IMO (Do you see i use it!!! ;O) ...
The only place i would use an LC or PI filter is to remove digital noise from SMPS running at 150 - 300KHz or noise from uC. At this point this type of filter works fine..
As you say 15Hz which means big inductors!!!
I think when you choose a well designed PSU you will have a high PSRR over a wide area (more than -60dB). And i do not think that a passive filter (inductors and caps) will provide you with -60dB @ 50Hz.
You will also be able to get a really low noise (less than 10nV/SQ root(Hz))from such an design when you look at the applicationnote from Walt G. Jung (AD797)
You also do not have to deal with large inrush currents in an preamp!
I think this is also cheaper than big inductors and caps!
Sonny
The only place i would use an LC or PI filter is to remove digital noise from SMPS running at 150 - 300KHz or noise from uC. At this point this type of filter works fine..
As you say 15Hz which means big inductors!!!
I think when you choose a well designed PSU you will have a high PSRR over a wide area (more than -60dB). And i do not think that a passive filter (inductors and caps) will provide you with -60dB @ 50Hz.
You will also be able to get a really low noise (less than 10nV/SQ root(Hz))from such an design when you look at the applicationnote from Walt G. Jung (AD797)
You also do not have to deal with large inrush currents in an preamp!
I think this is also cheaper than big inductors and caps!
Sonny
true, i was looking at the walt jung precision regulators using AD797, but harry, jam, etc. seem to have a distaste for active regulation... they seem to think that the "sound" of a power supply is really the sound of the components and topology used, and they dislike the sound of active regulation with lots of feedback (i can't really blame them). they seem to think such a regulator tends to add noise on the line, particularly with dynamic loads and changing input voltages. i don't have my doubts that choke input filter will have a coloration of its own though, particularly if the resonant frequency is not low enough - could end up doing funky things in the bass.
It does not have to be a regulator as we normally see (LM317, LM78XX etc.) it can be a currentsource and a shunt (Some kind of Zener but with a low noise level) to ground which dissipates the remaining current not used by the stage driven by the PSU.
This kind of circuit together with OSCON or Panasonic FC Caps (Any low impedance cap) as bypass will have a low impedance and a high PSRR over a wide area and does not add feedback loops.
Sonny
This kind of circuit together with OSCON or Panasonic FC Caps (Any low impedance cap) as bypass will have a low impedance and a high PSRR over a wide area and does not add feedback loops.
Sonny
hmm, i noticed digikey stopped carrying a lot of panasonic caps like FC. or maybe i am just missing it in the catalog. did panasonic discontinue HF/HFU? have you tried Nichicon Muse? someone who compared caps said Pana HF has among the lowest ESR at high frequencies and a nice, crisp sound quality but Muse has a smoother, warmer, more natural tonal quality... so i personally use Pana HFU for digital supplies and Muse for analog supplies. seems to work well, but i haven't really tried other combinations... have also tried some small black gate NPs and they seem to work ok, although i am not so sure replacing a .1uF stacked ceramic decoupling caps on my DAC supply lines with .1uF Black Gate BG-NX (claimed to have 1GHz effectiveness) was a good idea, i think the ceramic supressed noise a little better...
have you tried Nichicon Muse? - No.
I am a bit lost like you.. You see i have not before tried to change El-caps to hear the difference as an experiment. I have change caps and opamp in my CD-player. Which have maked an big improvement.
I have changed to parts i have tested at my work. Like testing caps in a SMPS which i think is a good way to compare different type of elcaps for their performance.... Thats my reason to choose Panasonic FC and Sanyo OSCON caps. Elna .. They simply perform better!
I have tested different types of filmcaps for their performance tried out LC filters after SMPS .. etc...
Tantal caps perform well in SMPS but they generate a lot of noise (You can hear it very easily)... They are an exception!!
What i have tested for sound improvement is MKT types versus Polyprop. types.
What i see from what people say about sound quality "mostly" matches the performance shown in the datasheet.
One important thing about decoupling of analog circuit is to keep lead length short... to minimize lead inductance which reduces performance of the decoupling.
I know that Jelmax says that there parts perform well up to 10GHz... I think this is a person in the sales department who have wrote it .. I do not believe that such a part perform better than film caps or ceramic caps above 100MHz
I would not change to a Blackgate but a good polyprop with short legs!
Sonny
I am a bit lost like you.. You see i have not before tried to change El-caps to hear the difference as an experiment. I have change caps and opamp in my CD-player. Which have maked an big improvement.
I have changed to parts i have tested at my work. Like testing caps in a SMPS which i think is a good way to compare different type of elcaps for their performance.... Thats my reason to choose Panasonic FC and Sanyo OSCON caps. Elna .. They simply perform better!
I have tested different types of filmcaps for their performance tried out LC filters after SMPS .. etc...
Tantal caps perform well in SMPS but they generate a lot of noise (You can hear it very easily)... They are an exception!!
What i have tested for sound improvement is MKT types versus Polyprop. types.
What i see from what people say about sound quality "mostly" matches the performance shown in the datasheet.
One important thing about decoupling of analog circuit is to keep lead length short... to minimize lead inductance which reduces performance of the decoupling.
I know that Jelmax says that there parts perform well up to 10GHz... I think this is a person in the sales department who have wrote it .. I do not believe that such a part perform better than film caps or ceramic caps above 100MHz
I would not change to a Blackgate but a good polyprop with short legs!
Sonny
yeah, the black gate promo material looks like a lot of hype and not much real empirical evidence. but people say they sound good, and i think they sound good, so that is good enough for me, at least in some applications. but as you say i would not rely on them for proper filtering in the RF range. i'd say even 1MHz is pushing it with any 'lytic, the ESR is pretty high by then.
i shoud really go open up my DAC and put some proper small-value film caps near the chips, maybe some small polystyrenes i have lying around. i would have used Panasonic P polypropylenes, but they are too big in the .1uF size and don't fit on my board. it would be nice to find some more compact film caps with excellent HF characteristics (low dissipation etc.)
btw, i remember there was a big debate on Usenet a while back on the "ultimate" bypass method for low-level circuits. the techies who did all the measuring said the widest-bandwidth decoupling was provided by a HF 'lytic (like Panasonic FC), bypassed by stacked or chip ceramic types. they claimed that this gave lowest and most stable ESR across all frequencies of interest (from audio to UHF). they felt film caps had too much parasitic inductance etc. to be effective in the high RF range. however this did not take into account the sound quality of ceramics (of course the techies say there is no such thing as "sound quality"), and the conclusions were hotly debated. this scheme probably works well form digital and mixed-signal supplies though.
sorry... what's SMPS? =p
cheers,
marc
Re: felt film caps had too much parasitic inductance etc. to be effective in the high RF
so maybe all those tweakers ripping ceramics out of there DACs are not doing themselves a favor after all huh... i guess it is pretty obvious to leave ceramics in digital circuits. what's not so clear is what to use for mixed signal supplies, e.g. the DAC itself. or even the analog supplies for the output stage of the DAC, which is subject to radiated noise from the digital circuits. with 50MHz opamps in there, it could be necessary to keep some small ceramics in there to ensure proper RF decoupling, yes? this is why i'm a little wary of the "ceramics suck" mentality so many 'philes take... yes they do suck, but what else are you gonna use here?
HarryHaller said:
so maybe all those tweakers ripping ceramics out of there DACs are not doing themselves a favor after all huh... i guess it is pretty obvious to leave ceramics in digital circuits. what's not so clear is what to use for mixed signal supplies, e.g. the DAC itself. or even the analog supplies for the output stage of the DAC, which is subject to radiated noise from the digital circuits. with 50MHz opamps in there, it could be necessary to keep some small ceramics in there to ensure proper RF decoupling, yes? this is why i'm a little wary of the "ceramics suck" mentality so many 'philes take... yes they do suck, but what else are you gonna use here?
hmm ok, sounds good. i will add some FC caps to my next digkey order (need to start collecting parts for prototyping). i usually use Nichicon Muse for analog supplies but i'd be interested in comparing them. they are comparable in size/value/voltage/price so maybe i will do some listening tests. i've also used Elna Cerafine a little but as far as i can tell they're discontinued.
recommended rectifiers
i have used HEXFREDs and harris hyperfasts in the past and thought they sounded good, but i dunno if they are worth the extra trouble/expense over a conventional bridge rectifier. i figure that bypassing each leg of a decent bridge with a small stacked film cap will keep the noise down. but mainly, i am too lazy/cheap to wire up discrete diodes.
at least for prototyping purposes, before the parts tweaking begins, i will be using conventional bridges for the supply. given that, is there much difference between different brands/types of bridge rectifiers, other than ratings? i was gonna use a fairly generic General Semi 6A/400V part, for my +/- 24V supply (using two 30VCT @1.7A transformers)...
i have used HEXFREDs and harris hyperfasts in the past and thought they sounded good, but i dunno if they are worth the extra trouble/expense over a conventional bridge rectifier. i figure that bypassing each leg of a decent bridge with a small stacked film cap will keep the noise down. but mainly, i am too lazy/cheap to wire up discrete diodes.
at least for prototyping purposes, before the parts tweaking begins, i will be using conventional bridges for the supply. given that, is there much difference between different brands/types of bridge rectifiers, other than ratings? i was gonna use a fairly generic General Semi 6A/400V part, for my +/- 24V supply (using two 30VCT @1.7A transformers)...
For all the Shunt reg fans DIYZONE has a redesign of the STAX design using easier to obtain transistors, MPS8599, MPS8099, TIP127 etc.
Its ±12V but that shouldn't be a problem for the brains trust here.
<a href="">Speedo high speed parallel connection steadily press the fiery is listed! </a>
Thats what the translation page I used called it.
If you are going to translate this page, I'd suggest <a href="http://sangenjaya.arc.net.my/index-e.html">Arcnet Translation</a> Tradition<i><font size="-1" >al</font> </i>Chinese > English, does a fairly good job, and is the only translator that does Traditional Chinese.
Regards
James
Its ±12V but that shouldn't be a problem for the brains trust here.
<a href="">Speedo high speed parallel connection steadily press the fiery is listed! </a>
Thats what the translation page I used called it.
If you are going to translate this page, I'd suggest <a href="http://sangenjaya.arc.net.my/index-e.html">Arcnet Translation</a> Tradition<i><font size="-1" >al</font> </i>Chinese > English, does a fairly good job, and is the only translator that does Traditional Chinese.
Regards
James
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