DCAudioDIY.com

DC Area Audio DIYer's Community
It is currently March 28th, 2024, 11:41 am

All times are UTC - 5 hours [ DST ]




Post new topic Reply to topic  [ 18 posts ]  Go to page Previous  1, 2
Author Message
PostPosted: June 1st, 2021, 11:12 am 
Offline
User avatar

Joined: February 28th, 2013, 3:31 pm
Posts: 1780
Someone asked me to compare the switcher/filter combo with a linear supply. I did the test of my lab grade linear power supply feeding the NUC directly. Before listening, I ran some scope traces of the power at the input of the NUC both straight from the supply and also with the filter in place. You can see that the unfiltered voltage is actually quite good with no major spikes but rather what appears to be random noise reaching about 50 mv at some places. It did not look as good as the switch mode supply with the filter but a whole lot better than the raw switcher. The supply itself had lower noise than shown when connected to the NUC but it appears the linear is not as good at filtering the noise from the input of the NUC as the filter. I also took measurements with the linear and the filter and it looked virtually identical to the filtered switcher.

I listened to the lab power supply without the filter and then the switcher/filter combo with the same test tracks I used before. To make a long story short, the linear supply unfiltered sounded basically the same as the switcher filtered. If I were splitting hairs, I would say the filtered switcher was slightly better at some points having a little more air and separation, but the differences were so small I would not want to try a blind test. It would probably take a lot more music trials and additional listeners to see if there was truly a difference. I did not try the linear with the filter because even unfiltered the results were so close if not identical that it was not worth the effort. In either case they were both significantly superior to the raw switcher. My take away is that as long as whatever supply is being used has enough voltage and current capability to run the NUC, the filter levels the playing field as far as sound is concerned. Certainly, the filter is a cost effective (if you are a DIYer) way to improve the sound of the NUC. I'm sure there are much better servers available that cost much more than the NUC that may have superior power supplies, making an external filter unnecessary. However, this combo represents great value. Charlie has a custom built server that Jim raves about. Jim says he will try to borrow it so we can compare to the NUC/filter combo. It will be interesting if it happens.


Attachments:
Linear lab grade power supply unfiltered.pdf [220 KiB]
Downloaded 314 times
Linear lab grade power supply filtered.pdf [165.21 KiB]
Downloaded 368 times
Top
 Profile  
 
PostPosted: June 2nd, 2021, 2:17 pm 
Offline
User avatar

Joined: January 15th, 2015, 7:19 am
Posts: 1697
Location: Baltimore MD
I found this on the DIYAudio Forum
https://www.diyaudio.com/forums/analog-line-level/354213-po89zb-inline-dc-filter-smps-wall-warts-preamps-hpa-korg-nutube-etc.html
from the dialogue, this seems to be blessed by Nelson Pass and is a very simple circuit
Attachment:
SMPS_filter_schematic_revA.png
SMPS_filter_schematic_revA.png [ 26.32 KiB | Viewed 5046 times ]


Top
 Profile  
 
PostPosted: June 2nd, 2021, 2:30 pm 
Offline
Site Admin
User avatar

Joined: February 28th, 2013, 10:38 am
Posts: 1682
Tom, in your schematic, what's the purpose of R2?

_________________
I can explain it to you, but I can’t understand it for you.


Top
 Profile  
 
PostPosted: June 2nd, 2021, 3:02 pm 
Offline
User avatar

Joined: February 28th, 2013, 3:31 pm
Posts: 1780
Pelliott321 wrote:
I found this on the DIYAudio Forum
https://www.diyaudio.com/forums/analog-line-level/354213-po89zb-inline-dc-filter-smps-wall-warts-preamps-hpa-korg-nutube-etc.html
from the dialogue, this seems to be blessed by Nelson Pass and is a very simple circuit
Attachment:
SMPS_filter_schematic_revA.png


This will work as a filter and will probably be better than nothing but there are a few things I would do differently:

D1 appears to be a varistor used as a clamp. However, it is rated at 68V with a maximum clamping voltage of 145V. If that voltage were reached, everything downline would probably be toast. In reality, I don't see the need for a varistor on the output of most wall wart power supplies.

The chokes used are only 2 uh which in conjunction with the capacitors used will have a turnover frequency much higher than the combination of the 2.5 mh choke I'm using in conjunction with much higher capacitance. This circuit will filter out the highest frequency noise but will not be effective at lower frequencies. How that will affect the sound I don't have a clue. It will depend on the circuit being fed.

All the capacitors used are electrolytics which are not very good at filtering out high frequencies. Remember that the monolithic ceramics I use on the output are doing double duty, not only filtering anything that might get to the output from the power supply side but also reducing any high frequency noise generated by the buck regulators internal to the NUC. You can see how the output of the linear power supply had the noise reduced by the addition of the filter. The linear supply probably could not reduce the noise being generated by the buck regulators.

The high amount of capacitance in my version also serves as a huge current sink so that any current pulsed caused by the bucking regulators will not affect the voltage on the input to the NUC nearly as much as the smaller storage in this circuit. Will it matter? Who knows?


One thing for sure, the circuit I am using is certainly bullet proof and may be overkill, but it is simple and cheap. In reality, this circuit seems to be no simpler or more complicated than the one I am using. Both should be a slam dunk for any DIYer to build.


Top
 Profile  
 
PostPosted: June 2nd, 2021, 3:04 pm 
Offline
User avatar

Joined: February 28th, 2013, 3:31 pm
Posts: 1780
Roscoe Primrose wrote:
Tom, in your schematic, what's the purpose of R2?

David Berning suggested that adding that would help damp any possible resonances between the filter output section and who knows what from the NUC. He certainly has had a lot of experience with switchers so I took his advice.


Top
 Profile  
 
PostPosted: June 2nd, 2021, 3:20 pm 
Offline
Site Admin
User avatar

Joined: February 28th, 2013, 10:38 am
Posts: 1682
tomp wrote:
Roscoe Primrose wrote:
Tom, in your schematic, what's the purpose of R2?

David Berning suggested that adding that would help damp any possible resonances between the filter output section and who knows what from the NUC. He certainly has had a lot of experience with switchers so I took his advice.


I don't see how it's going to do much considering all the rest of the caps after the mosfet have no resistor in series... Now, if all the caps from C11-C23 connected through R2, then I can see it actually having an effect.

Roscoe

_________________
I can explain it to you, but I can’t understand it for you.


Top
 Profile  
 
PostPosted: June 2nd, 2021, 5:00 pm 
Offline
User avatar

Joined: February 28th, 2013, 3:31 pm
Posts: 1780
David has had some crazy things happen in switch mode power supplies. In one amp he had a resonance develop between the power supply output and a bypass cap in the amplifier section input that blew a fuse that was higher rated than the current coming out of the power supply. He found that there was a resonant circuit that was passing enough current back and forth across the fuse that was higher than the DC draw and higher than the fuse rating. That is where damping can come in. I believe that the combination of the resistor and capacitor can help damp any resonance in the connection between the output and the NUC. The large electrolytic has enough internal impedance that it will probably not contribute to the problem and the monolithic ceramics are often specified especially in high gain Op Amp circuits because they also do not tend to resonate. The one capacitor and series resistor can act as a sink for resonant currents. That section may nor have any effect, but it couldn't hurt so I put it in.


Top
 Profile  
 
PostPosted: June 2nd, 2021, 5:36 pm 
Offline
User avatar

Joined: July 24th, 2015, 4:17 pm
Posts: 1701
Location: Parkville, Maryland
tomp wrote:
David has had some crazy things happen in switch mode power supplies. In one amp he had a resonance develop between the power supply output and a bypass cap in the amplifier section input that blew a fuse that was higher rated than the current coming out of the power supply. He found that there was a resonant circuit that was passing enough current back and forth across the fuse that was higher than the DC draw and higher than the fuse rating. That is where damping can come in. I believe that the combination of the resistor and capacitor can help damp any resonance in the connection between the output and the NUC. The large electrolytic has enough internal impedance that it will probably not contribute to the problem and the monolithic ceramics are often specified especially in high gain Op Amp circuits because they also do not tend to resonate. The one capacitor and series resistor can act as a sink for resonant currents. That section may nor have any effect, but it couldn't hurt so I put it in.

Anytime you have series L/C or parallel L/C circuits you will have the possibility of resonance -- and not in a good way. I have had great success damping speaker crossovers, pulse transformers in digital playback equipment, and last but certainly not least, damping amplifier inter-stage and output audio transformers. "Smearing the signal", the least objectionable problem, can be cleaned up with damping -- and the worst issue is when the resonance can be easily mistaken for mechanical issues or some sort of distortion that typically is blamed on other possibilities such as passive parts or active devices or both.

Every damn thing taking up residence in the signal path from the microphones through to the loud speakers, in this quest for the "Absolute Sound," can impact the end result.

_________________
Walt


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 18 posts ]  Go to page Previous  1, 2

All times are UTC - 5 hours [ DST ]


Who is online

Users browsing this forum: Bing [Bot], Google [Bot] and 41 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
cron
Powered by phpBB® Forum Software © phpBB Group