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schottky vs. soft/fast recovery diodes
schottky vs. soft/fast recovery diodes
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Old 11th October 2010, 06:05 AM   #21
RJM1 is offline RJM1  United States
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Old 12th October 2010, 10:14 PM   #22
goody75 is offline goody75  United States
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Thanks, RJM1.
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Old 12th October 2010, 11:46 PM   #23
Atilla is offline Atilla  Norway
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This article should be an obligatory read upon joining the forum by now. Sooner or later the thread says "read Jim Hagerman's article" and there's that.

I still want to see same measurements done for all the fancy diodes though. Many claims have been made, not many of them have ever been backed up.

I can see how soft recovery could be a nice thing in general.

Ultrafasts? Meh.
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Old 21st October 2010, 07:28 PM   #24
tomchr is offline tomchr  Canada
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Good article. It reflects what I learned in college...

Note that the values for the leakage inductance and circuit capacitance may also be found experimentally.

1) Using an oscilloscope, measure the frequency of oscillation (f_osc) at switch/diode turn-off.
2) Add snubber capacitance (zero series resistance) until the measured frequency of oscillation is reduced to f_osc/2.
3) The secondary circuit capacitance, C_sec, may now be calculated as C_sec = C_added/3, where C_added is the snubber capacitance added in step #2.
4) Calculate the secondary leakage inductance as L_sec = ((1/(2*pi*f_osc))^2)/C_sec.

Now follow Mr. Hagerman's article from the "Determining Values" section. Above procedure takes all leakage and parasitic inductances as well as parasitic capacitances into account. It doesn't require any special tools (unless you consider an oscilloscope to be special). It does, however, require an assortment of caps and a bit of experimenting.

The observant reader may wonder where the factor of three comes from in C_sec = C_added/3. That's quite simple...
Recall, f_osc = 1/(2*pi*sqrt(L_sec*C_sec)). Now add cap until f_osc(new) = f_osc/2 --> f_osc(new) = 1/(2*pi*sqrt(L_sec*(C_sec+C_added))) = 1/(2*2*pi*sqrt(L_sec*C_sec)).
2*2*pi*sqrt(L_sec*C_sec) = 2*pi*sqrt(L_sec*(C_sec+C_added))
2*sqrt(L_sec*C_sec) = sqrt(L_sec*(C_sec+C_added))
4*C_sec = C_sec+C_added
C_sec = C_added/3

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Old 21st October 2010, 08:56 PM   #25
barrows is offline barrows
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Default I have been

experimenting with the power supply on my TPA B-II DAC. First, used a stock parts Placid Bipolar power supply, this uses a standard, slow, Fairchild bridge rectifier. Then, I substitued a bridge built from discrete SMD schottkys from ON semi. The schottkys revealed a little more detail, but seemed to be producing some artifacts as well (perhaps RFI?) a little electronic edge to vocals and horns-the circuit uses .1 uF film caps across the transformer secondaries, but no snubbing directly across the diodes.
Next, I built a small sub board, using a full wave bridge of ON semi MSRF860G diodes (these are very soft recovery, medium speed parts) with a CRC arrangement (3300 uF-R47-3300 uF). Now I am getting fantastic results. Super quiet, lots of detail, and liquid sound with no electronic edge or glaze. I am pretty sold on these MSR soft diodes. I also used no snubbers, and no caps across the transformer secondaries either. It seems to me these super soft diodes do not need the extra circuitry, and this may be an advantage as well (especially for those without scopes) as one can avoid the potential of resonance inducing circuits via extra caps. Full disclosure: the transformer is an EI type, 56 VA.
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Old 24th October 2010, 04:31 AM   #26
Omega_Void is offline Omega_Void  United Kingdom
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It doesn't strike me as an entirely fair comparison.

The ability of radiated RF noise to interfere with other circuitry drops with frequency. Different diodes have different capacitance, so they will re-tune the LC frequency. So the difference in might not be due to intrinsic properties of the diodes themselves.

Eva put up photos of scope traces in another thread showing the addition of snubbers cleaning up the waveform. Especially if you have a scope to verify the results, IMO you should calculate correct snubber values for the different diodes and compare them under these optimised conditions.

I'm not sure that any diode operates entirely without exciting the LC resonance, but it seems to me that ringing could still be induced by external sources of interference, so snubbers would be in order anyway.

That's just how I figure it.
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Old 24th October 2010, 05:29 AM   #27
barrows is offline barrows
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Default No 'scope here,

so anytime I can avoid adding potentially resonance inducing components I am all for it. Certainly if I had a good 'scope, and I wanted to go deeper into this for any reason (sound problems) I would do so. But right now the sound with this component is great. Note that the PS is feeding a shunt regulator, so it may not be as sensitive to incoming noise as a simple three pin linear IC regulator might be.
The results are good enough to make me very impressed with the MSR style diodes in this application. I have also tried Qspeeds and Stealths, but both of these have higher voltage drops, and no apparent sonic advantages over the ON MSRs-once again, via listening tests.
The MSRs have great specs for soft recovery, that and the fact that they sound better is good enough for me.
I would be happy to see some measurements in circuits from those who have good 'scopes as well, and, perhaps, the results of using them with snubbers. Just wanted to share my experience, and am not claiming my experience is definitive.
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Old 29th January 2015, 01:28 PM   #28
carlmart is offline carlmart  Brazil
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At the first time this "diode question" I saw raised, an article in The Audio Amateur with a Gary Galo suggested supply, Rick Miller had made some test, measuring diodes and listening to supplies with them, and the best sounding at the time were the fast/slow decay types.

Back then GI types were the chosen ones, but I don't think GI is no more. Gagy Galo suggested some Vishay Hexfreds, but they are a bit too much (8A) for low current supplies, like on preamps or CD players.

Schottkies did not sound as well as those mentioned, and later reports seem to show that do well in digital circuitry, but not as well in analogue.
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Old 19th July 2016, 11:40 AM   #29
ginetto61 is offline ginetto61  Italy
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Location: Milano
Hi !
thanks a lot for the very much interesting thread.
I still wonder if anyone has direct experience of different diodes in low voltage low current applications.
What would be your first choice for a power supply of a dac ?
Moreover, I cannot locate soft recovery diodes.
If I search on ebay.com fast and ultra fast types pop up immediately, but slow does not provide any result.
I have bought some SB/SR5100 to try out but maybe soft recovery type are better for less RFI generation ?
I sse from datasheets that normal regulators have no suppression of RFI at all.
Thanks a lot again.
Thank you very much indeed
Kind regards,
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Old 20th July 2016, 12:35 AM   #30
phase is online now phase  United States
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I use NTE571 in my DACs, headphone amp, along with rcr snubber arrangements, am pleased with the results.
They are a Philips product rebadged, and while I generally stay away from NTE stuff, these are available near me, and work well.
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