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LM317 load capacitance
LM317 load capacitance
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Old 14th November 2017, 03:19 PM   #221
mchambin is offline mchambin  France
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Originally Posted by traderbam View Post
What's the big deal about noise?
It is big deal at front stages where signals are extremely small, when SR ( signal to noise level ) is poor.
Of a paramount importance about signals from deeper space probes sending pictures from far away planets.
Mostly BS about well designed power amplifiers.
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Old 14th November 2017, 03:31 PM   #222
traderbam is offline traderbam  Europe
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Sure.
What's the opinion on how much noise is too much for a MC amplifier psu? (you may have to make some qualification regarding PSRR)
And what is the effect on sound quality of too much psu noise?

And regarding the thread topic, how noisy is a smoothing cap compared to an LM317?
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Last edited by traderbam; 14th November 2017 at 03:34 PM.
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Old 14th November 2017, 10:04 PM   #223
dotneck335 is offline dotneck335  United States
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And regarding the thread topic,...............
How refreshing!!
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Old 14th November 2017, 10:44 PM   #224
dotneck335 is offline dotneck335  United States
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Originally Posted by traderbam View Post
how noisy is a smoothing cap compared to an LM317?
Well, in terms of ripple (which certainly is noise), every 10-fold increase in capacitance reduces ripple by 20db. An OnSemi LM317 reduces 120Hz ripple by 80 db. You'd have to use a MIGHTY big cap to equal the LM317.
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Old 14th November 2017, 11:02 PM   #225
mchambin is offline mchambin  France
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I think you misunderstood. Traderbaum is talking about noise induced by caps on the output of the power supply.
Caps as any componant do make thermal noise.
This has been oversighted in most fancy super duper calculations giving extremly low noise figures.
All componants make thermal noise. So a calculated noise going below, doesn't make any sense.
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Old 15th November 2017, 02:36 AM   #226
jackinnj is offline jackinnj  United States
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LM317 load capacitance
At 300K, a 100uF capacitor has the same thermal noise as a 2.5k resistor, about 6.4nV/RtHz...but
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Old 15th November 2017, 08:13 AM   #227
traderbam is offline traderbam  Europe
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Apologies for not having pulled my weight and done calculations or bench measurements. Im armchair brainstorming.
From a noise perspective, is more capacitor and less regulator better?
Eg: LM317 + 1mF vs LM317 + 1uF
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Old 15th November 2017, 08:42 AM   #228
nigel pearson is offline nigel pearson  United Kingdom
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The graphs I gave in No 194 are real ( up to 16 MHz and no peaks ). I was very surpised to see that is worked regardless of what I tried. A 1920's addition was not too bad. The load was typically a 24 bit DAC with class A headphone amp or whatever.
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Old 16th November 2017, 02:12 AM   #229
infinia is offline infinia  United States
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Originally Posted by traderbam View Post
I’m armchair brainstorming.

Eg: LM317 + 1mF vs LM317 + 1uF
uhh isn't that just moor capacitor?
RE Armchair quarterbacking >The play you are trying to call was tackled in the backfield.


How about just building it' and if it' doesn't suit your needs, upgrade / change the regulator part or roll your own. Folks seem to forget that a monolithic V regulator chip aka 3 terminal regulator, is the cheap-n-easy way of getting great ripple reduction without the BF'ing low-pass filter components. Adding them back on the output is pretty silly from my view, it doesn't make it doubly good. Understand that using a 3T linear regulator circuit is an engineering compromise for both noise and ripple, ideally the burden is distributed equally from a systems engineering perspective.
which can be interpreted as ..IF your fancy new audiophile' preamp requires exotic DC supplies, sumptin' aint right. Of course it might be a sales gimmick too. The earliest tube radios used all batteries, b/c most folks didn't have AC electricity. You are welcome to go back to the stone-ages. its a balance in life too see that fella at 02:20 LOL perfect electricity!
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Last edited by infinia; 16th November 2017 at 02:42 AM.
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Old 16th November 2017, 03:06 AM   #230
Monte McGuire is offline Monte McGuire
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LM317 load capacitance
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Originally Posted by jackinnj View Post
At 300K, a 100uF capacitor has the same thermal noise as a 2.5k resistor, about 6.4nV/RtHz...but
Just to keep things clear, only the real component of impedance of a capacitor, the actual DCR, creates Johnson (thermal) noise. The reactive component is noiseless. The same goes for inductance.

So, if the 100F capacitor has a DCR of 2.5kΩ, then it will be as noisy as 2.5kΩ. It probably does not, and something like 10-100mΩ is more likely. That's the thermal noise contributor, not the impedance of the cap.
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