfortunately schematics are not that common.
" Of course, you cannot go lower than the regulators self noise, but you can minimise the noise that gets to the regulator and past. Just there is a point where further improvements no longer help, due to build in limitations.
For fun, I can routinely make something that offers around 0.4uV of self-noise using less than one USD in parts for two channels (in 1KU), if all we need is 3.3...5V at 0.5...1A per channel and using quite generic parts. We can go as low as 0.15uV if we spend more money. Walt Jung is a good source "
wow ... that is very low indeed.
I understand that in order to suppress the noise generated by the regulator additional filtering after it would be extremely beneficial.
But i have no access to the schema and it is difficult to extract it from the pcb.
But i still could clean up a little the feed to the regulator.
Especially the HF noise that tends to pass through the regulator unsuppressed.
Even just a different transformer could be a good change.
" And if you are unlucky, they produce 400uV of noise... ;-)
Ciao T "
Yes. But as i said i cannot do anything for this.
Thinking about this a little more the idea to use an external decent SMPS or linear and put in the box just an additional filtering stage before the regulator caps is interesting.
I have just to place a new DC panel socket on the box and the filter inside.
I will look for some suitable schematic.
I see that many dvd/br player have passive mains filters.
I should be able to copy them.
Just some inductors and caps. Nothing out of this world.
I understand that the performance will be determined by the pcb design anyway.
But i can only try to feed the regulator as well as possible.
If i touch the pcb the unit i destroy everything.
And i do not like the idea to increase further the noise already generated by the regulators.
To end i have a strong feeling that the war to noise is a decisive one for sound. In the future i would like to be able to understand more on how the noise generates and how it can be suppressed.
I watched a very simple but also very interesting demo on Youtube.
The speaker compared the noise to a carpet. The more the noise the thicker the carpet.
If some objects of different sizes are then thrown on the carpet we can still see the bigger one but the smaller ones will be down in the carpet.
These small objects are like details in music.
A higher noise hides them. There is so much noise already in like.
So i think this is a very interesting field of study.
Thanks a lot again for the very kind and precious help.
Have a nice day.
Kind regards,
bg
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