Value of snubber cap on 700b bridge?

[premiumplus]

Hi guys,
I'm putting in my new filter caps from the group buy, and I don't have any snubber caps on my bridge.
What is the correct value to use for these? I'm seeing various opinions all over the net, and formulas to use, etc...but I'm a big fan on never re-inventing the wheel.
What's the preferred value? I'm thinking .01uF/400 to 600 volt range...is this going to work?
Thanks!

 

[premiumplus]

I've got some .01 1200v spragues that are going in. I'll give them a try, I should think they'd do the trick...let me know if I'm wasting my time though!

 

[Gepetto]

I've got some .01 1200v spragues that are going in. I'll give them a try, I should think they'd do the trick...let me know if I'm wasting my time though!

Those will work, I usually use the CDE Axials, 0.022uF at 400V. They fit well and are in the sweet spot.

 

[premiumplus]

Thank you, Joe. Question: is the value of the cap determined by the power line frequency or is it the switching speed of the diode that is the primary determinant? Or both, or none of the above?

 

[Gepetto]

Thank you, Joe. Question: is the value of the cap determined by the power line frequency or is it the switching speed of the diode that is the primary determinant? Or both, or none of the above?

Hi Dave
Diode switching speed. The cap softens the turnoff and eliminates the snap off and inductive ringing which gives rise to the RFI generated when the diode turns off.

 

[premiumplus]

Makes sense, thanks for a good explanation!
BTW, new filter caps are in and snubbers too. Actually turned out to be .012 uF, 1200V. Closer to the .022 suggested...at any rate, I'm happy with the improvement in perceived noise and more than that, the punch of the stereo now.
I was a little concerned, because the Sangamo caps that I replaced were actually 20,000uF/100v units. The new ones are 15,000uF but they seem to sound better. Go figure...

 

[laatsch55]

try some 35,000 at 120......heheheheheh.....

 

[laatsch55]

Those will work, I usually use the CDE Axials, 0.022uF at 400V. They fit well and are in the sweet spot.

so i can quit using the .01's I've been using?

 

[Gepetto]

so i can quit using the .01's I've been using?

Those are fine too Lee, the value is not super critical. You will get a bit more ring damping of the diode turnoff with a slightly larger value. A lot of it depends on the diode in the bridge, if a slow type, hardly any C is needed as the diode itself has enough of its own.

If using a fast recovery type diode bridge, it is necessary.

 

[laatsch55]

Schottky??

 

[Gepetto]

Schottky??

Well those are fast recovery types for sure Lee but are generally low voltage only. You are hard pressed to get above 100V rating on a Schottky diode due to the nature of the diode.

Generally speaking, fast recovery power bridge rectifiers in the ratings we are interested in are not very common. Within the slow category however you will find a lot of variation in the turnoff time of a diode.

 

[laatsch55]

Thanks Joe, appreciate that info..cause I have a LOT of those 400 volt .01's...

 

[Gepetto]

Thanks Joe, appreciate that info..cause I have a LOT of those 400 volt .01's...

I say, use them Lee

 

[laatsch55]

So be it.....or Amen...