snubber cap question

[wintermute]

Hi,

I've been thinking of adding some snubber caps to my PS, across the rectifier, but I'm unsure what type of caps to use.

I have seen a few PS designs that use .1uF caps, but they don't specify the type. I need something 100V or higher I think, but then possibly even more than that (rail voltage +- 63V)....

The only easily obtainable caps with voltage 100V and .1uF are MKT and I'm not sure these are really suitable. (I'm pretty sure electros are a no go!)

I found that WIMA make caps specifically for snubber duty, these would I guess be ideal, but I can't source them.... (adilam lists them but has no stock).....

Any Suggestions?

Tony.

[JOE DIRT®]

I would stick to a ceramic cap atleast rated at 100v...my only question is why do you feel you need them?

[Hybrid fourdoor]

what about crossover caps? Film and foils in the 400V range 0.1uf can be had for a couple $. Daytons and Solen for example.

[wintermute]

Thanks, Now I just have to find some High voltage ceramics, all the ones I could find (in high capacitance values) were 50V

Ummm, cause I figure it can't hurt .... I have some spurious noise in my amp, that I've been trying to get rid of for years, but haven't succeeded, thought it was worth a shot. (note that this noise is really quite low level (S/N is about 91db at least), but it bugs me!

edit: Hmmmm I had wondered about xover caps before, but thought the size might be a bit of a problem, if I can get the ceramics, I think I'll go with those.

Tony.

[JOE DIRT®]

you can read up on snubber networks Tony...you dont need exotic caps...ceramic caps will do the job

[wintermute]

Originally posted by JOE DIRT®
you can read up on snubber networks Tony...you dont need exotic caps...ceramic caps will do the job

Thanks shall do, I had been searching on snubber capacitor, I'll try snubber network.

Tony.

[Prune]

Originally posted by wintermute
I've been thinking of adding some snubber caps to my PS, across the rectifier

No no no! Putting capacitors across the rectifiers is a common mistake! Make sure to read this: Calculating Optimum Snubbers

[wintermute]

Thanks Prune, That article is pretty heavy going will take a while to digest, but at least I now know it's not just a simple matter of chucking a few caps on

I also found a few threads where people advised against using snubber caps because they made things worse, could be they should have read the article you posted

Tony.

[Prune]

Just using a capacitor lowers the ringing frequency but does not dampen it. Note also that the two capacitors and a resistor network discussed is across the transformer secondaries, not each rectifier.

The trouble with the article is that it is hard to get data on the transformers to plug into the calculations, and the alternative measurements are hard to perform; some trial and error and an oscilloscope is probably the easiest way to do it.

[Sch3mat1c]

You only need one cap, and it only needs to go across the main filter cap (this assumes that you have no ground loops, which would allow the RF hash through anyway!). Or an R+C (Zobel network) of appropriate values across the PT secondary.

Tim