Does a few mV of low-frequency noise matter in a digital
Depends what you call digital..... The PLL supply on your Crystal receiver, your D to A conversion chip.... your low noise oscillator circuit.... your comparator cicuits looking at low voltages, also keep in mind that many logic circuits have no PSRR and a logic high state couples the output directly to the supply voltage. I guess I would say yes it can matter very much. High PSRR circuits do not retain that high PSRR at high frequencies. Go read a few op amp datasheets.
Every bit helps,
Fred
P.S. "But things like diode noise and transformer saturation are well-understood, quite measurable with that nasty ol' scope, and are factors only insofar as they cause the rails to be something other than constant DC"
Stop it please you are making me hurt my self laughing.
They are not that easy to measure with even a good 100MHz scope in the presence of 120Hz signals that are several orders of magnitude higher than the high frequency noise that you are tring to reduce.
I am not saying not to measure things. I am saying knowing what to measure and what to do with the results of those measurements is the art involved here. As is usually the case, the devil is in the details.
Depends what you call digital..... The PLL supply on your Crystal receiver, your D to A conversion chip.... your low noise oscillator circuit.... your comparator cicuits looking at low voltages, also keep in mind that many logic circuits have no PSRR and a logic high state couples the output directly to the supply voltage. I guess I would say yes it can matter very much. High PSRR circuits do not retain that high PSRR at high frequencies. Go read a few op amp datasheets.
Every bit helps,
Fred
P.S. "But things like diode noise and transformer saturation are well-understood, quite measurable with that nasty ol' scope, and are factors only insofar as they cause the rails to be something other than constant DC"
Stop it please you are making me hurt my self laughing.
They are not that easy to measure with even a good 100MHz scope in the presence of 120Hz signals that are several orders of magnitude higher than the high frequency noise that you are tring to reduce. I am not saying not to measure things. I am saying knowing what to measure and what to do with the results of those measurements is the art involved here. As is usually the case, the devil is in the details.
Only if you really understand what you are doing. Do you understand what EMI slow diodes with high snap-off currents and high peak currents due to huge large capacitors an low Ri generates on the mains leads? and how this spoils the integrity of the signals on your small signal cables? And how it disturbs FM reception?
Bernhard, a spectrum analyser can tell you a lot. But watching the step response on an oscilloscope tells you enough to take the proper actions if the image does not suit what you intend. But it requires knowledge and experience
Pjotr, I suppose that I just haven't been silly enough to design a supply that badly! The supplies in my amps, preamps, and crossovers have been quiet, reliable, and low enough source Z to not show anything significant on the rails; maybe I "really understand what I'm doing, " but I doubt it. I just use Ohm, Kirchoff, data books, basic test equipment, and common sense. PS design *is* straightforward if you've got clear goals, set intelligent design parameters, and don't try to do something novel just for novelty's sake.
Don't get me started on switchers. I did that ONCE and never again.
Don't get me started on switchers. I did that ONCE and never again.
I just might have been a bit sarcastic myself. Sorry for being less-than-obvious. I've built a few hundred amps/preamps/xovers in my time (tube, solid-state, and hybrids), so I've got a fair idea of what's involved.
Let me say this carefully, because I truly do not want to offend: you have no idea of what I believe and don't believe, so assumptions in that regard would be more a reflection of your mindset than mine.
Let me say this carefully, because I truly do not want to offend: you have no idea of what I believe and don't believe, so assumptions in that regard would be more a reflection of your mindset than mine.
REGS
Guys,
I see a lot of mileage here on a rather simple issue.
-There's Patwen claiming he hears a difference between to regulators,in casu a bog standard run of the mill 7805 and a bit more sophisticated LM1085.
He prefers the 7805 over the latter,I would expect the reverse on a performance basis.However this is a purely subjective analysis on his part.
So that point is moot.
But I think I know why:the 78xxx series aren't the most extended in bandwidth, far from it and that may well smooth over some digital artifacts.
-A static analysis of a PSU is pretty much worthless as some of you claim.
I second that you have to do at least some measurements under real life conditions.
-The maximum capacitance after the reg is pretty much defined by the datasheet of the manufacturer.Going over it will invariably bring instability and to top it all of it will render the regulator useless.It just won't do its job.
And you better put some right at the output to make that reg behave.
-Try this:half the recommend value at the output ,the rest right where at where your circuit sits.(the consumer end I call it)
And nothing in between please.
-Don't even think about decoupling lousy caps with better ones,use good ones and where appropriate you can use a lot of smaller values in paralel to make a bigger C.
-I've seen some very valid points by Fred
(congratulations BTW,very good "laundry list" as it is being nicknamed)and ALW and some others.
-Why not put your money where your mouth is and build a prototype or two while only changing a regulator in a critical stage.
I know I would hear the difference long term or short term.
-Fact remains that no two different manufacturers offering a similar regulator will carry the same topology underneath.
In the computor industry we often say:RTFM.
And the translation isn't pretty.
Read the datasheet,see what this reg is made of and you'll soon understand why one is better suited for the job than the other.
-Claiming they all are the same and therefore they all sound the same is the biggest B.S. I've ever seen.
-And don't think for a minute this only applies to regulators.
-All too often I see regs used as a cheaper alternative to a well filtered PSU.
Yes, you can get away with it sometimes but definitely not if you're trying to advance the state of the art.
And it will show up even on the most modest S.A.
-Quite frankly I didn't expect this kind of arguement in the digital section where I (obviously wrongly so) assumed the brightest minds were at work.
Back to the bombshelter to duck for the backlash,
Guys,
I see a lot of mileage here on a rather simple issue.
-There's Patwen claiming he hears a difference between to regulators,in casu a bog standard run of the mill 7805 and a bit more sophisticated LM1085.
He prefers the 7805 over the latter,I would expect the reverse on a performance basis.However this is a purely subjective analysis on his part.
So that point is moot.
But I think I know why:the 78xxx series aren't the most extended in bandwidth, far from it and that may well smooth over some digital artifacts.
-A static analysis of a PSU is pretty much worthless as some of you claim.
I second that you have to do at least some measurements under real life conditions.
-The maximum capacitance after the reg is pretty much defined by the datasheet of the manufacturer.Going over it will invariably bring instability and to top it all of it will render the regulator useless.It just won't do its job.
And you better put some right at the output to make that reg behave.
-Try this:half the recommend value at the output ,the rest right where at where your circuit sits.(the consumer end I call it)
And nothing in between please.
-Don't even think about decoupling lousy caps with better ones,use good ones and where appropriate you can use a lot of smaller values in paralel to make a bigger C.
-I've seen some very valid points by Fred
(congratulations BTW,very good "laundry list" as it is being nicknamed)and ALW and some others.
-Why not put your money where your mouth is and build a prototype or two while only changing a regulator in a critical stage.
I know I would hear the difference long term or short term.
-Fact remains that no two different manufacturers offering a similar regulator will carry the same topology underneath.
In the computor industry we often say:RTFM.
And the translation isn't pretty.
Read the datasheet,see what this reg is made of and you'll soon understand why one is better suited for the job than the other.
-Claiming they all are the same and therefore they all sound the same is the biggest B.S. I've ever seen.
-And don't think for a minute this only applies to regulators.
-All too often I see regs used as a cheaper alternative to a well filtered PSU.
Yes, you can get away with it sometimes but definitely not if you're trying to advance the state of the art.
And it will show up even on the most modest S.A.
-Quite frankly I didn't expect this kind of arguement in the digital section where I (obviously wrongly so) assumed the brightest minds were at work.
Back to the bombshelter to duck for the backlash,
RESI
Fellows,
And is their any of you willing to explain this please?
I can tell where this idea comes from but I would be vey careful to implement it though.
Just think about the effect it will have on the PSU internal impedance would tell half the story.
And if you think I send you into the 54'th dimension you better think again.
Sleep well my Darlingtons,
Fellows,
And is their any of you willing to explain this please?
I can tell where this idea comes from but I would be vey careful to implement it though.
Just think about the effect it will have on the PSU internal impedance would tell half the story.
And if you think I send you into the 54'th dimension you better think again.
Sleep well my Darlingtons,
Max cap
"The maximum capacitance after the reg is pretty much defined by the datasheet of the manufacturer.Going over it will invariably bring instability and to top it all of it will render the regulator useless.It just won't do its job."
Nope I don't buy this one I'm afraid. The values shown in datasheets are usually the minimum for stability increasing the value most often increases stability. Larger cap values often work better by lowering the high frequency output noise and impedance of the regulator, sometimes well down into the audio frequency range.
Fred
P.S. From LT1083 data sheet:
"Normally, capacitor values on the order of 100mF are used in the output of many regulators to ensure good transient response with heavy load current changes. Output capacitance can be increased without limit and larger values of output capacitor further improve stability and transient response of the LT1083 regulators"
I am sure that one could go over board though.
"The maximum capacitance after the reg is pretty much defined by the datasheet of the manufacturer.Going over it will invariably bring instability and to top it all of it will render the regulator useless.It just won't do its job."
Nope I don't buy this one I'm afraid. The values shown in datasheets are usually the minimum for stability increasing the value most often increases stability. Larger cap values often work better by lowering the high frequency output noise and impedance of the regulator, sometimes well down into the audio frequency range.
Fred
P.S. From LT1083 data sheet:
"Normally, capacitor values on the order of 100mF are used in the output of many regulators to ensure good transient response with heavy load current changes. Output capacitance can be increased without limit and larger values of output capacitor further improve stability and transient response of the LT1083 regulators"
I am sure that one could go over board though.
HEY FRED
Sorry to wake you.Here it's almost five a clock...
The datasheets I got state a maximum Fred.
I'll stand by that.I've seen al too many a reg fall on its' face overdoing it.
And so could I.
My only problem with it is that I would not claim that to be a cure all unless you design with that in mind from the bottom up.
Cheers,
Sorry to wake you.Here it's almost five a clock...
The datasheets I got state a maximum Fred.
I'll stand by that.I've seen al too many a reg fall on its' face overdoing it.
And so could I.
My only problem with it is that I would not claim that to be a cure all unless you design with that in mind from the bottom up.
Cheers,
I'll be happy to. Send me the circuit you want powered, along with your specs for voltage and current. I'll design and build a supply for it. We'll evaluate the results using a procedure where neither you nor I know which is your supply and which is mine- assuming, of course, that both supplies show nothing but DC and have noise below, say, -100 dB. We'll post the results here.
Your place or mine for the evaluation? I probably have a better wine cellar, so I'd suggest the latter.
Your place or mine for the evaluation? I probably have a better wine cellar, so I'd suggest the latter.
fdegrove, I've posted a few things over at the tube section. The rectifier discussion didn't/doesn't interest me much. There are easier, cheaper, and more efficient ways to generate a stable DC rail, so I'm not real motivated.
No "challenge" intended, BTW, I just wanted to make the point that a power supply is part of an overall design. There are a lot of tools available to accomplish tasks in electronic devices, and how one chooses the tool is best influenced by understanding what you're actually trying to do in some box of gain with phono jacks and a power cord. Saying "submit a power supply design" is equivalent to saying, "design a cog."
And I'm always delighted to open a nice bottle when I have some excellent music playing, so...
No "challenge" intended, BTW, I just wanted to make the point that a power supply is part of an overall design. There are a lot of tools available to accomplish tasks in electronic devices, and how one chooses the tool is best influenced by understanding what you're actually trying to do in some box of gain with phono jacks and a power cord. Saying "submit a power supply design" is equivalent to saying, "design a cog."
And I'm always delighted to open a nice bottle when I have some excellent music playing, so...
smile
Anybody in his right mind would be absolutely delighted with the concentrated knowledge and experience he got for free.
Not this guy. He just started a new thread, complaining that on the other one they gave him so many different answers, and pleaded if someone now please give him the RIGHT answer.
janneman>
Please don't be offended. We are all discussing here, right? For some answers which from my limited experience, I cannot agree on, I expressed my opinions. Taking other's comments without self-thinking is, IMHO. counter productive.
Please don't take that as anything negative, as my opinions could well be wrong. But at least I am trying, testing, listening and try to learn and share as I go along, so please don't shoot.
Anyway, I will post the circuit diagram up when I am back in town in a few days, so we could have something more solid to discuss our opinions on.
Many thanks for all the inputs.
Anybody in his right mind would be absolutely delighted with the concentrated knowledge and experience he got for free.
Not this guy. He just started a new thread, complaining that on the other one they gave him so many different answers, and pleaded if someone now please give him the RIGHT answer.
janneman>
Please don't be offended. We are all discussing here, right? For some answers which from my limited experience, I cannot agree on, I expressed my opinions. Taking other's comments without self-thinking is, IMHO. counter productive.
Please don't take that as anything negative, as my opinions could well be wrong. But at least I am trying, testing, listening and try to learn and share as I go along, so please don't shoot.
Anyway, I will post the circuit diagram up when I am back in town in a few days, so we could have something more solid to discuss our opinions on.
Many thanks for all the inputs.
REGS
Hello,
Absolutely.
Let's also agree that still a fair amount of engineers will dismiss the idea that for a given circuit reg X doesn't sound the same as reg Y.
And after all this IS what we're discussing.
No measuring rig can acurately display what we hear.
OTH,there is far more that can be measured then most seem to believe.
That shows that the LT is a well designed regulator.
Saying you can do this with any off the shelf reg is where I would firmly disagree.
See you,
P.S. SY,can't help but wonder what delicacies you have sitting in your whine cellar....
Hello,
Absolutely.
Let's also agree that still a fair amount of engineers will dismiss the idea that for a given circuit reg X doesn't sound the same as reg Y.
And after all this IS what we're discussing.
No measuring rig can acurately display what we hear.
OTH,there is far more that can be measured then most seem to believe.
That shows that the LT is a well designed regulator.
Saying you can do this with any off the shelf reg is where I would firmly disagree.
See you,
P.S. SY,can't help but wonder what delicacies you have sitting in your whine cellar....
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