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Old 11th October 2010, 06:05 AM   #21
RJM1 is offline RJM1  United States
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Snubbers:

http://www.hagtech.com/pdf/snubber.pdf
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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  United States
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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

~Tom
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Old 21st October 2010, 08:56 PM   #25
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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
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@barrows:
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
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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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