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Old 17th May 2018, 01:06 PM   #211
cdsgames is offline cdsgames  Canada
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Finally the "complex interaction" ...was in fact EMI picked up by probes (differential probes )

1Mhz bandwidth..the ground noise (default) on oscilloscope its observed at 625uV

Attached is what we can read on Nirvana output at 1Mhz with a 1A load. (after active filter) at cables connector (pcb)

Noise and ripple of 721uV (150uV over ground noise)

Even better , at 20Mhz noise we observe the same (about 800 uV instead of 721) but we see some HF spikes of 6mV that are also observed in the ground of oscillator at about 3mV).

Still some issues remain..3A we see a drop of 350mV (too high) and testing on each load has to be completed. Of course more testing on the HF spike seen..


While testing all those issues , final PCB will be designed starting Monday .Box also needs to be designed.

Again. There is NO SMPS on the market coming even close to Nirvana. Test data is very clear .

Best 5V SMPS by any company , ever.


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Old 17th May 2018, 02:02 PM   #212
TNT is offline TNT  Sweden
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Spectral view please?

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Old 17th May 2018, 04:01 PM   #213
jean-paul is offline jean-paul  Netherlands
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So for true ultra low noise we still need to build linear PSU's ?
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Last edited by jean-paul; 17th May 2018 at 04:04 PM.
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Old 17th May 2018, 04:21 PM   #214
cdsgames is offline cdsgames  Canada
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JP , I dont think you have LPS that can go lower than 50uV peak/peak 1Mhz bandwidth unless they use a LDO. Nirvana has no LDOs .

Second , across the 0-20Khz we are measuring less than 1.5uV on AP but of course in my books thats meaningless since any DAC/device have LDOs that are great in 0-500Khz (even in Mhz for some devices)

At last , we will start earthing/casing ground next week
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Old 24th May 2018, 02:45 PM   #215
chris14 is offline chris14
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Originally Posted by cdsgames View Post
JP , I dont think you have LPS that can go lower than 50uV peak/peak 1Mhz bandwidth unless they use a LDO. Nirvana has no LDOs .

Second , across the 0-20Khz we are measuring less than 1.5uV on AP but of course in my books thats meaningless since any DAC/device have LDOs that are great in 0-500Khz (even in Mhz for some devices)

At last , we will start earthing/casing ground next week
Any conclusions from the earth/ground tests? My guess is that any effect will be system-equipment chain dependent so a switchable 'float/ground' option may be best. Noted this option in the new streamer from Naim...
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Old 24th May 2018, 03:40 PM   #216
cdsgames is offline cdsgames  Canada
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Yeap thats exactly what we will have (sw floating / ground)


This week we concentrated on common mode noise (differential noise stays at at about 300uV pk/pk at 1Mhz bandwith) and in our tests we have decrease from 150mV (tested with unbalanced probes 20Mhz/2A) to 9mV. We are concluding the CMN tests in the next few days. We found the alu box and every change will be incorporated in the new PCB (new pcb stays 99% same but we are adding 0.8cm to each side so we can slide it in alu casing.
We have also tested IFI, Nokia and some OEM brands SMPS and the minimum we have seen (with unbalanced probes at 20Mhz/2A) is 86mV.. (and yes that was the IFI)
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Old 28th May 2018, 08:18 AM   #217
cdsgames is offline cdsgames  Canada
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Bridge rectifier snubbing (RC)


We have found that a lot of EMI on the oputput comes from bridge rectifier diodes. Simply changing the RC snubber makes a lot of difference on the output (emi almost doubles on the output without RC snubber)


We are fine tuning the values of R (first) and C for the best EMI on the output.



This is the last element that we are "taming"
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Old 28th May 2018, 09:46 AM   #218
Markw4 is online now Markw4  United States
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Originally Posted by cdsgames View Post


We are fine tuning the values of R (first) and C for the best EMI on the output.
Soft recovery is probably more important than fast turn-off for rectifier diodes to help control or eliminate inductor or transformer ringing, but some combination of both is good. Schottky diodes are fast but not as soft as some, in some cases they can add more noise problems. Some soft recovery types here: soft recovery Discrete Semiconductors | Mouser
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Old 28th May 2018, 09:54 AM   #219
cdsgames is offline cdsgames  Canada
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Yeap we took care since starting to use soft recovery diodes.


Still RC snubber improves the noise we are seeing at output
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Old 28th May 2018, 11:04 AM   #220
nigel pearson is offline nigel pearson  United Kingdom
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I was very dubious about soft recovery diodes. I said to myself they can only be like perhaps an RC snubber to each diode. Well, I never equaled a soft recovery diode with an RC snubber. My feeling is it is just an internal capacitance, however it's perfectly placed. It's worth saying these things are not easy to measure, It's said an RC snubber makes a single event spike into a series of lower frequency ripples. That seems likely. Also either-net over mains is more easy to measure.

Douglas Self says says we are likely to get better results with a VAS transistor if the collector to base capacitance is very low and an external high grade capacitor is fitted. Various reasons about linearity given. Others say older amplifier designs were more stable due to the high capacitance of the VAS devices ( and many other reasons ). The soft recovery diode suggests it's not quite that simple. Doubtless to call it capacitance is too simplistic. It's the how and the why it is there. FET's tend to work well as rectifiers as they work differently. Alas too little is written on this.

Active rectification - Wikipedia

mosfet - Why does this Bridge Rectifier claim to have no [Diode] Forward Voltage drop - Electrical Engineering Stack Exchange
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