Peranders
A couple of points, whilst it is basic engineering science, it's also an audio product, hence listening comes in somewhere along the line
I'd be curious as to what references you feel are better, the LM329 is inexpensive and has low noise relative to it's output voltage.
This allows less noise gain within the system, resulting in less noise in the system as a whole.
Aboslute accuracy of the reference is irrelevant here as is long-term stability.
There's few, if any, bandgap devices that would beat it, sonically, and not many sub-surface zener alternatives.
And there is LOADS of tweaking in there.
But to test your authoritative statement, please tell us of the SONIC effects of altering various circuit parts
Andy.
A couple of points, whilst it is basic engineering science, it's also an audio product, hence listening comes in somewhere along the line
I'd be curious as to what references you feel are better, the LM329 is inexpensive and has low noise relative to it's output voltage.
This allows less noise gain within the system, resulting in less noise in the system as a whole.
Aboslute accuracy of the reference is irrelevant here as is long-term stability.
There's few, if any, bandgap devices that would beat it, sonically, and not many sub-surface zener alternatives.
And there is LOADS of tweaking in there.
But to test your authoritative statement, please tell us of the SONIC effects of altering various circuit parts
Andy.
Re: Peranders
This design can afford sufficient LP-filtering so the noise is less important I would say. You could use almost anything but if you required low tempco, low drift, etc you have to look at the reference itself. I still think most of the design is normal, nothing weird and not very tweaked in the sence in being weird.ALW said:
Well, here's a few questions to ponder: -
1. Why is the divider impedance around the op-amp still so low, when on the AD825 FET-input op-amp current noise would dominate (and hence imply a higher impedance)?
2. What are the disadvantages of trying to filter a noisy reference sufficiently, what effect does this have sonically, with the circuit as-is?
There's more, but it's easy to make the mistake that because a circuit looks simple, it is simple.
Measurement, Kirchoff or anything else will not answer those questions for you, but your ears will.
Andy (playing Fred's agent-provocatuer game)
1 Jung used the AD797 and to get low noise he used low resistor values. A basic rule is also to have as low values as possible so noise will be low and stray caps don't interfere too much. 1 kohms (if I have seen it right) is not very low, rather low.
2 No disadvantage at all! Possibly slow startup.
The reference Jung used is pretty much average, like the 431 but 6 dB lower noise. I think also Jung's text is straight forward, I agree to everything.
2 No disadvantage at all! Possibly slow startup.
The reference Jung used is pretty much average, like the 431 but 6 dB lower noise. I think also Jung's text is straight forward, I agree to everything.
Uh oh........ not even experts this time*
"The real benefit comes from the bootstrapping the op-amp."
Well................
This is really only true at frequencies where the PSRR of the op amp is high. As the PSRR drops with increasing frequency some issues arise. Here lies the paradox. The whole point of a very low impedance supply is to keep the voltage at the supply pins free from modulation. In this regulator the op amp supply is intimately coupled to the op amps (via two followers) output currents modulation of its own supply.
That is the very antithesis of the principle reducing the modulation of supply by load currents that regulation is designed to do. An additional RC filter for the op amp in the regulator seems prudent to me. The supply AC currents to the op amp would seem to be small enough (the AC load current demands of the regulator divided the Hfe of the two followers) to make the supply for the op amps increased impedance less important than the very significant improvement in the PSSR for the op amp.
The PSRR issue becomes very interesting at the point where the inductive output impedance of the regulator resonates with output capacitor and extremely interesting with a high Q low ESR capacitor! The very low inductance with a high gain bandwidth op amp pushes this to a high frequency where the PSRR for the op amp is poor.
This is more than just an academic exercise and is what seems to be a real life issue with the topology. The behavior of audio circuits at RF frequencies can have real implications for the sonics. This has been an area of some discussion on the forum in the area of diode bridge switching noise on audio circuits.
There is no such thing as a free lunch.
"2. What are the disadvantages of trying to filter a noisy reference sufficiently, what effect does this have sonically, with the circuit as-is?"
Leakage current in electrolytic capacitors can contribute to noise and voltage drift of the reference voltage seen by the op amp.
http://www.analog.com/UploadedFiles/Technical_Articles/3752210Publication_V-Ref.pdf page 18
I will now sit and wait for the fur to fly in the ensuing cat fight.....
* Andy is quite sharp but is too modest to call himself an expert.
"The real benefit comes from the bootstrapping the op-amp."
Well................
This is really only true at frequencies where the PSRR of the op amp is high. As the PSRR drops with increasing frequency some issues arise. Here lies the paradox. The whole point of a very low impedance supply is to keep the voltage at the supply pins free from modulation. In this regulator the op amp supply is intimately coupled to the op amps (via two followers) output currents modulation of its own supply.
That is the very antithesis of the principle reducing the modulation of supply by load currents that regulation is designed to do. An additional RC filter for the op amp in the regulator seems prudent to me. The supply AC currents to the op amp would seem to be small enough (the AC load current demands of the regulator divided the Hfe of the two followers) to make the supply for the op amps increased impedance less important than the very significant improvement in the PSSR for the op amp.
The PSRR issue becomes very interesting at the point where the inductive output impedance of the regulator resonates with output capacitor and extremely interesting with a high Q low ESR capacitor! The very low inductance with a high gain bandwidth op amp pushes this to a high frequency where the PSRR for the op amp is poor.
This is more than just an academic exercise and is what seems to be a real life issue with the topology. The behavior of audio circuits at RF frequencies can have real implications for the sonics. This has been an area of some discussion on the forum in the area of diode bridge switching noise on audio circuits.
There is no such thing as a free lunch.
"2. What are the disadvantages of trying to filter a noisy reference sufficiently, what effect does this have sonically, with the circuit as-is?"
Leakage current in electrolytic capacitors can contribute to noise and voltage drift of the reference voltage seen by the op amp.
http://www.analog.com/UploadedFiles/Technical_Articles/3752210Publication_V-Ref.pdf page 18
I will now sit and wait for the fur to fly in the ensuing cat fight.....
* Andy is quite sharp but is too modest to call himself an expert.
Attachments
"Its only 1.75" wide by 1.5" tall. I don't think thats very big.
I blew up the layout for readability.
Thanks for your comments,
Craig Beiferman"
ummmmm...... How high do the components stand off the board?
Pretty tight fit for even brand X
Yes Peranders I do have further information on the regulators pictured. Why give them free advertising here?
Meeeyowwww!
I blew up the layout for readability.
Thanks for your comments,
Craig Beiferman"
ummmmm...... How high do the components stand off the board?
Pretty tight fit for even brand X
Yes Peranders I do have further information on the regulators pictured. Why give them free advertising here?
Meeeyowwww!
Attachments
Re: bootstrapping
Hi Craig,
Sonically I found no advantage in powering the opamps from the regulated supply i.e. the output of the regulators.
RC filters on the supplies of the opamps as also suggested by Walt Jung seriously diminished the bass slam of the supply. This is done in the Mark Levinson PLS-150 powersupply for the ML-1 preamplifier with detrimental effect. A LM317/337 combo sounded better!
This one is interesting I think..........
http://headwize2.powerpill.org/projects/showproj.php?file=gilmore3_prj.htm
Though I found sound is better without preregulators......
dipchip said:peranders,
The real benefit comes from the bootstrapping the op-amp.
This means that the op-amp is powered directly from the regulated output voltage of the circuit.
Normally, if the op-amp were powered from the supply, any ripple on the op-amp supply would show up as noise on the output.
But now, the regulated output powers the op-amp,
and the regulated output is also the feedback to the op-amp.
So the noise is now much more common mode, and hence the
big 30 to 35 dB improvement over typical regulators.
Thanks,
Craig Beiferman
Hi Craig,
Sonically I found no advantage in powering the opamps from the regulated supply i.e. the output of the regulators.
RC filters on the supplies of the opamps as also suggested by Walt Jung seriously diminished the bass slam of the supply. This is done in the Mark Levinson PLS-150 powersupply for the ML-1 preamplifier with detrimental effect. A LM317/337 combo sounded better!
This one is interesting I think..........
http://headwize2.powerpill.org/projects/showproj.php?file=gilmore3_prj.htm
Though I found sound is better without preregulators......
"RC filters on the supplies of the opamps as also suggested by Walt Jung seriously diminished the bass slam of the supply.'
bigger cap, smaller resistor....... Actually the bootstrap gives extremely good input noise rejection at low frequencies. I think line noise rejection may be more important than output impedance. It may be the reason for the popularity of shunt regulators which also can be bootstraped.
bigger cap, smaller resistor....... Actually the bootstrap gives extremely good input noise rejection at low frequencies. I think line noise rejection may be more important than output impedance. It may be the reason for the popularity of shunt regulators which also can be bootstraped.
Re: regulator
That must have been an outstanding year, then.
I buy issues from the news-stand a couple times each year when I am traveling. I have yet to be impressed by that magazine on an issue to issue basis. There's nuggets of greatness (like the Zen, Thor etc) but then there is things like low voltage biased tube headphone amps designed for lots of distortion, silly Macintosh amp output tube modification plates when simple socket rewiring would be better in every way, and on and on. Then there's articles like the moving coil transformer project which entails putting a transformer in a plastic case with RCA jacks (not even balanced inputs for god's sake!).
Then there's a project with some meat, and instead of pushing the marginal crap out of a particular issue, they spread the article over several issues.
$20 for all the back issues strikes me as "well worth it"
Sheldon
janneman said:
That must have been an outstanding year, then.
I buy issues from the news-stand a couple times each year when I am traveling. I have yet to be impressed by that magazine on an issue to issue basis. There's nuggets of greatness (like the Zen, Thor etc) but then there is things like low voltage biased tube headphone amps designed for lots of distortion, silly Macintosh amp output tube modification plates when simple socket rewiring would be better in every way, and on and on. Then there's articles like the moving coil transformer project which entails putting a transformer in a plastic case with RCA jacks (not even balanced inputs for god's sake!).
Then there's a project with some meat, and instead of pushing the marginal crap out of a particular issue, they spread the article over several issues.
$20 for all the back issues strikes me as "well worth it"
Sheldon
Free advertising
http://www.audiocominternational.com/store/superregulators.asp
if you want to see the regulators Fred was referring to.
They also make a q power regulator that is even more expensive.
And I for one would be interested in a reasonably priced PWB or kit.
Randy
http://www.audiocominternational.com/store/superregulators.asp
if you want to see the regulators Fred was referring to.
They also make a q power regulator that is even more expensive.
And I for one would be interested in a reasonably priced PWB or kit.
Randy
"Uh oh........ not even experts this time"
Ouch that hurt!
--------------------------------------------------------------------------
"The real benefit comes from the bootstrapping the op-amp."
Well................
This is really only true at frequencies where the PSRR of the op amp is high. As the PSRR drops with increasing frequency some issues arise.
Yes, thank goodness the PSSR of the op-amp is so high in the audio range that
we are interested in.
---------------------------------------------------------------------------------
"Here lies the paradox. The whole point of a very low impedance supply is to keep the voltage at the supply pins free from modulation. In this regulator the op amp supply is intimately coupled to the op amps (via two followers) output currents modulation of its own supply."
Its not a paradox, its a benefit. Whats better. The ripple before the regulator's pass stage
or after. The inherent PSRR of the op-amp insures that the ripple after the pass stage will be less than before. The op-amps inputs
are also filtered insuring that the op-amp is not producing any oscillations, thereby not directly contributing self induced modulation.
-------------------------------------------------------------------------------
"An additional RC filter for the op amp in the regulator seems prudent to me. "
There is a RC filter already in the feedback return path.
But if a lowpass filter was added to the op-amps supply.
The R in series with the op-amps supply lines would limit slew rate
and probably decrease performance.
-Craig Beiferman (non-expert)
P.S. Fred I'm a dog person.
Ouch that hurt!
--------------------------------------------------------------------------
"The real benefit comes from the bootstrapping the op-amp."
Well................
This is really only true at frequencies where the PSRR of the op amp is high. As the PSRR drops with increasing frequency some issues arise.
Yes, thank goodness the PSSR of the op-amp is so high in the audio range that
we are interested in.
---------------------------------------------------------------------------------
"Here lies the paradox. The whole point of a very low impedance supply is to keep the voltage at the supply pins free from modulation. In this regulator the op amp supply is intimately coupled to the op amps (via two followers) output currents modulation of its own supply."
Its not a paradox, its a benefit. Whats better. The ripple before the regulator's pass stage
or after. The inherent PSRR of the op-amp insures that the ripple after the pass stage will be less than before. The op-amps inputs
are also filtered insuring that the op-amp is not producing any oscillations, thereby not directly contributing self induced modulation.
-------------------------------------------------------------------------------
"An additional RC filter for the op amp in the regulator seems prudent to me. "
There is a RC filter already in the feedback return path.
But if a lowpass filter was added to the op-amps supply.
The R in series with the op-amps supply lines would limit slew rate
and probably decrease performance.
-Craig Beiferman (non-expert)
P.S. Fred I'm a dog person.
Re: Re: regulator
Of course it is normal engineering, not voodoo. The trick is to get it all together in the optimum way. Surprisingly, the people that can do that seem to be just a very small proportion of those who know kirchoff and ohms law, even a very small proportion of all those with engineering degrees.
Could you give us the better references?
Jan Didden
peranders said:
Of course it is normal engineering, not voodoo. The trick is to get it all together in the optimum way. Surprisingly, the people that can do that seem to be just a very small proportion of those who know kirchoff and ohms law, even a very small proportion of all those with engineering degrees.
Could you give us the better references?
Jan Didden
Re: Re: Re: regulator
Hi Jan,
It surprises me Per Anders is suggesting better references while he is using the LM431 is his "Ultra Low Noise Power Suppy" QSXPS.
"Better" i.e. lower noise references would be f.a. AD586, LT1021-5, Ref02, MAX6250. Signigficantly lower noise are only the AD586 and the MAX6250 with 1µF noise reduction cap applied.
I have experimented a bit with these references compared to the LM329 fed by a constant current source comprised of a red LED and a transistor. The difference in SOUND is very small I concluded, except for the MAX6250 that seems to impose its own sonic footprint on the sound. Very weird.
As Fred remarked in a earlier discussion about these type of regulators the LM329 is easier to apply.
(You can not flipover these IC type references like the LM329 for the negative supply). But a way around is the approach by Kevin Gilmore using the negative regulator as a 1x inverting amplifier of the positive regulated supply. Is that a good thing to do?
janneman said:
Hi Jan,
It surprises me Per Anders is suggesting better references while he is using the LM431 is his "Ultra Low Noise Power Suppy" QSXPS.
"Better" i.e. lower noise references would be f.a. AD586, LT1021-5, Ref02, MAX6250. Signigficantly lower noise are only the AD586 and the MAX6250 with 1µF noise reduction cap applied.
I have experimented a bit with these references compared to the LM329 fed by a constant current source comprised of a red LED and a transistor. The difference in SOUND is very small I concluded, except for the MAX6250 that seems to impose its own sonic footprint on the sound. Very weird.
As Fred remarked in a earlier discussion about these type of regulators the LM329 is easier to apply.
(You can not flipover these IC type references like the LM329 for the negative supply). But a way around is the approach by Kevin Gilmore using the negative regulator as a 1x inverting amplifier of the positive regulated supply. Is that a good thing to do?
Re: Re: Re: Re: regulator
I think it's important to have low noise voltage references if you can't use heavy filtering (DAC's, ADC's). In audio it's cool to use a really expensive voltage reference but my design goal was to use normal parts, easy to get and I think 431 is a really good reference for the cost. In my case I have used a second order LP-filter and if you compare Jung's text you see that a LP-filter does wonders when we talk noise.Elso Kwak said:Hi Jan,
It surprises me Per Anders is suggesting better references while he is using the LM431 is his "Ultra Low Noise Power Suppy" QSXPS.
"Better" i.e. lower noise references would be f.a. AD586, LT1021-5, Ref02, MAX6250. Signigficantly lower noise are only the AD586 and the MAX6250 with 1µF noise reduction cap applied.
I have experimented a bit with these references compared to the LM329 fed by a constant current source comprised of a red LED and a transistor. The difference in SOUND is very small I concluded, except for the MAX6250 that seems to impose its own sonic footprint on the sound. Very weird.
As Fred remarked in a earlier discussion about these type of regulators the LM329 is easier to apply.
(You can not flipover these IC type references like the LM329 for the negative supply). But a way around is the approach by Kevin Gilmore using the negative regulator as a 1x inverting amplifier of the positive regulated supply. Is that a good thing to do?
supply
Elso, Per,
First of all I don't like to use an inverted version of a pos supply for a neg supply. What you are doing is copying noise and ripple from one supply to the other. Especially ripple, which is correlated to the signal, should be kept out as much as possible. I admit that this is not based on exhaustive testing, just my gut feeling.
I have to disagree with Per. In isolation, you CAN say that the filter does wonders. But don't forget that the end result is the outcome of a lot of related factors. Surely you agree that using both a low noise reference AND the noise filter give a better result than a mediocre reference and a filter? The same goes for the opamp. I think I read you still use the LM324 Per, really, you're doing yourself a big disserve. This opamp can't come close to a modern wideband one in terms of wideband ripple and input noise rejection, wideband very low output impedance etc. And please, don't tell me "but it sounds better". This is an engineering discussion.
Jan Didden
Elso, Per,
First of all I don't like to use an inverted version of a pos supply for a neg supply. What you are doing is copying noise and ripple from one supply to the other. Especially ripple, which is correlated to the signal, should be kept out as much as possible. I admit that this is not based on exhaustive testing, just my gut feeling.
I have to disagree with Per. In isolation, you CAN say that the filter does wonders. But don't forget that the end result is the outcome of a lot of related factors. Surely you agree that using both a low noise reference AND the noise filter give a better result than a mediocre reference and a filter? The same goes for the opamp. I think I read you still use the LM324 Per, really, you're doing yourself a big disserve. This opamp can't come close to a modern wideband one in terms of wideband ripple and input noise rejection, wideband very low output impedance etc. And please, don't tell me "but it sounds better". This is an engineering discussion.
Jan Didden
Re: supply
LM324 isn't so bad if they are used right but of course you can choose other types. I don't disagree on that.
16 uV noise isn't so bad (if you compare to a 78xx) but this noise is mostly generated by LM324 so it's easy to lowering the noise simply to change opamp.
My design idea was to use a slow opamp and creating a slow regulator because it was intended for rather constant loads. Noise isn't a big thing when opamps are used as ampiflying elements but if we talk MC, MM phono amp with discrete design it more important, very much more.janneman said:
LM324 isn't so bad if they are used right but of course you can choose other types. I don't disagree on that.
16 uV noise isn't so bad (if you compare to a 78xx) but this noise is mostly generated by LM324 so it's easy to lowering the noise simply to change opamp.
I'm pretty amazed by this discussion compared to this .
78xx is quite alright as long as the right brand is chosen and here is 431 a peice of junk. I'm really 
.
If you have no demands of speed I think regulator choice is rather unimportant as long as you can filter out noise and the load is rather constant och the application doesn't need extra stable voltage.
78xx is quite alright as long as the right brand is chosen and here is 431 a peice of junk. I'm really
.If you have no demands of speed I think regulator choice is rather unimportant as long as you can filter out noise and the load is rather constant och the application doesn't need extra stable voltage.
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