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pros and cons of monolithic bridge rectifiers for power amp PS
pros and cons of monolithic bridge rectifiers for power amp PS
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Old 14th August 2017, 01:01 AM   #41
Mark Johnson is offline Mark Johnson  United States
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pros and cons of monolithic bridge rectifiers for power amp PS
Might want to create a brand new thread (so as to avoid polluting this one with off-topic posts) perhaps entitled "Charlie Laub has questions about transformer snubbing"
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Old 14th August 2017, 01:07 AM   #42
CharlieLaub is online now CharlieLaub  United States
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pros and cons of monolithic bridge rectifiers for power amp PS
I dunno, the extreme need for snubbing is certainly related to "pros and cons of monolithic bridge rectifiers", is it not?
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Old 14th August 2017, 05:25 PM   #43
CharlieLaub is online now CharlieLaub  United States
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pros and cons of monolithic bridge rectifiers for power amp PS
Quote:
Originally Posted by CharlieLaub View Post
Can an analog scope also work?
I'm re-posing this question:

Can one use the QuasiModo board with an analog scope?
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Old 14th August 2017, 06:56 PM   #44
Mark Johnson is offline Mark Johnson  United States
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pros and cons of monolithic bridge rectifiers for power amp PS
Please see posts #405, #473, and #1127 in the Quasimodo thread. I tried linking to them here, but for some reason, all three links (which were different, I double checked!) took me to Quasimodo post #1 instead.
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Old 14th August 2017, 08:27 PM   #45
CharlieLaub is online now CharlieLaub  United States
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pros and cons of monolithic bridge rectifiers for power amp PS
Quote:
Originally Posted by Mark Johnson View Post
Please see posts #405, #473, and #1127 in the Quasimodo thread. I tried linking to them here, but for some reason, all three links (which were different, I double checked!) took me to Quasimodo post #1 instead.
Ah, OK, I should have figured that out seeing those images in the thread!

What you have created in the QM jig seems like some nice functionality. Please excuse my naiveté, but I am not sure why one could not just make these measurements on the PS itself, while it is "on"... it seems plausible that one could add the CRC components, choosing your suggested starting values of 10nF and >=150nF, and then trim the 1k pot while looking at a scope of the PS while it is powered on, into a low or no load so that conduction angles are low. I have a sneaky suspicion this doesn't' work for some reason, but am not sure what that is exactly. Is this because the measurement must be done with the transformer primary shorted?

I sort of know what is going on, but only to a shallow level - not enough to know what I don't know (and possibly be a danger to myself)! I would like to learn more about these finer details of PS design that don't seem to be widely disseminated. Learning how to use a scope correctly/safely is also on my to-do list... maybe the jig is a good opportunity to jump into this.
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Last edited by CharlieLaub; 14th August 2017 at 08:32 PM.
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Old 14th August 2017, 09:12 PM   #46
Mark Johnson is offline Mark Johnson  United States
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pros and cons of monolithic bridge rectifiers for power amp PS
You are asking: What would happen if I did X??

The correct answer is: do X and find out.

--------------------------------------------------

Suppose you used some the very best diodes, diodes whose ranking was near the top in the Linear Audio article. The ones that stimulated very very little transformer ringing.

Further suppose your transformer's secondary leakage inductance is very low. In my experience, transformer secondary leakage inductance can vary over a range of more than 100 to 1. Suppose you happen to have a transformer near the bottom end of the range.

Now you've got a low dI/dt (thanks to the use of an excellent diode) at turn-off, and a low leakage inductance L. Thus the voltage spike L*dI/dt at diode turn-off is very small, and you might not be able to trigger your scope on it. Certainly I've seen plenty of real-life power supplies where I couldn't trigger any of my scopes. (That's another reason why Quasimodo the Bellringer was born: no more of this feeble stimulus nonsense, let's make a jig that will deliver a Big Ol' Bohunker WHACK!, big enough to make ANY transformer ring with a dozen volts of peak to peak oscillation).

However, there does exist a (repulsive) workaround, if you're stubbornly determined not to use a Bellringer jig at all: Remove the excellent diodes and temporarily install some terrible diodes. Pick diodes near the bottom of the LA rankings. You'll get more ringing, and now you'll have an easier time of triggering your scope on the ringing waveform. Assuming that you can now see the ringing, tune the snubber. When you've found the optimum value of snubbing resistance, remove the terrible diodes and reinstall the excellent diodes. An extra one or two hours of pleasant DIY hobby time, right?

For me, personally, the answer was: wrong. I would rather spend ten minutes doing a Quasimodo test, than 60 minutes swapping diodes. Plus, the trimmer potentiometer is easy to adjust on the Quasimodo test jig; perhaps not so easy to adjust when it's buried inside the guts of the actual power supply, within the chassis of your audio equipment. And I find it just a little bit safer to perform a Quasimodo test using a 9V battery, than a live-equipment test using the (lethal) AC mains voltages. All other things being equal.
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