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Old 7th February 2006, 03:50 AM   #1
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Default Sound Quality from Snubbers

Hello -

I have read with some interests the threads surrounding CarlosFM's use of snubbers in power supplies. I have done some listening tests and would like to report my (preliminary) results.

First of all, CarlosFM's uses the term "snubber" to refer to a series R-C network used as a bypass across the main electrolytic capacitors in a power supply. The goal is to reduce the impedance rise at high frequencies due to the parasitic inductance of the main electrolytic capacitors. Sometimes the term "snubber" is used to refer to a series R-C network across the rectifier diodes, but that is not the subject of this report.

In some of the threads the question was raised, "Why does CarlosFM recommend using an additional bypass C along with the series R-C snubber network?" This seemed a reasonable question to me, as simulations (and also measurements performed by JosephK) seemed to indicate that using the R-C snubber *without* the additional bypass C would give a smoother impedance curve. CarlosFM's reply was essentially that the combination C + R-C sounds better.

In my listening tests I compared:

1) Bypass with only capacitors.
2) Bypass with only R-C snubber networks.
3) Bypass with both R-C snubbers and capacitors.

(Many years ago I compared case #1 against the case with no bypass network at all, and found that using the bypass capacitor sounded better. I therefore did not repeat that experiment at this time.)

With case #1, the presentation was very natural and coherent. However compared to case #2, the size of the soundstage was reduced and the resolution was somewhat lower.

With case #2, in addition to the increased resolution, there was also a increase in dynamic contrast. (The music seemed louder at the same volume setting.) However, the snubbers alone made it so that less-than-perfect recorded CDs sounded quite annoying. To me this is a very important point, as my experience has shown me that equipment which exhibits this type of behavior has some sort of distortion that is exacerbating (or possibly even creating) a problem.

Finally, in case #3 I tried using both together. This seemed to give the best of both worlds, in that it combined the resolution and expanded soundstage of the snubbers with the naturalness and ease of the bypass capacitors.

I have studied the simulated impedance curves produced by these variations, and am currently unable to explain (even in a general, hand-waving sort of way) why these audible differences should exist. However, my conclusion is that CarlosFM is absolutely correct in his recommendations. I would urge fellow readers to try these tests, as they are quite simple to implement and the resulting sonic differences are far from subtle.

Please note that these tests were performed with a discrete, zero-feedback amp, and not a chip amp. Also note that I would consider these sonic differences to be quite significant, and of greater magnitude than the changes produced by many variations in the audio circuits themselves.

Hope this helps,
Charles Hansen
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Old 7th February 2006, 04:06 AM   #2
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Thanks for sharing this with us, Charles. Yes, it does help.

This time, I'd really hope to see an on-topic discussion of people
who tried p-s snubbers out for themselves...
A foolish wish?
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Old 7th February 2006, 04:42 AM   #3
Eva is offline Eva  Spain
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For a scientific perspective on what snubbers actually do to a circuit and what electrical phenomena they are intended to prevent, check that thread. It features waveforms captured from real circuits:

Fast Recovery rectifier diodes

The most interesting stuff starts in page 6 or 7, altough it's worth read from the beginning to understand also the "vodoo" perspective.
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Old 7th February 2006, 05:17 AM   #4
duelbox is offline duelbox  United States
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Charles,

Thanks for taking the time for such a report, as I am considering the use of a snubber circuit. My question is what component values did you use for the test? If you chose component values published from someone else or if you calculated them for yourself and if you did calculate them yourself then what formula did you use?

Many thanks.
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Old 7th February 2006, 01:30 PM   #5
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Quote:
Originally posted by Eva
[B]For a scientific perspective on what snubbers actually do to a circuit and what electrical phenomena they are intended to prevent, check that thread.
Yes, some nice measurements. However, that thread is referring to the "snubbers" used on the rectifier diodes and/or power transformer. This thread is referring to the "snubbers" used on the electrolytic capacitors. I know the terminology is confusing, which is why I made the distinction in the original post.
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Old 7th February 2006, 01:35 PM   #6
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Quote:
Originally posted by duelbox
My question is what component values did you use for the test?
For the front-end power supply I used 3 x 1000 uF for each rail, each bypassed with a combination of 0.047 in parallel with a 1 ohm + 0.047 uF.

For the output stage power supply I used 4 x 6800 uF for each rail, with a single bypass network of 0.1 uF in parallel with a 1 ohm + 0.1 uF.

These values were selected simply because they were the easiest values I had to hand, and they seemed fairly close to what CarlosFM was recommending. I have no idea how he calculates his values. I have tried running simulations to see what would be optimal, but I haven't been able to make sense of it yet.
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Old 7th February 2006, 01:41 PM   #7
Eva is offline Eva  Spain
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I'm aware of the (evident) distinction between capacitor snubbers and diode snubbers. But since I only have evidence of the usefulness and efficiency of the later, I thought that it would be good to show it anyway.
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Old 7th February 2006, 02:07 PM   #8
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Yawn.
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Old 7th February 2006, 02:20 PM   #9
Eva is offline Eva  Spain
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Oh, by the way, the thread about the diode snubbers explains how to select the exact R and C values in order to tame a certain resonance to the desired extent, but in order to do that, you have to take the oscilloscope and expend some time to find such a resonance first. The wrong component values may do nothing or may boost the resonance if the R value chosen is too small
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Old 7th February 2006, 02:23 PM   #10
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Interesting findings, Charles.

I was under exactly same impression when I tried snubbers first time in PS. I expressed it here: http://www.diyaudio.com/forums/showt...ht=#post550100

Later however, I found some some defficiences that eventually put me off that aproach, which I'm not saying isn't good, it's just appeals to different tastes. Nevertherless, I may try it again:

http://www.diyaudio.com/forums/showt...431#post574431

http://www.diyaudio.com/forums/showt...230#post581230
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