Changing bridge. Advise needed

[Fidelity Audio]

I am replacing the bridge rectifier in my Marantz PM66 KI.

This is the circuit I plan on using, very simple but was wondering whether or not the 100uH coils are needed.
The Transformer is a toroidal. I will be using MBR20 20Amp Schottky diodes in TO-220 package on individual heatsinks.

[AndrewT]

Hi,
I think the 10mF aerovox is wrongly connected.

You have to preserve the bipolar DC supplies after the rectifier. Two aerovox at 50V would do this.

As an aside, the benefit of a high quality cap before the main smoothing will be lost.

I think you would do better by putting the inductors then the aerovox AFTER the standard smoothing caps.
Consider also adding substantial plastic caps just as the power leaves the PSU board (beside the snubbers?)
Again at the PCB adding high quality onboard decoupling (lesr//plastic) may give significantly cleaner sound.

[Fidelity Audio]

Yeah you are right about the caps. I will use 2 10000uF caps @ 50V using the same arrangement as the 12000uF caps.

I was thinking of using 100nF plastic caps ;-)

[AndrewT]

Hi,
100nF is probably in the middle of the range I would use.
The small interfence (ceramic) could be 1nF to 10nF. The high speed plastic decoupling could be 1uF to 10uF and the Lesr Electro 47uF to 470uF.
I often use a ratio between types of 100:1 but others have recommended tightening up the ratio to 20:1 .
Experiment till your ears are content.

[Fidelity Audio]

So you would fit say 10nF / 10uF and 470uF in parallel across the smoothing cap?

[AndrewT]

Hi,
try it, I did.
also as decoupling on board.

[Fidelity Audio]

Right

Bridge fitted.

http://img462.imageshack.us/img462/3...04small8zs.jpg

I have not changed the smoothing caps as I am waiting on a pair of Elna Silmic 22000uF caps :-)

In regard to the decoupling caps, I have seen in other circuit diagrams them fitted direct across the smoothers or with a resistor inline.

I pressume the resistor is there to protect the cap, is the resistor really necessary?

[AndrewT]

Hi,
the series resistor + cap (snubber) does a different job.
See the Wiki for details and search snubbers for design info. I thinks it's Perander's posts that have a link to his design info.

Decoupling is aimed at high frequency, low impedance slugging to ground.
I think caps & snubbers complement each other but I don't know the technicalities.

[Fidelity Audio]

cheers

I have included the resistors.

[John Tomac]

Hi,

Can you send me PM66KI's schematics please???

Happy new year

Greg

g.hache@free.fr