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comparing two diodes :
vishay BYV26A - ultra-fast, avalanche sinter glass diode
stm STTH8S12D - fast recovery
the application is a DAC PS... the vishays are in the DAC but thought about upgrading.. but even though the vishay are cheaper they have faster recovery.. seems not to be worth the bother... am I missing something ?
Follow Ups:
Many have found that using a snubber circuit (series resistor and capacitor parallel to transformer secondary, between secondary and diode bridge) is effective in reducing rectifier induced transformer ringing, and may be more effective than using expensive rectifiers.
John Swenson has recommended a version of this, using the same resistor and capacitor values for all transformers.
I use something similar, deriving the resistor value for each individual transformer using a test jig and oscilloscope.
https://www.diyaudio.com/forums/power-supplies/243100-simple-math-transformer-snubber-using-quasimodo-test-jig.html
Which also leads to the question - Which aspect of performance are you hoping to improve? And how do you know changing the diodes won't degrade it, assuming they have any effect at all?
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Buy Chinese. Bury freedom.
Edits: 09/18/18
trying to improve the PS... my thought would be if replacing the current diodes with one that have better specs, faster and softer recovery...
back to my original question... looking at the specs of the existing diodes and a potential replacement that is 2x the cost, the differences are not all that much and my thought is the the diodes in the dac are just fine... ***my original question - am I missing something regarding that ? ***
the DAC is an MHDT Pagoda and the tube buffer is using a 5670 tube...
There's no reason whatsoever to think that changing those diodes will improve performance. Spend your money where it counts. :)
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Buy Chinese. Bury freedom.
thanks Jack.. thats basically the conclusion I came to
The Tungsol BP 5670/2C51 are my all time favorite.
8^)
If your DAC has a bunch of voltage regulators, what's the point of what you're doing?
If you go to a Schottky diode and the raw DC rail(s) increase in voltage, that will increase the dissipation in your voltage regulators.
There just isn't a good reason to do this kind of mod, there are too many risks for unlikely rewards.
the PS has two rails... 15v and 8v... two sets of 4 diodes...
how would changing a diode increase the V coming out of the PS ?
not trying to argue and realize its difficult without seeing how
the dac is built...
Different diodes have very different voltage drops, and often times they will give their voltage drop at one temp/current, while another diode you compare the first to will use a different temperature/current.
thanks Paul ... very true... but you know as well as I do (moreso even) the OEM's look at cost.. if a $0.90 part fits the requirements great.. that does't mean there isn't a equivilent out there that's $9.00, same function but can add to squeezing out better performance.. resistors and capacitors are good examples...
so if there was a better diode that could be used I would consider it... but again looking at the specs of the Vishay avalanche diodes in the dac I think the upgrade gain is minimal... unless I'm missing something which circles back to my original post..
thanks again
It's not necessarily about cost. DAC boards are pricey, another couple of bucks for diodes is no big deal.What I find is that diode tech moves around a lot, and the great schottky diodes of 2-3 years ago aren't necessarily even available anymore.
Also, if you're going to make 2000-3000 DACs, you're best off buying a reel of diodes. If a better diode comes out, are you supposed to throw the diodes you have left away?
Edits: 09/18/18
true... an example is newer silicon carbide diodes... no recovery ?
reading about the differences between silicon diodes and silicon carbide made my head hurt... thanks Paul
HEXFREDs are great at this, see link
They handle heat better too, since they are in a TO-220 case. Usually no snubbing needed.
correct...
but if you look at the specs for the vishay avalanche in the dac they have that do they not ?... as I said I as just going to swap them out but saw they are as fast as most of the others mentioned...
looks like minimal if any improvement...
Yes- likely so. Soft recovery is part of the formula though.
Really what you are looking for is preventing a swept resonance which is caused by the capacitance of the rectifier in tandem with the inductance of the power transformer winding. If its a problem the power supply will be noisy with harmonics. Can't imagine that would be helpful for a DAC power supply :) but the DAC designer may have already done that homework...
thanks Ralph...
But if you are going to replace the diodes I would recommend the appropriate Schotkky diodes.
.
"Happy The Man who can tread thy paths and climb thy ways"
thanks..
have done this before with no issue..
again the question is "whats better ?"
just saying use a schottkky diode is the same problem...
a diode with better specs for the application is the question..
so what schottkky ?
thanks
Fast recovery is prolly good enough. Schottky, UF, whatever. What are you looking to do?
Unless there is an issue, I'd leave the diodes alone. You run the risk of heat damaging both the old ones and the new ones, unless you've replaced these things, before.
Just my 2¢ worth of 2¢.
8^)
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