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In Reply to: RE: replaced diodes/caps in power supply? posted by Thom on October 25, 2014 at 06:07:10
Well, your Crees have a lower impedance than the 1N5408 which causes the transformer to have higher current spikes. Adding a 50 ohm resistor right after the diode will fix it.
I don't usually like using 500uf caps as they are kind of like band aids. A better power supply can be made with a couple of 60 to 100 uf caps and a decent choke. I can understand why the manufacturer used the big caps as they are a cheaper way to make the background noise lower.
Follow Ups:
Didn't work, Chip. Under the load of the filters and just bleeders, the transformer is silent. Once I apply the full preamp load, the buzz starts :( Would a bit more resistance be wise?
Thanks, Chip! I'll give that a go.
I'm committed to film caps in the PS, these were just easy replacements and from what I'd read they would sound much better than existing ... and they did. The outboard PS will take some good size films, but the preamp chassis itself has zero real estate for anything like that so I'd like to find radial-lead, 1 3/8" films that could mount through the existing holes/clamps, but have not seen any candidates yet. I could also probably use round axial types with something close to that dia, but then I'd have to put the ground end up in the air out of the chassis with a wire running back down inside. Kind of kludgy.
Take a look here:
http://www.mouser.com/ds/2/88/UNL-9847.pdf
Mouser stocks the 30µF/400V, 35µF/500V and 30µF/600V Cornell-Dubilier radial cylindrical caps in this series. All are 35mm in diameter which is very close to what you need (1.375" = 34.9mm) so if your clamps have a screw adjustment they should fit perfectly.
Yes, they will fit fine. Thanks!
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