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Old 11th January 2013, 05:05 PM   #191
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I still wonder if a standard bridge rectifier, like the KBPC1004 has a predictable reaction common to the likely range of transformers and therefore could be snubbed approximately? For example, it is popular to add 4.7n X2 across the bridge (across the secondary), often, but not always, resulting in an audible improvement. Although the cap might make the transformer perform slightly worse, it has done the bigger job of confining the bridge rectifier noise away from the transformer. So, my question is how to get this particular job done somewhat more reliably with an RC?

Maybe it is possible to use RC values unlikely to make the transformer perform worse, but yet still manage to confine/muffle bridge rectifier noise to keep some of that out of the transformer? In this way, an RC seems more reliable/predictable than a "just the cap" approach.

In my opinion, the KBPC1004 prefab bridge rectifier is ideal for beginners projects because it is clearly marked and non-confusing to install.
Question:
Is there a recommendable, secondary snubbing, estimated RC that can make the KBPC1004 perform as nicely or better than a botique (muffled) bridge rectifier?
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Last edited by danielwritesbac; 11th January 2013 at 05:34 PM.
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Old 11th January 2013, 05:33 PM   #192
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I have a stupid idea, and no means to measure it. But, if there's merit, it probably needs checked out.

A series pair of 10n ordinary polyester capacitors is a 5n with double the loss. This is a cap at high pitches, and effectively an RC at low pitches.

If this were located upon the KBPC1004 from "~" to "~" then would it:
"muffle the power, not the audio?"
Well, that's the point.
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Old 11th January 2013, 06:02 PM   #193
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MKT is still relatively lossless. Now a 3.3u NP lytic? That's an idea. Assuming a NP lytic could handle the AC voltage without reduced lifespan, a relatively large 10u or so with series resistor could be highly effective. My 1.5u+16R snubber is only almost large enough to damp the 14KHz resonance. If I put R too low I end up with a 5KHz resonance.
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Old 11th January 2013, 09:34 PM   #194
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You guys do realize that the _resistor_ is the snubber, right? And you realize that the optional series capacitor is only used to try to ensure that only the unwanted frequencies get exposed to the snubbing/damping/terminating resistor, in cases where there would be too much power dissipated by the resistor otherwise, right?

You COULD "possibly" use an electrolytic, or other capacitor, by itself, IF you happened to find one that had an ESR that was equal to the characteristic impedance of the LC resonance that was causing the ringing or oscillation problem. But that would be extremely rare, I imagine. In every other case, a capacitor by itself is NOT a snubber.

Using a large electrolytic in any other case will likely just make the snubbing resistor get hotter than it needs to get. Or are you trying to make something other than a snubber?
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Old 12th January 2013, 02:14 AM   #195
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Gootee, my point was that my resonance was at 14KHz, and a 1.5u film is still too small to effectively snub it without causing another 5KHz resonance. I mistakenly construed that the cap was the problem. And yes, a lytic could of course be used with the appropriate snubbing resistor, it's just I've been around DIYAudio too long and am lytic phobic . And in this case we don't really need to worry much about the ESR as long as its reasonably low, we can just use a series resistor like we do with film caps.
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Old 12th January 2013, 05:58 PM   #196
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Still looking forward to the possibility of an answer to this:
Is there a recommendable, secondary snubbing, estimated RC that can make the KBPC1004 perform as nicely or better than a botique (muffled) bridge rectifier?
(trying to make a smaller request there)
In comparison, MUR860 can muffle both the AC side and the DC side, while also being very unkind to radio reception and possibly irritate the audio amplifier or at least make extra work. These and other random consequences indicate that "botique bridge rectifier" is not paradise. So, I'd much rather muffle just the AC side of a KBPC1004--That looks a bit more sensible and maybe less likely to randomly nuke a tuner. People who live at fringe range reception areas wouldn't appreciate having to turn off the power amp before listening to the radio. So, it seems that the main task is to confine the bridge rectifier's racket to the locale of the bridge rectifier.
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Old 12th January 2013, 06:14 PM   #197
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Perhaps 15uF+10R would do it. This sets the corner at 1KHz, low enough probably to get both my 14KHz and 5KHz resonances (hopefully not creating a 1KHz resonance). If your secondary output was over 28VRMS you would need more than a 1/4W resistor. I believe 28VRMS~39.5VDC? In any case I would choose a low-ESR lytic if possible. If the ESR of the cap shares a significant voltage with the R, then the cap will be dissipating a share of the heat, and we don't want lytics self-heating.
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Old 12th January 2013, 06:32 PM   #198
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Aren't there some people who use 47nF caps across each rectifier diode? I'm assuming somewhere around 10nF capacitance at the input of the rectifier, but a large variance here could be an issue.
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Old 12th January 2013, 09:16 PM   #199
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Quote:
Originally Posted by keantoken View Post
Perhaps 15uF+10R would do it. This sets the corner at 1KHz, low enough probably to get both my 14KHz and 5KHz resonances (hopefully not creating a 1KHz resonance). If your secondary output was over 28VRMS you would need more than a 1/4W resistor. I believe 28VRMS~39.5VDC? In any case I would choose a low-ESR lytic if possible. If the ESR of the cap shares a significant voltage with the R, then the cap will be dissipating a share of the heat, and we don't want lytics self-heating.
So, what could you do with a 2u2 polyester like http://www.mouser.com/ds/2/315/ABD0000CE29-44537.pdf And, they are rated safe for this application.
Quote:
Originally Posted by keantoken View Post
Aren't there some people who use 47nF caps across each rectifier diode? I'm assuming somewhere around 10nF capacitance at the input of the rectifier, but a large variance here could be an issue.
Technics production units had 10n caps per each diode (pair of specialty 3-pin ceramic caps internally like "pin-10n-pin-10n-pin"), and Mark Houston's gainclone has 10n polyester dip caps per each diode. Both cases, measured unloaded, produce about 1v to 2v less junk after snubbing the diodes. That looks silly expressed in volts; however, it looks impressive if expressed as a percentage. Smaller scale amplifiers are sometimes shown with less capacitance due to hit or miss audio caveats when the capacitance is too large.

I wanted to do something similar except avoiding the DC side, thus avoiding caveat.

So, far, I like the idea of a "snub the secondary" RC with a big enough resistor value to guarantee that it doesn't act like a cap. It would be nice to assure that whatever we did with the cap went into a known location--heating a resistor slightly. Based on the available data, I guess the resistor value to be somewhere in the range of 16 ohms to 96 ohms.

Can a resistor near that range be matched up with an X2 cap to create the needed RC?
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Last edited by danielwritesbac; 12th January 2013 at 09:19 PM.
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Old 13th January 2013, 03:57 AM   #200
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Quote:
Originally Posted by keantoken View Post
Gootee, my point was that my resonance was at 14KHz, and a 1.5u film is still too small to effectively snub it without causing another 5KHz resonance. I mistakenly construed that the cap was the problem. And yes, a lytic could of course be used with the appropriate snubbing resistor, it's just I've been around DIYAudio too long and am lytic phobic . And in this case we don't really need to worry much about the ESR as long as its reasonably low, we can just use a series resistor like we do with film caps.
Again, capacitance does not snub.

For such a low-frequency resonance, you will probably just need a large-value resistor across the secondary, with no capacitor. If you could calculate the characteristic impedance, you could use the optimal R value.

If you know either the L or the C in the LC that is resonating, you can calculate the other one, because you know the resonant frequency.

Here is the usual procedure:

1. Measure the frequency of the resonance or ringing, using an
oscilloscope (or a circuit simulator, if you've modeled the parasitics well).

2. Add a shunt capacitor and adjust the value of this capacitor until the frequency of the ringing is reduced by a factor of two. I've left out the math but the value of this resulting capacitor will be three times (3X) the value of the parasitic capacitance that is creating the resonance.

3. Because the parasitic capacitance is now known, the parasitic inductance can be determined using the formula:

L = 1 / [(2 Pi F) C]

where F = (original) resonant frequency and C = parasitic capacitance.

4. Now that both the parasitic capacitance and inductance are known, the
characteristic impedance of the resonant circuit can be determined using the following formula:

Z = √(L/C)

where L = parasitic inductance and C = parasitic capacitance.

5. The resistor value used for the terminator or for the RC snubber circuit should be equal to Z, the value of the characteristic impedance, and the capacitor, if used, should be sized between four and ten times the parasitic capacitance. The use of larger (than 4X) capacitors slightly reduces the voltage overshoot at the expense of greater power dissipation in the resistor.

NOTE: The resistor, alone, is all that is needed to prevent or damp-out the ringing (or reflections, as the case may be). But if power dissipation in the R would then be too high, a C is added in series with the R, so that only the unwanted frequencies cause currents in the resistor. (And that is the only reason there's a capacitor in a snubber.)
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